Solar panel efficiency, solar cell efficiency, or energy conversion efficiency, is the ratio of the electrical output of a solar cell to the incident energy in the form of sunlight. The maximum theoretically possible conversion efficiency for sunlight is 86%. The actual solar panel efficiency depends on many different factors. One of the main factors is the angle at which the sunlight hits the solar panel. Therefore some systems use motors to adjust the panels for maximum efficiency.
Solar panel efficiency also depends on the type of solar cell. Emerging PV converts up to about 14% of the sunlight into electricity, Thin-Film Technologies up to about 20%, Crystalline Si Cells (crystalline silicon solar cells) up to about 25% and Multijunction Cells up to about 44% (data from National Renewable Energy Laboratory (NREL), Golden, CO).
It is also interesting to compare the solar panel efficiency values with those of solar thermal systems. Of course, also with different solar thermal systems individual ratios vary significantly. However, some systems might be able to convert up to about 60%.
You have to study the details of all candidates for your solar energy system, but keep in mind that solar thermal plants might be cheaper and more efficient than solar panels. On the other hand they might require more maintenance, could produce more noise and may have other drawbacks (Do you want to sell excess energy or apply for rebates?).
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