I worked on this CSP project back in 2009 when it was still on paper. It's really exciting to see forecasts/estimates/hypothesis that do work out i.e. store heat energy to serve peak hours when the sun isn't shinning. More importantly, and what I really look forward to, is that this carbon-free technology is to a large extent "validated" meaning that this kind of projects are now less risky, more viable and financeable. Hopefully this will push down the price of CSP + storage, which will make it more attractive to both utility incumbents and new entrants/energy startups.
Ditto, xP. Although, I imagine in 5-10 years solar will be a big player in energy, so I'm trying to stay current. Just gotta make it through the next 5-10 years.
I've been puzzled for some time: Is anyone / why isn't anyone working on more flexible and responsive coal and nuclear plants? Instead of storing renewable energy, it would be more efficient, less complex, and less capital-intensive (one would think) to consume the renewable energy immediately and make up the difference between supply and demand with flexible traditionally-fueled plants.
I'm sure there's a good reason. I just don't know what it is.
By flexible, do you mean "able to ramp up to meet demand and ramp down when not needed"?
Any power plant that uses steam turbines is going to have a long ramp-up time to boil a huge quantity of water needed to produce the steam. Nuclear plants do this, and I imagine most/all coal plants do as well. Hydroelectric plants don't need to because the falling water drives the turbines directly.
The first thing I thought of when I read the article is that this power plant can't be very efficient. It's using steam turbines, but six hours after sunset there isn't enough heat to keep the turbines going. That means they need to reheat every morning. It seems like it would have been better for them to include a coal plant for nighttime operations to keep the steam boilers hot and keep the turbines going all night. That would be flexible, because the coal burners could start up quickly to keep the already-hot water boiling. (Can't use nuclear this way because you can't really turn a nuclear reactor on and off.)
I'm totally guessing here, but I suspect they didn't include an alternate nighttime operations fuel because this is a "100%-Green" project that either wouldn't have gotten funding if there was a coal plant involved or it was just intended as a demonstration of the solar capability and didn't need to be practically efficient.
If they could've collocated near a landfill, they could burn methane at night. Still environmentally friendly/neutral (all landfills have to flare the methane they generate), and you don't need as large of a methane supply as you're just burning it when the sun is down.
There's also a given that 6hrs after sunset there isn't a need for as much power... most of the population is asleep, lights off, TVs off, etc. There are other traditional power plants (Hydro and Nuclear) in AZ that provide overflow service for off hours. It actually takes a combination of plants to offer the best load distribution.
In parts of AZ there are serious brown outs and rolling blackouts in the summers as A/C kicks in everywhere, which is probably the biggest draw.
I'm opposed to coal altogether for pollution reasons alone. It's bad enough between the cars and airport traffic, don't need more.
Do you have any kind of source on that? I've lived in Arizona all my life, and the only rolling brownouts I've experienced and heard about have been in California. Who I believe already buy surplus power from AZ.
I lived in Prescott Valley, and several years in a row saw brown/blackouts in mid-summer. Also saw them a number of times in the Peoria & I-17 area in phx (closer to cactus)
I've seen outages lasting a couple hours from components like transformers breaking, but that's a different issue from the grid itself not producing enough power to meet demand. Can't speak for Prescott Valley though.
Interestingly, the only article on a Phoenix area blackout due to high load I was able to source happened in the winter... probably caught SRP totally off guard:
There might be one reason they let this spin up and down.
We mostly power the grid through a bunch of constantly humming systems, but our usage has all kinds of peaks (diurnal, seasonal... the British grid has a massive peak right around the time Eastenders ends and everyone puts on a kettle[1]).
If you are adding some power to the baseline, that's helpful. If you're promising the grid you can add some power during one of the daily or seasonal peaks, that's almost as valuable as adding a new source of always-on power. By providing energy for even just six hours a day, you might save the grid from requiring a new always-on plant. So in terms of opportunity costs, even by being twice as expensive moment to moment, you're still cutting costs in half (unless everyone followed your strategy).
So there's probably some number of hours of shutdown where it's worth the coal, some number where it's not, all contingent on what plants are nearby, and how close your customers typically are.
Related but tangential, one of the unintended benefits of electric cars would be adding a bunch of consumption at night, smoothing the diurnal cycle, letting us pursue more lower-cost always-on generation. (This is before you even consider distributed storage proposals that let the grid draw from parked cars in emergencies.)
Predictability is almost as good as a natural resource.
> six hours after sunset there isn't enough heat to keep the turbines going
Note that's when running at "maximum power". You don't have to extract the heat that fast. Given a hypothetical and utterly irresponsible grid supplied solely by this design, you'd overbuild to the point that you'd have enough stored heat to last all night.
> Any power plant that uses steam turbines is going to have a long ramp-up time to boil a huge quantity of water needed to produce the steam.
This is a matter of tradition and convenience. It is quite possible to use a just-in-time steam generator.
In fact many steam power systems are vapor phase only (non-condensing) to avoid corrosion and droplet impact damage. Steam is used because it is cheap and nontoxic.
Nuclear reactors are easy to turn on and off once a day. Naval reactors do it as a matter of course. There's just no point. If you build a grid scale reactor, you might as well leave it running all the time, at which point you optimize away the rapid start capability.
As an uninformed guess: you want to minimize the number of heating and cooling cycles because that causes joints to crack. They used to keep steam trains running for days at a time (meaning they were kept fired overnight even when not used) to avoid cooling cycles.
Actually I would also be interested to know the real answer to this too. There was an interesting article in the Economist this week about the problems of the constant power output of nuclear and coal plants.
Reminds me of a story I heard from a guy in mining. Some sort of furnace they used took $1m of power to heat from a cold start. So they were reluctant to ever power down.
Pretty sure coal plants are already used in that way, but on a 'grid-wide' level; based on predictions based on the time of day, time of year, and other factors, traditional power plants get scaled up / down or powered up / down, preferably with minimal waste. Wasting fuel and powering up/down isn't profitable for the energy companies either. I can imagine that the fast-responding power plants are the hydroelectric ones, since their power output can be adjusted by just closing off some valves. Of course, if their reservoir is empty or low they can't scale up easily.
For the nukes there are a few so called SMR (small modular reactors) being worked on, and some of the are in process of licensing with NRC.
The main selling pint is that these units with a capacity of about 200MWe can be deployed under 1bil dollars when compared to 15bil dollars for a large plant (>1000MWe). Most of these small plants can operate in a load follow mode, similar to gas plants. Also their footprint is similar to that of a gas plant rather than to that of a large nuke.
There are already 'peaker plants' which are generally gas fired turbines which can be activated to supply power on demand, but they are more expensive to operate as start/stop systems (startup consumes a lot of energy in its own right).
So generally 'peakers' aren't good fits for the other side of the energy generation equation.
Pumped-storage Hydro is a solution for storing power that is generation-method agnostic; it works with electricity from nuclear just as well as it works with electricity from wind. Basically the PSH station buys cheap electricity, and uses it to pump water up a hill into a reservoir. When electricity becomes expensive, it reverses the flow, generates electricity with the falling water, and sells it to the grid for a profit. These setups can switch to power generation rather quickly.
The only problem is that you need suitable geography. It's a bit more forgiving than finding proper geography for regular hydroelectric, but it is still a restriction.
I remember reading a typically opinionated article on the The Register where the claim was made that pumped storage doesn't scale very well. Or rather, it scales fine, but your country will look very different when you've finished the necessary building work.
There's a very interesting project in Finland to build a pumped storage facility that uses a 1400m deep abandoned gold mine as the storage location. The idea is to use a relatively small amount of water but at very high pressure provided by the depth of the mine -- the high potential difference makes generation more efficient and reduces capital costs. If this thing turns out to be profitable, this will probably be done to all sufficiently deep mine shafts and other deep enough holes.
France uses nuclear plants for load following. It more or less has to; its only other significant source of power is hydro. It works, but it not as economical as it might be.
That just means running the plants below capacity, which is certainly done when electricity price falls below running costs. But since fixes costs are high, it is rarely a good investment to build a lot of overcapacity for these. Gas plants are low fixed / high running cost and quick to ramp up so are better for peak production.
Such nuclear designs are being worked on. In fact they're essentially ready now, but one does not simply get approval to spool up a nuclear plant. There's no inherent reason why either type cannot supply variable power needs instead of baseload, but it tends to be more inefficient overall to use a design with a wide variance of generation capacity, which is likely why utilities try to stray away from that.
I'm sure there's other problems though that an actual power distribution engineer could describe. E.g. the wide variance of wind/solar production from second to second would require a lot of energy storage and filtering to allow it to be placed on the grid (especially the rickety U.S. grid) without a series of transients accidentally opening circuit breakers and causing a blackout.
This is already the case. Gas plants take very little time to start up and shutdown. Combining thermal storage with the solar plant allows it to act as more of a base load power system. I would guess the goal is allowing utility companies to decommission more costly intermittent plants with solar replacements.
While not exciting this weekend the link shows a graph of Ontario's electricity supply mix. During the week you can see the variations in gas plant performance, from no work output to full work output within an hour.
The fuel costs are a small portion of the running costs of a nuclear plant, and the other costs don't go down when you shut it down, so there is very little reason to ever produce at less than maximum.
I assume that responsiveness isn't the issue but that the economics don't work for Arizona Public Service to maintain 750MW worth of coal/nuclear waiting offline for intermittent use only.
You don't build a coal power plant speccing in how much variable renewable energy will be produced. You spec for over the max power - in the middle of summer, with all the air conditioners on, and then you throttle down from there. As a utility, you wouldn't depend on someone else's renewable energy if your job is ensure that an area gets power.
That said - the best time for renewable energies to provide power is when the sun is shining the hottest, which for solar based power, coincides nicely with the maximum power use.
I find it interesting that we're still using water to transfer the energy. Has there been much research into finding better ways to create electricity than stream => turbine? Is there anything interesting happening in this area?
It just seems to me that the process of turning water to steam to impart kinetic energy to a turbine is incredibly wasteful, and all we seem to be researching are fancier turbines. I would love to be shown otherwise.
It is not all that wasteful; the water is recondensed from the steam so that when you boil it again it is already quite hot. This process is 1/2 to 2/3 as efficient as the theoretical maximum efficiency of any possible device, (hot temp - cold temp)/(hot temp). The difference is mostly materials science - we don't have any materials strong enough and heat-resistant enough to operate the cycle at thousands of degrees. But people are certainly working on it. There is more in universities and in labs than is dreamed of on Hacker News.
Even if one does use advanced coolant cycles of some sort, water is extremely effective as a coolant. It has one of the highest volumetric heat capacities of any pumpable liquid at low temperatures, a very low viscosity and manageable reactivity, and a very low-temperature, high-energy phase transition that we understand well for higher temperature applications, which does not even require exotic pressure conditions to achieve. Water is likely to show up at some stage of the cycle in any complex thermodynamic infrastructural engineering.
Steam turbines are the most efficient way of turning heat into mechanical and electrical energy. You can get a slight efficiency boost at tremendous cost by changing the working fluid to something lighter, but nobody bothers with that.
There's some interesting research in using fuel cells to extract energy from natural gas and oil, which potentially could be more efficient. This doesn't work for coal, though.
It's actually really efficient, so much so that I think an interesting question is scaling that technology down rather than making a new technology to replace it.
There are a lot of interesting technology advances related to better manufacturing processes & material science for turbine blades. The closer we can get to the "ideal" shape, the higher performance the turbine. Single crystal turbine blades are an incredible feat.
This is a big deal, one of the key benefits of Coal/Gas/Oil power stations is their ability to provide frequency response (where the power output is adjusted to keep the AC as close to 50 Hz as possible) or to participate in a balancing mechanism (where generators place bids on providing minute by minute changes to their power output). Until now the only thing a solar/wind/nuclear generator could do was turn their generators on or off. That severally limits the proportion of renewables you can reasonably have on your grid[1]. But this technology looks like it'll give a renewable generator a way of dynamically adjusting their output to match demand.
[1] You do get controlled generation with biomass, but the efficiency is terrible and you need that land to grow food, so it'll (hopefully) only ever be a niche technology.
> I agree that massive expansion of biomass generation would impact agricultural land.
It would; just look at the amount of farmland currently used to produce plants used for the production of biofuels. It's a big impact on the food production capacity of the world, and it's mainly used to mix with regular oil-based fuels so that the oil/gas companies adhere to government standards, tax reductions and customer goodwill, whilst the biofuel producers get government grants and fundings and more tax deductions.
Of course, that's (iirc) first-generation biofuel, second/third generation (or grade) biofuel uses biowaste (shells, green stuff, animal waste, stuff that would otherwise be processed into compost or fertilizer).
3 square miles is 7.77 square km. Just over 1 kW of sunlight falls per square meter, so I will round up and say that there are 8 GW falling on the plant total.
So 280 MW of production is 3.5% efficient of peak irradiance.
It looks like 5 kWh/m2 for Arizona, so that's 38.85 GW per day irradiance on 7.77 sq km. Assuming the plant can put out its maximum capacity for the 18 hours it runs each day, that's 280 times 18 = 5 GW per day.
So it's operating at almost 13% efficiency of average irradiance.
That is very good, considering that they are able to store heat much more cheaply and environmentally friendly than storing electricity in batteries.
The most important thing of all is that it doesn't have to wait for innovations in photovoltaics. Anyone can buy land, set up parabolic mirrors, and tinker with forgotten heat engines like Stirling cycle engines or Tesla turbine engines that easily achieve 30, 40, 50% efficiency and approach the Carnot limit. Conversion of motion to electricity is a solved problem at 95% efficiency.
Oh and these plants can be supplemented by biomass, say biodiesel from algae or fuel pellets made of hemp. If that's too granola for the fossil fuel industry, they can also use natural gas.
In fact if you study this long enough, you find that there are only two real hurdles: energy storage and connection to the grid (made difficult because of resistance from established utilities). Generation turns out to be relatively inexpensive because there's a sea of free energy all around us. To put it in perspective, Grand Coulee dam puts out less power than the irradiance falling on the solar plant. It's just more efficient at converting the motion of falling water to electricity:
It puts out 6.8 times 24 = 163 GW/day. That's 33 of these solar plants. So every 100 sq miles (260 sq km) of desert is equal to the 324 sq km of area flooded by Grand Coulee.
Solar thermal is the hydroelectric of the future and uses less land, which will only improve going forward. IMHO this will someday dwarf wind and nearly eliminate intermittency issues.
> (...) that's 280 times 18 = 5 GW per day. (...)
> (...) It puts out 6.8 times 24 = 163 GW/day. (...)
GW (GigaWatt) is already energy over time (Joules per second), you don't multiply it by the number of hours a day (why hours, why not seconds or anything else for example). Unless you're counting multiple plants you're adding, but that's not the case here.
edit after finishing this post: actually, you seem to be using W(att) for both W (watt, a unit of power) and Wh (Watt-hour, a unit of energy), which, besides being wrong, leads to confusion. Your post is very coherent under this new light.
So this :
> It looks like 5 kWh/m2 for Arizona, so that's 38.85 GW per day irradiance on 7.77 sq km. Assuming the plant can put out its maximum capacity for the 18 hours it runs each day, that's 280 times 18 = 5 GW per day.
Actually becomes :
5 kWh/m²/day -> 5/24 kW/m² (since there are 24 hours a day and a kWh is the energy of 1 kW power over 1 hour), so 7.77 x 1000000 x 1000 x 5 / 24 Watt = about 1.6 GW for 7.77 km².
And assuming the plant can run at 280 MW for 18 hours per day, its average power output is 280 x 18 / 24 = 210 MW.
Unfortunately I'm unable to edit my post now because it's too old. For anyone finding this, cataflam is partially right, I had some typos but the math is the same. I stand by using total power output per day to calculate efficiencies. cataflam's right that over a 24 hour period, you could say the average output would be 210 MW. Here is the corrected version:
---
3 square miles is 7.77 square km. Just over 1 kW of sunlight falls per square meter, so I will round up and say that there are 8 GW falling on the plant total. 280 MW over 8 GW = 0.035.
So 280 MW of production is 3.5% efficient of peak irradiance.
It looks like 5 kWh per m2 per day for Arizona, so that's 5 kWh per m2 times 7,700,000 sq m = 38.85 GWh per day irradiance on 7.77 sq km. Assuming the plant can put out its maximum capacity for the 18 hours it runs each day, that's 280 MW times 18 hrs = 5 GWh per day. 5 GWh over 38.85 GWh = 0.1287.
So it's operating at almost 13% efficiency of average irradiance.
That is very good, considering that they are able to store heat much more cheaply and environmentally friendly than storing electricity in batteries.
The most important thing of all is that it doesn't have to wait for innovations in photovoltaics. Anyone can buy land, set up parabolic mirrors, and tinker with forgotten heat engines like Stirling cycle engines or Tesla turbine engines that easily achieve 30, 40, 50% efficiency and approach the Carnot limit. Conversion of rotational motion from a turbine to electricity with a generator is a solved problem at 95% efficiency.
Oh and these plants can be supplemented by biomass, say biodiesel from algae or fuel pellets made of hemp. If that's too granola for the fossil fuel industry, they can also use natural gas.
In fact if you study this long enough, you find that there are only two real hurdles: energy storage and connection to the grid (made difficult because of resistance from established utilities). Generation turns out to be relatively inexpensive because there's a sea of free energy all around us. To put it in perspective, Grand Coulee dam puts out less power than the irradiance falling on the solar plant. It's just more efficient at converting the motion of falling water to electricity:
It puts out 6.8 GW times 24 hrs = 163 GWh/day. That's 33 of these solar plants. So every 100 sq miles (260 sq km) of desert is equal to the 324 sq km of area flooded by Grand Coulee.
Solar thermal is the hydroelectric of the future and uses less land, which will only improve going forward. IMHO this will someday dwarf wind and nearly eliminate intermittency issues.
No. To be honest, I was a bit baffled by your question: why would you think that it would take the same time to heat as to cool?
It will heat depending on how quickly you can get energy to it, and it will cool depending on how quickly you can remove energy from it. Have you never seen an electric heater or oven and noticed they heat quickly and take a while to cool down? Or rapidly cooled something by putting it in iced water or a freezer?
There's nothing to be baffled about, it's a fair question. You even provided the answer: "It will heat depending on how quickly you can get energy to it, and it will cool depending on how quickly you can remove energy from it."
On the other hand, there's no "electric heater" here to use to heat up the liquid used to absorb solar heat (not to mention ice or freezers...); it's the sun or nothing. Given that the sun doesn't give us peak solar flux until the midday it's entirely possible that solar energy production in the first few hours of the day would only keep up with instantaneous energy needs instead of having enough of an excess to reheat the heat storage fluid for energy production later that night.
Whether this is actually an issue or not depends on the numbers, but it's not a baffling question at all and there's no reason to be so condescending about it.
It's baffling to me because it makes no sense based on everyday experience to think that things have a set amount of time that they heat up or cool down. Why would anyone think that?
If you think my comment was condescending, stop reading it in a condescending tone.
If the goal is to heat up the reserve tanks as quickly as possible, I would think so, else I guess the plant can simply divert some of the heated oil from the water boiler to the tanks and slowly heat them while the sun is shining.
I don't think the plant needs to warm up that long before it can produce energy, since only the oil between the collectors and steam generators has to be heated.
You can size your solar field to collect much more over the day than the tanks can store. So if your field were 100MW and tanks were 200MWh, it would only take 2 hours to fill them (assuming no electricity production). But after those two hours, you better have turbine capacity to take up the excess heat. Baseload CSP designs usually have storage in the range of 6-10 hours (real storage hours vary based on the solar input).
Very good question. It depends on thermal mass. I believe they must be 'charging' a thermal mass all day and using it to taper off at night. It probably can start instantly once the sun is up, but their 'thermal capacitor' may indeed take 6 hours to recharge.
Availability is a big issue when it comes to solar energy. As you can guess, producing solar energy during the day ins't that much of a problem, but supplying the demand in the evening or at night with solar energy is a much bigger challenge.
So, even if takes 6 hours to heat up in the morning, it still expand the usability of solar energy for electricity production.
I assume this is a molten salt plant? If so, I didn't think that was a new thing because I've heard about it plenty before now. Is this the largest solar-thermal plant doing this? The first?
"In addition to creating steam, the heat transfer fluid is used to heat molten salt in tanks adjacent to the steam boilers. The thermal energy storage system includes six pairs of hot and cold tanks with a capacity of 125,000 metric tons of salt, and the molten salt is kept at a minimum temperature of 530 degrees Fahrenheit."
