5 ms·

I saw a video like a month ago on YouTube where somebody pumped something like 250 liters of water on his roof (7 meters elevation, if I remember correctly) and

I saw a video like a month ago on YouTube where somebody pumped something like 250 liters of water on his roof (7 meters elevation, if I remember correctly) and let it run through a homebuild generator. The power capacity of that setup was like that of an AA battery, if I remember correctly. You need huge amounts of water and lots of height difference.

ed312 4y ago
Based on some extremely back of napkin math (e.g. doing one of those activities where you cycle to power a light bulb) that seems pretty far off. Was the flow rate extremely low? Have a link?
- rootusrootus 4y ago
  Sounds like this one: https://www.youtube.com/watch?v=CMR9z9Xr8GM https://www.youtube.com/watch?v=CMR9z9Xr8GM They do say it is about equivalent to a single AA alkaline. It is not exactly an optimized efficient setup, but still, it gets the point across. Pumped hydro is a grid scale option, in places that have the ability to store a lot of water.
  - martin_a 4y ago
    That's the one!
- dmurray 4y ago
  250 litres x 7 metres is 1750 kilogram-force-metres. Wolfram Alpha [0] says this is about 5 Watt-hours, and gives some other handy comparisons: > ≈ 0.45 × metabolic energy of one gram of fat ( ≈ 38000 J ) > ≈ 0.63 × energy released by burning 1 gram of ethanol ( ≈ 27000 J ) > ≈ metabolic energy of one gram of sugar or protein ( ≈ 17000 J ) > ≈ (0.02 to 0.09) × typical kinetic energy of a car at highway speeds ( 200000 to 900000 J ) > ≈ 0.5 × typical battery energy content of an alkaline long-life C battery ( ≈ 9.6 W h ) > ≈ 0.55 × typical battery energy content of a nonrechargeable Lithium-Thionyl Chloride AA battery ( ≈ 8.6 W h ) > ≈ 0.92 × typical battery energy content of a carbon-zinc D battery ( ≈ 5.2 W h ) Gravitational potential energy is just really, really low energy density. Fortunately it's reasonable to have pumped-storage reservoirs that contain trillions of litres of water. [0] https://www.wolframalpha.com/input?i=1750+kg+metres+in+watt-hours https://www.wolframalpha.com/input?i=1750+kg+metres+in+watt-...
  - RosanaAnaDana 4y ago
    Would you be able to help me figure out the gravitational potential energy of the red hill tanks? https://www.epa.gov/red-hill/what-red-hill-bulk-fuel-storage-facility https://www.epa.gov/red-hill/what-red-hill-bulk-fuel-storage... They were recently decommissioned due to leaks, but I've often wondered if they could be repurposed as gravity battery storage. edit: if you want to check my math. I calculated the tanks at ~567 million liters, and am saying there is 120 meters of vertical distance. They would be equivalent to a 0.1856 GW h (gigawatt hours) battery if repurposed in this way. https://www.wolframalpha.com/input?i=567810000*120+kg+metres+in+watt-hours https://www.wolframalpha.com/input?i=567810000*120+kg+metres...
    - dmurray 4y ago
      I think a bit more than that, the article says 250 million gallons which is more like 960 million litres. That squares with the dimensions given: 15m x 15m x pi x 75m x 20 tanks = 1 million cubic metres = 1 billion litres. Oahu uses about 225MW on average in residential electricity [0], so this could store an hour or so of excess capacity. That's not nothing, but you might want to 5x or 10x it to really smooth out demand and supply peaks for the island. Note that you also need a set of tanks or a lake at the bottom of the hill. The tanks are 75m tall, so how are you accounting for that in your 120m of vertical distance? [0] https://www.eia.gov/todayinenergy/detail.php?id=49036 https://www.eia.gov/todayinenergy/detail.php?id=49036 gives 2,018 kWh per person in Hawaii
      - RosanaAnaDana 4y ago
        I subtracted 100 from their position on red hill at 220-ish meters to account for the fact that the tanks are buried in the ground (I don't know precisely where). >Oahu uses about 225MW on average in residential electricity [0], so this could store an hour or so of excess capacity. That's not nothing, but you might want to 5x or 10x it to really smooth out demand and supply peaks for the island. https://spectrumlocalnews.com/hi/hawaii/top-stories/2022/08/15/mililani-i-solar-is-now-online https://spectrumlocalnews.com/hi/hawaii/top-stories/2022/08/... This solar plant & battery system was completed last month. The battery is able to store 144 MWh. This shows me that planners and people thinking about this are willing to invest & commit to power solutions at this scale. I don't know if you are aware or have read up on the red hill controversy. These tanks were used to store fuel by the Navy. They leaked earlier this year and poisoned the Red Hill aquifer and have caused quite a bit of local controversy. I'm struggling with the idea of writing a letter to the editor outlining this concept, but also emphasizing how converting these tanks to a water storage/ energy storage facility would improve local resilience to drought, bring down water costs, improve environmental conditions etc.
- raphaelj 4y ago
  250L x 7m is 17kN, or about 5W/h, or about 2 AA 2450mAh cells from IKEA. Pumped storage scales well though, as the stored volume scales squarely to the required container material (e.g. storing 25,000L will only take 10x the material while storing 100x the energy).
jandrese 4y ago
Yeah, pumped hydro is one of those power sources that doesn't scale down at all. However, home scale conventional hydro is a thing. If you live on a hill with a creek that runs down it you can install a generator that produces a usable amount of consistent power for the cost of a few hundred meters of PVC pipe, a barrel, some connectors, and a small electric turbine. Search for micro-hydro if you want to know more. Like all hydro solutions it's heavily dependent on the geography and only suitable for well under .1% of the population, but where it is feasible it can be a huge step towards off-grid living. Add in some batteries, maybe supplement with some solar panels, and you've got all of the electricity you need year round at a somewhat affordable price.
- martin_a 4y ago
  > Search for micro-hydro if you want to know more. I've probably seen everything YT has to offer on that. :-D While I really enjoy those videos and the "let's just do it" vibe with old washing machines as generators, I'm also somewhat happy that Germany has rather strict regulations on how to use water from streams and rivers. Some installations are quite disturbing for local ecosystems. But being off-grid in remote areas these solutions seem like a probable compromise.
  - jandrese 4y ago
    Most micro-hydro setups seem to divert only part of the stream and only do it for a few hundred meters or so. These streams are typically much too small to be salmon spawning grounds or the like so the ecological impact seems pretty minimal. It's not like they're drinking all of the water, it gets returned to the stream right below the turbine.

ed312 4y ago

Based on some extremely back of napkin math (e.g. doing one of those activities where you cycle to power a light bulb) that seems pretty far off. Was the flow rate extremely low? Have a link?

rootusrootus 4y ago
Sounds like this one: https://www.youtube.com/watch?v=CMR9z9Xr8GM https://www.youtube.com/watch?v=CMR9z9Xr8GM They do say it is about equivalent to a single AA alkaline. It is not exactly an optimized efficient setup, but still, it gets the point across. Pumped hydro is a grid scale option, in places that have the ability to store a lot of water.
- martin_a 4y ago
  That's the one!
dmurray 4y ago
250 litres x 7 metres is 1750 kilogram-force-metres. Wolfram Alpha [0] says this is about 5 Watt-hours, and gives some other handy comparisons: > ≈ 0.45 × metabolic energy of one gram of fat ( ≈ 38000 J ) > ≈ 0.63 × energy released by burning 1 gram of ethanol ( ≈ 27000 J ) > ≈ metabolic energy of one gram of sugar or protein ( ≈ 17000 J ) > ≈ (0.02 to 0.09) × typical kinetic energy of a car at highway speeds ( 200000 to 900000 J ) > ≈ 0.5 × typical battery energy content of an alkaline long-life C battery ( ≈ 9.6 W h ) > ≈ 0.55 × typical battery energy content of a nonrechargeable Lithium-Thionyl Chloride AA battery ( ≈ 8.6 W h ) > ≈ 0.92 × typical battery energy content of a carbon-zinc D battery ( ≈ 5.2 W h ) Gravitational potential energy is just really, really low energy density. Fortunately it's reasonable to have pumped-storage reservoirs that contain trillions of litres of water. [0] https://www.wolframalpha.com/input?i=1750+kg+metres+in+watt-hours https://www.wolframalpha.com/input?i=1750+kg+metres+in+watt-...
- RosanaAnaDana 4y ago
  Would you be able to help me figure out the gravitational potential energy of the red hill tanks? https://www.epa.gov/red-hill/what-red-hill-bulk-fuel-storage-facility https://www.epa.gov/red-hill/what-red-hill-bulk-fuel-storage... They were recently decommissioned due to leaks, but I've often wondered if they could be repurposed as gravity battery storage. edit: if you want to check my math. I calculated the tanks at ~567 million liters, and am saying there is 120 meters of vertical distance. They would be equivalent to a 0.1856 GW h (gigawatt hours) battery if repurposed in this way. https://www.wolframalpha.com/input?i=567810000*120+kg+metres+in+watt-hours https://www.wolframalpha.com/input?i=567810000*120+kg+metres...
  - dmurray 4y ago
    I think a bit more than that, the article says 250 million gallons which is more like 960 million litres. That squares with the dimensions given: 15m x 15m x pi x 75m x 20 tanks = 1 million cubic metres = 1 billion litres. Oahu uses about 225MW on average in residential electricity [0], so this could store an hour or so of excess capacity. That's not nothing, but you might want to 5x or 10x it to really smooth out demand and supply peaks for the island. Note that you also need a set of tanks or a lake at the bottom of the hill. The tanks are 75m tall, so how are you accounting for that in your 120m of vertical distance? [0] https://www.eia.gov/todayinenergy/detail.php?id=49036 https://www.eia.gov/todayinenergy/detail.php?id=49036 gives 2,018 kWh per person in Hawaii
    - RosanaAnaDana 4y ago
      I subtracted 100 from their position on red hill at 220-ish meters to account for the fact that the tanks are buried in the ground (I don't know precisely where). >Oahu uses about 225MW on average in residential electricity [0], so this could store an hour or so of excess capacity. That's not nothing, but you might want to 5x or 10x it to really smooth out demand and supply peaks for the island. https://spectrumlocalnews.com/hi/hawaii/top-stories/2022/08/15/mililani-i-solar-is-now-online https://spectrumlocalnews.com/hi/hawaii/top-stories/2022/08/... This solar plant & battery system was completed last month. The battery is able to store 144 MWh. This shows me that planners and people thinking about this are willing to invest & commit to power solutions at this scale. I don't know if you are aware or have read up on the red hill controversy. These tanks were used to store fuel by the Navy. They leaked earlier this year and poisoned the Red Hill aquifer and have caused quite a bit of local controversy. I'm struggling with the idea of writing a letter to the editor outlining this concept, but also emphasizing how converting these tanks to a water storage/ energy storage facility would improve local resilience to drought, bring down water costs, improve environmental conditions etc.
raphaelj 4y ago
250L x 7m is 17kN, or about 5W/h, or about 2 AA 2450mAh cells from IKEA. Pumped storage scales well though, as the stored volume scales squarely to the required container material (e.g. storing 25,000L will only take 10x the material while storing 100x the energy).

jandrese 4y ago

Yeah, pumped hydro is one of those power sources that doesn't scale down at all. However, home scale conventional hydro is a thing. If you live on a hill with a creek that runs down it you can install a generator that produces a usable amount of consistent power for the cost of a few hundred meters of PVC pipe, a barrel, some connectors, and a small electric turbine. Search for micro-hydro if you want to know more. Like all hydro solutions it's heavily dependent on the geography and only suitable for well under .1% of the population, but where it is feasible it can be a huge step towards off-grid living. Add in some batteries, maybe supplement with some solar panels, and you've got all of the electricity you need year round at a somewhat affordable price.

martin_a 4y ago
> Search for micro-hydro if you want to know more. I've probably seen everything YT has to offer on that. :-D While I really enjoy those videos and the "let's just do it" vibe with old washing machines as generators, I'm also somewhat happy that Germany has rather strict regulations on how to use water from streams and rivers. Some installations are quite disturbing for local ecosystems. But being off-grid in remote areas these solutions seem like a probable compromise.
- jandrese 4y ago
  Most micro-hydro setups seem to divert only part of the stream and only do it for a few hundred meters or so. These streams are typically much too small to be salmon spawning grounds or the like so the ecological impact seems pretty minimal. It's not like they're drinking all of the water, it gets returned to the stream right below the turbine.