If we could harness every single photo that hit a solar panel, one would probably be enough for each person. But solar cell efficiency is variable and unfortunately not very efficient. New technologies are being developed every year that allow for better conversion of solar energy and solar panels are much more efficient than they were in the 1980′s but we still have trouble breaking through the 30-40% range of conversion, which is the standard for third generation solar technologies. A number of different types of solar cells have been developed to produce more energy.
As of 2010 the most efficient solar cell produced are by Solar Junction and are three-junction concentrators at 43.5%, followed by single junction concentrators at 29%. But these are not produced for industrial or even residential usage, but are research productions and it’ll be a long time until you see one of them on someones roof top. On top of that they are produced by using rare and expensive elements that wouldn’t be available for mass production of public models.
Most common multicrystalline Silicon solar cells have efficiencies of 14-19%. These are the ones you’ll find in a store like home depot and the most likely ones you’ll see on residential properties. Some newer models, called concentrators ( like the ones in the last paragraph), use optics to increase the solar light intensity and can do so by 15% or more.
The factors reducing solar efficiency are the type of solar cells being used, the amount of dirt and dust on the panel, which is a serious problem in dry or desert like environments and the amount of irradiation that the solar panel is subject too. There is also a theoretical limit to solar energy efficiency of 86% due to the Carnot limit. Consult Wikipedia and a calculus book to get the most out of that.
Solar energy is still very expensive compared to other forms of energy. In average irradtin zones such as Europe, the energy produced is done at a cost of $.60/kWh. In high irradiation zones where the sun is always shining the price drops to $.30/kWh. A nice advantage of the panels is that they have long lives of up to 35 years and generally have warranties on them for a decade or more to guard against defects. This means that unless your electricity is sourced from a renewable resource such as hydro, wind or solar, your price for energy will cheaper down the line as energy prices worldwide are only increasing as we run out of non renewable resources.
