Geothermal may beat batteries for energy storage • Hacker News Board

Re: Geothermal may beat batteries for energy storage

#201

Post by xyzzyz » Tue, Oct 11, 2022, 11:24 PM UTC

cupofpython wrote: post #113

merely-unlikely wrote: post #90

Earlier quoted context omitted.

> I was always wondering why there are no systems converting the unused electricity in potential energy by moving water to a higher ground There are a bunch of pumped storage facilities around [1]. But they work best at massive scale, so suitable locations are somewhat limited. Plus they are expensive to build and often face environmental protests (similar to building dams). Still, it's a solution I'm a fan of. [1] h…

emphasis on massive scale. Moving 500,000 kg (over 1 million pounds) 7.5 meters (~25 feet aka the height of a house) will give you about 10 kWh of energy. This is equivalent to running a 425W device all day, like a small air conditioner. The relationship is linear. Double the weight or the distance to double the energy. All of the metal at a scrap yard I know of amounts to less than half that weight, for reference. I…

> Moving 500,000 kg (over 1 million pounds) 7.5 meters (~25 feet aka the height of a house) will give you about 10 kWh of energy.

In dollar terms, 10kWh is worth around $1. 1 million pounds is the weight of 2-5 residential homes, depending on size. Think about it: the cost to lift a couple of entire houses three stories up into the air is literally just one dollar. That’s why gravity energy storage only makes sense at a massive scale.

Re: Geothermal may beat batteries for energy storage

#202

Post by wavesquid » Tue, Oct 11, 2022, 11:26 PM UTC

Dylan16807 wrote: post #193

rgmerk wrote: post #190

Earlier quoted context omitted.

One minor but interesting exception - farmers have historically often put domestic water tanks on top of towers to ensure even water pressure. Direct pumping leads to cycles where the pressure in the system rises and falls as the pump cycles on and off, which is very unpleasant if you’re trying to take a shower! I believe modern off-grid home water pumps use more sophisticated motor control to avoid the need for the…

That's not an exception, that's an entirely different use for a raised tank. And not a very big one either.

It depends what you're calling "not a very big one". On our farm we have a 5000 litre galvanised high tank for house-water.

Re: Geothermal may beat batteries for energy storage

#203

Post by Schroedingersat » Tue, Oct 11, 2022, 11:29 PM UTC

robocat wrote: post #151

Schroedingersat wrote: post #29

Earlier quoted context omitted.

The interesting thing is when they've been around for 30 years (providing they don't decay too much with time). A sodium battery with 100 useful cycles and 10 years left in it is great for cycling once a month. But even without that, if we see costs of $50/kWh then you only need to cycle 300 times to make it more worthwhile than some generation technologies..

Don’t some battery chemistries have much higher self-discharge rates as they get older? If so, it might be uneconomic/wasteful to try to use old batteries.

That's one consideration (and if storage gets as cheap as variable generation it will be the most important one). With the advent of cheap solar the value of moving the energy is a fair bit higher than its cost. So the economics become mostly a matter of cost of storage vs. duration.

If you can move energy from a time where it's the least valuable generation of a system that costs $15/MWh net (or even less in future systems) to a time when the cheapest scalable generation is $50/MWh then you've got a lot of room for losing some.

There's incentive for the solar system to overbuild 2x or 3x just to sell that 3pm-sunset energy so from their point of view they can sell the sunrise-3pm energy at any price over $0 and be profitable.

A hypothetical bad second hand battery might be the most valuable (and thus highest bidding) use, but it will have to compete with other opportunistic loads.

Re: Geothermal may beat batteries for energy storage

#204

Post by lillecarl » Tue, Oct 11, 2022, 11:31 PM UTC

Dylan16807 wrote: post #193

rgmerk wrote: post #190

Earlier quoted context omitted.

One minor but interesting exception - farmers have historically often put domestic water tanks on top of towers to ensure even water pressure. Direct pumping leads to cycles where the pressure in the system rises and falls as the pump cycles on and off, which is very unpleasant if you’re trying to take a shower! I believe modern off-grid home water pumps use more sophisticated motor control to avoid the need for the…

That's not an exception, that's an entirely different use for a raised tank. And not a very big one either.

I'd say it's a quite big one, "every city" has water towers to provide pressure to the people living in it, or they rely on the water source if it's higher up than the city.

There are probably exceptions, where this isn't true, but raised tanks make modern society possible.

https://youtu.be/yZwfcMSDBHs more on water towers, which are raised tanks of water.

We also pump water into fake lakes to later extract electricity from it. (https://youtu.be/66YRCjkxIcg)

Another good thing with water towers is that we can keep running the pumps at a lower RPM where efficiency than if we were trying to build a system with pumps to keep pressure.

Great channel if you're curious about everything related to humans relationship with water.

Re: Geothermal may beat batteries for energy storage

#205

Post by jcrben » Tue, Oct 11, 2022, 11:37 PM UTC

kenhwang wrote: post #182

cupofpython wrote: post #113

Earlier quoted context omitted.

emphasis on massive scale. Moving 500,000 kg (over 1 million pounds) 7.5 meters (~25 feet aka the height of a house) will give you about 10 kWh of energy. This is equivalent to running a 425W device all day, like a small air conditioner. The relationship is linear. Double the weight or the distance to double the energy. All of the metal at a scrap yard I know of amounts to less than half that weight, for reference. I…

It's not "beyond niche", it accounts for 95%+ of worldwide stored energy and is the de-facto energy storage mechanism that all new battery storage technologies are compared against. It also has round trip efficiency comparable to the li-ion batteries (80-90%), which is incredibly hard to beat.

It also doesn't consistently depreciate the way that batteries do.

Re: Geothermal may beat batteries for energy storage

#206

Post by xyzzyz » Tue, Oct 11, 2022, 11:40 PM UTC

jandrese wrote: post #135

londons_explore wrote: post #132

Earlier quoted context omitted.

From that paper, the average COP measured was 3.06 (averaged between 2 and 7 degree outdoor temperatures, typical of the UK). The UK electricity price is currently fixed at 34p/kwh for electricity and 10.3p for gas. A new gas boiler has a COP(efficiency) of 1.054 (it can manage efficiency higher than 100% because gas is metered by the 'lower heating value', which assumes the exhaust gas escapes as steam, but the boil…

However, the ASHP can also be used to cool your home in the summer. In the past this has been a dubious benefit for most of northern Europe, but heat waves have been getting stronger, last longer, and happen more frequently as time goes on. This is turning into a serious consideration. Also, you can theoretically power a ASHP with renewable energy, while there are few if any carbon neutral replacements for natural ga…

Yeah, these can make ASHP a good idea anyway, but the grandparent was nevertheless correct saying that they don’t beat gas for heat in terms of cost in normal (I.e. not current) circumstances.

Re: Geothermal may beat batteries for energy storage

#207

Post by xyzzyz » Tue, Oct 11, 2022, 11:41 PM UTC

distances wrote: post #192

jws wrote: post #134

Earlier quoted context omitted.

It's not as bad as this. In climates where you will have a bed of snow during the winter months, your optimum tilt angle for a fixed solar panel is something like 30° off of vertical or steeper. I find that on mine the snow falls off since it is a south facing, steep, dark surface. You engineer to make sure you have enough energy captured each month to meet that months needs. That might lead you to a tilting mount, o…

Interesting. Last winter my parents' rooftop solar had zero output until April, as it produces nothing until all the panels are clear of snow. Granted their installation is at a fixed angle that matches the roof, and this is in the Nordics. During summer months the production mostly covers and partly exceeds their use, but the sell price is so much lower that it doesn't even begin to pay for the rest of the year. But…

I wonder if it makes sense to build some simple resisting heating elements into the panels, to allow the snow to slide off. Shouldn’t use all that much energy to run it occasionally.

Re: Geothermal may beat batteries for energy storage

#208

Post by xyzzyz » Tue, Oct 11, 2022, 11:47 PM UTC

teucris wrote: post #93

jonstewart wrote: post #91

Earlier quoted context omitted.

Selling PV electricity back to the grid is almost always many times worse, depending on state incentives, than consuming the electricity. For example, my utility sells electricity to me at 9 cents/KWh, but only buys from me at 2.5 cents, and charged me a fixed monthly fee for the meter to boot. If the commenter’s house doesn’t have gas, then it doesn’t seem to make sense to install it, and the price differential in t…

Huh. We have a 1:1 credit system here in Washington.

This is an enormous subsidy to residential PV. Electricity wholesalers would love to be able to sell it to the grid at retail prices, like you are. Instead, they sell it for something like a quarter of retail price. This huge subsidy is only sustainable for so long as the PV penetration is low in residential market.

Re: Geothermal may beat batteries for energy storage

#209

Post by dwiel » Wed, Oct 12, 2022, 12:02 AM UTC

xyzzyz wrote: post #207

distances wrote: post #192

Earlier quoted context omitted.

Interesting. Last winter my parents' rooftop solar had zero output until April, as it produces nothing until all the panels are clear of snow. Granted their installation is at a fixed angle that matches the roof, and this is in the Nordics. During summer months the production mostly covers and partly exceeds their use, but the sell price is so much lower that it doesn't even begin to pay for the rest of the year. But…

I wonder if it makes sense to build some simple resisting heating elements into the panels, to allow the snow to slide off. Shouldn’t use all that much energy to run it occasionally.

You can actually push a bit if current backwards through the cell to heat it up. Some people have tried this but not sure about what prevents this from being more wide spread

https://www.pv-magazine.com/2020/03/18/heating-solar-panels-...

Re: Geothermal may beat batteries for energy storage

#210

Post by jasonwatkinspdx » Wed, Oct 12, 2022, 12:21 AM UTC

cookiengineer wrote: post #68

LinuxBender wrote: post #67

Many of the greenhouse Youtube channels I watch do a smaller DIY version of this. They have either dark barrels of water in the greenhouse with the windows facing south to the sun, or a thin metal wall filled with clay and pipes acting as a sun-heat-battery. They pump the water through the barrels or clay battery into pipes that are under ground to store the heat. In winter time they extract the heat from the ground…

This reminds me a lot of the Earthship community in the middle of the desert, which always focusses on smart ways of reusing water for different purposes, and by not wasting water as much as possible. The houses usually have a clean/grey/blackwater + a rainwormbox system to process fecals and reuse it for growing plants. Their air conditioning system is basically just a pipe in the ground where the hot air flows thro…

The efficiency of pumped hydro storage depends heavily on the height difference involved. There's not that many suitable sites, most have been developed already. It's not a technology that scales down well other than vanity projects.

Rooftop cisterns are very common globally, usually places where the water utility if it exists is unreliable. A huge number of humans get their water from a truck that comes by weekly or such to fill the cistern.

In more high income nations, this isn't necessary because the utility does the same thing at a larger scale with one or more large water towers interconnected.

Someone I know built an off grid air bnb on the beach in Mexico using Earth Ship concepts. I helped out with one of the buildings a little bit, doing the earth bag construction. The passive temperature regulation of those nice thick walls is impressive. He uses well water, and solves the water pressure problem by having a pump that sends it up hill to a pair of cisterns, for hot and cold water respectively. The hot one is the big black plastic ones you see on rooftops everywhere in Mexico. The cold one is made of reused plastic soda bottles and concrete underground. They both are surprisingly effective at what they do. The hot water is frankly way to hot to use without a mixer.

It'd be entirely pointless to use it as energy storage though. The pressure just isn't that high, and the total volume of water involved in the system isn't sufficient. He uses a battery array to buffer his solar.

As cool as all that is, you couldn't build an entire city that way. It's just not dense enough, and again ends up being mostly a vanity or tourist thing.