Rather than having just a handful of ageing and polluting power stations we now have the possibility of decentralisation; millions of small generators producing power where it is needed, solving the problem of large energy losses during transmission.
Although photovoltaics work better in direct sunlight, they are not reliant on it. They only need daylight to produce electricity.
PV's are silent and unobtrusive, they are designed to withstand the elements and weather very little with age.
PV's have no moving parts and are very reliable. Most PV modules are guaranteed for 20/25 years, with a life expectancy far exceeding this. Maintenance requirements are negligible.
Solar PV produces electricity, not hot water. Please see our solar thermal page for information on thermal systems.
A PV (photovoltaic) panel, which is made up of a number of 'cells', each of which produces a small electrical charge under light.
kWp (kilo-watt peak)
The number of thousand watts a photovoltaic system will produce in peak conditions.
kWh (kilo watt hours)
A unit of electricity. This is defined as power of 1000 watts (being consumed or produced) over the period of one hour. e.g. 2000w over 1/2 hour or 100w over 10 hours.
A PV module could have a rating of 200 Wp (produces 200 watts in peak conditions). 12 modules are connected together on a roof to form a 2.4 kWp array (200 * 12 = 2400 Wp or 2.4kWp). Using SAP (see 'electricity produced' below), this array will generate 2.4 * 858 = 1992kWh / year (30/40 deg pitch, south-facing & un-shaded).
Module Types and Efficiency
Solstice Energy can supply and install any PV module accredited for use in the UK, such as Sanyo, Sunpower, Sharp, Kyocera, BP or any others. If you have a particular requirement or preference for any reason please let us know.
People often confuse efficiency with quality, but all it means is that high efficiency modules can generate the same amount of power as lower efficiency modules in a smaller area. For example, 210Wp Sanyo hybrid and Sunpower monocrystalline modules are almost the same dimensions as 170Wp Sharp polycrystalline modules. Our design team tends to recommend the (proportionally more expensive) high efficiency modules for smaller roof areas or where a client really wants to maximise output, and less expensive polycrystalline modules for large roof areas.
Despite some manufacturers claims, we have found that hybrid, mono and polycrystalline all give the same kWh yield / kWp over the year. Quality and guarantee periods are similarly high with all the common brands available for use in the UK.
Daylight levels in the UK mean that PV will produce an average of 858 kWh of electricity per kWp system size, per year (South-facing & un-shaded). This figure is reached by Standard Assessment Procedure, and forms the basis of our predictions.
An average UK household uses around 3000 kWh per year (so a 1kWp system would supply a quarter of the yearly use). Simple energy efficiency measures in the building will increase the proportion of energy coming from the PV's.
The PV array will usually be mounted on a Southerly facing, pitched roof.
The "solar sundial" below shows that a fair bit of deviation in the positioning of the array will still yield a large percentage of the energy expected from an optimum orientation (a pitch of 30/40 degrees facing due South).
Whenever shading decreases the power output of any one module in an array, then the output of the whole array is similarly decreased. It is therefore very important to avoid shading (from trees, other buildings etc) when siting a PV array. However, if, for example, the shading only occurs late on winter afternoons then it will have less impact on the annual output of the array than shading that occurs every morning until 12:00.
For complicated shading situations, our designers can plot the PV array and the surrounding objects and run a PVSYST simulation to show predicted output throughout the year.
Roof Area Required
Allow approximately 8m2 of pitched roof area (16m2 of flat roof) for every 1kWp of PV. Obstructions like dorme