9 ms·

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 b

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 through, cools down, and automatically gets pushed through the house when they open the windows on the roof. I was always wondering why there are no systems converting the unused electricity in potential energy by moving water to a higher ground. And more importantly: Why there are no water storages on the roof. [1] https://www.youtube.com/watch?v=wVp5koAOu9M https://www.youtube.com/watch?v=wVp5koAOu9M

someweirdperson 4y ago
Water can freeze.
chriswarbo 4y ago
> I was always wondering why there are no systems converting the unused electricity in potential energy by moving water to a higher ground. And more importantly: Why there are no water storages on the roof. Gravity is an incredibly feeble force, compared to electromagnetism (i.e. chemical bonds). Storing a practical amount of energy require a large mass × height.
merely-unlikely 4y ago
> 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] https://en.wikipedia.org/wiki/List_of_pumped-storage_hydroelectric_power_stations https://en.wikipedia.org/wiki/List_of_pumped-storage_hydroel...
- bobthepanda 4y ago
  Also, any sort of hydro-based solution is susceptible to drought evaporating water below sufficient operation levels.
- cupofpython 4y ago
  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'm also a fan because pumped storage is a really interesting storage method, but it is beyond niche. It is very tough to move that kind of weight around efficiently for what you get back. Pumping water to great heights is not easy either. (see also: moving rail-carts up a mountain)
  - PaulHoule 4y ago
    They are building a lot of them in China https://en.wikipedia.org/wiki/List_of_pumped-storage_hydroelectric_power_stations https://en.wikipedia.org/wiki/List_of_pumped-storage_hydroel...
    - cupofpython 4y ago
      Makes sense, it is definitely a useful tool. I just think it is insufficient to act as storage. It can be good at producing variable amounts of Watts on demand but not so good at storing enough Watt-hours to keep things running for very long. I can see a great appeal for it to help with load-balancing for a significant amount of choppiness between supply and demand on the hour timescale. For something like solar, where we will want to store over half our daily energy production at peak storage (ideally 2-3 days worth I think) - I don't think it holds up. Additionally, it doesnt seem like a good bet as a primary mechanism for either storage or on-demand generation if energy consumption continues to increase due to the rather large coefficients involved for scaling it up. "The United States generated 4,116 terawatt hours of electricity in 2021"[1] 4,116 TWh/year = 11.2 TWh/day The storage capacities for the largest items listed on the wiki is on the magnitude of GWh. The scale goes kilo-, Mega-, Giga-, then Terra. So we are talking about a need on the order of a thousand pumped storage facilities per country. The US would need over 50 of them per state (on average) in order to keep everything running without production for 24 hours. Doesnt matter how many solar panels we have, if we get 1 dark day then we would run out of power. If we tried to rely on solar entirely, we'd also still need very roughly half that amount of storage just to get through the night. lithium batteries are obviously much better suited for overnight storage, but I have no idea what the numbers are on how much lithium is physically available to use as such storage. If we want to get on the order of monthly to yearly storage to allow, for example, solar panels in alaska to provide enough energy for a resident to get through months of darkness - I have no idea what the leading storage options are, probably lithium still [1]https://www.statista.com/statistics/188521/total-us-electricity-net-generation/ https://www.statista.com/statistics/188521/total-us-electric...
dahfizz 4y ago
> Why there are no water storages on the roof. Quick math - 100 gallons of water 15 meters up off the ground has enough potential energy to run a microwave for 30 seconds. Gravitational storage is pathetically weak. It only makes sense on massive, massive scales. In a residential setting, the storage will never outweigh the extra cost and risk of having so much water on your roof.
- soperj 4y ago
  they do it a lot in NZ. Solar hot water heating.
  - throw__away7391 4y ago
    Solar hot water is great, but that's not gravitational storage, e.g. pumping water up a hill with pumps and later using the flow of water back down to generate power.
    - soperj 4y ago
      You're right it isn't, but it is storing the water on top of the house.
      - adamc 4y ago
        Yes, but I'd expect it's much lesser amounts. 80 gallons is a decent sized water heater.
        soperj 4y ago
        ahhh i understand what you were saying now.
  - wharfjumper 4y ago
    NZ has a lot of hydro and a reasonable amount of geo thermal generation. Solar, not so much.
- 4y ago
psadri 4y ago
energy storage density of heating water >> lifting water. 1m^2 of water heated by 50C (20C → 70C) = 58KWh lifting 1m^2 of water by 10 meters (~ 3 stories!) = 0.03Kwh :-(
- psadri 4y ago
  I think in the future we will see more homes with: Gray water recovery Thermal batteries (hot and cold) - Excess solar energy can be use to "charge" the hot or cold reservoirs for later use depending on season. Effluent heat recovery - Home appliances generate lots of heat (clothes driers, ovens, refrigerators, ...) that is currently vented to the atmosphere. Capture and use it to "charge" the hot battery. - I'd imagine a water (or other liquid) line that connects to each appliance's exhaust via a heat exchanger to make the above more efficient as a standard part of home plumbing. Smart appliances that sync with the home's energy system - eg: clothes dryer that has the option to turn only when there is excess electricity available. Same with EV charging, etc... [Edited for typos]
  - starlust2 4y ago
    > Lots of home appliances generate lots of heat (clothes driers, ovens, refrigerators, ...) that is currently vented to the atmosphere. it'd love to capture that and use it to "charge" the hot battery. I've seen systems that use waste heat from central A/C to heat a swimming pool. In addition to the condenser they have a heat exchanger connected to the coolant line. Pool water is pumped through the heat exchanger and back out to the pool.
jammaloo 4y ago
There is a great youtube channel that tests out different energy storage and harvesting setups, a lot of them focused around water. This is one where they use solar to pump water to the roof, and then use the potential energy overnight: https://www.youtube.com/watch?v=CMR9z9Xr8GM https://www.youtube.com/watch?v=CMR9z9Xr8GM
- dahfizz 4y ago
  A top comment on that video puts it into perspective well. That whole setup can store the energy of a single AA battery. He would be so much better off just charging a cheap battery. All the money wasted on pumps, wood, barrel, pipes....
cogman10 4y ago
> Why there are no water storages on the roof. Depends on the area, but sometimes collecting rain water is illegal. The other issue is that when dealing with rainwater, you need to clean it. Untreated, rainwater will likely develop a bad case of algae.
- lazide 4y ago
  It’s also really heavy - any amount likely to even light up a lightbulb for an hour or two would collapse a house without major reinforcement. Which would far outweigh any value of the storage.
jasonwatkinspdx 4y ago
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.
- pfdietz 4y ago
  There are not many suitable sites on existing rivers, but the potential off river PHES resource is vast. This involves building two reservoirs, charging them with water brought in from elsewhere, then cycling the water back and forth. Additional water will be needed only to make up for evaporation and seepage, but this amount is at least an order of magnitude less than the water evaporated by a nuclear power plant of the same time-averaged power.
kragen 4y ago
> This reminds me a lot of the Earthship community … I was always wondering why … there are no water storages on the roof. All the standard Earthship designs I've studied do store their water on the roof, but they use batteries instead of water pumping to store unused electricity, because to run a conventional house's electrical systems at night you need to store tens of megajoules, and lifting water three meters only stores 0.029 MJ per cubic meter. A cubic meter of water weighs a tonne. So you'd need hundreds of tonnes of water to store the requisite amount of energy that way. A 12-volt 24-amp-hour deep-cycle lead-acid battery goes for US$61 at retail, and that's nominally a megajoule; it replaces 33 tonnes of water at 3 meters of head, you can pick it up in one hand, and it doesn't require an electromechanical pump/turbine to convert the energy into a useful form. And if it shorts out, though it might cause a fire in your electrical room, it won't flood your house. If you're building on a plain, you either need to support your upper water tank with earthworks (say, 2 tonnes per cubic meter of earth) or dig out a hole for a lower water tank for water to flow down into (also 2 tonnes per cubic meter of earth). If we want to store 700 cubic meters of water in a 2-meter-deep water tank whose bottom is 3 meters above grade, we need to pile up 2100 tonnes of dirt covering a water-tank-holding area of 350 m², a tank area with minimally a diameter of 21 meters. And you need a similarly sized tank down at grade level for it to drain into. You can cut this in half by putting the downhill tank in the hole you dug to get all that dirt, but it's still over a thousand tonnes of dirt. Aside from the 1400 square meters of water tank top and bottom surfaces, this would increase the earthmoving effort involved in building an Earthship by over an order of magnitude. Then you need to pump the 700 tonnes of water out of a well, because that's four years' worth of rainfall on the area covered by your giant water tanks (assuming 250 mm rainfall per year). This is a feasible thing to do, and it's less water use than what cattle ranchers evaporate from their windmill-fed water tanks, but it would probably clash with the sensibilities of many Earthship types. Alternatively you can put 20 deep-cycle batteries on shelves in a closet-sized concrete room. So that's what they do. If your Earthship is situated at the foot of a 100-meter-tall mesa, the situation changes, because now you can store a megajoule per tonne of water. So you could use more reasonably sized tanks, like, 20 tonnes. But Earthships are mostly not designed for that situation, because it's rare.
- Schroedingersat 4y ago

someweirdperson 4y ago

Water can freeze.

chriswarbo 4y ago

> I was always wondering why there are no systems converting the unused electricity in potential energy by moving water to a higher ground. And more importantly: Why there are no water storages on the roof. Gravity is an incredibly feeble force, compared to electromagnetism (i.e. chemical bonds). Storing a practical amount of energy require a large mass × height.

merely-unlikely 4y ago

> 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] https://en.wikipedia.org/wiki/List_of_pumped-storage_hydroelectric_power_stations https://en.wikipedia.org/wiki/List_of_pumped-storage_hydroel...

bobthepanda 4y ago
Also, any sort of hydro-based solution is susceptible to drought evaporating water below sufficient operation levels.
cupofpython 4y ago
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'm also a fan because pumped storage is a really interesting storage method, but it is beyond niche. It is very tough to move that kind of weight around efficiently for what you get back. Pumping water to great heights is not easy either. (see also: moving rail-carts up a mountain)
- PaulHoule 4y ago
  They are building a lot of them in China https://en.wikipedia.org/wiki/List_of_pumped-storage_hydroelectric_power_stations https://en.wikipedia.org/wiki/List_of_pumped-storage_hydroel...
  - cupofpython 4y ago
    Makes sense, it is definitely a useful tool. I just think it is insufficient to act as storage. It can be good at producing variable amounts of Watts on demand but not so good at storing enough Watt-hours to keep things running for very long. I can see a great appeal for it to help with load-balancing for a significant amount of choppiness between supply and demand on the hour timescale. For something like solar, where we will want to store over half our daily energy production at peak storage (ideally 2-3 days worth I think) - I don't think it holds up. Additionally, it doesnt seem like a good bet as a primary mechanism for either storage or on-demand generation if energy consumption continues to increase due to the rather large coefficients involved for scaling it up. "The United States generated 4,116 terawatt hours of electricity in 2021"[1] 4,116 TWh/year = 11.2 TWh/day The storage capacities for the largest items listed on the wiki is on the magnitude of GWh. The scale goes kilo-, Mega-, Giga-, then Terra. So we are talking about a need on the order of a thousand pumped storage facilities per country. The US would need over 50 of them per state (on average) in order to keep everything running without production for 24 hours. Doesnt matter how many solar panels we have, if we get 1 dark day then we would run out of power. If we tried to rely on solar entirely, we'd also still need very roughly half that amount of storage just to get through the night. lithium batteries are obviously much better suited for overnight storage, but I have no idea what the numbers are on how much lithium is physically available to use as such storage. If we want to get on the order of monthly to yearly storage to allow, for example, solar panels in alaska to provide enough energy for a resident to get through months of darkness - I have no idea what the leading storage options are, probably lithium still [1]https://www.statista.com/statistics/188521/total-us-electricity-net-generation/ https://www.statista.com/statistics/188521/total-us-electric...

dahfizz 4y ago

> Why there are no water storages on the roof. Quick math - 100 gallons of water 15 meters up off the ground has enough potential energy to run a microwave for 30 seconds. Gravitational storage is pathetically weak. It only makes sense on massive, massive scales. In a residential setting, the storage will never outweigh the extra cost and risk of having so much water on your roof.

soperj 4y ago
they do it a lot in NZ. Solar hot water heating.
- throw__away7391 4y ago
  Solar hot water is great, but that's not gravitational storage, e.g. pumping water up a hill with pumps and later using the flow of water back down to generate power.
  - soperj 4y ago
    You're right it isn't, but it is storing the water on top of the house.
    - adamc 4y ago
      Yes, but I'd expect it's much lesser amounts. 80 gallons is a decent sized water heater.
      - soperj 4y ago
        ahhh i understand what you were saying now.
- wharfjumper 4y ago
  NZ has a lot of hydro and a reasonable amount of geo thermal generation. Solar, not so much.
4y ago

psadri 4y ago

energy storage density of heating water >> lifting water. 1m^2 of water heated by 50C (20C → 70C) = 58KWh lifting 1m^2 of water by 10 meters (~ 3 stories!) = 0.03Kwh :-(

psadri 4y ago
I think in the future we will see more homes with: Gray water recovery Thermal batteries (hot and cold) - Excess solar energy can be use to "charge" the hot or cold reservoirs for later use depending on season. Effluent heat recovery - Home appliances generate lots of heat (clothes driers, ovens, refrigerators, ...) that is currently vented to the atmosphere. Capture and use it to "charge" the hot battery. - I'd imagine a water (or other liquid) line that connects to each appliance's exhaust via a heat exchanger to make the above more efficient as a standard part of home plumbing. Smart appliances that sync with the home's energy system - eg: clothes dryer that has the option to turn only when there is excess electricity available. Same with EV charging, etc... [Edited for typos]
- starlust2 4y ago
  > Lots of home appliances generate lots of heat (clothes driers, ovens, refrigerators, ...) that is currently vented to the atmosphere. it'd love to capture that and use it to "charge" the hot battery. I've seen systems that use waste heat from central A/C to heat a swimming pool. In addition to the condenser they have a heat exchanger connected to the coolant line. Pool water is pumped through the heat exchanger and back out to the pool.

jammaloo 4y ago

There is a great youtube channel that tests out different energy storage and harvesting setups, a lot of them focused around water. This is one where they use solar to pump water to the roof, and then use the potential energy overnight: https://www.youtube.com/watch?v=CMR9z9Xr8GM https://www.youtube.com/watch?v=CMR9z9Xr8GM

dahfizz 4y ago
A top comment on that video puts it into perspective well. That whole setup can store the energy of a single AA battery. He would be so much better off just charging a cheap battery. All the money wasted on pumps, wood, barrel, pipes....

cogman10 4y ago

> Why there are no water storages on the roof. Depends on the area, but sometimes collecting rain water is illegal. The other issue is that when dealing with rainwater, you need to clean it. Untreated, rainwater will likely develop a bad case of algae.

lazide 4y ago
It’s also really heavy - any amount likely to even light up a lightbulb for an hour or two would collapse a house without major reinforcement. Which would far outweigh any value of the storage.

jasonwatkinspdx 4y ago

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.

pfdietz 4y ago
There are not many suitable sites on existing rivers, but the potential off river PHES resource is vast. This involves building two reservoirs, charging them with water brought in from elsewhere, then cycling the water back and forth. Additional water will be needed only to make up for evaporation and seepage, but this amount is at least an order of magnitude less than the water evaporated by a nuclear power plant of the same time-averaged power.

kragen 4y ago

> This reminds me a lot of the Earthship community … I was always wondering why … there are no water storages on the roof. All the standard Earthship designs I've studied do store their water on the roof, but they use batteries instead of water pumping to store unused electricity, because to run a conventional house's electrical systems at night you need to store tens of megajoules, and lifting water three meters only stores 0.029 MJ per cubic meter. A cubic meter of water weighs a tonne. So you'd need hundreds of tonnes of water to store the requisite amount of energy that way. A 12-volt 24-amp-hour deep-cycle lead-acid battery goes for US$61 at retail, and that's nominally a megajoule; it replaces 33 tonnes of water at 3 meters of head, you can pick it up in one hand, and it doesn't require an electromechanical pump/turbine to convert the energy into a useful form. And if it shorts out, though it might cause a fire in your electrical room, it won't flood your house. If you're building on a plain, you either need to support your upper water tank with earthworks (say, 2 tonnes per cubic meter of earth) or dig out a hole for a lower water tank for water to flow down into (also 2 tonnes per cubic meter of earth). If we want to store 700 cubic meters of water in a 2-meter-deep water tank whose bottom is 3 meters above grade, we need to pile up 2100 tonnes of dirt covering a water-tank-holding area of 350 m², a tank area with minimally a diameter of 21 meters. And you need a similarly sized tank down at grade level for it to drain into. You can cut this in half by putting the downhill tank in the hole you dug to get all that dirt, but it's still over a thousand tonnes of dirt. Aside from the 1400 square meters of water tank top and bottom surfaces, this would increase the earthmoving effort involved in building an Earthship by over an order of magnitude. Then you need to pump the 700 tonnes of water out of a well, because that's four years' worth of rainfall on the area covered by your giant water tanks (assuming 250 mm rainfall per year). This is a feasible thing to do, and it's less water use than what cattle ranchers evaporate from their windmill-fed water tanks, but it would probably clash with the sensibilities of many Earthship types. Alternatively you can put 20 deep-cycle batteries on shelves in a closet-sized concrete room. So that's what they do. If your Earthship is situated at the foot of a 100-meter-tall mesa, the situation changes, because now you can store a megajoule per tonne of water. So you could use more reasonably sized tanks, like, 20 tonnes. But Earthships are mostly not designed for that situation, because it's rare.

Schroedingersat 4y ago