Hi,

This is a good question! Efficiency is the energy output divided by the energy input. We are used to talking about the efficiency of processes that use limited and costly fuels, such as petroleum, coal, etc. Using these fuels efficiently is extremely important!

There is a lot of talk in the media about the efficiency of photovoltaics (PV). This ignore a couple of facts. First the sun beams down more energy than we will ever need, so it is sustainable and relatively unlimited. Second, there is no cost for this fuel in money or environmental. So when we talk about how efficient the PV process is, we are less concerned because of these two facts.

Plants, which are pretty successful at converting sunlight to useful products, are only about 10% efficient. Again since the source is vast and cheap, the efficiency is not important.

So when considering the efficiency of processes, a smart scientist considers the cost of the fuel!

Blessings,
Kelly