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World's Largest Solar Array to use Stirling Engine
An anonymous reader writes "Stirling engines are not a neglected or forgotten technology after all, according to a story at PESN. With 20 years of in-the-field fine-tuning, Stirling Energy Systems is now ready to go big -- real big. They signed a purchase agreement Tuesday with Southern California Edison (SEC), to install a 20,000 dish array that will cover 4,500 acres and will be capable of generating 500 megawatts of electricity -- more than all other U.S. solar projects combined -- making this the largest solar installation in the world. Each collector has a 37-foot-diameter array of mirrors to focus the sun's rays on the Stirling engine, which turns the heat into rotational torque for electricity generation. According to a spokesperson for SCE, this purchase will be in their commercial interest, requiring no subsidy in order to compete, implying that the efficiencies of the technology will give them an edge in the market."
I'm glad to see alternative energy sources being developed, I just wish public opinion would change faster so we can get some more nuclear plants as well.
4500 acres of solar collectors? This must throw hardcore environmentalists into a infinite loop.
Cheap, not free. Cheap.
The pictures have huge dishes to collect heat, but what about the other end? How do they keep the cool part of the cycle cool?
I was expecting to see the engine behind the dish (receiving light via a secondary mirror) and big radiator fins attached to the engine in the shadow of the dish.
Quattuor res in hoc mundo sanctae sunt: libri, liberi, libertas et liberalitas.
... and based on a 37ft dia dish, 20,000 count we're talking 21,504,183 sqft of total collector area. Divide that into 500,000,000W, the projected peak output of the installation, and you end up with around 23W per sqft.
Now I could swear I've seen a higher efficiency per sqft specified using a related but different technology: steam turbines. I can't find the link right now, but I was hoping to build one of these things one day myself to take some real world measurements. The projections I read admittedly may have been inaccurate which is why I want to build my own to find out, but the project site was claiming the potential to pull approaximately 3KW of usable power out of a steam turbine from a 6 ft diameter parabolic dish.
There are a few completed collector dishes out there in this size and they are making between 600-1100 deg fahrenheit at the focus where a heat exchanger is placed to boil water into steam pressure which drives a turbine. The only thing that leaves me questioning the accuracy of the projections is that the turbine is a somewhat unconventional one, called a "Tesla Turbine".
Nonetheless, if the figures are remotely accurate, you'll find that a 6ft dish putting out 3KW is worth over 100W per sqft. I believe this possibility alone makes it well worth examining the potential for higher thermal conversion efficiency than the sterling engine model because it could potentially reduce the size of this installation to 25%... or quadruple the output!
Regardless, both approaches are quite fascinating because they're so simple - it's mind numbing that nothing like this is yet operational. It's so technologically unsophisticated that it could be built and installed nearly anywhere. Even the sun tracking circuit can be done on the cheap for about $25US in bits & pieces.
RTF post I wrote: "The only real advantage to hydrogen is that it burns very cleanly, in theory making it an ideal vehicle fuel." Also, you may have noticed that we're not talking about hydrogen's suitablility as a vehicle fuel, we're talking about how SCE is going to store solar energy for nighttime use. Get with the program. Read what people are writing so you can actually follow the conversation.
If a job's not worth doing, it's not worth doing right.
The rest of the equipment: heat collector at the focus, flexible piping, insulation, pipes, evaporators, heat sinks, pumps, working fluid, turbines, gears, cogs, lubricants, generators, buildings, staff, land
What do you need all that stuff for?
With the exception of land (which you will need a lot of but it's all desert and not suited for much else) and a minimal staff, none of that junk is required.
The Stirling cycle runs at 10% efficiency. { Note: most Stirling engines are about 5x less efficient that this}.
This is a little ambiguous. The theoretical Stirling engine can achieve the ideal Carnot efficiency. Real Stirlings can reach 50 percent of this maximum theoretical value.
With a ambient (sink) temperature of, say, 110F (316K) and a temperature of 1400F (1033K - Actually a conservative estimate) our Carnot efficiency is 69.4%. A real high-end Stirling can reach 50% of that, or nearly 35% thermal. After you generate the electricity you are *still* looking at 25% overall efficiency or better.
All that stuff cleans and maintains itself at no cost.
Practically would! If a crew of 3 guys can take a hose truck and rinse the dust off the mirrors of each dish in ~15min, they can do about 30 dishes per day. Each dish would probably only need to be washed once a month, so 30*30 = 900 dishes a month. You'd need 23 crews of 3 men each to maintain 20,000 dishes, or 67 people. A 500MW coal plant would employ about 100. (Guestimated from here) Moreover, the people running a coal plant would have to be skilled to maintain the high pressure steam equipment, which means they would cost more. You would not need special training and licensing to operate a hose truck.
As for the Stirling gen sets themselves, they are hermetically sealed and virtually maintenance free. You can contract out any service that might be required rather than having your own staff. In fact, I would think SES would offer a nice warranty that includes service, so if one does go down simply replace it with a spare unit (They are small and modular, you know) and send them back for service.
The tracking systems are also fairly low maintenance and could be contracted out.
So in light of the above, you may wish to revisit your calculations.
They make a breakthrough and develop an efficient Stiring regenerator, which is simultaneously long and short, conductive and insulating. See : www.tinaja.com/glib/muse116.pdf
So you based your argument on three sentences (one copied almost verbatim) from a journal that seems to deal mostly with electronics? Brilliant. You, sir, seem woefully uninformed about how Stirling engines operate. I will grant you that the regenerator is perhaps the biggest hang up when it comes to design, but by no means is it impossible to create. What you are tying to do is make a medium that stores and rejects heat quickly ("highly conductive") with minimal internal volume ("long and thin") and low pressure loss for gas flow ("short and fat") and does not create a thermal short ("highly insulating"). In practice, a stack of fine mesh stainless steel screens works quite well. I have also read storied about people stuffing the passages in the engine with brass wool to great effect.
=Smidge=