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> Photovoltaic solar is vastly better as it provides more power, does not need direct sunlight, and costs less. And produces nothing during the night. The big

> Photovoltaic solar is vastly better as it provides more power, does not need direct sunlight, and costs less. And produces nothing during the night. The big reason for solar thermal is that you can store hot molten salt for the night, and use it to generate power when PV doesn't do anything.

toomuchtodo 10y ago
So then it comes down to which is cheaper: having hot molten salt maintained on site, or dropping cargo containers full of lithium batteries on-prem to provide dispatchability for the facility. I argue batteries will get cheaper, faster, than trying to manage hot molten salt.
- nickff 10y ago
  Managing a hot molten salt pool is not as difficult as trying to deal with many lithium cells. You mention dropping cargo containers on site, but that is not the whole problem; you need to manufacture these containers and have a way of continuously monitoring the cells, either finding and isolating the 'bad' ones, or replacing whole containers. In addition, the molten salt will last far more cycles than the batteries, while costing less to replace and being simpler to service.
  - toomuchtodo 10y ago
    https://www.teslamotors.com/powerpack https://www.teslamotors.com/powerpack That's the benefit though, right? I can write Tesla a check and they can ship me an entire utility scale energy storage system by rail/truck multi-modal. I can't do that with molten salt.
    - nickff 10y ago
      You are vastly underestimating the cost and complexity of running this system at an affordable cost. You would end up with Tesla running the majority of your facility (by cost), and consequently would not be a competitive plant. Let's do some simple math: An average natural gas plant seems to be around 800MW, and we might assume that they are running somewhere around 1/2 capacity when there is not much solar irradiation (evening and night), giving us an average power level of 400MW. Wikipedia says that Lithium Ion cells have a specific energy of about 100-240 W.h/kg, and I'll assume that Tesla uses some good 200W.h/kg cells. If the plant has to run with no irradiation for 10 hours at half capacity, it needs 4000 MW.h of energy in batteries, which is 4000M/200 = 20Mkg of batteries not including any losses during discharge or wasted energy for cooling. 20 million kilograms of batteries would be very expensive to store and maintain; they would also take up a lot of containers. A 20' container is usually maxed out at about 20 tons, so you would need a thousand of them. The basic problem is that unlike molten salt, there are no economies of scale to be had with batteries or photovoltaic panels.
      - Retric 10y ago
        There is no need for Li-Ion for grid storage as weight is a non issue it's just a question of cost. Don't forget we ship train loads of coal across several states just to burn it.
        nickff 10y ago
        I mentioned weight to give some idea of the amount of batteries that would be required, and how many containers would be needed (as I was responding to a suggestion of using containerized batteries), not because the weight is a significant factor.
- SAI_Peregrinus 10y ago
  Also, if molten salt is good enough and cheap enough as an energy storage solution you can take an efficiency hit and use PV solar to melt the salt electrically.
Retric 10y ago
Actual real world solar thermal plants are a long way from 24/7. EX: https://en.wikipedia.org/wiki/Solar_Energy_Generating_Systems https://en.wikipedia.org/wiki/Solar_Energy_Generating_System... Capacity factor 21%. That's 7 hours a day for 5 days a week. A huge problem is any cloud cover prevents them from working, so unless your willing to burn something they become useless randomly. PS: Molton salt sounds cool, but it's horribly inefficient as you can only really use a small temperature range before it's to cold so you need crazy amounts of the stuff and can't ever let it cool. https://en.wikipedia.org/wiki/Carnot_cycle#Efficiency_of_real_heat_engines https://en.wikipedia.org/wiki/Carnot_cycle#Efficiency_of_rea...
- rgbrenner 10y ago
  The Crescent Dunes facility has a capacity factor of 52%. It doesn't use any natural gas or other fossil fuels. And it's not affected by intermittent cloud cover. https://en.wikipedia.org/wiki/Crescent_Dunes_Solar_Energy_Project https://en.wikipedia.org/wiki/Crescent_Dunes_Solar_Energy_Pr... http://www.digitaltrends.com/cool-tech/peek-inside-nevada-solar-plant-247-power-molten-salt/ http://www.digitaltrends.com/cool-tech/peek-inside-nevada-so...
  - deleted 10y ago
    [deleted]
  - Retric 10y ago
    Yea, add in molten salt and they can almost get apoximatky PV capacity factor just even more random due to slight cloud cover being such an issue. Though, you will note 52% still needs backup power all for the low low cost of 13.5 cents per kWh vs sub 4 cents per kWh for PV. You can get PV + storage for 24/7 operation for less than 13.5 cents. PS: Which is why most places gave up on molton salt in the first place and burning stuff is the real backup that you know actually works.
  - deleted 10y ago
    [deleted]

toomuchtodo 10y ago

So then it comes down to which is cheaper: having hot molten salt maintained on site, or dropping cargo containers full of lithium batteries on-prem to provide dispatchability for the facility. I argue batteries will get cheaper, faster, than trying to manage hot molten salt.

nickff 10y ago
Managing a hot molten salt pool is not as difficult as trying to deal with many lithium cells. You mention dropping cargo containers on site, but that is not the whole problem; you need to manufacture these containers and have a way of continuously monitoring the cells, either finding and isolating the 'bad' ones, or replacing whole containers. In addition, the molten salt will last far more cycles than the batteries, while costing less to replace and being simpler to service.
- toomuchtodo 10y ago
  https://www.teslamotors.com/powerpack https://www.teslamotors.com/powerpack That's the benefit though, right? I can write Tesla a check and they can ship me an entire utility scale energy storage system by rail/truck multi-modal. I can't do that with molten salt.
  - nickff 10y ago
    You are vastly underestimating the cost and complexity of running this system at an affordable cost. You would end up with Tesla running the majority of your facility (by cost), and consequently would not be a competitive plant. Let's do some simple math: An average natural gas plant seems to be around 800MW, and we might assume that they are running somewhere around 1/2 capacity when there is not much solar irradiation (evening and night), giving us an average power level of 400MW. Wikipedia says that Lithium Ion cells have a specific energy of about 100-240 W.h/kg, and I'll assume that Tesla uses some good 200W.h/kg cells. If the plant has to run with no irradiation for 10 hours at half capacity, it needs 4000 MW.h of energy in batteries, which is 4000M/200 = 20Mkg of batteries not including any losses during discharge or wasted energy for cooling. 20 million kilograms of batteries would be very expensive to store and maintain; they would also take up a lot of containers. A 20' container is usually maxed out at about 20 tons, so you would need a thousand of them. The basic problem is that unlike molten salt, there are no economies of scale to be had with batteries or photovoltaic panels.
    - Retric 10y ago
      There is no need for Li-Ion for grid storage as weight is a non issue it's just a question of cost. Don't forget we ship train loads of coal across several states just to burn it.
      - nickff 10y ago
        I mentioned weight to give some idea of the amount of batteries that would be required, and how many containers would be needed (as I was responding to a suggestion of using containerized batteries), not because the weight is a significant factor.
SAI_Peregrinus 10y ago
Also, if molten salt is good enough and cheap enough as an energy storage solution you can take an efficiency hit and use PV solar to melt the salt electrically.

Retric 10y ago

Actual real world solar thermal plants are a long way from 24/7. EX: https://en.wikipedia.org/wiki/Solar_Energy_Generating_Systems https://en.wikipedia.org/wiki/Solar_Energy_Generating_System... Capacity factor 21%. That's 7 hours a day for 5 days a week. A huge problem is any cloud cover prevents them from working, so unless your willing to burn something they become useless randomly. PS: Molton salt sounds cool, but it's horribly inefficient as you can only really use a small temperature range before it's to cold so you need crazy amounts of the stuff and can't ever let it cool. https://en.wikipedia.org/wiki/Carnot_cycle#Efficiency_of_real_heat_engines https://en.wikipedia.org/wiki/Carnot_cycle#Efficiency_of_rea...

rgbrenner 10y ago
The Crescent Dunes facility has a capacity factor of 52%. It doesn't use any natural gas or other fossil fuels. And it's not affected by intermittent cloud cover. https://en.wikipedia.org/wiki/Crescent_Dunes_Solar_Energy_Project https://en.wikipedia.org/wiki/Crescent_Dunes_Solar_Energy_Pr... http://www.digitaltrends.com/cool-tech/peek-inside-nevada-solar-plant-247-power-molten-salt/ http://www.digitaltrends.com/cool-tech/peek-inside-nevada-so...
- deleted 10y ago
  [deleted]
- Retric 10y ago
  Yea, add in molten salt and they can almost get apoximatky PV capacity factor just even more random due to slight cloud cover being such an issue. Though, you will note 52% still needs backup power all for the low low cost of 13.5 cents per kWh vs sub 4 cents per kWh for PV. You can get PV + storage for 24/7 operation for less than 13.5 cents. PS: Which is why most places gave up on molton salt in the first place and burning stuff is the real backup that you know actually works.
- deleted 10y ago
  [deleted]