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We could use heating elements like those in electric showers to heat sand using electricity from photovoltaic solar panels, during day hours. That super hot sand could be stored in some tanks with thermal insulation, to be used at night time for boiling water to generate steam and turn a turbine to generate electricity.
Sand is so cheap, and can be heated to temperatures above 500, 600, 700 degrees Celsius without melting.
Would it be possible? I suppose so, but it would be incredibly inefficient.
Whether a substance remains solid or not is irrelevant to storage at scale. To the contrary, phase change (from solid to liquid, liquid to solid, liquid to vapor, etc.) usually stores or releases large amounts of thermal energy. Boiling water to create pressurized vapor (steam) is an example. It isn't that water vapor is magic, what makes it worthwhile is that there can be huge amounts of it easily produced under pressures sufficient to push turbine wheels around or pistons in steam engines.
Something akin to what you suggest for thermal storage was proposed years ago using sodium sulfate:
Would it be possible? I suppose so, but it would be incredibly inefficient.
Whether a substance remains solid or not is irrelevant to storage at scale. To the contrary, phase change (from solid to liquid, liquid to solid, liquid to vapor, etc.) usually stores or releases large amounts of thermal energy. Boiling water to create pressurized vapor (steam) is an example. It isn't that water vapor is magic, what makes it worthwhile is that there can be huge amounts of it easily produced under pressures sufficient to push turbine wheels around or pistons in steam engines.
Something akin to what you suggest for thermal storage was proposed years ago using sodium sulfate:
Concrete makes a better thermal battery than loose material like sand. I've seen houses with a concrete floor and a bunch of south-facing windows to allow the floor to absorb the heat from the sun in the morning and then radiate it back through the house throughout the afternoon. Put an overhang over the windows so the sun doesn't shine through the windows in the summer when the sun is higher and it's all good. Concrete floors are also amenable to in-floor heating systems.
If thermoelectric generator modules (TEGs) based on Peltier effect or Seeback effect were cheaper, this approach could have some viability. But it would require a great cut in the costs of TEGs compared to present day costs.
We could use heating elements like those in electric showers to heat sand using electricity from photovoltaic solar panels, during day hours. That super hot sand could be stored in some tanks with thermal insulation, to be used at night time for boiling water to generate steam and turn a turbine to generate electricity.
Sand is so cheap, and can be heated to temperatures above 500, 600, 700 degrees Celsius without melting.
Sand also cools rapidly depending on ambient temperature. You would have to insulate the hot sand all the way around for it to reduce the rate of cooling, but that would be too expensive and cumbersome to accomplish. Lets say that you have a large container full of hot sand, perhaps a tank that holds 1,000 gallons of sand. Are you aware of how heavy sand can be? The average weight of 5-gallon bucket full of sand is around 45-65 pounds. How are you going to warm the sand inside the tank after it cools?
Instead of storing hot sand inside the house, use heat pumps in the hot sand to bring the heat to your home.
Sand also cools rapidly depending on ambient temperature. You would have to insulate the hot sand all the way around for it to reduce the rate of cooling, but that would be too expensive and cumbersome to accomplish. Lets say that you have a large container full of hot sand, perhaps a tank that holds 1,000 gallons of sand. Are you aware of how heavy sand can be? The average weight of 5-gallon bucket full of sand is around 45-65 pounds. How are you going to warm the sand inside the tank after it cools?
Probably a large tank with thermal insulation would be needed to store the hot sand, and prevent it from cooling.
To warm the sand inside the tank I guess it would be needed to have the heating elements (like those used in electric showers) permanently inside the tank. A small orifice in the tank wall would be needed as a way in for the power cables that would supply the electricity for the heating elements.
For recovering the thermal energy and turning it back into electricity at night I guess the best idea would be using thermoelectric generator modules (TEGs) based on Peltier effect or Seeback effect. But they are still too expensive and too inefficient in 2020.
It's just speculation, I can't imagine all the possible drawbacks of this approach.
- it can be heated to more than 700 or 800 degrees Celsius without melting
When you are on a beach covered with hot sand, you only have to kick downward about two inches to hit cool sand. This indicates that sand would not be a very good storage medium. Concrete heats much deeper, but a liquid like water probably trumps them both for thermal storage.
When you are on a beach covered with hot sand, you only have to kick downward about two inches to hit cool sand. This indicates that sand would not be a very good storage medium. Concrete heats much deeper, but a liquid like water probably trumps them both for thermal storage.
The big problem with water is that if you heat it above 100 degrees Celsius on normal atmospheric pressure it becomes a gas, and dealing with a gas is much more complicated. Water at 98 or 99 degrees Celsius could be a thermal storage medium, but with sand you can have much higher temperatures, even one thousand degrees maybe....
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