The German solar research institute Fraunhofer (PDF) put the payback time at “around 2.5 years” for PV arrays in northern Europe, and that figure even drops to 1.5 years and less in sunnier locations. Keep in mind that solar panels sold over the past few years have had performance guarantees of around 80 percent for 25 years, meaning that, a 2.0 kilowatt array is guaranteed to still be able to peak at 1.6 kilowatts after 25 years of operation.
Clearly, the energy payback of PV is tremendous – the energy you get back is an order of magnitude greater than what you put in.
The payback time for wind turbines is even better; it is counted in months, not years. As a British newspaper The Guardian put it, “The average wind farm produces 20-25 times more energy during its operational life that was used to construct and install its turbines.”
With coal, efficiency always represents a loss, whereas it is always a gain with solar; the coal that is consumed is gone for good, so at 33 percent efficiency, two thirds is lost. Had it not been used, it would still be in the ground.
In contrast, the planet gets a certain amount of solar every day. If a solar panel is 16 percent efficient, around 5/6 of the sun’s energy is lost, but if a roof does not have solar, all of that energy is lost. The 16 percent efficiency rating is a gain. The planet roughly receives the same amount of solar energy every day, but yesterday’s solar energy will be gone forever if not harvested.
In other words: coal, use it and lose it; solar, use it or lose it.