4 ms·

> 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

> 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.
sidewndr46 4y ago
Secondary point: most residential structures are not designed to have 1000s or even 100s of gallons of water stored on the roof. Even 100 gallons is a huge amount of static load to add to a structure.
biggoodwolf 4y ago
rgmerk 4y ago
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 raised tank.
- Dylan16807 4y ago
  That's not an exception, that's an entirely different use for a raised tank. And not a very big one either.
  - wavesquid 4y ago
    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.
    - Dylan16807 4y ago
      Right, but do you need more than 50 of those for the specific purpose of evening out pressure?
  - lillecarl 4y ago
    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 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 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.
tharkun__ 4y ago
Here's some "slow math" in video form ;) https://youtu.be/CMR9z9Xr8GM https://youtu.be/CMR9z9Xr8GM I find him entertaining. Put a 55 gallon drum on his roof, pumping water up via solar and running lights at night. Closed loop system. He also "does the math" and mentions exactly what you are saying in entertaining format. Just not worth it if you're not doing it on a massive scale, preferably way out of sight and danger.
dsq 4y ago
Thanks for that dose of information. Basic arithmetic is so lacking in all these discussions. People throw all sort of fantastic pseudo-facts with little or no anchor to reality.

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.

sidewndr46 4y ago

Secondary point: most residential structures are not designed to have 1000s or even 100s of gallons of water stored on the roof. Even 100 gallons is a huge amount of static load to add to a structure.

biggoodwolf 4y ago

rgmerk 4y ago

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 raised tank.

Dylan16807 4y ago
That's not an exception, that's an entirely different use for a raised tank. And not a very big one either.
- wavesquid 4y ago
  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.
  - Dylan16807 4y ago
    Right, but do you need more than 50 of those for the specific purpose of evening out pressure?
- lillecarl 4y ago
  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 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 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.

tharkun__ 4y ago

Here's some "slow math" in video form ;) https://youtu.be/CMR9z9Xr8GM https://youtu.be/CMR9z9Xr8GM I find him entertaining. Put a 55 gallon drum on his roof, pumping water up via solar and running lights at night. Closed loop system. He also "does the math" and mentions exactly what you are saying in entertaining format. Just not worth it if you're not doing it on a massive scale, preferably way out of sight and danger.

dsq 4y ago

Thanks for that dose of information. Basic arithmetic is so lacking in all these discussions. People throw all sort of fantastic pseudo-facts with little or no anchor to reality.