Heat pump geothermal does offer low cost inter-seasonal energy storage. Check out prior Volts interviews. It doesn't make electricity but it greatly reduces demand for energy for heating and cooling.
Heat pump geothermal does offer low cost inter-seasonal energy storage. Check out prior Volts interviews. It doesn't make electricity but it greatly reduces demand for energy for heating and cooling.
Yes, I remember that interview and fully agree that geothermal seasonal storage is an excellent option for heating and cooling of buildings and potentially industrial heat as well. We will need some options for electric power too, and those are not so clear to me.
Ehhh. Geothermal is great for how it offers a source of heat differential year round. I donтАЩt know that IтАЩd say itтАЩs as effective for _storage_. ItтАЩs not like you can take excess solar in the summer, and pump superheated water down to heat up the earth, and then recover that heat months later. There are serious long term thermal storage ideas (like molten salt, and the box-oтАЩ-rocks approach where they line the box with IR-PV) which probably work on a time scale of days out to a week or two. IтАЩm not sure whether any of those is plausible for season-to-season storage, though.
That is incorrect; such systems can and do give true inter-seasonal energy storage, where heat derived from summer cooling of buildings (and sometimes solar energy or waste heat or other sources adding heat on purpose) adds to the thermal mass, to be used as heat during winter. Larger, "busy" buildings with borehole heat pumps can add more heat over a full year to the underground thermal mass than they draw back for winter heating and often require some cooling towers to keep it balanced.
For cold climates the amount of energy for heating is large; reducing the need for direct energy use greatly reduces demands for energy.
Huh. How efficient is that? While thermal conductivity down there isn't that high, it's still not _zero_, I'd think over months, added heat would diffuse away into the background, and the immediately-accessible mass would move back closer to the ambient temp.
I am no expert in the thermodynamics but practical experience shows they do work very efficiently, superior in energy in vs energy out to almost any other options. A previous Volts interview featured thermal heating networks based on geothermal heat pumps that had COP"s (thermal efficiency) of above 5, that is 5 times more energy utilized than was used by the system. https://www.volts.wtf/p/thermal-energy-networks-are-the-next
My limited understanding is that whilst there will be losses at the peripheries earth and rock effectively act as an insulator over longer distances and the larger the heat mass the more efficient. With large fields of boreholes the volume and mass is much larger compared to the "surface area" (where leakage occurs) than for small thermal masses. As the volume around the working mass warms the rate of loss at the peripheries drop off and the system works more efficiently.
Yes I listened to that piece. But the reason these networks get high efficiency (units of energy expended, per unit of energy applied to the environment) is precisely that the earth stays at an extremely steady temperature regardless of season and regardless of how much energy you pump in or out (at least at the scale plausibly used for HVAC). These heat pump systems expend a small amount of energy, to _move_ a larger amount of energy. For this specific purpose, the fact that your "reservoir" can provide or soak up a nearly unlimited amount of energy is a feature. You can keep heating the homes and businesses on the network, by sucking heat out of the ground, and the ground doesn't get notably colder. And equally, you can dump heat into the ground during the summer, and the ground doesn't get notably warmer. I don't believe it's meaningfully the case that you're "recovering" the same heat in winter that you dumped in during the summer. The rock around the deep wells gives you an enormous thermal mass, and diffuses heat reasonably-efficiently over the course of days. If it didn't, it _wouldn't_ work as the heat sink / heat source for these HVAC systems. But the same property would seem to make it a poor heat sink / heat source for long-term storage.
If you run 100 GWh of energy through resistive heaters, apply that heat to water, and run that water down into the ground, you will at that time raise the local temperature some amount. But by six months later, I feel fairly certain, most of that energy will have diffused through the ground out to distances of _miles_, and will be effectively unrecoverable. I could be persuaded otherwise, but I'd want to see actual data. The thermal network piece you're talking about absolutely _does not_ talk about trying to store and recover significant amounts of energy.
There's also the separate technology of deep-geothermal (exploiting fracking techniques to get down deep enough that you can get geothermal heat without sitting on top of a shallow volcanic resource). But that too is reliant on the fact that the temperature at the depths you're drilling to is more-or-less constant, with heat diffusing from other parts of the deeper hotter crust, into the part you're extracting heat from, faster than you can extract that heat. If you tried to inject extra heat to store it, it would be lost to distant parts of that same layer of crust by six months later.
I am quite sure that you are not correct. Large buildings adding more heat to the heat mass than they draw out over each year - and the heat mass temperature rising outside of the ideal range of the heat pumps, thus requiring cooling towers - is a real thing.
You may be better reading up some more or discussing this with people with more expertise.
Well, googling around, I do see that people are exploring this seriously.
There are cases where it works, but it's not universal -- what you need, apparently, is a rock formation that is suitable for fracturing, surrounded by a formation that naturally seals it off, so that water isn't moving back and forth between your well area and the surrounding rocks, carrying large amounts of heat with it.
тАЬEGS reservoirs are created in rock formations that are naturally impermeable; everything outside the artificial reservoir is sealed off,тАЭ says Ricks. тАЬItтАЩs very similar to a hydropower reservoir, where you choose when to have water go through the dam and generate electricity.тАЭ
Depending on the geology and traits of the rocks, Ricks and his colleaguesтАЩ simulations found that the systems could store energy with up to 90 percent efficiency over one cycle.
</quote>
So that's interesting, and perhaps could grow to be a significant long-term storage option. But it's _not_ an option that's near-universally available like the thermal networks for HVAC.
Heat pump geothermal does offer low cost inter-seasonal energy storage. Check out prior Volts interviews. It doesn't make electricity but it greatly reduces demand for energy for heating and cooling.
Yes, I remember that interview and fully agree that geothermal seasonal storage is an excellent option for heating and cooling of buildings and potentially industrial heat as well. We will need some options for electric power too, and those are not so clear to me.
Ehhh. Geothermal is great for how it offers a source of heat differential year round. I donтАЩt know that IтАЩd say itтАЩs as effective for _storage_. ItтАЩs not like you can take excess solar in the summer, and pump superheated water down to heat up the earth, and then recover that heat months later. There are serious long term thermal storage ideas (like molten salt, and the box-oтАЩ-rocks approach where they line the box with IR-PV) which probably work on a time scale of days out to a week or two. IтАЩm not sure whether any of those is plausible for season-to-season storage, though.
That is incorrect; such systems can and do give true inter-seasonal energy storage, where heat derived from summer cooling of buildings (and sometimes solar energy or waste heat or other sources adding heat on purpose) adds to the thermal mass, to be used as heat during winter. Larger, "busy" buildings with borehole heat pumps can add more heat over a full year to the underground thermal mass than they draw back for winter heating and often require some cooling towers to keep it balanced.
For cold climates the amount of energy for heating is large; reducing the need for direct energy use greatly reduces demands for energy.
Huh. How efficient is that? While thermal conductivity down there isn't that high, it's still not _zero_, I'd think over months, added heat would diffuse away into the background, and the immediately-accessible mass would move back closer to the ambient temp.
I am no expert in the thermodynamics but practical experience shows they do work very efficiently, superior in energy in vs energy out to almost any other options. A previous Volts interview featured thermal heating networks based on geothermal heat pumps that had COP"s (thermal efficiency) of above 5, that is 5 times more energy utilized than was used by the system. https://www.volts.wtf/p/thermal-energy-networks-are-the-next
My limited understanding is that whilst there will be losses at the peripheries earth and rock effectively act as an insulator over longer distances and the larger the heat mass the more efficient. With large fields of boreholes the volume and mass is much larger compared to the "surface area" (where leakage occurs) than for small thermal masses. As the volume around the working mass warms the rate of loss at the peripheries drop off and the system works more efficiently.
Yes I listened to that piece. But the reason these networks get high efficiency (units of energy expended, per unit of energy applied to the environment) is precisely that the earth stays at an extremely steady temperature regardless of season and regardless of how much energy you pump in or out (at least at the scale plausibly used for HVAC). These heat pump systems expend a small amount of energy, to _move_ a larger amount of energy. For this specific purpose, the fact that your "reservoir" can provide or soak up a nearly unlimited amount of energy is a feature. You can keep heating the homes and businesses on the network, by sucking heat out of the ground, and the ground doesn't get notably colder. And equally, you can dump heat into the ground during the summer, and the ground doesn't get notably warmer. I don't believe it's meaningfully the case that you're "recovering" the same heat in winter that you dumped in during the summer. The rock around the deep wells gives you an enormous thermal mass, and diffuses heat reasonably-efficiently over the course of days. If it didn't, it _wouldn't_ work as the heat sink / heat source for these HVAC systems. But the same property would seem to make it a poor heat sink / heat source for long-term storage.
If you run 100 GWh of energy through resistive heaters, apply that heat to water, and run that water down into the ground, you will at that time raise the local temperature some amount. But by six months later, I feel fairly certain, most of that energy will have diffused through the ground out to distances of _miles_, and will be effectively unrecoverable. I could be persuaded otherwise, but I'd want to see actual data. The thermal network piece you're talking about absolutely _does not_ talk about trying to store and recover significant amounts of energy.
There's also the separate technology of deep-geothermal (exploiting fracking techniques to get down deep enough that you can get geothermal heat without sitting on top of a shallow volcanic resource). But that too is reliant on the fact that the temperature at the depths you're drilling to is more-or-less constant, with heat diffusing from other parts of the deeper hotter crust, into the part you're extracting heat from, faster than you can extract that heat. If you tried to inject extra heat to store it, it would be lost to distant parts of that same layer of crust by six months later.
I am quite sure that you are not correct. Large buildings adding more heat to the heat mass than they draw out over each year - and the heat mass temperature rising outside of the ideal range of the heat pumps, thus requiring cooling towers - is a real thing.
You may be better reading up some more or discussing this with people with more expertise.
Well, googling around, I do see that people are exploring this seriously.
There are cases where it works, but it's not universal -- what you need, apparently, is a rock formation that is suitable for fracturing, surrounded by a formation that naturally seals it off, so that water isn't moving back and forth between your well area and the surrounding rocks, carrying large amounts of heat with it.
https://asmedigitalcollection.asme.org/energyresources/article-abstract/143/1/010906/1085944/Using-Concentrating-Solar-Power-to-Create-a?redirectedFrom=fulltext
https://spectrum.ieee.org/geothermal-energy
<quote>
тАЬEGS reservoirs are created in rock formations that are naturally impermeable; everything outside the artificial reservoir is sealed off,тАЭ says Ricks. тАЬItтАЩs very similar to a hydropower reservoir, where you choose when to have water go through the dam and generate electricity.тАЭ
Depending on the geology and traits of the rocks, Ricks and his colleaguesтАЩ simulations found that the systems could store energy with up to 90 percent efficiency over one cycle.
</quote>
So that's interesting, and perhaps could grow to be a significant long-term storage option. But it's _not_ an option that's near-universally available like the thermal networks for HVAC.