Friday, May 27, 2016
Publication Date:09/1/2007
ARCHIVE >  September 2007 Issue >  Tech-Op-Ed > 

Sunblock Anyone?
Walter Salm, Editor
Not long ago, I was taking my weekly stroll through the Thursday night Farmer's market — a summertime event that shuts down several blocks of downtown Chico, California in the evening — when I was amazed to find one vendor selling solar generated electricity. They were not selling solar panels; they were selling solar power. There is a distinct difference, since the customer does not lay out any cash for the hardware or the installation. The company, Citizenre ( will install banks of solar cells on the customer's rooftop or in a backyard, or wherever, and will only charge the customer for the electricity actually consumed. The contract guarantees the customer locked-in rates equal to the present rate currently going to the power utility, and this rate is good for 25 years! Whatever excess the solars generate goes to the grid. If you use more power than the solar banks can provide, you pay the same rate, even though the extra energy you use is coming from the grid. It certainly sounds like a win-win situation.

Let's see, this means there is no system purchase outlay, no installation cost, no maintenance fees, no permit hassles, no performance worries and no rate increases. Better, if there's a power blackout, your home or factory will continue to have electricity. This happens is because of the way we generate and distribute electricity. That grid out there means that the electricity you use may be coming from a generating plant hundreds or even thousands of miles away. No matter how you slice it, those high-voltage AC transmission lines cost money to build, to use, to maintain. And even using high voltage/low amps, there is still some energy loss due to resistive conductor heating, leakage, storm interruptions, and all the other nice things that can go wrong with a transmission line.

The lead photo in the website shows a fairly common type of a red brick Victorian house with a difference: the porch roof is covered with solar panels. A solar-powered Victorian? Well, why not? Victorians use electricity, too.

Solar cells, like fuel cells and batteries, provide DC; the output has to go through an inverter to create the AC power we need. In most home systems, the solar panels route the DC to a central inverter, which converts it to AC. This system has some disadvantages. First, there is power line loss in the DC circuits. Second, if the inverter fails, then all the solar power is lost until the inverter can be replaced. Citizenre's REnU system uses AC solar panels; each solar panel has its own inverter sandwiched onto its underside, so the output is AC instead of DC. There is no DC line loss, and if an inverter fails, only the power from that panel is lost. Reading between the lines, it would appear that there is some concern about inverter failure. Is this a significant problem in power plant design? This might be an issue that our industry could address with design innovations.

A lower-tech approach to solar power doesn't use solar cells at all. Instead, it uses solar collectors — long half-cylinder-shaped parabolic mirrors up to 400 meters long, that concentrate the sun's energy on absorber tubes made of stainless steel. The absorber tubes are installed at the focus of the parabolic reflector. The cover tube of the receiver has an abrasion-proof anti-reflection layer that reportedly allows 96 percent of the reflected solar radiation to penetrate to the "special fluid" that absorbs the energy. This goes to a heat exchanger which heats water, augmented by additional heating from a gas or oil burner. The resulting steam turns a generator turbine.

While this system isn't 100 percent solar, the technology is considered to be "mature", meaning it has reached the zenith of its development. Several such fields of solar steam turbine plants are in operation in Arizona and Southern California, feeding energy into the grid, and it is expected that this type of sustainable power will grow as world oil and gas prices continue to rise. The National Renewable Energy Laboratory, the largest research center for renewable energy sources in the U.S., performed a geographic analysis to see what parts of the country were appropriate for such centralized solar power plants. They found that we can expect to build about 200,000 Megawatts of power (about 17 percent of the total U.S. power requirements) using central solar energy in such places as California and Nevada, along with New Mexico, Colorado and Arizona. Bordering states Utah and Texas are expected to follow.

Okay, we still need fossil fuels, but as they get more costly, nuclear power looks better and better as an alternative energy source, especially handy to have when the sun isn't shining.  

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