Good question. Few people know that for the bulk of the world’s energy production–photosynthesis by plants and algae–the process is really inefficient: something on the order of 0.1% for plants and up to 2% for algae. Much of this has to do with simple, natural factors: plant leaves don’t always have the right orientation with the sun, they can be shaded by other plants, reflection of sunlight, etc. There are also a few other complicated issues relating to respiration and converting harvested energy into biomass, like sugars and other compounds needed for a plant to grow.
Luckily, a solar panel array can be much more efficient because we can control for these variables, and we have another advantage: we’re only turning sunlight into electricity, not biomass, so we lose a lot less energy in the process.
The average efficiency for solar panels these days is 10-15%, although the most efficient solar panels can convert sunlight at up to 20%. In the lab, new technologies have achieved even greater efficiencies, but these developments don’t always make it onto the market.
For more information, see the following posts on this website: