Renewable energy storage technology

[Gumby]

I just ran across this interesting article about new technologies to store the electric energy generated by solar and wind plants, and I know that some of you are interested in the topic, so I thought I would share. If these can be commercially successful, it will greatly improve our ability to wean ourselves off fossil fuels.

https://www.nytimes.com/2024/03/18/...e_code=1.eE0.DUST.gY_eonncjq72&smid=url-share

 

[sengsational]

I wonder what the efficiency is of compressing carbon dioxide and capturing the energy when it expands compares to pumping water up to a reservoir and spinning generators when it's drained (which is already employed at scale for excess nuclear generated electricity). For that hydro, the efficiency is dismal, but better than nothing.

 

[Fermion]

I have always wondered why they don't use the excess to do industrial tasks which don't have a specific time requirement.

An example might be to use excess power to do cryogenic separation of gasses for storage and later use in the industry (or for rockets!)

 

[Chuckanut]

I follow this with great interest. I live in part of the country where the coldest days are often the days with well under 10 yours a day of sunlight and the wind also dies down quite a bit. We had a week in January where it never got above freezing. Our leaders want to get rid of carbon based fuels, even natural gas, ASAP. Where we get our power electric during those cold weeks when the sun don’t shine much and the wind don’t blow is unknown at this time.

 

[GaryInCO]

Heat storage is another promising storage technology. They heat large blocks of graphite or other materials to white-hot, 2000°C or so. The blocks can hold the heat for long periods, and the heat can be tapped on demand. It can be used to generate electricity (basically using a special type of solar panel), or used directly as process heat for industrial processes (like melting steel). Great way to time-shift energy from when it's available (e.g. midday when there's lots of solar energy) to when it's needed (e.g. night).

https://carboncredits.com/bill-gate...ge-revolutionizes-industrial-decarbonization/

 

[jimbee]

Thanks for the shared/free article Gumby, very interesting. Although some of the photos gave me w*rk flashbacks.

 

[Koolau]

The technique seems viable under certain circumstances. But it's centralized storage. I prefer, where possible to store energy "on site." With the assumption that energy is ultimately fungible, space heating and domestic hot water consumes a lot of fossil fuels. Reducing that need may be as valuable as storing electricity. I assume that "zero" carbon will take a LOT of technologies, w*rking together. Co-generation might be an intermediary step in reducing carbon dependence. That a whole other subject.

Over 30 years ago, I toured a "solar heated home" where the attic (purpose built to store heat) contained (IIRC) plastic containers of hydrated sodium acetate crystals. Upon being heated by the solar collectors on the roof, the solid crystals in the plastic containers "melted" (absorbing significant quantities of "waste" day-time heat.) At night (no sun) these "melted" crystals reformed, releasing their stored heat to the (highly insulated) attic space. Simple forced air moved the heat to where it was needed. Domestic hot water was (IIRC) also produced. Also (IIRC) the attic could be supplied with enough of the salt solution to heat the house for several days between good 10 hour sun in winter. The site was at around 41 degrees N lat - roughly in line with Chicago. Supplemental heat was available (probably resistance back then, but could be heat pump now.)

No idea if this caught on. It certainly did not in my area of the mainland as it required a fair amount of purpose-built space and up-front costs. No idea about maintenance costs.

My thinking (in general) is that "vast" centralized storage makes it just one more utility with fees and regulatory limits and "boards of directors" and public utility commissions and (dare I say it) politics.

Storing your own energy means you have a very vested interest in doing it right and maintaining it and learning the best way to make the most of the potential. NW-Bound's experiences are sort of a model of what could be, though "every man for himself" could be problematic.

Turn-key systems installed on site (and, therefore, appropriate to the site) are my idea of making the best use of available non-carbon based resources (wind, solar, thermal, hydro, radioactive waste etc.)

Here's a site on salt storage:

https://www.technology.org/2020/01/27/energy-for-future-heating-systems-can-be-stored-in-salt/

Returning you now...

 

[ncbill]

For residential installations something like a Trombe wall would be much simpler.

 

[Koolau]

For residential installations something like a Trombe wall would be much simpler.

I think the reason a salt storage unit has appeal is not its simplicity but its similarity to a typical heating system. Once set up, you simply adjust a thermostat and, assuming everything w*rks as intended, your house is heated. From the outside of the house, you wouldn't know that the system is there as the house looks conventional (though there are solar heat collectors on the roof.)

The thermal wall idea is probably a lot cheaper and the idea of a more passive system is appealing. But most of us just want to turn a thermostat and forget the rest. Years ago, I read about a guy who had a huge passive solar system in which his window wall heated (wait for it) 55 gallon drums (painted matte black) of water. Lots of thermal mass there too. But regulating the heat in a house with a passive system might be problematic though YMMV.

 

[ERD50]

I wonder what the efficiency is of compressing carbon dioxide and capturing the energy when it expands compares to pumping water up to a reservoir and spinning generators when it's drained (which is already employed at scale for excess nuclear generated electricity). For that hydro, the efficiency is dismal, but better than nothing.

But as they point out in the article, pumped storage requires a lot of area, and the right geology - a nearby high spot to store water. Efficiency is actually not so bad, ~ 75~80% round trip IIRC.

The typical compressed air storage is inefficient because a gas heats as it is compressed, and that heat is lost during storage and expansion. I wonder if the idea of a phase change with the CO2 circumvents this? BTW, CO2 becomes liquid at ~ 860 PSI at room temperature.

I have always wondered why they don't use the excess to do industrial tasks which don't have a specific time requirement.

An example might be to use excess power to do cryogenic separation of gasses for storage and later use in the industry (or for rockets!)

I thin k the problem is that any large industrial process takes a large investment in capital. So to be competitive, that investment needs to run 24/7/365.

But there must be some good applications (or maybe not, which is why we don't see it done routinely?), not sure what they are.

-ERD50

 

[Jeffman52]

I saw something a couple of years ago which is similar to the Hydro application. Gravity batteries


https://www.bbc.com/future/article/20220511-can-gravity-batteries-solve-our-energy-storage-problems


When green energy is plentiful, use it to haul a colossal weight to a predetermined height. When renewables are limited, release the load, powering a generator with the downward gravitational pull.

 

[Masquernom]

Kentucky is launching a new pumped hydro project.

https://www.whas11.com/article/mone...ucky/417-9e3dbce9-6686-45d2-a936-ad73a296fc18

 

[Koolau]

I saw something a couple of years ago which is similar to the Hydro application. Gravity batteries


https://www.bbc.com/future/article/20220511-can-gravity-batteries-solve-our-energy-storage-problems


When green energy is plentiful, use it to haul a colossal weight to a predetermined height. When renewables are limited, release the load, powering a generator with the downward gravitational pull.

From what I understand (and I'm no expert) the storage with weight is not very energy intensive. Right now, we already do that (as pointed out with pumped storage.) Water is relatively easy to w*rk with IF you already have the two reservoirs needed to store the water. BUT the key problem for energy storage is that gravity is still a rather weak force. If you doubt this,consider how easily you can "defeat" gravity with a small magnet.


I ran into this example: See: https://physics.stackexchange.com/questions/305563/why-dont-we-use-weights-to-store-energy


(LIFTED FROM THE SITE):

Let's spin some numbers to further illustrate the poor energy density of gravity-based storage systems. Assume that you have a 100 kilogram lead weight that you can lower into a 10 meter deep hole in your yard.
Now, how much energy can it store? This is given by potential energy formula 𝐸=𝑚𝑔ℎ, thus 𝐸=100kg⋅9.8m/s2⋅10m=9.8kJ≈2.7Wh.
For comparison, a single AA-sized battery stores about 2Wh
of energy.

(END OF LIFT)


So, I had once thought that each windmill across the landscape could be fitted with a large chunk of waste concrete or tank of water to be lifted by the excess electricity during good wind. During windless periods, the process would be reversed to give up energy to the grid. I'm not an engineer, but based on the above example, to get any meaningful amount of electrical storage from a windmill, the windmill tower would have to be built to hold a massive weight and the building process would likely consume more energy in doing so than the weight-storage would ever supply going forward. Also, imagine the cumbersome maintenance issues. YMMV

 

[ERD50]

I saw something a couple of years ago which is similar to the Hydro application. Gravity batteries


https://www.bbc.com/future/article/20220511-can-gravity-batteries-solve-our-energy-storage-problems


When green energy is plentiful, use it to haul a colossal weight to a predetermined height. When renewables are limited, release the load, powering a generator with the downward gravitational pull.

(edit - woooops, I missed Koolau's previous pst!)

We discussed the math on this a while back in another thread.

There is a reason that physicists refer to gravity as the "weak force". It tales a lot of mass, and a great height difference to store/generate much energy.

From wiki:

potential energy U; mass m; gravitational force g; height h

U = m g h

g on Earth 9.8 m/s2

So calculate what you need to store even a single hours worth of energy for say, 1000 homes. You might be surprised at what is involved.

Better, calculate for one day for one home - imagine that in your yard, or over your home.

OK, this site does the work for you - an avg US home uses 29~30 kWh per day:

https://www.omnicalculator.com/physics/potential-energy

260,000 Pounds, lifted 300 feet has the potential energy of 29.4 kWh.

Of course, there are round trip losses, so add to that.

Hmmm, gravel is ~ 105# per cubic foot, so 2600 cubic feet is a cube ~ 13.5' per side. Imagine the structure required to lift 260,000 pounds! Now, there are plans to use railroad track up a hill, but as some reasonable grade, and if a hill is available, that takes up a lot of space.


-ERD50

 

[Out-to-Lunch]

There is a reason that physicists refer to gravity as the "weak force".

Because I know how much you value exactitude, let me point out that physicists don't refer to gravity as the weak force. When we say "the weak force," we are referring to the weak nuclear force. This is the very short-ranged interaction that is involved in, for example, beta decay, or any transformation that changes the flavor of the particles involved.

But you are certainly correct that gravity is a very, very weak force compared to the other three interactions (the strong nuclear force, electromagnetism, and the weak nuclear force).

 

[skyking1]

@Gumby I am working on that right now for the new home.
The current idea is a simple thermal storage mass.
https://en.wikipedia.org/wiki/Seasonal_thermal_energy_storage

Scroll down to GIITS or the pit storage descriptions.

I got a quote for insulation yesterday.
My tentatlve plan is to build a thermal mass from a mix of existing soils and possibly some imported sands, measuring 12' wide by 6' high by 60' -ish long.
That's 120 cubic yards, and if I build it with high moisture content the mass is ~150,000 kg.
soil has a heat capacity of ~1000 joules per kg per degree C.
using a range of 40C to 65 C the mass has about 3.5 million BTU of storage, which is 160 hours times the the Manual J heat requirements for our home.
That assumes no input and the vacuum tube solar collectors make heat year round if they get sun.

I have several months to fine tune the requirements. The house is being built with chases from the basement equipment room to the roof to allow addition of more panels for scalability.
Floor hydronics run at a maximum temperature of 40C. When the mass is > 40C a simple mixing valve will condition the fluid as it goes into the hydronics.

 

[Koolau]

@Gumby I am working on that right now for the new home.
The current idea is a simple thermal storage mass.
https://en.wikipedia.org/wiki/Seasonal_thermal_energy_storage

Scroll down to GIITS or the pit storage descriptions.

I got a quote for insulation yesterday.
My tentatlve plan is to build a thermal mass from a mix of existing soils and possibly some imported sands, measuring 12' wide by 6' high by 60' -ish long.
That's 120 cubic yards, and if I build it with high moisture content the mass is ~150,000 kg.
soil has a heat capacity of ~1000 joules per kg per degree C.
using a range of 40C to 65 C the mass has about 3.5 million BTU of storage, which is 160 hours times the the Manual J heat requirements for our home.
That assumes no input and the vacuum tube solar collectors make heat year round if they get sun.

I have several months to fine tune the requirements. The house is being built with chases from the basement equipment room to the roof to allow addition of more panels for scalability.
Floor hydronics run at a maximum temperature of 40C. When the mass is > 40C a simple mixing valve will condition the fluid as it goes into the hydronics.

Sounds cool (er, hot, er, I mean warm - anyway) Keep us informed how it w*rks out for you. I love this stuff and now kinda wished I'd paid more attention back when I learned about thermodynamics (50++ years ago!)

 

[ncbill]

@Gumby I am working on that right now for the new home.
The current idea is a simple thermal storage mass.
https://en.wikipedia.org/wiki/Seasonal_thermal_energy_storage

Scroll down to GIITS or the pit storage descriptions.

I got a quote for insulation yesterday.
My tentatlve plan is to build a thermal mass from a mix of existing soils and possibly some imported sands, measuring 12' wide by 6' high by 60' -ish long.
That's 120 cubic yards, and if I build it with high moisture content the mass is ~150,000 kg.
soil has a heat capacity of ~1000 joules per kg per degree C.
using a range of 40C to 65 C the mass has about 3.5 million BTU of storage, which is 160 hours times the the Manual J heat requirements for our home.
That assumes no input and the vacuum tube solar collectors make heat year round if they get sun.

I have several months to fine tune the requirements. The house is being built with chases from the basement equipment room to the roof to allow addition of more panels for scalability.
Floor hydronics run at a maximum temperature of 40C. When the mass is > 40C a simple mixing valve will condition the fluid as it goes into the hydronics.

Those are normally used to heat water for DHW needs.

So why not store the heat using water instead of soil?

 

[Koolau]

Those are normally used to heat water for DHW needs.

So why not store the heat using water instead of soil?

Heh, heh, there are two kinds of water tanks. Those that leak and those that will. The corollary to that truism: The deeper you bury the tank, the more likely it will leak.

 

[Gumby]

As I recall from back in the 70s, that was the original idea with solar - to heat your domestic water supply. When we moved into our neighborhood in 1992, there was still a house down the street with a device much like the one shown up on its roof (long gone now) for just that purpose. I also recall reading about using the sun to heat a "sun room" or "solar wall" and then circulating the hot air. So not a new idea, but I'd bet Skyking1's thermal mass will hold a lot more heat energy, due to it's size alone, than would the typical sun room/wall or hot water tank.

 

[Koolau]

As I recall from back in the 70s, that was the original idea with solar - to heat your domestic water supply. When we moved into our neighborhood in 1992, there was still a house down the street with a device much like the one shown up on its roof (long gone now) for just that purpose. I also recall reading about using the sun to heat a "sun room" or "solar wall" and then circulating the hot air. So not a new idea, but I'd bet Skyking1's thermal mass will hold a lot more heat energy, due to it's size alone, than would the typical sun room/wall or hot water tank.

My dad was into stuff like that. He had a creative mind but no engineering skills. He installed an old hot water tank (painted black) in his tiny hobby green house. Under the RIGHT circumstances, it meant he didn't have to heat the space nearly as much in spring and fall. In summer, he barely had enough ventilation to prevent his plants from cooking in the sun (with the added heat load radiating from the tank.) He learned to white-wash the glass panels to block the sun. It took a fair amount of managing to make it all w*rk but he really enjoyed it. I'm sure I picked up his passion for such things though I never learned more than the rudiments of engineering either.

 

[skyking1]

Those are normally used to heat water for DHW needs.

So why not store the heat using water instead of soil?

It is just math. The size of water storage really gets out of hand when you get to the numbers I posted.
I found out today that I may have a source for free insulation panels. The quote I had for new geofoam was in excess of 8K, so this is a really interesting development.
My original heating plan had two Ground Source Heat Pumps (GSHP), one that did water to water for the hydronics, and another that did normal air HVAC so we could have a little air conditioning as needed.
They are about 8K each, and now I am working on doing all the hydronic heat with the solar system and freeing up that capital to purchase the collectors and infrastructure.
The HVAC is sized such that it could heat the whole home without the hydronics.
Hydronic warm floors are more of a lifestyle decision.
When I plumb out of the basement slab I will include a second set of conduit to add a second mass if needed. I can build it adjacent to the first one and use that wall of insulation for one side.

 

[kumquat]

Well, here's the result of a Canadian experiment: https://www.cbc.ca/news/canada/calgary/okotoks-drake-landing-solar-energy-repairs-future-1.7148389

 

[skyking1]

Well, here's the result of a Canadian experiment: https://www.cbc.ca/news/canada/calgary/okotoks-drake-landing-solar-energy-repairs-future-1.7148389

Thanks for sharing that. It will be interesting to get the specifics of the failures if we ever do.

 

[Koolau]

Well, here's the result of a Canadian experiment: https://www.cbc.ca/news/canada/calgary/okotoks-drake-landing-solar-energy-repairs-future-1.7148389

Yeah the theory is sound and exciting. Engineering it to be affordable and reliable - not so much. 70 years ago, my dad put in-floor heating in the family business. It was oil fired hot-water. It was extremely effective and comfortable. The family cats just loved it!!

Big problem was that it was not expandable (and dad always was looking to expand.) Also, no possibility for AC without DRAMATIC engineering. The other issue was old oil boilers were notoriously inefficient AND oil was expensive. It turned out to be cheaper to switch to gas fired forced air with AC. Great ideas need great engineering. YMMV