How efficient are photovoltaic panels?
If you mean, how efficient are they in converting light into electricity, then the answer ranges between 10% and about 25%, though research groups have announced efficiencies of up to 44%. The higher efficiency cells typically operate best under very intense light, so people often use some kind of concentrator with them, like focusing mirrors. But most commercially available pv panels operate at about 14% efficiency. (The rest of the light is converted to heat, making the panel warmer.) There is research going on into so-called quantum dot technology, which could create efficiency as high as 65%. If you mean, how much electricity do you get from PV panels for the dollar, PV typically costs something like $5 per watt of electricity (there is currently a shortage of PV cells worldwide.) That cost is high, but
