Exploring Hydrocarbon Depletion
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Bas wrote:Tanada wrote:PV panal convert 20% or less of light into electricity, why not build a reflector array like that one with PV cells as the pnanl material? Get twice the use from the same light, as it were.
I don't think you can reflect the light and use it in solar panels at the same time; as it is, mirrors in this set up are far more effiecient than stand alone solar panels. Drawback is that you need to do this on a relatively big scale (like it's being done here) to get those kind of efficience rates. Also mirrors are far less expensive to produce and replace than solar panels.
September 19, 2007
Sunny Outlook: Can Sunshine Provide All U.S. Electricity?
Large amounts of solar-thermal electric supply may become a reality if steam storage technology works—and new transmission infrastructure is built
By David Biello:
In the often cloudless American Southwest, the sun pours more than eight kilowatt-hours* per square meter of its energy onto the landscape. Vast parabolic mirrors in the heart of California's Mojave Desert concentrate this solar energy to heat special oil to around 750 degrees Fahrenheit (400 degrees Celsius). This hot oil transfers its heat to water, vaporizing it, and then that steam turns a turbine to produce electricity. All told, nine such mirror fields, known as concentrating solar power plants, supply 350 megawatts of electricity yearly.
"The maximum you can get into the grid is about 25 percent from solar," including photovoltaics
http://www.us.schott.com/solarthermal/e ... tails.html
The absorber tube (SCHOTT), which is made of steel and is located on the inside, must be capable of absorbing a lot of solar radiation without emitting significant amounts of heat. To achieve this, SCHOTT developed a coating that offers an absorption rate of 95%. At a temperature of approximately 400° Celsius, only a maximum of 14% of the total heat is emitted.
joe1347 wrote:I was surprised to read that solar thermal power plants (for generating electricity) are currently limited to about 25% efficiency.
"The maximum you can get into the grid is about 25 percent from solar," including photovoltaics, Mills says. But "once you have storage, it changes from this niche thing to something that could be the big gorilla on the grid equivalent to coal."
skyemoor wrote:"The maximum you can get into the grid is about 25 percent from solar," including photovoltaics, Mills says. But "once you have storage, it changes from this niche thing to something that could be the big gorilla on the grid equivalent to coal."
Reading the quotes again, you will see that they were talking about the mix of energy on the grid, not the efficiency. Intermittent sources are limited because they can only provide power at certain times (i.e., tidal, solar during daytime), or when certain conditions are right (i.e., wind, and solar in partly cloudy areas). What happens during the times of low power output? There are a number of answers (i.e., spot pricing, demand side management, etc) and if those intermittent sources are coupled with energy storage, they will be able to reduce the supply intermittency, allowing them to provide a greater percentage of grid power.
http://www.volker-quaschning.de/article ... dex_e.html
Trough Power Plant Efficiencies
The efficiency of a solar thermal power plant is the product of the collector efficiency, field efficiency and steam-cycle efficiency. The collector efficiency depends on the angle of incidence of the sunlight and the temperature in the absorber tube, and can reach values up to 75%. Field losses are usually below 10%. Altogether, solar thermal trough power plants can reach annual efficiencies of about 15%; the steam-cycle efficiency of about 35% has the most significant influence. Central receiver systems such as solar thermal tower plants can reach higher temperatures and therefore achieve higher efficiencies.
joe1347 wrote:1. I believe that thermodynamic efficiency is increased if the temperature is increased, so wouldn't a larger parabolic or fresnel concentrator heat up the oil (or steam) to a higher temperature and thus improve efficiency?
joe1347 wrote:2. Desert land and mirrors seem to be fairly inexpensive. Or is the 400C temperature a maximum for some other reason. Such as, above 400C the heat emitted (lost) increases rapidly or does the downstream hardware fail in some way because it is unable to handle higher (>400C) temperatures.
joe1347 wrote:3. Alternatively, is there a law of diminishing returns associated with concentrator optics?
http://www.greenpeace.org/raw/content/i ... -Power.pdf
From page 13.
The use of oil-based heat transfer
media restricts operating
temperatures today to 400°C,
resulting in only moderate steam
PARABOLIC TROUGH SYSTEMS
Parabolic trough systems represent the most mature solar
thermal power technology, with 354 MWe connected to the
Southern California grid since the 1980s and over 2 million
square metres of parabolic trough collectors operating with a
long term availability of over 99%. Supplying an annual
924 million kWh at a generation cost of about 12 to 15 US cents/
kWh, these plants have demonstrated a maximum summer
peak efficiency of 21% in terms of conversion of direct solar
radiation into grid electricity
With these facts (observations actually), I wonder what can be done technically to improve solar thermal efficiency?
Professor Membrane wrote: Not now son, I'm making ... TOAST!
joe1347 wrote:With these facts (observations actually), I wonder what can be done technically to improve solar thermal efficiency?
There's a world of difference between losing subsidies/tax breaks they managed to get by earlier, and actually loosing ground to a clean competitor. It's kinda like the vast sum of money that was spent opposing the CA gas tax a couple years ago. If they stand to loose out on enough cash, they'll start flexing their muscle. They have in the past...HydroLuver wrote:The fossil fuel lobby doesn't have much clout with the current congress. Many of their tax breaks, during the first 6 years of the Bush Admin, are currently at risk. The current energy bill is partially funded by allowing the oil industry tax breaks to expire. The new tax breaks are for solar and wind subsidies.
Professor Membrane wrote: Not now son, I'm making ... TOAST!
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