Super Solar Cells

Scientists are researching new techniques for better and more efficient solar cells.

| June/July 2007

For decades, scientists have sought to improve the efficiency of solar power technology. Today, silicon cells generally convert less than 15 percent of the sun's energy into electricity, according to Keith Emery, a research engineer with the National  Renewable Energy Laboratory (NREL). But a new kind of photovoltaic (PV) cell promises to be even more efficient. Conceived and designed at NREL, Boeing-Spectrolab is now manufacturing record-breaking PV cells that can convert more than 40 percent of the solar radiation striking them into electricity. The magic is in their "multijunction" design: each of three layers harnesses a different range of the solar spectrum. "I have no doubt the efficiency will continue to go up," Emery says. Right now these PV cells are only viable for large-scale operations, but the improvements may eventually trickle down to residential applications and help lower PV electricity costs.

12/28/2007 6:13:57 AM

i have a large wood supply and am looking to build off grid. can i convert my wood heat to electricity thru trickle charge of the exhaust? also, steam engine?

12/16/2007 6:05:09 PM

Ken: A stirling engine converts heat energy into mechanical energy. A striling engine could be attached to a generator to produce electricity. There are a wide variety of Stirling engine designs. The one that would best suit your needs would depend on how you plan to extract the heat from the heated oil. You should look into the different design types to get an idea of what is feasible in your situation. However, if you are considering using a stirling engine in order to get higher efficiency, then it would probably be best that you simply design a system whereby the Stirling engine is directly powered by the sun rahter than through stored heated oil. There are already commercialized soalr dish Sterling engine systems available for sale, but they are very large they are designed for commercial energy production. I do not think producing electricity from your stored heated oil will be more efficient than a PV panel system of decent conversion efficiency (15%). Furthermore, I would be more concerned about your battery charging setup. If you are concerned about money , you will end up buying non-sealed lead-acid batteries. These batteries last longest when they are kept as charged as possible at all times. If you intend to cycle down to 50% or less every day, your batteries will not last long. even if you are cycling down to 70% every day, they may not last nearly as long as they possibly could. The more often and more severly you drain the batteries, the sooner they will be junk. Connecting a good-sized PV array to a battery bank will be, in most cases, more beneficial for the batteries. Of course, if you intend to buy a large battery bank and will be using only a very small percentage of the battery bank capacity every day, then daily generator charging is not too bad. But batteries are not cheap, and a very large battery bank will be a significant investment. And batteries will only last between 5 to 15 years, depending on their quality

12/6/2007 2:20:30 PM

This is a question for your alternative guys. I want to power an off-grid house using batteries and use a generator to charge the batteries once a day for a couple of hours. I could use a diesel engine attached to the generator to do that but I would like to take a different route. I would like to build a trough solar collector and store the heated oil as an energy storage device. I could then use it for all my heating needs. I would have a tank of 400 degree oil I could use for turning a 10KW generator. How can I use this stored thermal energy and convert it to mechanical energy to turn the generator in a closed loop system on a cheap budget? I would like to use this method of solar collection vs PV because of the costs and because I don't believe that PV has the same efficiency as solar to thermal energy.

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