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The time has finally come for geothermal energy

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Re: The time has finally come for geothermal energy

#271

Post by dns_snek »

kragen wrote: post #187
dns_snek wrote: post #48

Earlier quoted context omitted.

> In most places on Earth it's somewhere around 40 mW/m2 (i.e. accounting for conversion losses you need to capture heat from ~500 m2 to renewably power one LED light bulb!) Ground-source heat pumps extract about 1000 times more power from ground loops, where does the difference come from?

Ground-source heat pumps are irrelevant to geothermal energy sources, and it's unfortunate that the article mentioned them. Ground-source heat pumps are just storing heat from the air during the summer and retrieving it during the winter.

Hmm, that doesn't sound right. Many homes don't use these heat pumps for cooling in the summer because getting convectors and plumbing installed is just as expensive as getting a separate AC, and then you have some redundancy in the system too.

I'm sure that battery effect is a factor but it must be a relatively minor one.

Re: The time has finally come for geothermal energy

#272

Post by kragen »

MathMonkeyMan wrote: post #207
kragen wrote: post #192

Earlier quoted context omitted.

The US and Russian Navies deciding to remain mostly petroleum-fueled is one of the strongest arguments against nuclear becoming very cheap: surely they would do it if it wasn't ruinously expensive, because it eliminates the national security risk of a petroleum blockade and simplifies at-sea logistics immediately.

I don't know much about militaries or nuclear reactors, but I know that reactors are used in some submarines and in some aircraft carriers -- situations where you want a vessel to to remain at sea for long periods of time without refueling, and weight is not a primary concern. That's pretty niche, though. Think about trucks, tanks, aircraft, generators for outposts, etc. It might be cool if you could safely package a…

The Aircraft Reactor Experiment https://en.wikipedia.org/wiki/Aircraft_Reactor_Experiment, yielding 2.5 megawatts, was about two meters tall and one meter in diameter; the fuel was 15kg of U-235, but I think the reactor as a whole may have weighed several hundred kg. (It couldn't have been more than about 40 tonnes, just because no material would be dense enough, but I think it was much lighter than that.

Oh, here it is: https://media.githubusercontent.com/media/openmsr/msr-archiv... page 24/139 budgets 48400 "pounds" for "reactor and reactor shield", which is 22 tonnes, about 110kW/tonne.

The smallest nuclear submarine was NR-1, which had a total displacement of 400 "tons": https://en.wikipedia.org/wiki/American_submarine_NR-1 so the reactor must have weighed less than that.

The 10MW version of SSTAR was supposed to weigh 200 tonnes, 50kW/tonne, while the 100MW version was 500 tonnes, thud 200kW/tonne: https://en.wikipedia.org/wiki/Small,_sealed,_transportable,_...

A 4.95-kg americium thermal reactor design outline has been published: https://www.researchgate.net/publication/239521070_The_Small...

Arleigh Burke class destroyers have 80MW of propulsion and displace 8300 to 9700 tons, compared to which the SSTAR's 500 tonnes is almost insignificant. So weight isn't an issue for ships, and weight doesn't get ridiculously high until you're down below the megawatt scale.

So, you may be right that existing proven reactors won't scale down to a single truck or tank. There isn't a known physical reason it's impossible, or even impossible to do safely, but it hasn't been achieved.

Probably you are right that many small reactors would be more dangerous, but warships exist so that they can go into dangerous situations. You have to weigh the risk of a reactor problem against the risk of being unable to fight because you have no fuel. And we've certainly seen that many militaries have little concern for sailor safety.

Despite all this, no navy has switched all their ships to nuclear fuel. The only explanation I can come up with is that it's unsustainably expensive.

Re: The time has finally come for geothermal energy

#273

Post by kragen »

dns_snek wrote: post #271
kragen wrote: post #187

Earlier quoted context omitted.

Ground-source heat pumps are irrelevant to geothermal energy sources, and it's unfortunate that the article mentioned them. Ground-source heat pumps are just storing heat from the air during the summer and retrieving it during the winter.

Hmm, that doesn't sound right. Many homes don't use these heat pumps for cooling in the summer because getting convectors and plumbing installed is just as expensive as getting a separate AC, and then you have some redundancy in the system too. I'm sure that battery effect is a factor but it must be a relatively minor one.

It's not minor at all. For a ground-source heat pump to work at all, you need to sink the pipes deep enough that the soil temperature is pretty stable year-round, which means the heat it can exchange with the aboveground air is minor or insignificant. So the vast majority of heat flux into or out of that soil is due to the heat exchange fluid circulating in the pipes.

After a few years of pumping heat out of the ground below the frost line during the winter, they'll freeze the ground solid and stop working (and possibly destroy the foundation of the house in the process, since often the pipes are installed in trenches around the house).

The only exception is if they're one of these few borderline systems that drill so deep they really are bringing up fresh energy from the depths, like some of the systems mentioned in the article.

Re: The time has finally come for geothermal energy

#274

Post by Spooky23 »

andbberger wrote: post #205
Spooky23 wrote: post #153

Earlier quoted context omitted.

A nuclear plant about 50 miles from my house was closed 15 years ago. The spent fuel rods will be stored there indefinitely until a federal facility is built.

that seems fine

Forever is a long time.

Re: The time has finally come for geothermal energy

#275

Post by asacrowflies »

Archelaos wrote: post #180
bryanlarsen wrote: post #74

Earlier quoted context omitted.

But is it usefully dispatchable? Nuclear can be made dispatchable but it's not usefully dispatchable because the costs are fairly similar whether the plant is on or off. Like nuclear, I believe geothermal has high capital cost and low running costs, suggesting that it isn't usefully dispatchable. But that's too simplistic. A big limitation of geothermal is that rock has poor thermal conductivity. So once you remove h…

Nuclear produces very dangerous substances. The long term cost to guard us from them for a million years and the risk that something gets out of control are extemly high.

Solar doesn't? As far as I know the process for mining the panel and batteries is the same sulphuric acid process with extremely toxic tailings. And you get uranium in this process of rare earth mining. These toxins are orders of magnitude greater in risk and in volume/ quantity than process's nuclear fuel waste.

Re: The time has finally come for geothermal energy

#276

Post by adrianN »

kragen wrote: post #269
adrianN wrote: post #266

Earlier quoted context omitted.

There are lots of houses getting the majority of their heat from ground source heat pumps. Not so many that are heated with vigorous exercise.

Ground-source heat pumps (with a few exceptions and borderline cases like those mentioned in the article) are not sources of heat, so you can only "get heat from" them in the short term; as with a battery or an interest-free checking account, though you may be able to temporarily run a debit balance, in the long run you can only get out what you put in. This is a fundamental difference from energy sources. Energy sto…

Ground source heat pumps as used for heating buildings source their energy from the sun and work very well. They are outcompeted by air source heat pumps despite better efficiency because digging is expensive.

Re: The time has finally come for geothermal energy

#277

Post by zeckalpha »

cbmuser wrote: post #110
bryanlarsen wrote: post #57

Baseload generation is useless in 2025. It's in the name; it's called "base load", not "base generation". Base generation was a cost optimization. Planners noticed that load never dropped below a specific level, and that cheapest power was from a plant designed to run 100% of the time rather than one designed to turn on and off frequently. So they could reduce cost by building a mix of base and peaker generation plan…

Or just build out nuclear like France and pay just 20 Cents per kWh. https://particulier.edf.fr/content/dam/2-Actifs/Documents/Of...

I pay 21 cents per kWh and only 11% of my grid is nuclear.

Re: The time has finally come for geothermal energy

#278

Post by user____name »

psunavy03 wrote: post #100
davidw wrote: post #90

Earlier quoted context omitted.

A lot of housing politics from 'old school' environmentalist groups are a pretty big own goal as well. Denser urban living is pretty energy efficient, and forcing lengthy commutes on people because of NIMBYism is a huge waste.

People want houses. Planners can either yell and stomp their feet about this or adapt to circumstances. It's like electric cars. People want cars. Better they have the ability to have an electric SUV or pickup, because if you try to force them into little tiny econoboxes or lecture them about how they should really be using mass transit, they're just going to flip you the bird and walk away. Similarly, better to have…

Its funny how mass transit was once seen as a way out of the crisis of too many city horse carriages and all the manure they produce. Metro and rail was simply considered the natural solution, which combined with denser living space allowed for labor intensive industries to sprout up around cities. But then came the horseless carriage and suburbian sprawl became a thing and now we have too much of that. Too much hardened soil and flooding is becoming a much bigger problem, animal and insect populations wither, road networks have upkeep, transport and storage costs make everything imperceptably more expensive. In my scifi fantasy future vertical farming will become a thing which should allow a major shrinking of hinterlands around dense population areas, though preferably not replaced with suburbia. Maybe we could go live in the clouds too.

Re: The time has finally come for geothermal energy

#279

Post by thinkcontext »

ahmeneeroe-v2 wrote: post #72
thinkcontext wrote: post #62

Earlier quoted context omitted.

It could be but the US and EU have so far been unable to build commercial fission reactors without going 2x+ over budget in time and money. China is having success but even they are not projected to have nuclear account for more than single digit percentages of their generation. Maybe SMR's, thorium, 4th gen, etc will work out, but maybe not.

The US Navy consistently builds reactors on-time and in-budget

The US Navy doesn't build them, private companies do. None of the SMR companies that I am aware of have attempted to use designs from naval reactors. Perhaps it has something to do with the fact that they use highly enriched fuel which is a no-no for civilian reactors.

In any event, if your more general point is that naval reactors indicate its possible that SMRs can be built on time and budget, I don't disagree. It certainly is possible. NuScale was the furthest along of the SMR companies and had their project implode before it got off the ground. So, its also possible for them to crash and burn.

So, I'll stick with my classification of SMRs as "maybe it will work out, maybe not".

Re: The time has finally come for geothermal energy

#280

Post by frankus »

frankus wrote: post #171
anotherevan wrote: post #132

Purely as an aside, I had the pleasure of visiting Iceland in August and it was great. Truly beautiful, rugged land. Another way they've utilised geothermal energy is with large, sophisticated greenhouses which allow growing of many produce they would otherwise import. I only had the opportunity for a brief visit but a lot of it looked hydroponic with really interesting monitoring and control technology. (Plus the bi…

My favorite memory is following a map to a small isolated hot spring off of some random gravel road in the middle of nowhere. It consisted of a hot-tub-sized pool and a shower. Whoever was there before had left the shower running. We were the only people there, and hadn't seen anyone pass us on the (dead end) road, so it must have been on for quite a while. Only when I went to for my pre-soak shower did I realize tha…

Showering in hot water is one of the more energy-intensive things people do on a daily basis. I have a 14.4 kW on-demand heater that just barely keeps up with a 1.5 gallon (~6 liter) per minute shower head with 50°F/10°C incoming water.

On a per-minute basis that's comparable to highway driving in a smallish electric car.

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