81–90 of 108 posts
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That is why there is also solar
And there is also night. And clouds. Texas is good for solar but December and January still have relatively high variance - for example, in December 13 solar produced only 19.3 GWh while it produced 103 GWh two weeks later on December 27.
There are a lot of near-surface options for heating and cooling. They reduce electrical usage rather than generate it. I worked on geo control systems for FL buildings. We'd pump water up from the aquifer, transfer heat from the building into it and dump it back. It starts getting cost effective above 10k or 15k sqft. In northern states they do large closed loops wound over a large yard or field and buried just below…
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Ideal thermodynamic efficiency is 1-Tcold/Thot in an absolute temperature scale. This means given a perfect mechanism to turn heat into work this is the upper bound of how much of the heat can be turned into useful work. Say ambient air is 20 deg C, with your 90 deg C heat source then you get 1-293/363 which is about 20%. So it's not to say you can't get work out of this system, but it's not great compared to having…
would it be possible to use a heat pump to increase the temperature to a more efficient range? Or would all of the efficiency gained be lost by operating the heat pump?
Make drilling cheaper. This would also help with water access. The biggest cost of small geothermal and water projects is always the drilling. Drill rig time is always a limiting factor.
I was hopeful that all of the unused drilling capacity after the shale boom/bust would allow some of the know how and equipment to be reallocated to geothermal but the grid operators and markets are not offering the premium to firm capacity that is required for the longer lead time and increased capital requirements and increased risk in geothermal projects vs wind and solar which can be augmented with battery storag…
>If prices come down, and if it can be deployed widely enough Drilling deep holes is expensive, prices are unlikely to come down much. Steam generators are expensive too.
Why is the cost of drilling so high? I'm sure the rigs are an expensive capital outlay, but do the operators require advanced skills? Once a hole is drilled, does it have a limited lifespan, or is that investment something that can be hypothetically used for eternity?
The materials you're using when drilling are expensive. The steel casings that you're putting down the hole are specialized alloys. You're using very large amounts of expensive specialized fluids to fill the hole during drilling (drilling mud) that are relatively hazardous and need to be treated after use. You're going through large numbers of very expensive consumable parts (e.g. drill bits are _not_ cheap, and there are a lot of even more expensive consumables). A large amount of the equipment and consumables are custom built for the specific conditions you're working in. There are certainly cases where you can use things that are a bit more of a commodity, but deep and hot wells usually don't fall into that category. And yes, there are a ton of companies that specialize in making all of these things either en masse or custom built to order, but they're still expensive. You're also going to need to run logs (i.e. downhole measurements) using a wide variety of very expensive and very specialized tools.
It's not just a hole. You're also building a subsurface structure and collecting information about the subsurface.
Any well has a limited lifespan. Geothermal wells aren't that different from hydrocarbon wells in this sense. You're not actually able to extract heat from the bulk of the rock mass. Rocks are _very_ poor conductors of heat. So you're extracting heat from relatively tiny depth within the rock mass along the surface of a pore network. You're flowing water from one well (an injector) to another well (a producer). As that flows and temperatures and water chemistry change, various minerals precipitate out and block the pore throats. Even in cases where you can avoid those reactions, you eventually block different pores and fracture networks with debris. You can and do use techniques to restore that (aka "workovers"). However, they are expensive and have diminishing returns. And even if none of the before-mentioned things happen, you'll eventually hit diminishing returns on the temperature you can produce, as the heat can't migrate from the bulk of the rock to the water-rock interface very quickly.
Either way, eventually you drill new injectors and producers. The cycle you need to do that on varies quite a bit depending on the specifics of the project. In some cases, it's a couple years, in others it's a decade or two. Either way, you need continued redevelopment plans to continue production.
All of that is not a problem and is work as normal. I'm just trying to lay out what subsurface projects entail (be they geothermal, oil, methane, or even large scale water production). It doesn't mean geothermal is impractical or overly expensive (far from it). But it does mean that there are very large initial captial expenses and then periodic capital expenses needed at later dates to continue optimal operation.
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Only for short term storage. Hydrogen is meant for longer term storage where batteries have too high of a losses. E.g. winter vs summer.
Way way way cheaper to 10x overbuild renewables than produce (and store) hydrogen at that scale.
There are a lot of near-surface options for heating and cooling. They reduce electrical usage rather than generate it. I worked on geo control systems for FL buildings. We'd pump water up from the aquifer, transfer heat from the building into it and dump it back. It starts getting cost effective above 10k or 15k sqft. In northern states they do large closed loops wound over a large yard or field and buried just below…
My understanding is that, while you can do surface loops with enough area, its easier and less disruptive to just do vertical holes for ground loops. At least in Northern Virginia drill ~150ft of well per ton. At 400ft the wells maintain temperature a relatively consistent temperature year round year round.
District heating loops can be done almost for free with greenfield development and it should be highly incentivized to slash the energy required to heat and cool the new structures.
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And there is also night. And clouds. Texas is good for solar but December and January still have relatively high variance - for example, in December 13 solar produced only 19.3 GWh while it produced 103 GWh two weeks later on December 27.
No single source has ever provided all electricity for any major region. To pretend otherwise is disingenuous.
So really you're the one being disingenuous.
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> Make drilling cheaper. How?
we can power it with free geothermal! the deeper the hole gets, the faster the drilling goes. it's power all the way down!
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I wonder if geothermal can offer mild battery storage by using excess energy to pre-heat the water.
I don’t think thermodynamics lets that work. You can’t move heat from something cold to something hot so unless you are preheating your water to a temperature higher than your deep borehole rocks, all you’re doing is putting the first N joules of heat energy into the water you’re going to pump into your steam turbines using excess grid energy instead of geothermal energy.
Funny thought: if you use a heat pump to store heat energy in summer to be used in winter.. and your reservoir can retain the heat efficiently (think the heavily insulated sand reservoir used in a project in Finland for instance)… could that make the battery effectively more than 100% efficient?