Luz Plant Size (wasre: Practical Applications Of Solar Energy)

Q: I believe the 10MW size of the Luz plant was mentioned. The owner of Luz stated in an article in Solar Today that the size was limitied by PURPA rules. When PURPA was modified to permit larger sizes, the next Luz plant matched that size, 80MW I believe. They had to stay within this limit partly to get tax breaks but also to insure that the utilities would be required to buy the power they generated.

A: Sandia is working on the heliostats, but there's no reason to yank the glass heliostats that are already in place -- they work fine, but were too expensive up front for commercial units. Solar 2 is to test the new receiver and associated equipment. I was under the impression that they are going to be using a salt mixture. Sodium nitrate melts at 310 C; the sodium/potassium nitrate eutectic melts at 220 C. They could push the melting point down still further using Ca/K or various ternary eutectics (especially with lithium), but 220 C sounds about right. The 10 MW was for Solar 1, not the Luz plants. Note that the utility considered the Luz plants something of a dead end, believing (probably correctly) the power towers would ultimately be cheaper. Note also that absent tax breaks the Luz plants were simply uneconomical, as was demonstrated when the breaks were delayed and Luz went belly up. It will be right where Solar 1 used to be (Barstow, wasn't it, or was it Daggett?). They are reusing some components, but are replacing Solar 1's water-heating receiver with a newer molten salt receiver (I don't know if the salt is to flow in tubes or down the exterior face for direct irradiation.) You can see the site when driving along the interstate from Los Angeles to Las Vegas. There are many practical ways. They are not economic, in some cases, but they do exist. Possible, practical, and economic uses abound. For example, you can preheat the domestic water and send it into the same old insulated tank that serves as your water heater today. Done all over the place. Some folks go so far as to add a larger insulated tank upstream of the standard water heater. These systems often store from one to 4 days of hot water. Practical and economical. Trombe walls are often used in passive solar homes. Practical and economical. Stores heat from one day to the next. Ditto for thermal tiles, and, in greenhouses, barrels of water. Which is the supplementary and which is the primary?... If I have a solar water heater that provides all my domestic hot water in spring, summer, and fall, is it then only a 'supplementary' system if I need to use gas in winter? In 1/4 of the days of winter? Or is it the gas that is 'supplementary'?... Pretty much all the solar designs I've seen use some SUPPLEMENTARY energy from {gas, oil, electric mains,...} for the odd case where the sun doesn't shine for weeks on end (that only comes once per long long time). That, in my book, makes the solar primary and the conventional fuels the supplementary... But then, I don't see 'supplementary' as a pejorative term... Storing solar heat is almost trivial. Passive home designs work because it is so trivial. (i.e. use masonry for floors and put in a Trombe wall). Storing solar electricity is possible, but not economical for folks hooked to a grid.

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