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grambell789 t1_irwfv7m wrote

Reply to comment by El_Minadero in Geothermal May Beat Batteries for Energy Storage: Enhanced geothermal systems are well suited to store excess renewable power as heat. by filosoful

if you doing steam turbine to make electricity you have to condense the low pressure steam that came out of turbine to be able to pump it back into the boiler. its part of the carnot cycle and limits heat engine efficiency to no more than 40%.

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platoprime t1_irwiyuw wrote

Pumping water up and letting it fall down to generate electricity is 80% efficient over a complete cycle. Am I crazy to think talking about storing electricity as heat in the ground is stupid?

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El_Minadero t1_irx1uyb wrote

Yes. Because we can't make the entire planet a hydroelectric dam. Dams are great! but they require lots of fresh water.

Geothermal and hydroelectric power are both incredibly low carbon sources of electric power and potential energy storage mechanisms. It makes sense to use both depending local economics and logistical constraints.

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FinndBors t1_irwlvy5 wrote

It's pretty stupid unless we are getting to the point where we are generating too much electricity at the wrong time and wasting it anyway.

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platoprime t1_irwm0ko wrote

But it has no advantages over water storage and is half as efficient? Why not store the extra electricity as water?

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FinndBors t1_irwmv5p wrote

Water storage requires favorable geography.

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platoprime t1_irwo399 wrote

It doesn't require it. You can create closed loop systems and dig a hole.

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sunsparkda t1_irx0om5 wrote

Digging a hole that has enough volume to store significant gravity based energy storage and won't collapse in on itself when the bottom reservoir is empty raises the price for it, both construction and maintenance. Presumably enough to make geothermal storage cost competitive.

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Jiecut t1_irwnd8b wrote

I think it's much easier to develop storage. With water storage you need a big reservoir at a higher elevation.

With this, you're storing the energy underground.

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killcat t1_irzmaxl wrote

You need somewhere to pump it up TO, not always available.

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El_Minadero t1_irx1lz3 wrote

Sure. but the way newer geothermal binary cycle plants work is the hot geothermal water goes through a heat exchanger at the surface but is never allowed to change into a gas. The intermediate working fluid is typically something like butane. round trip cycle efficiency is limited by the carnot cycle but its not like closed cycle geothermal plants are just leaking water left and right into the ground.

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grambell789 t1_irx2pfv wrote

i wouldn't let the well water from a geothermal system anywhere close to something like a turbine that has precise moving parts. I will look into butane as intermediate.

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El_Minadero t1_irx40cb wrote

Lots of geothermal plants use a binary cycle. Look up Ormat or the FORGE project.

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