How Many Dimensions Are Important in Solar PV?

I volunteer to answer questions on renewable energy on Quora.com.  From today’s feed:

Question: What is the most hyperactive solar power product (per cubic volume) that is coming in 2016? Volume because transparent solar panels have been invented already. So “transparent cubes with layers and layers of solar panels inside” would be a good product.

My Answer: You are right that depth plays a certain role, insofar as solar PV efficiency is augmented by trapping the photon in a space, thus improving the probability that it will eventually kick out an electron. But this is really a game of two dimensions, not three. On average, the sun’s irradiation on the Earth’s surface is 1004 Watts/meter^2, and the quest is to convert as much of that as possible into electrical power. While it’s true that some photons pass through the panel and could theoretically be productive in layers below, adding these layers doesn’t help too much and isn’t a cost-effective approach.