Heavy ion fusion

Heavy ion fusion is a fusion energy concept that uses a stream of high-energy ions from a particle accelerator to rapidly heat and compress a small pellet of fusion fuel. It is a subclass of the larger inertial confinement fusion (ICF) approach, replacing the more typical laser systems with an accelerator.
Accelerators have the potential to be much more efficient in terms of delivering energy to the fuel pellet; typical laser-based "drivers" have overall efficiency on the order of 1%, while heavy-ion systems aim for 30% or more. Additionally, they can produce pulses of energy many times a second, while existing high-energy laser systems require lengthy cooling periods between "shots". These advantages would be useful in a commercial setting, as they would greatly lower the cost of operation, and somewhat lower the cost of building the plant compared to a laser system.
The basic concept had been suggested on occasion before 1970, using either electrons or protons. Fundamental limits on the beam focusing using electrons and stopping distances of protons led to the concept of using heavy ions, whose higher mass allows them to remain more focussed and stop more rapidly. A major meeting in 1976 led to the rapid uptake of the concept through the late 1970s and early 1980s. In the late 1970s, heavy ion fusion (HIF) was described as "the conservative approach" to a working fusion reactor. Further work culminated in the HYLIFE-II design, prepared at the Lawrence Livermore National Laboratory (LLNL) in the early 1990s.
Since that time, in spite of continued interest, no large-scale experimental device using the approach has been built. It has the disadvantage that accelerators with the required energies can only be built in a large size, on the order of kilometres, which makes it difficult to test with low-cost systems. In contrast, even small lasers can reach the desired conditions, which is why they remain the focus of the ICF approach.
Background.
Fusion basics.
Fusion takes place when atoms come into close proximity and the nuclear force pulls them together to form a single larger nucleus. Counteracting this process is the positive charge of the nuclei, which repel each other due to the electrostatic force. In order for fusion to occur, the nuclei must have enough energy to overcome this "coulomb barrier". The barrier is lowered for atoms with less positive charge, those with the fewest protons. The nuclear force is increased with additional nucleons, the total number of protons and neutrons. This means that a combination of deuterium and tritium has the lowest coulomb barrier, at about 100 keV (see requirements for fusion), as they contain a single proton and one or two neutrons.
When the fuel is heated to high energies, the electrons separate from the nuclei, leaving individual ions and electrons mixed in a gas-like plasma. Particles in a gas are distributed across a wide range of energies known as the Maxwell–Boltzmann distribution. At any given temperature the majority of the particles are at lower energies, with a "long tail" containing smaller numbers of particles at much higher energies. So while the 100 keV threshold represents a temperature of over one billion degrees, in order to produce fusion events the fuel does not have to be heated to this temperature as a whole; some reactions will occur at lower bulk temperatures due to the small number of high-energy particles in the mix.
The fusion reactions give off large amounts of energy, and some of that energy will be deposited back in the fuel, heating it. There is a critical temperature at which the rate of reactions, and thus the energy deposited in the fuel, balances losses to the environment through escaping particles and radiation. At this point the reaction becomes self-sustaining, a point known as "ignition". For D-T fuel, the self-heating is primary through alpha particles and the corresponding temperature is between 50 and 100 million degrees. The overall rate of fusion is dependent on the combination of temperature, density and energy confinement time, known as the fusion triple product.
Fusion reactors.
Two primary approaches have developed for the fusion energy problem. The most widely studied approach is magnetic confinement. Since the plasma is electrically charged, it will follow magnetic lines of force and a suitable arrangement of fields can keep the fuel away from the container walls. The fuel is then heated over an extended period. At the densities that are possible using magnets, the fusion process is fairly slow, so this approach requires long confinement times on the order of tens of seconds. Confining a gas at millions of degrees for this sort of time scale has proven difficult, although modern experimental machines are approaching the conditions needed for net power production, or "breakeven".
The second major approach is inertial confinement. The alphas from the fusion reactions travel a distance that is dependent on the density of the fuel. In the low-densities of a magnetic reactor, often described as "a good vacuum", this may be on the order of many meters, but at very high densities this is greatly reduced, down to microns. The inertial approach takes advantage of this effect by compressing the fuel to extremely high density, at which point a tiny drop of fuel on the order of milligrams will be enough to allow ignition. Additionally, the collapse causes the temperature of the fuel to rise through the adiabatic process, providing two of the three inputs of the triple product.
There is no attempt to maintain these conditions for any significant period of time, the fuel explodes outward soon after the driver pulse ends, slowed only by the inertia of the particles. The confinement time is on the order of microseconds, so the temperatures and density have to be very high in order for any appreciable amount of the fuel to undergo fusion. This approach has been successful in producing fusion reactions, but to date, the devices that can provide the compression, typically lasers, require much more energy than the reactions produce.
ICF details.
There are two separate effects in the ICF process, one is to compress the fuel so the alphas are captured within it, and the second is to heat the fuel to the temperatures needed for the reactions to begin. In order to efficiently capture the alphas, a density of about 1000 times that of water is desired, which requires a beam energy of about 107 Joules per gram (J/g) of target mass. In contrast, heating the fuel to fusion temperatures requires about 109 J/g. For this reason, effort has been put into ways to separately heat the fuel; the typical solution is to shape the energy delivery to create a brief period of higher energy, creating a shock wave that travels into the compressing fuel. This is known as "hot spot ignition".
Most ICF systems to date have used lasers as the "driver". In the simple case when the laser is shone directly on the fuel target, known as "direct drive", the heat created by the laser causes the outer layer of the plastic capsule to explode outward. Due to Newton's Third Law, this causes the interior of the capsule to be driven inward. Direct drive places very strong limits on the focussing and delivery time, and is difficult to achieve. For this reason, most large ICF devices use the "indirect drive" process, in which the driver heats a metal cylinder known as a "hohlraum" so hot that it begins to release X-rays, which in turn shine on a capsule suspended inside. This allows the heating process to take place over a longer period and reduces the need to focus as tightly but has the disadvantage that much of the original beam energy is used to heat the cylinder, and does not contribute to the implosion.
Delivering a pulse with the required energy levels and timing is a significant challenge. To date, the energy requirements have normally been met using complex neodymium-doped phosphate glass lasers that have an overall efficiency around 1%. Optical systems needed to focus and control the beam remove an additional 50% of the energy, and in the case of indirect drive, significant amounts of what remain are lost heating the metal cylinder. For the National Ignition Facility, the largest and most powerful ICF system to date, only about 10 to 14 kJ of the original 4 MJ of the original laser energy reaches the target, which required 422 MJ of electrical power to generate.
In order for the fusion reactions to produce enough energy to match the original energy of the laser, it will have to produce at least 4 MJ, and for practical reasons, at least three times that, implying the ratio of input laser energy to output fusion energy, or gain, has to be on the order of hundreds or thousands. To date, the record on NIF is 54 kJ of fusion from 4 MJ of laser output, from 422 MJ of electricity, so it is extremely unlikely the current approach could ever be used for power production.
Alternate drivers.
In 1963, Friedwardt Winterberg introduced the concept of igniting fusion using small groups of particles that have been accelerated to about 200 km/s, a concept that is now known as cluster impact fusion. This concept is not similar to modern ICF, as the accelerated particles are intended to undergo fusion directly, and are not being used solely a driver as in the ICF concept. The publication of several ICF-related papers in the late 1960s prompted Winterberg to publish a 1968 paper outlining the use of accelerated electrons or ions in place of the laser systems in an ICF arrangement.
Al Maschke, working at the Brookhaven National Laboratory's Alternating Gradient Synchrotron (AGS), suggested the use of a proton synchrotron, like the AGS, as the basis for an ICF driver. This could deliver the desired energy with relatively minor upgrades. However, further study demonstrated a problem with this approach; the beam would diverge excessively due to like-charge repulsion and it would be difficult to get the intensity needed for ICF. Additionally, the protons would stop within the fuel target at different depths, which would make it difficult to control the implosion dynamics. These problems both led Maschke to suggest, around 1975, the switch from protons to heavier ions, like cesium, xenon, mercury or lead. In early 1976, Dennis Keefe proposed that the linear induction accelerator would work for this purpose.
A significant event in HIF's history was a two-week July 1976 meeting at the Claremont Hotel in Berkeley, California where Maschke’s ideas were studied by around fifty participants from all of the major particle accelerator and fusion labs and universities. Their report on the meeting demonstrated there were no red-flag issues and that that concept's potential suggested a more detailed study. This resulted in several follow-up studies, at Brookhaven in 1977, Argonne in 1978 and Oakland in 1979, all with similar promising results. In a May 1979 review of the entire ICF field, John S. Foster Jr. concluded that HIF was the best bet for an ICF fusion reactor "if you wanted to make a conservative approach".
After further wrangling, in 1983 the Department of Energy was finally persuaded to provide some funding to form an official organization to manage these efforts, the Heavy Ion Fusion Accelerator Research program, or HIFAR. Over the next decade, the HIFAR group at Lawrence Berkeley, along with similar groups at Lawrence Livermore and elsewhere, continued studying the basic concept. Studies continued for the next decade, resulting in two proposed complete power plant designs, HYLIFE and HYLIFE-II.
Another look.
During this same period, the classical laser-based approach to ICF suffered a series of significant setbacks. Much of the predicted performance of these designs was based on computer simulations using programs like LASNEX. Early simulations suggested that some fusion gain could be expected even at relatively low beam energies on the order of 10 kJ, but when this prediction was tested in the Shiva system a host of unforeseen issues dramatically lowered the performance by a factor of about 10,000. Updates to LASNEX suggested a larger system with several hundred kJ of power would do it, but the resulting Nova system built to this scale instead demonstrated yet another set of significant problems and once again failed to meet predictions.
Experiments using nuclear weapons as the driver in place of the laser, part of Halite/Centurion, suggested dramatically higher energies were required, perhaps as much as 100 MJ, well beyond the capabilities of any laser system. Even in the best-case scenarios, with various advances in target shaping and timing of the energy pulse, at least 2 MJ would be needed. This would require about 200 MJ of electricity to power the lasers, so fusion gains on the order of "Q"=100 would be needed for the energy to balance out, even ignoring all the loss mechanisms.
This series of events led to renewed interest in HIF. Because the driver efficiency was so much higher, the required gain was correspondingly lower, on the order of "Q"=10. Lower gain meant much less demanding implosion dynamics, as well as less powerful explosions which could be contained in a smaller device. Since the late 1990s, a fairly continuous stream of papers on the topic continues to be generated by labs around the world, and some small-scale experimentation on suitable accelerators has been carried out.
Current Status.
A practical problem for the HIF approach is the fact that in order to deliver the correct energy and timing the accelerator has to be large. One would desire that most of the ions would stop at about the same location in the target in order to produce a symmetrical effect. To do this, the energy of the ions has to be quite precise. In the case of a commonly-used ion type, lead, that energy is about 8 GeV in order to have the ions stop at an average distance of 1 mm while also delivering enough energy to the target. An accelerator capable of giving lead ions this level of energy is neither small nor inexpensive, even for low numbers of ions, making it difficult to produce in a small-scale device.
In contrast, lasers with the required performance can be built at practically any scale. This is the primary reason that HIF has not seen development; the smallest possible machine is still quite large and expensive. For development purposes, lasers would be simpler and less expensive while ultimately working in a similar fashion in terms of implosion physics. That said, as the laser ICF program continued, it has demonstrated that ever-larger drivers are required, culminating in the NIF which, at about 4 billion dollars and the size of two football fields, is neither small nor inexpensive.
In 2003, DOE decided to focus all of its ICF efforts on the NIF program as many post-NIF projects would be based on its results. Plans for various smaller test concepts for the HIF program largely ended at that time. NIF's failure to achieve ignition, , casts doubt on the HIF approach as well.
Description.
Target physics.
The energy needed to compress an ICF target to the required density is about 107 J/g, so for small amounts of fuel on the order of 1 mg the energy requirement is about 10 kJ. However, additional energy is required to heat the fuel to fusion temperatures, compression alone will not be sufficient until about 109 J/g. This leads to a variety of mechanisms to lower this requirement to about 108 J/g, and thus about 100 kJ in total for 1 mg of fuel. A variety of loss mechanisms during compression loses about 90% of that energy, and thus drivers have to be on the order 1 MJ.
In the 1970s when the concept was first being considered, the most powerful accelerators, typically using electron or proton, accelerated small numbers of particles to high energies. Those that could reach 1 MJ generally did so with protons with energies around 20 GeV. These highly relativistic particles pass right through small objects without slowing, making them unsuitable for ICF. A driver would ideally want to use much larger numbers of lower-energy particles that will stop more rapidly. At non-relativistic energies, less than 20 MeV, they have a reasonable chance of stopping in a small object. At these energies, the numbers of particles, or "luminosity", required to deliver the needed energy is well beyond any existing technology.
Moving to heavier particles has some advantage in terms of lowering velocity, as energy = mv2, but the mass is linear with energy while velocity is a square, so the reduction in velocity is not great. The key advantage is the way that the particles slow within a target. As they pass the atoms in the target, their electrical charge ionizes the target atoms, and it is these interactions that slow the particle in a scattering process known as the Coulomb collision. A curious effect in the Coulomb collision is the Bragg peak, which is caused by the slowing of the ion near the end of its trajectory. This effect means that when ions are shot into a substance, most of them will be deposited at a well-defined distance. For any selected stopping distance and chosen particle energy, a heavy ion will stop in about three orders of magnitude shorter distance than a proton, making the system much easier to arrange.
Target design.
As is the case with laser-driven ICF, HIF can be built using either the direct or indirect drive concepts, and the primary reasons for using one or the other are the same; direct-drive requires much higher beam accuracy of the driver, but delivers about 15% of the energy from the driver to the fuel, while indirect-drive is less critical of beam placement and timing while delivering only about 5% of the energy to the target.
In the indirect drive case, the system is almost identical to that of the laser-driven systems, the differences are mostly in the hohlraum design. In laser devices, the hohlraum are in the form of open cylinders and the laser beams shine in through the ends and onto the inner walls. In the case of an ion driver, the stopping distance would lead to the X-rays being captured inside the hohlraum walls. Instead, the hohlraum is in the form of a thin shell, typically an ovoid, with small metal plates suspended within. The wall of the hohlraum is thin enough to be invisible to the beams, which instead strike the thicker plates, heating until they begin to emit X-rays that fill the shell. The X-rays then cause the fuel capsule to collapse in exactly the same fashion as the laser case. There is one advantage to the HIF driver in this case, however, as it can be quickly oscillated at high frequencies, allowing the beams to be moved within the hohlraum to even out the heating. The formation of hot spots on the hohlraum walls has proven to be an issue in laser devices, which this could avoid.
Because the stopping distance of the ions is on the order of 1 mm, targets for direct-drive HIF are generally larger and much thicker than those in laser systems. A typical design is about 4 mm in radius, with an outer layer of lead or gold, a pusher made of lighter metal like aluminum, and then a thin layer of D-T fuel frozen to the inner layer of the aluminum. The inner core, about 2.8 mm, is empty. Such a design, with higher density on the outside and lighter on the inside, is a formula for Rayleigh-Taylor instability (R-T), so the targets and illumination must be extremely uniform. Considerations of the illumination suggest 16 to 32 beams are required. Some capsule designs add a thin layer of foam to buffer the compression to reduce R-T.
A significant problem in early ICF systems was that the laser pulses were roughly uniform in time. It was found that this deposited energy more rapidly than it could be absorbed by the capsule, leading to the fuel being heated instead of simply pushed. This led to the modern concept of the "foot", an initial period of much lower energy that begins the driver process while avoiding pre-heating, and then the "main pulse" that follows near the end of the process that drives the final high-compression stage. Because of the mass of the pusher layer, the entire process is slower than in laser systems, with the pulse as a whole lasting about 35 ns, compared to perhaps that for laser pulses.
Driver designs.
There are two main design concepts for the driver systems, with US teams concentrating on induction accelerators and European and Japanese teams on radio-frequency accelerators.
RF accelerators consist of a pipe with periodic gaps in it, each of them enclosed in a resonant cavity. When a radio frequency signal is applied across the gap, each one begins to resonate at a chosen frequency. This produces an electric force across the gap that accelerates the ions along the pipe. The signal is timed so that it reaches a peak as a group of ions passes. This means it can only accelerate short pulses of ions, and therefore requires some way to combine the pulses back together.
Induction accelerators consist of a series of solenoids spaced out along the beamline. Each is powered as the ions pass it, accelerating them. This has the advantage of allowing the accelerators to be wrapped around multiple beamlines, accelerating them all at the same time.
In either case, the need for very large beam power in very short pulses, along with the need to focus those beams down to about 3 mm, demands a number of new design factors. In order to meet the focussing requirement, the initial ion source must have a very low emittance, the spread of the ions in space and velocity. This is essentially a measure of their random motion when created, which is a function of their temperature. To provide the desired emittance, new low-temperature injectors have to be developed.
The ion's positive electric charge forces them away from each other over time, leading to the concept of the space charge limit, the maximum number of ions in a given volume that can remain focused. This value is far below the requirements to produce a pulse that will compress the target. US designs approach this problem by having a large number of parallel beam lines that combine just as they approach the target chamber. European designs favor the use of storage rings for this role. In both cases, an initial long pulse of ions is reduced in length to produce an ever-shorter pulse. For instance, in one US design the initial pulse is 27 µs long, and undergoes repeated compression until it is only 10 ns.
In any version, the resulting designs are very long. US illustrations generally use a folded beamline that is shaped like a U, with a total length on the order of . This is the HIF approach's major downside; although it is possible to build an accelerator with less beam current for testing purposes, the individual ions still require the same energy and thus the accelerator will be a similar size as a higher-current version for a production reactor.
Advantages over lasers.
There are significant practical advantages to the use of ions over lasers. To start with, lasers that can reach the desired energy levels are extremely inefficient, on the order of 1% of the electricity supplied to them ends up as photons in the beam. In contrast, HIF drivers put perhaps 30 to 40% of the input energy into the beam. This significantly eases the required performance of the targets if the goal is to produce net energy output; a 4 MJ laser requires approximately 400 MJ of electrical energy, and considering a modern Rankine cycle generator is about 40% efficient, the output from the capsule must be at least about 1 GJ to recharge the laser. In contrast, the same 4 MJ beam energy could be produced by 10 MJ HIF driver, requiring about 40 MJ of fusion output, a dramatically simpler goal. Considering additional losses in the process, HIF devices generally target gain on the order of 50 to 70.
Another significant advantage for the HIF design is its ability to rapidly fire in succession. The glass systems used in lasers are heated by the passage of the beam, causing them to swell and become defocussed, requiring some time to cool before they can be used again. In practice, this limits devices like NIF to perhaps a few "shots" a day, and while this can be increased through the use of advanced cooling systems, these might reduce the firing times to minutes or perhaps tens of seconds. In contrast, HIFs have no in-line focussing or beam control components, all of that is handled by magnets surrounding the beamlines. This allows them to fire continually, and rates of 10 to 15 shots per second seem possible. This is an enormous advantage in the case of an operational plant where the shot timing should be quick enough so that the output looks relatively continual.
The ability to control the beam electrically offers significant operational advantages. Small scale beam steering, or "wobbling", is useful during the pulse to smooth out the energy. On a longer time frame, the continual motion of the device due to sagging and seismic events has to be accounted for over the long travel distances of the beams. In a laser system, this requires a lengthy recalibration effort, whereas this can be performed easily, and perhaps continually, in the HIF case through minor changes of the fields in the final steering magnets. This can also be used to steer the beams between completely different reaction chambers, which offers fail-over operations and the ability to fire into different chambers in succession if the desired pulse rate is faster than any one chamber can be cleared.
Finally, the final optics where the laser enters the reaction chamber is subject to the direct output of the fusion events, including high-energy neutrons and various other particles and radiation. This leads to constant erosion of the windows, which can cause significant problems with the high-energy light. This has emerged as a significant problem in laser-driven ICF devices. HIF's ability to be easily steered offers a number of simple solutions to these problems, allowing the beamlines to be isolated from the reactions using rotating mechanical shutters or other concepts.
Economics.
Several design studies were published through the 1990s and into the 2000s, aided by ever-better simulations of the ICF process as well as continued improvements in accelerator design. A high point was the October 1990 publication of the HYLIFE-II design study for a HIF power plant using molten flibe to protect the walls of the reaction chamber as well as breed tritium for fuel. The baseline 1 GWe design resulted in an expected levelized cost of electricity (LCOE) of 9 cents/kWh in 1988 dollars, or . This was not a competitive figure even at that time, and the system only became competitive when the reactor scaled up to a very large 2 GWe size, which would significantly limit its commercial applicability. The paper concludes:
To be competitive with future coal and LWR nuclear power, the cost of electricity needs to be reduced by a factor of 2.
A more modern review comes to the same conclusion:
Finally, research aimed at cost reduction is critically important.


GU-50

The GU-50 (Russian: ГУ-50) is a power pentode vacuum tube intended for 50 watt operation as a linear RF amplifier on frequencies up to 120 MHz. It is, in fact, a Soviet-produced copy of the Telefunken LS-50 power pentode, possibly reverse-engineered from German (Wehrmacht) military radios captured during World War II, or based on documentation, machines and materials captured as a trophy. It is one of the more unusual types of tube because of its non-standard 8-pin base and a metal "cap" (not connected to any of the tube internal elements) with a plastic "handle" on top of the envelope - which is meant to ease extracting the tube from its socket (especially when the tube is hot). One stock Russian-produced socket includes a rugged die-cast metal cage-like enclosure for the tube with spring-loaded locking lid. (The cap was made for fixation of the tube in the metal can, since tubes were designed for mobile operations). Another stock Russian-produced socket is stamped of light aluminium sheet metal, without a lid on top.
In the past the tube was very popular with Soviet and Eastern European amateur radio operators because it was commonly available (from military and government warehouses) and could produce fairly large amounts of output power using relatively simple designs. Also, it was popular in Soviet-era DIY audio amplifiers for hi-fi and musical instruments. GU-50 tubes were used also in early TV sets as a horizontal sweep output stage, and in medical devices as RF generators. The tube was never used in mass production amplifiers for civil usage because of relatively expensive technology and materials used.
During the Soviet years, the tube was produced by one of the major Soviet transmitting-tube manufacturers in the city of Ulianovsk. It was also made in Poland, in the Unitra factory. At this time it is unclear if current production of the tube exists; however, large quantities of New Old Stock (NOS) GU-50s appear to be available in the former Soviet Union and Eastern Europe and the type is far more readily found than the original LS-50.
GU-50 was not alone. There were other successors of LS-50 designed by Telefunken. Switzerland's BBC produced P50/1 and later modified version P50/2. They had the same base and pinout as the original LS-50. German Democratic Republic made a P50 that had the same bulb as Soviet ГУ-50. Later RFT made a P50-1 version of their tube. Unlike Soviet TV designers that used stock military GU-50 for their first TV sets, Eastern German manufacturers offered P50-2 especially made for TV horizontal sweep duties. There were also versions with simplified bulbs made for civil usage, but internals were still too expensive to compete with civil tubes like rugged clones of RCA 6L6 and especially designed later sweep tubes like EL500. The Western German version was called FL152 (or, with 6.3-volt heater, EL152); Eastern German version was called SRS552N.
The tube, despite its European popularity, was not well known in U.S.A. and Canada until audiophiles rediscovered it after the collapse of Eastern political block and Soviet Union.
The Chinese version of this tube is called FU-50 and production still continues, probably by Shuguang, the major Chinese tube builder.
The tube was originally designed for mobile operations, so its filament draws only 0.705 amps of current, while anode power dissipation allowed is up to 40 watts, quite big for such low filament power. It determines the need for high anode voltage, 800 V typically. The screen grid is quite dense, so its voltage when working in pentode mode is limited by 300 volts, otherwise power dissipated by the grid when anode voltage goes below screen grid voltage would damage it. That's why the tube cannot be efficiently used in so-called "Ultra - Linear" regime when anode and screen grid have the same voltage at idle. However, in triode mode anode voltage never goes below screen grid voltage, so 400–450 volts of B+ is acceptable.
The tube can work also in so-called "Right-handed triode" mode, or "High Mu" mode, when all 3 grids are connected together and used with positive bias. In such regime, B+ voltage can be up to 1200 V, and anode curves resemble pentode ones, with higher than in the "left-handed" triode mode impedance.
Anode of the tube is made of a special nickel alloy, specially coated, so it can shortly dissipate more than 100W on anode without destruction. However, such regime causes too high temperature to be used continuously, but instead of destroying the tube like it can be expected in case of so-called "Audio Tubes" like 6L6 and successors, it causes absorption of gases making vacuum cleaner.


Simply Energy

Simply Energy is an Australian energy retailer, providing electricity and gas to more than 700,000 accounts across Victoria, South Australia, New South Wales, Queensland and Western Australia, with sales totalling 12% of the Australian market. It is the Australian retail arm of ENGIE, which fully owns Simply Energy.
Products and services.
Simply Energy provides electricity and gas to homes and businesses in Victoria, New South Wales, South Australia, Queensland and Western Australia
History.
International Power was launched as a retail brand in 2005 by EnergyAustralia, which had recently been purchased by International Power.
In August 2007, International Power Australia completed a buy out of EnergyAustralia interests in Victoria and South Australia. Subsequently, International Power launched the retail brand called Simply Energy in those two states. Simply Energy became part of GDF Suez in 2012. It is now owned by ENGIE with the French Government having control of this entity.
Controversy.
Simply Energy have been subject to many high profile complaints regarding the practices of their doorknockers and billing issues.


Grid energy storage

Grid energy storage (also called large-scale energy storage) is a collection of methods used for energy storage on a large scale within an electrical power grid. Electrical energy is stored during times when electricity is plentiful and inexpensive (especially from intermittent power plants such as renewable electricity from wind power, tidal power and solar power) or when demand is low, and later returned to the grid when demand is high, and electricity prices tend to be higher.
, the largest form of grid energy storage is dammed hydroelectricity, with both conventional hydroelectric generation as well as pumped storage hydroelectricity.
Developments in battery storage have enabled commercially viable projects to store energy during peak production and release during peak demand, and for use when production unexpectedly falls giving time for slower responding resources to be brought online.
Two alternatives to grid storage are the use of peaking power plants to fill in supply gaps and demand response to shift load to other times.
Benefits.
Any electrical power grid must match electricity production to consumption, both of which vary drastically over time. Any combination of energy storage and demand response has these advantages:
Energy derived from solar, tidal and wind sources inherently varies – the amount of electricity produced varies with time of day, moon phase, season, and random factors such as the weather. Thus, renewables in the absence of storage present special challenges to electric utilities. While hooking up many separate wind sources can reduce the overall variability, solar is reliably not available at night, and tidal power shifts with the moon, so slack tides occur four times a day.
How much this affects any given utility varies significantly. In a summer peak utility, more solar can generally be absorbed and matched to demand. In winter peak utilities, to a lesser degree, wind correlates to heating demand and can be used to meet that demand. Depending on these factors, beyond about 20–40% of total generation, grid-connected intermittent sources such as solar power and wind power tend to require investment in grid interconnections, grid energy storage or demand-side management.
In an electrical grid without energy storage, generation that relies on energy stored within fuels (coal, biomass, natural gas, nuclear) must be scaled up and down to match the rise and fall of electrical production from intermittent sources (see load following power plant). While hydroelectric and natural gas plants can be quickly scaled up or down to follow the wind, coal and nuclear plants take considerable time to respond to load. Utilities with less natural gas or hydroelectric generation are thus more reliant on demand management, grid interconnections or costly pumped storage.
The French consulting firm Yole Développement estimates the "stationary storage" market could be a $13.5 billion opportunity by 2023, compared with less than $1 billion in 2015.
Demand side management and grid storage.
The demand side can also store electricity from the grid, for example charging a battery electric vehicle stores energy for a vehicle and storage heaters, district heating storage or ice storage provide thermal storage for buildings. At present this storage serves only to shift consumption to the off-peak time of day, no electricity is returned to the grid.
The need for grid storage to provide peak power is reduced by demand side time of use pricing, one of the benefits of smart meters. At the household level, consumers may choose less expensive off-peak times to wash and dry clothes, use dishwashers, take showers and cook. As well, commercial and industrial users will take advantage of cost savings by deferring some processes to off-peak times.
Regional impacts from the unpredictable operation of wind power has created a new need for interactive demand response, where the utility communicates with the demand. Historically this was only done in cooperation with large industrial consumers, but now may be expanded to entire grids. For instance, a few large-scale projects in Europe link variations in wind power to change industrial food freezer loads, causing small variations in temperature. If communicated on a grid-wide scale, small changes to heating/cooling temperatures would instantly change consumption across the grid.
A report released in December 2013 by the United States Department of Energy further describes the potential benefits of energy storage and demand side technologies to the electric grid: "Modernizing the electric system will help the nation meet the challenge of handling projected energy needs—including addressing climate change by integrating more energy from renewable sources and enhancing efficiency from non-renewable energy processes. Advances to the electric grid must maintain a robust and resilient electricity delivery system, and energy storage can play a significant role in meeting these challenges by improving the operating capabilities of the grid, lowering cost and ensuring high reliability, as well as deferring and reducing infrastructure investments. Finally, energy storage can be instrumental for emergency preparedness because of its ability to provide backup power as well as grid stabilization services". The report was written by a core group of developers representing Office of Electricity Delivery and Energy Reliability, ARPA-E, Office of Science, Office of Energy Efficiency and Renewable Energy, Sandia National Laboratories, and Pacific Northwest National Laboratory; all of whom are engaged in the development of grid energy storage.
Energy storage for grid applications.
Energy storage assets are a valuable asset for the electrical grid. They can provide benefits and services such as load management, power quality and uninterruptable power supply to increase the efficiency and supply security. This becomes more and more important in regard to the energy transition and the need for a more efficient and sustainable energy system.
Numerous energy storage technologies (pumped-storage hydroelectricity, electric battery, flow battery, flywheel energy storage, supercapacitor etc.) are suitable for grid-scale applications, however their characteristics differ. For example, a pumped-hydro station is well suited for bulk load management applications due to their large capacities and power capabilities. However, suitable locations are limited and their usefulness fades when dealing with localized power quality issues. On the other hand, flywheels and capacitors are most effective in maintaining power quality but lack storage capacities to be used in larger applications. These constraints are a natural limitation to the storage's applicability.
Several studies have developed interest and investigated the suitability or selection of the optimal energy storage for certain applications. Literature surveys comprise the available information of the state-of-the-art and compare the storage's uses based on current existing projects. Other studies take a step further in evaluating energy storage with each other and rank their fitness based on multiple-criteria decision analysis. Another paper proposed an evaluation scheme through the investigation and modelling of storage as equivalent circuits. An indexing approach has also been suggested in a few studies, but is still in the novel stages. In order gain increased economic potential of grid connected energy storage systems, it is of interest to consider a portfolio with several services for one or more applications for an energy storage system. By doing so, several revenue streams can be achieved by a single storage and thereby also increasing the degree of utilization. To mention two examples, a combination of frequency response and reserve services is examined in, meanwhile load peak shaving together with power smoothing is considered in.
Forms.
Air.
Compressed air.
One grid energy storage method is to use off-peak or renewably generated electricity to compress air, which is usually stored in an old mine or some other kind of geological feature. When electricity demand is high, the compressed air is heated with a small amount of natural gas and then goes through turboexpanders to generate electricity.
Compressed air storage is typically around 60–90% efficient.
Liquid air.
Another electricity storage method is to compress and cool air, turning it into liquid air, which can be stored, and expanded when needed, turning a turbine, generating electricity, with a storage efficiency of up to 70%.
A commercial liquid-air energy storage plant is under construction in the North of England,
with commercial operation planned for 2022.
The energy storage capacity of 250MWh of the plant will be nearly twice the capacity of the world’s largest existing lithium-ion battery, the Hornsdale Power Reserve in South Australia.
Batteries.
 Battery storage was used in the early days of direct current electric power. Where AC grid power was not readily available, isolated lighting plants run by wind turbines or internal combustion engines provided lighting and power to small motors. The battery system could be used to run the load without starting the engine or when the wind was calm. A bank of lead-acid batteries in glass jars both supplied power to illuminate lamps, as well as to start an engine to recharge the batteries. Battery storage technology is typically around 80% to more than 90% efficient for newer lithium ion devices.
Battery systems connected to large solid-state converters have been used to stabilize power distribution networks. Some grid batteries are co-located with renewable energy plants, either to smooth the power supplied by the intermittent wind or solar output, or to shift the power output into other hours of the day when the renewable plant cannot produce power directly (see Installation examples). These hybrid systems (generation and storage) can either alleviate the pressure on the grid when connecting renewable sources or be used to reach self-sufficiency and work "off-the-grid" (see Stand-alone power system).
Contrary to electric vehicle applications, batteries for stationary storage do not suffer from mass or volume constraints. However, due to the large amounts of energy and power implied, the cost per power or energy unit is crucial. The relevant metrics to assess the interest of a technology for grid-scale storage is the $/Wh (or $/W) rather than the Wh/kg (or W/kg). The electrochemical grid storage was made possible thanks to the development of the electric vehicle, that induced a fast decrease in the production costs of batteries below $300/kWh. By optimizing the production chain, major industrials aim to reach $150/kWh by the end of 2020. These batteries rely on a lithium-ion technology, which is suited for mobile applications (high cost, high density). Technologies optimized for the grid should focus on low cost and low density.
Grid-oriented battery technologies.
Sodium-ion batteries are a cheap and sustainable alternative to lithium-ion, because sodium is far more abundant and cheaper than lithium, but it has a lower power density. However, they are still on the early stages of their development.
Automotive-oriented technologies rely on solid electrodes, which feature a high energy density but require an expensive manufacturing process. Liquid electrodes represent a cheaper and less dense alternative as they do not need any processing.
Molten-salt batteries.
These batteries are composed of two molten metal alloys separated by an electrolyte. They are simple to manufacture but require a temperature of several hundred degree Celsius to keep the alloys in a liquid state. This technology includes ZEBRA, sodium-sulfur batteries and liquid metal. Sodium sulphur batteries are being used for grid storage in Japan and in the United States. The electrolyte is composed of solid beta alumina. The liquid metal battery, developed by the group of Pr. Donald Sadoway, uses molten alloys of magnesium and antimony separated by an electrically insulating molten salt. It is still in the prototyping phase.
Flow batteries.
In rechargeable flow batteries, the liquid electrodes are composed of transition metals in water at room temperature. They can be used as a rapid-response storage medium. Vanadium redox batteries are a type of flow battery. Various flow batteries are installed at different sites including; Huxley Hill wind farm (Australia), Tomari Wind Hills at Hokkaidō (Japan), as well as in non-wind farm applications. A 12 MW·h flow battery was to be installed at the Sorne Hill wind farm (Ireland). These storage systems are designed to smooth out transient wind fluctuations. Hydrogen Bromide has been proposed for use in a utility-scale flow-type battery.
Examples.
In Puerto Rico a system with a capacity of 20 megawatts for 15 minutes (5 megawatt hour) stabilizes the frequency of electric power produced on the island. A 27 megawatt 15-minute (6.75 megawatt hour) nickel-cadmium battery bank was installed at Fairbanks Alaska in 2003 to stabilize voltage at the end of a long transmission line.
In 2014, the Tehachapi Energy Storage Project was commissioned by Southern California Edison.
In 2016 a zinc-ion battery was proposed for use in grid storage applications.
In 2017 the California Public Utilities Commission installed 396 refrigerator-sized stacks of Tesla batteries at the Mira Loma substation in Ontario, California. The stacks are deployed in two modules of 10 MW each (20 MW in total), each capable of running for 4 hours, thus adding up to 80 MWh of storage. The array is capable of powering 15,000 homes for over four hours.
BYD proposes to use conventional consumer battery technologies such as lithium iron phosphate (LiFePO4) battery, connecting many batteries in parallel.
The largest grid storage batteries in the United States include the 31.5 MW battery at Grand Ridge Power plant in Illinois and the 31.5 MW battery at Beech Ridge, West Virginia. Two batteries under construction in 2015 include the 400 MWh (100 MW for 4 hours) Southern California Edison project and the 52 MWh project on Kauai, Hawaii to entirely time shift a 13MW solar farm's output to the evening. Two batteries are in Fairbanks, Alaska (40 MW for 7 minutes using Ni-Cd cells), and in Notrees, Texas (36 MW for 40 minutes using lead-acid batteries). A 13 MWh battery made of used batteries from Daimler's Smart electric drive cars is being constructed in Lünen, Germany, with an expected second life of 10 years.
In 2015, a 221 MW battery storage was installed in the US, with total capacity expected to reach 1.7 GW in 2020.
The UK had a 50 MW lithium ion grid-battery installed in Hertfordshire in 2018.
In November 2017 Tesla installed a 100 MW, 129 MWh battery system in South Australia. The Australian Energy Market Operator stated that this "is both rapid and precise, compared to the service typically provided by a conventional synchronous generation unit".
Electric vehicles.
Companies are researching the possible use of electric vehicles to meet peak demand. A parked and plugged-in electric vehicle could sell the electricity from the battery during peak loads and charge either during night (at home) or during off-peak.
Plug-in hybrid or electric cars could be used for their energy storage capabilities. Vehicle-to-grid technology can be employed, turning each vehicle with its 20 to 50 kWh battery pack into a distributed load-balancing device or emergency power source. This represents two to five days per vehicle of average household requirements of 10 kWh per day, assuming annual consumption of 3,650 kWh. This quantity of energy is equivalent to between of range in such vehicles consuming . These figures can be achieved even in home-made electric vehicle conversions. Some electric utilities plan to use old plug-in vehicle batteries (sometimes resulting in a giant battery) to store electricity However, a large disadvantage of using vehicle to grid energy storage would be if each storage cycle stressed the battery with one complete charge-discharge cycle. However, one major study showed that used intelligently, vehicle-to-grid storage actually improved the batteries longevity. Conventional (cobalt-based) lithium ion batteries break down with the number of cycles – newer li-ion batteries do not break down significantly with each cycle, and so have much longer lives. One approach is to reuse unreliable vehicle batteries in dedicated grid storage as they are expected to be good in this role for ten years. If such storage is done on a large scale it becomes much easier to guarantee replacement of a vehicle battery degraded in mobile use, as the old battery has value and immediate use.
Flywheel.
Mechanical inertia is the basis of this storage method. When the electric power flows into the device, an electric motor accelerates a heavy rotating disc. The motor acts as a generator when the flow of power is reversed, slowing down the disc and producing electricity. Electricity is stored as the kinetic energy of the disc. Friction must be kept to a minimum to prolong the storage time. This is often achieved by placing the flywheel in a vacuum and using magnetic bearings, tending to make the method expensive. Greater flywheel speeds allow greater storage capacity but require strong materials such as steel or composite materials to resist the centrifugal forces. The ranges of power and energy storage technology that make this method economic, however, tends to make flywheels unsuitable for general power system application; they are probably best suited to load-leveling applications on railway power systems and for improving power quality in renewable energy systems such as the 20MW system in Ireland.
Applications that use flywheel storage are those that require very high bursts of power for very short durations such as tokamak and laser experiments where a motor generator is spun up to operating speed and is partially slowed down during discharge.
Flywheel storage is also currently used in the form of the Diesel rotary uninterruptible power supply to provide uninterruptible power supply systems (such as those in large datacenters) for ride-through power necessary during transfer – that is, the relatively brief amount of time between a loss of power to the mains and the warm-up of an alternate source, such as a diesel generator.
This potential solution has been implemented by EDA in the Azores on the islands of Graciosa and Flores. This system uses an 18 megawatt-second flywheel to improve power quality and thus allow increased renewable energy usage. As the description suggests, these systems are again designed to smooth out transient fluctuations in supply, and could never be used to cope with an outage exceeding a couple of days.
Powercorp in Australia have been developing applications using wind turbines, flywheels and low load diesel (LLD) technology to maximize the wind input to small grids. A system installed in Coral Bay, Western Australia, uses wind turbines coupled with a flywheel based control system and LLDs. The flywheel technology enables the wind turbines to supply up to 95 percent of Coral Bay's energy supply at times, with a total annual wind penetration of 45 percent.
Hydrogen.
Hydrogen is being developed as an electrical energy storage medium. Hydrogen is produced, then compressed or liquefied, cryogenically stored at −252.882 °C, and then converted back to electrical energy or heat. Hydrogen can be used as a fuel for portable (vehicles) or stationary energy generation. Compared to pumped water storage and batteries, hydrogen has the advantage that it is a high energy density fuel.
Hydrogen can be produced either by reforming natural gas with steam or by the electrolysis of water into hydrogen and oxygen (see hydrogen production). Reforming natural gas produces carbon dioxide as a by-product. High temperature electrolysis and high pressure electrolysis are two techniques by which the efficiency of hydrogen production may be able to be increased. Hydrogen is then converted back to electricity in an internal combustion engine, or a fuel cell.
The AC-to-AC efficiency of hydrogen storage has been shown to be on the order of 20 to 45%, which imposes economic constraints. The price ratio between purchase and sale of electricity must be at least proportional to the efficiency in order for the system to be economic. Hydrogen fuel cells can respond quickly enough to correct rapid fluctuations in electricity demand or supply and regulate frequency. Whether hydrogen can use natural gas infrastructure depends on the network construction materials, standards in joints, and storage pressure.
The equipment necessary for hydrogen energy storage includes an electrolysis plant, hydrogen compressors or liquifiers, and storage tanks.
Biohydrogen is a process being investigated for producing hydrogen using biomass.
Micro combined heat and power (microCHP) can use hydrogen as a fuel.
Some nuclear power plants may be able to benefit from a symbiosis with hydrogen production. High temperature (950 to 1,000 °C) gas cooled nuclear generation IV reactors have the potential to electrolyze hydrogen from water by thermochemical means using nuclear heat as in the sulfur-iodine cycle. The first commercial reactors are expected in 2030.
A community based pilot program using wind turbines and hydrogen generators was started in 2007 in the remote community of Ramea, Newfoundland and Labrador. A similar project has been going on since 2004 in Utsira, a small Norwegian island municipality.
Underground hydrogen storage.
Underground hydrogen storage is the practice of hydrogen storage in caverns, salt domes and depleted oil and gas fields. Large quantities of gaseous hydrogen have been stored in caverns by Imperial Chemical Industries (ICI) for many years without any difficulties. The European project Hyunder indicated in 2013 that for the storage of wind and solar energy an additional 85 caverns are required as it cannot be covered by PHES and CAES systems.
Power to gas.
Power to gas is a technology which converts electrical power to a gas fuel. There are 2 methods, the first is to use the electricity for water splitting and inject the resulting hydrogen into the natural gas grid. The second less efficient method is used to convert carbon dioxide and water to methane, (see natural gas) using electrolysis and the Sabatier reaction. The excess power or off peak power generated by wind generators or solar arrays is then used for load balancing in the energy grid. Using the existing natural gas system for hydrogen, fuel cell maker Hydrogenics and natural gas distributor Enbridge have teamed up to develop such a power to gas system in Canada.
Pipeline storage of hydrogen where a natural gas network is used for the storage of hydrogen. Before switching to natural gas, the German gas networks were operated using towngas, which for the most part consisted of hydrogen. The storage capacity of the German natural gas network is more than 200,000 GW·h which is enough for several months of energy requirement. By comparison, the capacity of all German pumped storage power plants amounts to only about 40 GW·h. The transport of energy through a gas network is done with much less loss (<0.1%) than in a power network (8%). The use of the existing natural gas pipelines for hydrogen was studied by NaturalHy
The power-to-ammonia concept.
The power-to-ammonia concept offers a carbon-free energy storage route with a diversified application palette. At times when there is surplus low-carbon power, it can be used to create ammonia fuel. Ammonia may be produced by splitting water into hydrogen and oxygen with electricity, then high temperature and pressure are used to combine nitrogen from the air with the hydrogen, creating ammonia. As a liquid it is similar to propane, unlike hydrogen alone, which is difficult to store as a gas under pressure or to cryogenically liquefy and store at −253 °C.
Just like natural gas, the stored ammonia can be used as a thermal fuel for transportation and electricity generation or used in a fuel cell. A standard 60,000 m³ tank of liquid ammonia contains about 211 GWh of energy, equivalent to the annual production of roughly 30 wind turbines. Ammonia can be burned cleanly: water and nitrogen are released, but no CO2 and little or no nitrogen oxides. Ammonia has multiple uses besides being an energy carrier, it is the basis for the production of many chemicals, the most common use is for fertilizer. Given this flexibility of usage, and given that the infrastructure for the safe transport, distribution and usage of ammonia is already in place, it makes ammonia a good candidate to be a large-scale, non-carbon, energy carrier of the future.
Hydroelectricity.
Pumped water.
In 2008 world pumped storage generating capacity was 104 GW, while other sources claim 127 GW, which comprises the vast majority of all types of grid electric storage – all other types combined are some hundreds of MW.
In many places, pumped storage hydroelectricity is used to even out the daily generating load, by pumping water to a high storage reservoir during off-peak hours and weekends, using the excess base-load capacity from coal or nuclear sources. During peak hours, this water can be used for hydroelectric generation, often as a high value rapid-response reserve to cover transient peaks in demand. Pumped storage recovers about 70% to 85% of the energy consumed, and is currently the most cost effective form of mass power storage. The chief problem with pumped storage is that it usually requires two nearby reservoirs at considerably different heights, and often requires considerable capital expenditure.
Pumped water systems have high dispatchability, meaning they can come on-line very quickly, typically within 15 seconds, which makes these systems very efficient at soaking up variability in electrical "demand" from consumers. There is over 90 GW of pumped storage in operation around the world, which is about 3% of "instantaneous" global generation capacity. Pumped water storage systems, such as the Dinorwig storage system in Britain, hold five or six hours of generating capacity, and are used to smooth out demand variations.
Another example is the 1836 MW Tianhuangping Pumped-Storage Hydro Plant in China, which has a reservoir capacity of eight million cubic meters (2.1 billion U.S. gallons or the volume of water over Niagara Falls in 25 minutes) with a vertical distance of 600 m (1970 feet). The reservoir can provide about 13 GW·h of stored gravitational potential energy (convertible to electricity at about 80% efficiency), or about 2% of China's daily electricity consumption.
A new concept in pumped-storage is utilizing wind energy or solar power to pump water. Wind turbines or solar cells that direct drive water pumps for an energy storing wind or solar dam can make this a more efficient process but are limited. Such systems can only increase kinetic water volume during windy and daylight periods.
Hydroelectric dams.
Hydroelectric dams with large reservoirs can also be operated to provide peak generation at times of peak demand. Water is stored in the reservoir during periods of low demand and released through the plant when demand is higher. The net effect is the same as pumped storage, but without the pumping loss. Depending on the reservoir capacity the plant can provide daily, weekly, or seasonal load following.
Many existing hydroelectric dams are fairly old (for example, the Hoover Dam was built in the 1930s), and their original design predated the newer intermittent power sources such as wind and solar by decades. A hydroelectric dam originally built to provide baseload power will have its generators sized according to the average flow of water into the reservoir. Uprating such a dam with additional generators increases its peak power output capacity, thereby increasing its capacity to operate as a virtual grid energy storage unit. The United States Bureau of Reclamation reports an investment cost of $69 per kilowatt capacity to uprate an existing dam, compared to more than $400 per kilowatt for oil-fired peaking generators. While an uprated hydroelectric dam does not directly store excess energy from other generating units, it behaves equivalently by accumulating its own fuel – incoming river water – during periods of high output from other generating units. Functioning as a virtual grid storage unit in this way, the uprated dam is one of the most efficient forms of energy storage, because it has no pumping losses to fill its reservoir, only increased losses to evaporation and leakage.
A dam which impounds a large reservoir can store and release a correspondingly large amount of energy, by controlling river outflow and raising or lowering its reservoir level a few meters. Limitations do apply to dam operation, their releases are commonly subject to government regulated water rights to limit downstream effect on rivers. For example, there are grid situations where baseload thermal plants, nuclear or wind turbines are already producing excess power at night, dams are still required to release enough water to maintain adequate river levels, whether electricity is generated or not. Conversely there's a limit to peak capacity, which if excessive could cause a river to flood for a few hours each day.
Superconducting magnetic energy.
Superconducting magnetic energy storage (SMES) systems store energy in the magnetic field created by the flow of direct current in a superconducting coil which has been cryogenically cooled to a temperature below its superconducting critical temperature. A typical SMES system includes three parts: superconducting coil, power conditioning system and cryogenically cooled refrigerator. Once the superconducting coil is charged, the current will not decay and the magnetic energy can be stored indefinitely. The stored energy can be released back to the network by discharging the coil. The power conditioning system uses an inverter/rectifier to transform alternating current (AC) power to direct current or convert DC back to AC power. The inverter/rectifier accounts for about 2–3% energy loss in each direction. SMES loses the least amount of electricity in the energy storage process compared to other methods of storing energy. SMES systems are highly efficient; the round-trip efficiency is greater than 95%. The high cost of superconductors is the primary limitation for commercial use of this energy storage method.
Due to the energy requirements of refrigeration, and the limits in the total energy able to be stored, SMES is currently used for short duration energy storage. Therefore, SMES is most commonly devoted to improving power quality. If SMES were to be used for utilities it would be a diurnal storage device, charged from base load power at night and meeting peak loads during the day.
Superconducting magnetic energy storage technical challenges are yet to be solved for it to become practical.
Thermal.
In Denmark the direct storage of electricity is perceived as too expensive for very large scale usage, albeit significant usage is made of existing Norwegian Hydro. Instead, the use of existing hot water storage tanks connected to district heating schemes, heated by either electrode boilers or heat pumps, is seen as a preferable approach. The stored heat is then transmitted to dwellings using district heating pipes.
Molten salt is used to store heat collected by a solar power tower so that it can be used to generate electricity in bad weather or at night.
Building heating and cooling systems can be controlled to store thermal energy in either the building's mass or dedicated thermal storage tanks. This thermal storage can provide load-shifting or even more complex ancillary services by increasing power consumption (charging the storage) during off-peak times and lowering power consumption (discharging the storage) during higher-priced peak times. For example, off-peak electricity can be used to make ice from water, and the ice can be stored. The stored ice can be used to cool the air in a large building which would have normally used electric AC, thereby shifting the electric load to off-peak hours. On other systems stored ice is used to cool the intake air of a gas turbine generator, thus increasing the on-peak generation capacity and the on-peak efficiency.
A pumped-heat electricity storage system uses a highly reversible heat engine/heat pump to pump heat between two storage vessels, heating one and cooling the other. The UK-based engineering company Isentropic that is developing the system claims a potential electricity-in to electricity-out round-trip efficiency of 72–80%.
Gravitational potential energy storage with solid masses.
Alternatives include storing energy by moving large solid masses upward against gravity. This can be achieved inside old mine shafts or in specially constructed towers where heavy weights are winched up to store energy and allowed a controlled descent to release it. In rail energy storage, rail cars carrying large weights are moved up or down a section of inclined rail track, storing or releasing energy as a result;
In disused oil-well potential energy storage, weights are raised or lowered in a deep, decommissioned oil well.
Economics.
The levelized cost of storing electricity depends highly on storage type and purpose; as subsecond-scale frequency regulation, minute/hour-scale peaker plants, or day/week-scale season storage.
Using battery storage is said to be $120-$170 per MWh. This compares with open cycle gas turbines which, as of 2020, have a cost of around $151-198/MWh.
Generally speaking, energy storage is economical when the marginal cost of electricity varies more than the costs of storing and retrieving the energy plus the price of energy lost in the process. For instance, assume a pumped-storage reservoir can pump to its upper reservoir a volume of water capable of producing 1,200 MW·h after all losses are factored in (evaporation and seeping in the reservoir, efficiency losses, etc.). If the marginal cost of electricity during off-peak times is $15 per MW·h, and the reservoir operates at 75% efficiency (i.e., 1,600 MW·h are consumed and 1,200 MW·h of energy are retrieved), then the total cost of filling the reservoir is $24,000. If all of the stored energy is sold the following day during peak hours for an average $40 per MW·h, then the reservoir will see revenues of $48,000 for the day, for a gross profit of $24,000.
However, the marginal cost of electricity varies because of the varying operational and fuel costs of different classes of generators. At one extreme, base load power plants such as coal-fired power plants and nuclear power plants are low marginal cost generators, as they have high capital and maintenance costs but low fuel costs. At the other extreme, peaking power plants such as gas turbine natural gas plants burn expensive fuel but are cheaper to build, operate and maintain. To minimize the total operational cost of generating power, base load generators are dispatched most of the time, while peak power generators are dispatched only when necessary, generally when energy demand peaks. This is called "economic dispatch".
Demand for electricity from the world's various grids varies over the course of the day and from season to season. For the most part, variation in electric demand is met by varying the amount of electrical energy supplied from primary sources. Increasingly, however, operators are storing lower-cost energy produced at night, then releasing it to the grid during the peak periods of the day when it is more valuable. In areas where hydroelectric dams exist, release can be delayed until demand is greater; this form of storage is common and can make use of existing reservoirs. This is not storing "surplus" energy produced elsewhere, but the net effect is the same – although without the efficiency losses. Renewable supplies with variable production, like wind and solar power, tend to increase the net variation in electric load, increasing the opportunity for grid energy storage.
It may be more economical to find an alternative market for unused electricity, rather than try and store it. High Voltage Direct Current allows for transmission of electricity, losing only 3% per 1000 km.
The United States Department of Energy's International Energy Storage Database provides a free list of grid energy storage projects, many of which show funding sources and amounts.
Load leveling.
The demand for electricity from consumers and industry is constantly changing, broadly within the following categories:
There are currently three main methods for dealing with changing demand:
The problem with standby gas turbines is higher costs, expensive generating equipment is unused much of the time. Spinning reserve also comes at a cost, plants run below maximum output are usually less efficient. Grid energy storage is used to shift generation from times of peak load to off-peak hours. Power plants are able to run at their peak efficiency during nights and weekends.
Supply-demand leveling strategies may be intended to reduce the cost of supplying peak power or to compensate for the intermittent generation of wind and solar power.
Portability.
This is the area of greatest success for current energy storage technologies. Single-use and rechargeable batteries are ubiquitous, and provide power for devices with demands as varied as digital watches and cars. Advances in battery technology have generally been slow, however, with much of the advance in battery life that consumers see being attributable to efficient power management rather than increased storage capacity. Portable consumer electronics have benefited greatly from size and power reductions associated with Moore's law. Unfortunately, Moore's law does not apply to hauling people and freight; the underlying energy requirements for transportation remain much higher than for information and entertainment applications. Battery capacity has become an issue as pressure grows for alternatives to internal combustion engines in cars, trucks, buses, trains, ships, and aeroplanes. These uses require far more energy density (the amount of energy stored in a given volume or weight) than current battery technology can deliver. Liquid hydrocarbon fuel (such as gasoline/petrol and diesel), as well as alcohols (methanol, ethanol, and butanol) and lipids (straight vegetable oil, biodiesel) have much higher energy densities.
There are synthetic pathways for using electricity to reduce carbon dioxide and water to liquid hydrocarbon or alcohol fuels. These pathways begin with electrolysis of water to generate hydrogen, and then reducing carbon dioxide with excess hydrogen in variations of the reverse water gas shift reaction. Non-fossil sources of carbon dioxide include fermentation plants and sewage treatment plants. Converting electrical energy to carbon-based liquid fuel has potential to provide portable energy storage usable by the large existing stock of motor vehicles and other engine-driven equipment, without the difficulties of dealing with hydrogen or another exotic energy carrier. These synthetic pathways may attract attention in connection with attempts to improve energy security in nations that rely on imported petroleum, but have or can develop large sources of renewable or nuclear electricity, as well as to deal with possible future declines in the amount of petroleum available to import.
Because the transport sector uses the energy from petroleum very inefficiently, replacing petroleum with electricity for mobile energy will not require very large investments over many years.
Reliability.
Virtually all devices that operate on electricity are adversely affected by the sudden removal of their power supply. Solutions such as UPS (uninterruptible power supplies) or backup generators are available, but these are expensive. Efficient methods of power storage would allow for devices to have a built-in backup for power cuts, and also reduce the impact of a failure in a generating station. Examples of this are currently available using fuel cells and flywheels.


China Energy Investment

China Energy Investment Corporation, more commonly known as China Energy (), is a state-owned mining and energy company administrated by the SASAC of the State Council of the People's Republic of China.
History.
On August 28, 2017, SASAC announced that China Guodian Corporation and Shenhua Group will be jointly restructured. Shenhua Group will become China Energy Investment Corporation Limited and will absorb China Guodian Corporation. It will be the largest power company in the world by installed capacity.
Operations.
China Energy is engaged in development, investment, construction, operation and management of power plants and power generation for electricity supply in China. It also mines coal; operates railroads, ports and seaborne shipments; produces polyethylene and polypropylene; and undertakes research, development, and demonstrations activities.


Hydroelectric power in India

India is 5th globally for installed hydroelectric power capacity. As of 31 March 2020, India's installed utility-scale hydroelectric capacity was 46,000 MW, or 12.3% of its total utility power generation capacity. Additional smaller hydroelectric power units with a total capacity of 4,683 MW (1.3% of its total utility power generation capacity) have been installed. India's hydroelectric power potential is estimated at 148,700 MW at 60% load factor. In the fiscal year 2019–20, the total hydroelectric power generated in India was 156 TWh (excluding small hydro) with an average capacity factor of 38.71%.
The hydro-electric power plants at Darjeeling and Shivanasamudram were established in 1898 and 1902, respectively. They were among the first in Asia and India has been a dominant player in global hydroelectric power development. India also imports surplus hydroelectric power from Bhutan.
Small hydropower, defined to be generated at facilities with nameplate capacities up to 25 MW, comes under the ambit of the Ministry of New and Renewable energy (MNRE); whilst large hydro, defined as above 25 MW, comes under the ambit of Ministry of Power.
Hydroelectric potential.
India's economically exploitable and viable hydroelectric potential is estimated to be 148,701 MW. An additional 6,780 MW from smaller hydro schemes (with capacities of less than 25 MW) is estimated as exploitable. 56 sites for pumped storage schemes with an aggregate installed capacity of 94,000 MW have also been identified. In central India, the hydroelectric power potential from the Godavari, Mahanadi, Nagavali, Vamsadhara and Narmada river basins has not been developed on a major scale due to potential opposition from the tribal population.
The public sector accounts for 92.5% of India's hydroelectric power production. The National Hydroelectric Power Corporation (NHPC), Northeast Electric Power Company (NEEPCO), Satluj Jal Vidyut Nigam (SJVNL), THDC, and NTPC-Hydro are some of the public sector companies producing hydroelectric power in India. The private sector is also expected to grow with the development of hydroelectric energy in the Himalayan mountain ranges and in the northeast of India.
Indian companies have also constructed hydropower projects in Bhutan, Nepal, Afghanistan, and other countries.
Bhakra Beas Management Board (BBMB), a state-owned enterprise in north India, has an installed capacity of 2.9 GW. The generation cost after four decades of operation is about per kWh. BBMB is a major source of peaking power and black start capability to the northern grid in India and its large reservoirs provide wide operational flexibility. BBMB reservoirs also supply water for the irrigation of of agricultural land in partner states, enabling the green revolution in the northern India.
The International Hydropower Association estimates that the total hydropower potential in India is 660,000 GWh/year, of which 540,000 GWh/year (79%) is still undeveloped. India ranks as the fourth country in the world by undeveloped hydropower potential, after Russia, China and Canada, and fifth by total potential, surpassed also by Brazil.
Pumped storage units.
India has transformed from an electricity deficit state to an electricity surplus state. Peak load shortages can be met making use of pumped storage schemes which store surplus power to meet peak load demands. The pumped storage schemes also contribute secondary, seasonal power at no additional cost when rivers are flooded with excess water. India has already established nearly 4,800 MW pumped storage capacity with the installation of hydropower plants.
Pumped storage units can also be used as pumping stations to supply river water for upland irrigation, industrial needs, and drinking water. In a tropical country like India, abundant water for agriculture is needed due to a very high annual evaporation rate. The amount of water necessary to meet this demand can be harnessed from India's rivers via pumped storage units. Food security in India is improved with water security which in turn is possible from the energy security to supply the power needed for the pumped storage schemes.
More and more solar power generation is becoming available at cheaper cost and it has advantage in terms of environmental impact. Solar power can meet daytime and night time energy demands with the help of pumped storage units.
Many of the existing hydro power stations on the west-flowing rivers located in the Western Ghats of Kerala and Karnataka are to be expanded to include pumped storage units in an effort to solve the water deficit of east-flowing rivers like the Kaveri, the Krishna, etc.


COBRAcable

COBRAcable ("COpenhagen-BRussels-Amsterdam cable") is a ±320 kV, 700 MW HVDC submarine power cable pair between Eemshaven, the Netherlands and Endrup near Esbjerg, Denmark. The cable is jointly owned by Energinet.dk and TenneT. Its purpose is to improve the European transmission grid and thus increase the amount of variable wind power in the system while improving supply reliability. Its 700 MW capacity corresponds to an annual transmission capacity of 6.1 TWh.
Construction.
The interconnector has a length of , consists of two parallel cables each with a diameter of and includes fiber-optic communication. The connection has been designed in such a way as to enable the connection of an offshore wind farm at a later stage. This contributes to the realisation of a sustainable international energy landscape, a key aim of the European Union.
On the Danish side the interconnector reaches land on the western coast of the island of Fanø and end on the mainland at the converter station near Endrup where an existing power facility has been extended with . The building itself has a footprint of 125 m × 36 m and a height of 21 m. A group of local residents have collaborated with Energinet.dk in deciding the outer appearance of the building and its surrounding vegetation.
The COBRAcable is a cross-border project of European significance. The European Commission has therefore allocated a subsidy to the project under the EU Economic Recovery Plan, and has designated the COBRAcable as a Project of Common Interest (PCI). In November 2015, the project was put on the EU "Projects of Common Interest" list, along with Viking Link between Denmark and England, and Kriegers Flak Combined Grid Solution between Denmark and Germany.
Construction contracts were signed with Siemens and Prysmian in 2016 and in June 2016 Prysmian subcontracted the marine survey for the cable placement to the Swedish marine survey provider MMT.
Onshore construction started in Denmark in October 2016 and in the Netherlands in January 2017.
In 2015 COBRACable was expected to be operational from early 2019, in Q1 2019 commercial operation was expected to start during Q3 of 2019.
Operation.
After tests between July and September 2019, the COBRAcable was commissioned in September 2019. In its first half year of operation, it had a 79% capacity factor and transported 1,400 GWh to Netherlands and 700 GWh to Denmark. It became inoperable in September 2020 due to a cable fault, and became operational in January 2021 after repairs.


Upper American Fork Hydroelectric Power Plant Historic District

The Upper American Fork Hydroelectric Power Plant Historic District is a historic district in American Fork Canyon in northeastern Utah County, Utah, United States, that is listed on the National Register of Historic Places (NRHP).
Description.
The district consists of one contributing building and three contributing structures. It included the power plant; the Upper American Fork Dam, which is about long and tall, which traps the unnamed stream that flows through the American Fork Canyon (and becomes the American Fork river at the mouth of the canyon); and the pedestrian footbridge over the unnamed stream .
The district was listed on the NRHP on April 20, 1989.


AC module

An AC module is a photovoltaic module which has a small AC inverter mounted onto its back side which produces AC power with no external DC connector.
AC modules are defined by Underwriters Laboratories as the smallest and most complete system for harvesting solar energy.


Yukon Energy

Yukon Energy Corporation (YEC; ) is a Crown corporation which is the primary producer of electricity in the Canadian territory of Yukon. It also distributes electricity to a small number of locations not served by the privately-owned ATCO Electric Yukon. YEC was established in 1987 to take over the Yukon assets of the Northern Canada Power Commission and is currently organised as a subsidiary of the Yukon Development Corporation. The company's headquarters is in Whitehorse, Yukon near the Whitehorse Rapids hydroelectric generating station.
Profile.
YEC generates virtually all of Yukon's electricity supply, and distributes power to a third of the locations outside of Whitehorse. Their largest customer (a wholesale buyer) is the Yukon Electrical Company (YECL), a private business that has been operating since 1901, which itself has some smaller hydro operations, and serves primarily the Whitehorse area plus two thirds of the rural communities. YEC itself provides customer electricity directly in Dawson City, Mayo, Faro, Champagne and to some isolated individual customers.
YEC has developed a grid that connects hydro facilities in Whitehorse (Schwatka Lake Dam - 40 MW from four wheels, the fourth added in 1983), Aishihik Lake - 30 MW, and the YECL facilities at Fish Lake near Whitehorse. The communities on the "Whitehorse-Aishihik-Faro" grid include Whitehorse, Champagne, Johnson's Crossing, Faro, and the following communities where it is distributed by YECL: Haines Junction, Carcross, Tagish, Marsh Lake, Teslin, Carmacks and Ross River.
YEC operates two wind turbines on Haeckel Hill near Whitehorse connected to the Whitehorse-Aishihik-Faro grid. The first turbine is a Bonus Energy 150 kW MARK III installed in 1993. The second turbine, a Vestas 660 kW V47 LT II was later installed in 2000. These units need to be specially adapted to deal with icing and the northern environment.
A second grid, brought on-line in 2004, connects Dawson City (reliant on diesel power from 1966 to 2004) via Stewart Crossing to Mayo, and beyond to the YECL-served communities of Elsa and Keno City, all drawing on the 5 MW hydro facility just north of Mayo that had mines at Elsa as primary customer until 1989.
The government of John Ostashek (1992-1996) had promised to connect Mayo, Stewart Crossing and YECL-served Pelly Crossing to the main southern grid at Carmacks. During their mandate, and the subsequent N.D.P. and Liberal party mandates, this project was not developed, and Pelly Crossing remained on its own YECL diesel generator. The project was finally proceeded with during the later part of the 2000s, partly to meet power requirements for mines in the Minto area, and on June 17, 2011, the two grids began to operate together. The YECL generator at Pelly Crossing is now on standby to the grid.
Off the grid, Yukon Electrical Company Limited operates diesel generators to serve its customers in Watson Lake-Upper Liard, Swift River, Burwash Landing, Destruction Bay, Beaver Creek and Old Crow. The possibility of a grid connection to Atlin, British Columbia has probably been eliminated by a decision to construct a hydro project near Atlin, but talk in Atlin of an expansion could still raise that possibility.
Yukon has no connections to the continental power grid, therefore, YEC cannot sell to or buy from networks in Alaska, British Columbia, Alberta or the Northwest Territories. In addition to the extreme expense of such transmission lines, they would also be subject to disruption from solar flares.


Nonode

A nonode is a type of thermionic valve that has nine active electrodes. The term most commonly applies to a seven-grid vacuum tube, also sometimes called an enneode. An example was the EQ80/UQ80, which was used as an FM quadrature detector. It was developed during the introduction of TV and FM radio and delivered an output voltage large enough to directly drive an end pentode while still allowing for some negative feedback. As most of the grids were tied together, even an 8-pin Rimlock base was sufficient in the case of the EQ40.


Shinfox

The Shinfox Co., Ltd. (Shinfox; ) is an electricity company of Taiwan.
History.
Shinfox was established in 2009.
Transportation.
The company headquarter office is accessible within walking distance north east from Dingpu Station of Taipei Metro.


Shetland HVDC Connection

Shetland HVDC Connection is a high-voltage direct current submarine power cable under construction to connect the Shetland Islands to the Scottish mainland.
Current status.
Construction earthworks have started at both ends of the link, at Kergord in Shetland, and in Caithness.
As of April 2021, preparation work on installing the land cable in Shetland was expected to start imminently, with the cable itself due in the summer of 2022.
The subsea cable installation is expected in 2022 and 2023.
Route.
The interconnector will start at the Upper Kergord Valley converter station in Shetland. From the converter station an underground cable will be laid to a landing area in Weisdale Voe. From there, a subsea cable will run to landfall at Noss Head in Caithness, with onward connection to an HVDC switching station north of the village of Staxigoe in Caithness.
The route of the cable will cross TAT-10, TAT-14 and Atlantic Crossing 1 telecommunication cables and the Piper–Flotta oil pipeline.
Technical description.
The interconnector will connect to the existing 320kV Caithness - Moray Link to form a three terminal HVDC network, with converter stations at Spittal in Caithness; Blackhillock Substation in Moray; and Upper Kergord on Shetland. The Shetland leg will have a power rating of 600MW; the Spittal and Blackhillock converters are rated at 800MW and 1,200MW respectively. This will be the first multi-terminal HVDC interconnection in Europe.
Project developer.
The project is being developed by Scottish Hydro Electric Transmission, a subsidiary of SSE plc.
Project economics.
It is estimated that it will cost more than £600 million.
The project is needed for development of Shetland's renewable energy potential and it is necessary for the projects such us the Viking Wind Farm and the Aegir wave farm.
It also contributes to the security of Shetland's elelctricity supply, especially as Lerwick Power Station is nearing the end of its operational life.
History.
The project was proposed in 2007. In January 2008, the report published by the Crown Estate found the project would be "economically and technically possible". At the same year, Scottish Hydro Electric Transmission filed planning application and started public consultations.
Originally, the cable was planned to run from Shetland to to Portgordon on the Scottish mainland, and then on to Blackhillock substation, near Keith, Moray via underground cable. However, the end point was moved to Caithness, and the remaining part of the connection was constructed separately as the Caithness - Moray Link.
In 2019, Ofgem announced that it was minded to authorise construction, subject to the Viking windfarm winning a CfD contract in the government auction held in September 2019. Viking Energy was unsuccessful in this auction, putting the future of the interconnector in doubt.
SSEN submitted a revised proposal in January 2020. Ofgem carried out a final consultation on this revised proposal, and concluded in April 2020 that it would grant conditional approval for the link, conditional on Ofgem receiving sufficient evidence by the end of 2020 that the 457 MW Viking Wind Farm project is likely to go ahead.
In April 2020, Ofgem approved revised proposals for the project, subject to "evidence that the Shetland Viking Wind Farm project will go ahead".
On 17 June 2020, the Viking Wind Farm sponsor, SSE Renewables, made a final investment decision to proceed with the wind farm investment, conditional on certain industry code modifications, and "the outcome of the consultation on Ofgem’s minded-to position to approve the transmission link, expected in July 2020". According to "Shetland News", this meant that both the Windfarm and the HVDC Connection "are likely to go ahead".
On 16 July, Ofgem gave final approval for the connection.
Contracts for construction were awarded in August 2020.


Sun-free photovoltaics

Sun-free photovoltaics is a photovoltaics technology which does not require sunlight to produce electricity. This technique was developed by research team at Massachusetts Institute of Technology Photovoltaic cells convert light to electricity most efficiently at specific wavelengths. The surface featured of Sun-free photovoltaics is engineered such that it converts heat energy into the specific wavelengths. This increases the efficiency of existing thermophotovoltaic (TPV) systems.
Principle of working.
The surface of this material is etched with billions of nanoscale pits, so that it emits wave at the specified wavelengths and suppresses other wavelengths which are not required. When the surface is exposed to heat energy, it radiates light energy at required wavelengths. The atoms liberates free electrons when radiation is applied, thus generating electricity.
Development.
A device that uses radioisotopes is capable of producing electricity for up to 30 years without interruption using a process called radioactive decay. Another similar device was developed by researchers from MIT, which uses butane as a fuel source. It has the size of a button and is estimated to operate three times longer than a similarly sized lithium-ion battery and has the advantage of recharging immediately upon refuelling. Thermo-photovoltaics, which is a technology developed in the 1960s, is capable of converting heat energy into electricity. It was previously known that sunlight is not absolutely necessary for photovoltaic cells to operate. Infrared radiation is not utilized efficiently in photovoltaic materials which are characterized by low band gap, though the performance is comparatively better than normal silicon photovoltaic cells. One example of photovoltaics utilizing heat is a photovoltaic diode which produces electricity from heat given off by a hydrocarbon fuelled thermal emitter.
In Sun-free photovoltaics, the thermal emitter described above is finely tuned to emit specific wavelengths that the photovoltaic diode can utilize, while at the same time stopping the wavelengths that cannot be used by the diode. This is achieved by etching features of nanoscale like ridges and holes on a photonic crystal so that the light passing through the crystal can be modified.
Operation.
A slab of tungsten is used as a thermal emitter with billions of nanoscale pits on the surface, with each pit acting like a resonator. On heating, specific wavelengths are radiated by the slab as it generates an altered emission spectrum.
Applications.
Sun-free photovoltaics can be applied in electronic devices like smartphones. Its value of current density has the capability to be tripled in the coming years, when it could power a smartphone for more than 20 days without needing to recharge in between. It can also be used to utilize waste heat from electric appliances like televisions and electronic appliances like mobile phones.


Stage loading

Stage Loading is a measure of the load on a turbomachinery stage, be it a part of a compressor, fan or turbine.
The parameter, which is non-dimensional, is defined as:
formula_1
where:
Imperial Units (SI Units)
formula_2 acceleration of gravity ft/s/s (1.0)
formula_3 mechanical equivalent of heat ft.lb/(s.hp) (1.0)
formula_4 change in specific enthalpy over stage hp.s/lb (KW.s/Kg)
formula_5 peripheral blade speed ft/s (m/s)
Average stage loading has a very similar definition, where the number of stages, n, within the compressor, fan or turbine is used to provide an average value:
formula_6
In this case the change in enthalpy is across the whole unit, not just a stage. Similarly, the blade speed used is a mean for the whole device.
The above equation shows that if blade speed cannot be increased for, say, mechanical or aerodynamic reasons, the number of stages has to be increased to get the
average stage loading back to an acceptable level, to obtain a satisfactory level of efficiency. The ideal average stage loading for a turbine is about 1.8.


KT90

The KT90 is a vacuum tube used in audio applications. Typically, it is used in hi-fi or electric guitar amplifier applications. KT90 was developed by Elektronska Industrija Niš (Ei). KT90 is designed by Blagomir Bukumira,a leading engineer at Ei
Features.
The KT90, or in full, "Kinkless Tetrode 90", is a beam power tetrode and features the same octal socket as its smaller variant, the KT88. It may therefore be used as a substitute, given appropriate re-biasing when used in push-pull configuration.
The KT90 is currently manufactured by Electro-Harmonix, who claim that, despite its different construction, it possesses similar sound characteristics to the EL34 valve. Semi-formal research has been conducted by U.K. supplier Watford Valves who have published a test report. (This research is described here as "semi-formal" because it consists primarily of listening evaluations which may be subjective, rather than electrical analyses of performance parameters in either numerical or graphical form.)