Basic thermodynamics: converting heat into work is inefficient. A photovoltaic can go straight from the energy of the photons (admittedly restricted to a particular band that they were designed for) with less loss.
That's a slightly glossed over interpretation of thermodynamics. Perhaps photovoltaics have a higher theoretical efficiency than a thermal cycle plant, but in practice they don't. Thermal cycle power plants are the mainstay of our power generation - nuclear, coal, gas, geothermal - all those power sources make use of a steam based heat to work cycle. We've got 100 years of experience in developing thermal cycle power. Peak photovoltaic efficiency is currently ~20%, while most affordable cells are closer to 10-15%. A simple cycle thermal plant might have an efficiency of 30-40%. It'll be some time before photovoltaics are more efficient for a given area of collecting space.
Cost is a different question. Photovoltaics have fallen dramatically in cost recently. As the space taken up by a solar plant isn't really an issue (the collecting area could take up 10 times more space without really impacting anything), the winner in solar energy will be the cheapest option per kWh.
I can't help myself to think of "Fallout: New Vegas".. you know, a massive solar-power plant near Last Vegas with mirrors "aiming" for a huge tower.. :D.
Other than that, really interesting read :)
Very cool stuff. I have to say I'm very impressed to see a project like this actually getting off the ground. After working for a few years in California's energy regulatory sphere you can become very cynical about the ability to build much of anything, especially when environmental impact statement proceedings can be used by NIMBY (or any other) concerns to stonewall just about any project for just about any reason, if they've got money.
Looks like Brightsource found the right location where there aren't too many folks worried about the development, and whether or not solar thermal will indeed become a growth industry they've at least set a precedent for this kind of work (and regulatory process) in the 21st century, which is an important development.
I hope Brightsource's decision not to go public was only a good rational choice rather than a sign of a company going under.
I love the juxtaposition of this facility with the absurd desert golf resort. A good contrast of America's disastrous 20th century with a glimmer of hope for the future.
Does anyone know the long (really long?) term effects of turning sun energy in to electrical? I refuse to beleive it has a zero impact. We take heat energy away from the ground, so the ground gets cooler right ? And over a long period the ground is no longer heated the same as it use to, so that cools the top crust, which would cool the crust below etc. Thoughts? (I am nowhere near qualified to ask these questions)
Indeed. The geological effects of mining are much more serious than solar energy, which are not zero still (you need mining to produce solar panels/mirrors).
Most side effects are focused on local biosphere I'd guess.
I wish that, when quoting the maximum output of a power plant, news articles would also quote the capacity factor - basically, the percent of the maximum output that a plant achieves long-term.
This plant is likely to have around a 40% capacity factor, which is much better than the 20% or so photovoltaic solar achieves, but it's much lower than the 85-90% that baseload plants achieve.
Capacity factor is location- and weather-dependent, and not always known for certain with a new technology (or in this case a known technology this much larger).
Concentrated solar thermal also allows for storage, making the capacity factor percentage adjustable, and allowing for on-peak optimization, which would have a lower capacity factor but a significantly higher benefit to the power company.
If it's peak capacity syncs with peak demand for air-conditioning that might work.
Environmentally you would probably do much better (energy wise) by covering the roofs of building in Las Vegas with similar mirrors to lower their albedo and reduce air conditioning use.
Don't know about tarnishing, but for cleaning they most likely use water.
From an article on solar thermal plants in the Middle East [1]:
But harsh desert conditions in parts of the MENA region generate large amounts of airborne dust which collects on the solar panels used in CSP systems, reducing their efficiency. They need regular cleaning, which consumes large amounts of water.
Personally, I think this is the most ridiculous concept. I have not seen the math but in order to achieve any meaningful scale it needs to be huge, but on the flip side the farther you get from the center the efficiency reduces drastically.
Moreover, this is a dusty desert, what are their plans for cleaning those mirrors, at such a huge scale. The only guy who will make money in this is the one with that contract.
The inventor had tried this earlier, I believe in Israel, but that had failed.
Oh well, with federal loan guarantees that it has, we have another Solyndra on our hands.
> I have not seen the math but in order to achieve any meaningful scale it needs to be huge
How can you make a statement like that? If you're not aware of the mathematical basis for the plant then you can't quantify "huge". You're either regurgitating something you read elsewhere without any real understanding, or you're simply making untrue statements.
If this is a ridiculous concept, what do you propose instead? Further oil exploration? More coal? This project is making a meaningful step towards reducing our dependence on fossil fuels. If you want to criticise, fine, but please at least take the time to properly understand the costs involved and the alternative options.
Anyway you may be right that the tower concept isn't going to last long, but the troughs have been shown to last decades (see Victorville, California) and obviously they have the same issue of dust... so there must be a known solution for that engineering challenge.
They probably keep it at under 1000 degrees by circulating a molten salt at whatever rate is necessary to carry away the heat.
No matter what the target is made out of, without that circulation to withdraw heat, it wouldn't get much hotter before it vaporized and there was no target. No doubt it'd be possible to get a much higher temperature if that was the goal.
Maybe, if you mean Celsius. Salt melts at 1474F (801C), so it'd have to be kept above that or it'd crystallize.
I've always wondered what they do if the conditions don't provide a high enough temperature... seems they'd have to drain it entirely of it's salt before it solidifies, or they'd never be able to get it restarted. That is, unless they have some form of heater all the way through the plumbing to melt the salt so it'll flow.
I first read about using salt this way back in (Popular Science? in) the early/mid-'80s with a parabolic reflector heating the salt to be pumped to a Stirling engine. They didn't address that question then either.
I referred to "a molten salt", which in practice is never sodium chloride; probably because its melting point is higher than some superior alternatives.
Molten salt is used for two reasons.
It is the best real-world conductor of heat you will find. If you heat a miles-long pipe of molten salt on one end, that heat will make its way to a temperature rise on the other end in surprisingly rapid fashion. But this is only true when it is molten. Naturally, if molten salt encounters its solid salt, the solid melts pretty easily to expand the volume of molten salt.
Molten salt stores quite a bit of energy in its phase change, and of course as a salt solidifies, it becomes more dense. This means the top salt (at the collector) will always be the slowest to solidify.
Not sure where all this worry about "freezing to death" comes from. The salt's effectiveness comes from its conduction, not its flow.
If you have enough liquid salt, it will (mostly) stay liquid for days, just like icebergs survive for months above freezing temperatures. They will have enough molten salt, if only in order to be able to keep it liquid when the sun is down (as a bonus, that buffering of solar heat in the molten salt allows these devices to deliver power around the clock)
I also think having solid salt inside your pipes isn't that bad; the stuff is water soluble at room temperature. To get rid of clogged pipes, I would consider pumping in hot water, replacing it when it gets too salty. That might take lots of time, but is fairly safe (I think you would need to dry the inside of your tubing very well afterwards; molten salt and water probably isn't a nice combination)
