8 ms·

Arizona solar plant achieves six hours after sun goes down

128 points by bromagosa 13y ago

pkulak 13y ago
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?
- phorese 13y ago
  "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." (link at bottom of OP's article)
- Xylakant 13y ago
  From what I gathered the one that has the largest storage capacity measured in "minutes at maximum power."
- ndonnellan 13y ago
  I believe salt is used for thermal storage, but oil is the heat transfer fluid used to generate steam. solar -> oil -> steam || salt salt -> oil -> steam
antr 13y ago
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.
- ndonnellan 13y ago
  I'm curious, what are you doing now? Still in CSP? The projects I worked on haven't yet come to light (ha), which is a bit disappointing.
  - antr 13y ago
    I'm now doing the startup thing, but not in the energy space.
    - ndonnellan 13y ago
      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.
jzwinck 13y ago
The aerial photograph at the top of TFA looks a whole lot like SimCity[1]. Awesome. [1] One of the old versions, not the 2013 one nobody plays.
- _mulder_ 13y ago
  "not the 2013 one nobody plays" Haha, so true. But ironically on the 2013 one you can actually build a massive solar farm that will look just like that.
jwcacces 13y ago
So, does it take 6 hours to heat up in the morning?
- phorese 13y ago
  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.
- phaemon 13y ago
  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?
  - mpyne 13y ago
    > I was a bit baffled by your question: 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.
    - phaemon 13y ago
d4nt 13y ago
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.
- maxerickson 13y ago
  Biomass generally means wood or agricultural waste/residue. Tree plantations probably use some land suitable for farming, but not all that much. Most biomass generation occurs at plants that have other operations involving wood, so even much of the wood burned is byproduct. I agree that massive expansion of biomass generation would impact agricultural land.
  - Cthulhu_ 13y ago
    > 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). source: my memory
TheCraiggers 13y ago
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.
- jessriedel 13y ago
  My understanding is that converting heat to steam to turbine power is actually extremey efficient. I wish I had a cite for you, but I don't.
- comicjk 13y ago
  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.
- baq 13y ago
  water has certain nice properties: cheap, not toxic and very high heat capacity. there are probably more, but i'm not a powerplant engineer.
- mapt 13y ago
  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.
quarterto 13y ago
That headline feels like they accidentally a word.
Lagged2Death 13y ago
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.
- mpyne 13y ago
  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.
- DougWebb 13y ago
  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.
sergiosgc 13y ago
Is this a big deal? Molten salt plants have achieved almost a day with no sun. Example: http://www.torresolenergy.com/TORRESOL/gemasolar-plant/en http://www.torresolenergy.com/TORRESOL/gemasolar-plant/en
- cinquemb 13y ago
  I think it is a bigger deal for people who haven't been following CSP tech these past couple of years.
deleted 13y ago
[deleted]
zackmorris 13y ago
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. BUT average irradiance is smaller than peak: http://rredc.nrel.gov/solar/old_data/nsrdb/1961-1990/redbook/atlas/ http://rredc.nrel.gov/solar/old_data/nsrdb/1961-1990/redbook... 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: http://en.wikipedia.org/wiki/List_of_largest_hydroelectric_power_stations http://en.wikipedia.org/wiki/List_of_largest_hydroelectric_p... 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.
- deleted 13y ago
  [deleted]
- cataflam 13y ago
  > (...) 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.

128 points by bromagosa 13y ago

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?

phorese 13y ago
"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." (link at bottom of OP's article)
Xylakant 13y ago
From what I gathered the one that has the largest storage capacity measured in "minutes at maximum power."
ndonnellan 13y ago
I believe salt is used for thermal storage, but oil is the heat transfer fluid used to generate steam. solar -> oil -> steam || salt salt -> oil -> steam

antr 13y ago

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.

ndonnellan 13y ago
I'm curious, what are you doing now? Still in CSP? The projects I worked on haven't yet come to light (ha), which is a bit disappointing.
- antr 13y ago
  I'm now doing the startup thing, but not in the energy space.
  - ndonnellan 13y ago
    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.

jzwinck 13y ago

The aerial photograph at the top of TFA looks a whole lot like SimCity[1]. Awesome. [1] One of the old versions, not the 2013 one nobody plays.

_mulder_ 13y ago
"not the 2013 one nobody plays" Haha, so true. But ironically on the 2013 one you can actually build a massive solar farm that will look just like that.

jwcacces 13y ago

So, does it take 6 hours to heat up in the morning?

phorese 13y ago
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.
phaemon 13y ago
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?
- mpyne 13y ago
  > I was a bit baffled by your question: 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.
  - phaemon 13y ago

d4nt 13y ago

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.

maxerickson 13y ago
Biomass generally means wood or agricultural waste/residue. Tree plantations probably use some land suitable for farming, but not all that much. Most biomass generation occurs at plants that have other operations involving wood, so even much of the wood burned is byproduct. I agree that massive expansion of biomass generation would impact agricultural land.
- Cthulhu_ 13y ago
  > 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). source: my memory

TheCraiggers 13y ago

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.

jessriedel 13y ago
My understanding is that converting heat to steam to turbine power is actually extremey efficient. I wish I had a cite for you, but I don't.
comicjk 13y ago
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.
baq 13y ago
water has certain nice properties: cheap, not toxic and very high heat capacity. there are probably more, but i'm not a powerplant engineer.
mapt 13y ago
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.

quarterto 13y ago

That headline feels like they accidentally a word.

Lagged2Death 13y ago

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.

mpyne 13y ago
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.
DougWebb 13y ago
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.

sergiosgc 13y ago

Is this a big deal? Molten salt plants have achieved almost a day with no sun. Example: http://www.torresolenergy.com/TORRESOL/gemasolar-plant/en http://www.torresolenergy.com/TORRESOL/gemasolar-plant/en

cinquemb 13y ago
I think it is a bigger deal for people who haven't been following CSP tech these past couple of years.

deleted 13y ago

[deleted]

zackmorris 13y ago

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. BUT average irradiance is smaller than peak: http://rredc.nrel.gov/solar/old_data/nsrdb/1961-1990/redbook/atlas/ http://rredc.nrel.gov/solar/old_data/nsrdb/1961-1990/redbook... 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: http://en.wikipedia.org/wiki/List_of_largest_hydroelectric_power_stations http://en.wikipedia.org/wiki/List_of_largest_hydroelectric_p... 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.

deleted 13y ago
[deleted]
cataflam 13y ago
> (...) 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.