Absorbing all light isn't the problem. There are materials that absorb wide range of wavelengths. That produces heat. Solar-thermal panels are pretty efficient.
With PV, electrons need to be knocked out of their shell and across a diode junction. Any photon with less energy than is required to knock out the electron (e.g. IR) passes right through silicon. Silicon is transparent to IR, and I have an IR microscope that can look through silicon chip from the back side, see the circuit on the front.
Photons with more energy knock out the electron and produce PV current. Any excessive energy beyond what was needed to knock out the electron gets wasted as heat. So a silicon photo cells is most efficient close to a single wavelength. Today, you can buy PV panels of single-crystal or poly-crystaline cells that convert about 20% of the 1000 W/m^ sunshine to electricity.
There are more efficient panels. By layering thin films of different materials, they first capture higher energy photons, and let lower energy photons pass through to the next layer. Thin layers don't capture all the photons of right energy due to probability of interaction. A few micron thick layer misses some photons. A 10 mil thick wafer catches most. And, price of thin-film processing makes these panels more expensive per watt.
Today, silicon single-crystal and poly-crystaline panels are in the sweet spot of price-performance. Lower cost technologies take up more area, which costs materials and labor. Higher efficiency technologies cost more per watt, are useful for applications that have to be launched by rocket.
Best deal today is slightly used high quality panels. You can pay $0.12 to $0.50/watt from vendors like SanTan Solar. Cost of PV panels may be just 25% of what you spend on a grid-tie system, less of a battery-backup system.
Quality of panels is key, because some brands/models have failed. Here's a link; you can register and download free reports for a number of years. Try to buy brands rated has high performing in accelerated stress tests.
Well that sounds like a heck of a deal! Glad you placed your order and can't wait to see how it all works. That is a very good price, and I should not be surprised but that confirms they get a great deal when they upgrade. I wonder if they went with Trina on the replacement units? Any idea?
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