One minute of full sunlight provides sufficient energy to meet global energy needs for a year. Despite this, current renewable energy use in the US accounts for only seven percent of US total energy consumption. Moreover, solar power contributes a meager one percent to this already meager total.
Why is this? Quite simply, research and development is slow compared to current energy needs and yearly growth with an expanding global population. Fortunately, the sun still shins providing heat (thermal) and light (photovoltaic) energy for our use. Comparing solar power systems should include both forms of solar energy.
Solar thermal technologies continue to move from concept to application. Heating of water dominates the short history of residential solar use as heat storage to augment hot water supplies or outdoor pools. In a solar thermal system, a “collector” transfers the sun’s heat to water passing through the collector’s plumbing on its way to storage or immediate use.
Today the most efficient systems for panels use vacuum enclosed tubes to prevent heat loss. Power plants utilize concentrated solar collectors (mirrors or parabolic dishes) for heat collection to transform water to steam to drive turbine generators.
Photovoltaic (PV) systems improve slowly with incremental increases in efficiency requiring massive R&D costs. Current PV production consists of the mono-crystalline, polycrystalline, and thin film silicon-based panel markets.
Comparing solar power system efficiencies show that most consumer affordable systems range from 5%-19% conversions. Solar concentrators with tracking systems can attain about 34% but the costs limit them to commercial power production. Only 65% efficiency and improvements in production costs can bring this technology to the consumer.
When comparing solar power systems, mono-crystalline silicon panels are the most efficient averaging about 15% but are the most expensive. Manufacturing the desired crystal size and mono-dispersity is costly. However, in comparing solar power systems mono-crystalline panels are best for conditions with less than optimal light. Therefore, if roof size, orientation, or climate is a problem mono-crystalline panels are the best choice.
More easily manufactured polycrystalline solar panels cost less than mono-crystalline systems but are not as efficient and require a larger area. The manufacturing process involves casting molten silicon into block form that goes through cutting procedures to produce wafers for assembly into panels. A polycrystalline ribbon, a thin strip slowly drawn out of the molten silicon, eliminates most cutting costs.
The production of thin film panels is very different from that for polycrystalline panels. Instead of shaping molten silicon into blocks or ribbons, these panels are a thin film of amorphous, non-crystalline silicon spread directly onto various base materials. Although these panels are the least efficient of the three, they have found a market for small power applications such as battery rechargers, RVs, boats, or campsites.
In comparing solar power systems, special note should be made of recent advances from doped-silicon use in a variation of film technology that includes small amounts of more efficient but more costly materials such as copper indium diselenide (CIS) and cadmium telluride (CdTe) added to the mix before film application. These panels can achieve efficiencies comparable to mono-crystalline silicon panels.