Even working on seemingly unrelated projects, energy questions come up in the conversation. My son, Nathan, is working on his Eagle Project. It involves some sawing. One of the boys helping is using a hacksaw to cut some PVC pipe and asks, "Where does the energy come from to cut this pipe?"
Well, that's quite a question. The boys start spouting their knowledge. One says "from your muscles!" Well, sure, but... Another says "food!" Getting a little better, cellular respiration anyone? I whisper to one of the dads about a series of energy conversions. He says, "Chemical energy." I say, "the Sun."
Whoa. How did solar energy make it into this worksite conversation? It seems to happen that way a lot.
Especially interesting about bringing up Solar energy is that my son’s project is the construction of raised garden boxes for the Temple Israel garden. (These should make it easier for some of the older congregants to tend some of the vegetables.) Of course, solar energy is what makes the plants grow. How this happens is not a mystery to us, but how efficiently do plants use the sun’s energy? – well THAT is a good question.
Using the sun to make electricity is, of course, a great idea, and scientists have been working hard to improve the PhotoVoltaic cell to convert more of the solar energy into electrical energy. Recently, best efforts have PV cell efficiency at about 27.6%. (see this August 2011 IEEE Spectrum article: http://spectrum.ieee.org/green-tech/solar/solar-cell-breaks-efficiency-record.) Then there’s some decrease in efficiency once the cells are packaged into panels, and of course further loss as the electricity is converted to AC and ultimately delivered to a load.
But what about plants? You might think that they are much better, given that they are Nature’s own design for capturing the sun, and they’ve had billions of years to evolve and improve the process. Well, it looks like Man has the lead on this one! The USDA reported on some very interesting research in this article: http://www.ars.usda.gov/is/pr/2012/120112.htm. Plants don’t make electricity (not YET, anyway), but rather convert the sun’s energy into chemical energy. So agricultural scientists put the plant and PV solar conversion processes on a direct comparison (apples-to-apples), and found that plants have a year-round average conversion efficiency of 1%, while solar PV converts 10% on average. Wow! That surprised me. It says we need to apply man’s expertise in crop science – focusing the science to improve efficiency could lead to improved crop yields – and that could be a great benefit to our growing population!
--David Byrne
