Solar Panel Efficiency
Of the approximately 1000 watts of light energy the Sun shines on a square meter, most Solar panels
provide slightly more than 10% of that energy as electicity.
The rest turns into heat or is reflected back into space.
There are some exotic solar cell materials that have shown up to 30%
efficiency, but they are way too expensive to be practical on home roofs.
At the other extreme, thin film silicon solar cells and others can be produced at much
lower cost than the typical silicon crystaline cells, but they require much more roof
area to produce the same amount of electricity.
As the solar cells age, they develop internal defects which decreases their efficiency.
It is a difficult balancing act to trade off efficiency, area, cost and availability
of different solar panels. Here are a few articles related to solar panel efficiency.