Super Solar Cells

June/July 2007
By Erika Bentson 
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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.

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  • don 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?

  • spanish_houston 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

  • Ken 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.

  • chtank 6/5/2007 9:14:25 PM

    Please correct the code for this article, as it is is unreadable. I
    would love to read what Mother Earth says about this but until this
    is fixed, I will not know. I do HTML, too, but I make sure it meets
    the W3C Accessibility standards plus our blind and vision impaired
    users have a very difficult time with javascript when it is not
    written correctly.

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