Congratulations Jess Kaneshiro, PhD

Last week, my friend Jess Kaneshiro successfully defended his PhD dissertation, "I-III-VI2 (Copper Chalcopyrite-based) Materials for Use in Hybrid Photovoltaic/Photoelectrochemical Water-Splitting Devises". Yes, that's the real title. It might set a record for the most punctuation in a title...(-but-/probably-not).. :)

The talk was interesting not only because it represents a lot of work put in over the years, but also because it was a public offering of knowledge about a source of renewable energy that most people have yet to hear about. Jess studies methodologies and materials that can convert the sun's light energy directly into hydrogen gas. People in the know call this process photo-electrochemical conversion (or PEC) in order to differentiate it from photo-voltaic conversion (PV). PV generation is distinct because it aims to convert the sun's light into electric power (that's the voltaic in photo-voltaic). It's an interesting distinction because the media (and most commercial enterprises) focus solely on PV cells.

The tripping point that I initially had with this research was that the theoretical efficiency of PV cells (the fraction of the sunlight's energy to can be converted into usable electric energy) is higher than the theoretical efficiency of PEC cells (the fraction of the sunlight's energy that can be converted into the chemical energy associated with H2 gas). So then why research PEC at all? I believe the answer lies in the lies---or at least the obfuscations of multiple energy conversions. When a solar cell (either PV or PEC) generates more energy than is needed, we either store or waste that energy. When this happens to a PV cell, we can either send the electric power into a battery (which, by the way, is a form of chemical energy storage), or we could possibly send it "into the grid" so that someone else can use it. The argument for PEC is that if you consider the efficiency "chain" of PV: Sunlight-to-voltage-to-battery (or -to-grid), the end-to-end efficiency is going to be lower than the one-shot PEC conversion: sunlight-to-hydrogen.

This makes some sense to me, but has an obvious shortcoming: batteries are getting more and more efficient all the time, so this argument may in fact break down later on.

Source: J. Kaneshiro, N. Gaillard, R. Rocheleau, E. Miller, Advances in copper-chalcopyrite thin films for solar energy conversion, Solar Energy Materials and Solar Cells, Volume 94, Issue 1, January 2010, Pages 12-16.

Jess's defense outlined another use for PEC power: Why not use it in conjunction with PV cells? Jess's most recent research has been in hybridizing cells to contain both PEC and PV subcells. This appears to hold great promise because each sub-cell can be tuned to capture different segments of the sunlight's spectrum. In effect, they are sequentially picking up the pieces of light that fall through the other sub-cells.

This looks like challenging and real-world-relevant work, and I wish Jess continued success and a bit more media attention for his field!

Stay illuminated,

Clay