5 ms·

"All night" isn't quite true. It has 10 hours of storage. And if you want full capacity, you have to start tapping into that in the evening. Also what's cool a

"All night" isn't quite true. It has 10 hours of storage. And if you want full capacity, you have to start tapping into that in the evening. Also what's cool about this plant, is that it doesn't use natural gas in the morning to heat up the molten salt (like other plants). The salt never cools completely during the lifetime of the plant. Expensive though.. on a 25 year contract at 13.5 cents per kwh. That'll be renegotiated after the 25 years at a much lower rate. Utilities pay higher prices for new plants (gas, oil, etc) to pay off the cost of building it. After that, it drops to a more reasonable price. https://en.wikipedia.org/wiki/Crescent_Dunes_Solar_Energy_Project https://en.wikipedia.org/wiki/Crescent_Dunes_Solar_Energy_Pr...

honkhonkpants 10y ago
Doesn't "hours of storage" necessarily imply a rate of discharge? If you don't take any steam off it, doesn't it last more than 10 hours? It seems like they should just state the storage in terms of extractable energy stored. And why sodium? It does not have a spectacular specific heat. Is it just convenient due to its high boiling point?
- foota 10y ago
  I believe it's because of the large temperature range between solid and gaseous phases, there is a ~800 degrees Kelvin difference between the boiling and melting points, which at a specific molar heat of 29 J/mol/K is greater than the energy to heat water to boiling for a ~100 degree difference at ~56 J/mol/K
- rgbrenner 10y ago
  Yes.. they do state the storage in terms of energy. When plants state hours, it's at full capacity. So 110MW capacity x 10 = 1.1 GWH of storage. Of course it will operate longer if you use less than full capacity. Molten salt is used because it's liquid at atmospheric pressure, is low-cost, its operating temperatures are compatible with the most efficient steam turbines, and it is non-flammable and nontoxic.
dang 10y ago
> "All night" isn't quite true. Ok, we've replaced that title with representative language from the article.
taneq 10y ago
Expensive indeed. I wonder how concentrated solar thermal compares with a simple photovoltaic plant these days? Given the precipitous drop in price for PV panels, even if solar thermal is currently cheaper, how much longer until it's just not competitive?
- rgbrenner 10y ago
  PV is down to around 5 cents/kwh. I seem to remember a new plant recently that was 2-3 cents, but can't find it. The only problem with PV is its variability. When there's cloud cover, in the evening, etc.. power drops. Which means you need some kind of storage to even it out and probably a gas plant for the evening/night time. In comparison, CSP has a steady output, which lets them make adjustments easier.
  - taneq 10y ago
    Sounds like a hybrid plant would be the best approach, with a large molten salt reservoir which is 'charged' while the sun is shining and used to run a steam generator when PV isn't available. Of course, the way battery storage prices are going, I wouldn't be surprised if battery backup becomes more economical than all that messy pipework in the near future anyway.
    - Tharkun 10y ago
      I don't share your optimism. It'll be a while before we can produce useful, grid sized batteries for this kind of use. The hybrid approach you describe would require twice the surface area and probably wouldn't double the output. I think I prefer the idea of having large plants like these, with 'night'-time capabilities and a relatively steady output. That sounds like it would work pretty well in combination with decentralized roof top solar + smallish home batteries.
      - taneq 10y ago
        The whole point is that solar thermal power costs 2x - 5x what solar photovoltaic power costs, so you use solar photovoltaic when possible and back it up with solar thermal. It does increase the area required but that's the price you pay for fully renewable baseload power. You could just use thermal but it'd be much more expensive and still require the same footprint for similar power output. Of course, there's nothing wrong with the photovoltaic part being distributed in the form of rooftop solar, which is what's already increaslingly happening. Home storage batteries for load leveling are picking up nicely too, which is good because they're going to become mandatory within the next decade if we want metropolitan power grids to survive tens of megawatts of sometimes-rapidly-fluctuating solar power being dumped into them.

honkhonkpants 10y ago

Doesn't "hours of storage" necessarily imply a rate of discharge? If you don't take any steam off it, doesn't it last more than 10 hours? It seems like they should just state the storage in terms of extractable energy stored. And why sodium? It does not have a spectacular specific heat. Is it just convenient due to its high boiling point?

foota 10y ago
I believe it's because of the large temperature range between solid and gaseous phases, there is a ~800 degrees Kelvin difference between the boiling and melting points, which at a specific molar heat of 29 J/mol/K is greater than the energy to heat water to boiling for a ~100 degree difference at ~56 J/mol/K
rgbrenner 10y ago
Yes.. they do state the storage in terms of energy. When plants state hours, it's at full capacity. So 110MW capacity x 10 = 1.1 GWH of storage. Of course it will operate longer if you use less than full capacity. Molten salt is used because it's liquid at atmospheric pressure, is low-cost, its operating temperatures are compatible with the most efficient steam turbines, and it is non-flammable and nontoxic.

dang 10y ago

> "All night" isn't quite true. Ok, we've replaced that title with representative language from the article.

taneq 10y ago

Expensive indeed. I wonder how concentrated solar thermal compares with a simple photovoltaic plant these days? Given the precipitous drop in price for PV panels, even if solar thermal is currently cheaper, how much longer until it's just not competitive?

rgbrenner 10y ago
PV is down to around 5 cents/kwh. I seem to remember a new plant recently that was 2-3 cents, but can't find it. The only problem with PV is its variability. When there's cloud cover, in the evening, etc.. power drops. Which means you need some kind of storage to even it out and probably a gas plant for the evening/night time. In comparison, CSP has a steady output, which lets them make adjustments easier.
- taneq 10y ago
  Sounds like a hybrid plant would be the best approach, with a large molten salt reservoir which is 'charged' while the sun is shining and used to run a steam generator when PV isn't available. Of course, the way battery storage prices are going, I wouldn't be surprised if battery backup becomes more economical than all that messy pipework in the near future anyway.
  - Tharkun 10y ago
    I don't share your optimism. It'll be a while before we can produce useful, grid sized batteries for this kind of use. The hybrid approach you describe would require twice the surface area and probably wouldn't double the output. I think I prefer the idea of having large plants like these, with 'night'-time capabilities and a relatively steady output. That sounds like it would work pretty well in combination with decentralized roof top solar + smallish home batteries.
    - taneq 10y ago
      The whole point is that solar thermal power costs 2x - 5x what solar photovoltaic power costs, so you use solar photovoltaic when possible and back it up with solar thermal. It does increase the area required but that's the price you pay for fully renewable baseload power. You could just use thermal but it'd be much more expensive and still require the same footprint for similar power output. Of course, there's nothing wrong with the photovoltaic part being distributed in the form of rooftop solar, which is what's already increaslingly happening. Home storage batteries for load leveling are picking up nicely too, which is good because they're going to become mandatory within the next decade if we want metropolitan power grids to survive tens of megawatts of sometimes-rapidly-fluctuating solar power being dumped into them.