Post by blueshoes on Oct 18, 2020 15:18:34 GMT 10
As background to this post, me/partner/family have watched a couple of videos lately that explored catastrophe - one was the asteroid one someone linked recently, and the other was a youtube doco about a theoretical volcano eruption in 536, resulting in a volcanic winter, global cooling and prolonged drought in many areas. What struck me in both those cases is that you can't just rely on Solar in a nuclear/volcanic winter. As a result i have been trying to work out what other forms of energy generation are possible...
== What is Pumped Hydro and where is it used ==
Solar generation is used to pump water up to the top dam, then the water runs down and generates power by spinning turbines.
Pumped Hydro is used in retired open-pit mines in FNQ and a few other places to smooth out power production from solar farms, like this one (250 MW Kidston Pumpt Storage Hydro Project: www.genexpower.com.au/project-details.html)
ANU thinks there are a hundred times more possible sites for pumped hydro dams/systems than we need, to back up renewable electricity for basically the whole world... www.anu.edu.au/news/all-news/anu-finds-530000-potential-pumped-hydro-sites-worldwide
Australia has a massive advantage to many other countries in that we have so much less population density, and lots of varied terrain and open space, which makes Hydro generation workable - however this was about pumped hydro, which requires some form of energy to get the water up to the top reservoir and then can generate electricity from it. Solar or Wind seem to be our main choices for that at the moment...
== Would it work, or would that defy the laws of physics... ==
The thing I keep coming up against is the principle of conservation of energy, and how much water you actually need to make a system generate enough power to be useful
Case study #1: Theoretical minimum: start with 5V, 2A... charging a phone. It's about the minimum *useful* amount of electricity (but nowhere near enough to run your house!)
I worked out that to charge a phone - 5V, battery capacity of 5,400mAh - you would need at least a 5.000L tank and a 2metre height drop (assuming perfect energy conversion). Not impossible - one could put a 5000L tank underground and another one 2M up a hill, there are blocks with a 2M drop across them - but not really worth it!
5,000kg water * 2m drop * 9.81 m/s^2 gravity = 98100 J or 27.25 Wh
and
27Wh at 5V = 5400 mAh
Case #2:
To generate 10kWh (enough to power a 'normal' house for a day or so) you'd need, say, 200 cubic metres of water (200,000L) and a 20m drop (as well as really efficient turbines - an 85% efficient turbine - like the snowy hydro ones - would bump that up to needing a 22m drop or an extra 30k litres of water).
Then you still need some way of generating power to get the water pumped back up to the top.
You wouldn't lose capacity the same way a battery does, but you'd have evaporation losses and rainfall instead.
Look... if you were really desperate and there was no diesel or anything to run a REAL generator, and you were nowhere near a creek and in a solar winter... i could see the value of a gravity-fed one.
On a property you have choices - there's a US list of available turbines here: ecavo.com/best-hydroelectric-generators/
But realistically, it looks like Pumped Hydro is not really going to be a workable solution for urban/city households. If you have acreage with dams, a decent elevation drop between them and wind turbines or solar panels to pump the water back up, it might well be a thing. But a toy system with a few hundred litres in a tank and a drop less than a metre isn't going to generate enough power to do anything interesting.
As a side note, there are small generators that use ?80psi household water pressure to generate small amounts of electricity, like this one (not for sale yet/still in development) vorticaltech.com/index.html which says it can generate up to 120W at the point where water comes in from the street, *when water is being used*.
== What is Pumped Hydro and where is it used ==
Solar generation is used to pump water up to the top dam, then the water runs down and generates power by spinning turbines.
Pumped Hydro is used in retired open-pit mines in FNQ and a few other places to smooth out power production from solar farms, like this one (250 MW Kidston Pumpt Storage Hydro Project: www.genexpower.com.au/project-details.html)
ANU thinks there are a hundred times more possible sites for pumped hydro dams/systems than we need, to back up renewable electricity for basically the whole world... www.anu.edu.au/news/all-news/anu-finds-530000-potential-pumped-hydro-sites-worldwide
Australia has a massive advantage to many other countries in that we have so much less population density, and lots of varied terrain and open space, which makes Hydro generation workable - however this was about pumped hydro, which requires some form of energy to get the water up to the top reservoir and then can generate electricity from it. Solar or Wind seem to be our main choices for that at the moment...
== Would it work, or would that defy the laws of physics... ==
The thing I keep coming up against is the principle of conservation of energy, and how much water you actually need to make a system generate enough power to be useful
Case study #1: Theoretical minimum: start with 5V, 2A... charging a phone. It's about the minimum *useful* amount of electricity (but nowhere near enough to run your house!)
I worked out that to charge a phone - 5V, battery capacity of 5,400mAh - you would need at least a 5.000L tank and a 2metre height drop (assuming perfect energy conversion). Not impossible - one could put a 5000L tank underground and another one 2M up a hill, there are blocks with a 2M drop across them - but not really worth it!
5,000kg water * 2m drop * 9.81 m/s^2 gravity = 98100 J or 27.25 Wh
and
27Wh at 5V = 5400 mAh
Case #2:
To generate 10kWh (enough to power a 'normal' house for a day or so) you'd need, say, 200 cubic metres of water (200,000L) and a 20m drop (as well as really efficient turbines - an 85% efficient turbine - like the snowy hydro ones - would bump that up to needing a 22m drop or an extra 30k litres of water).
Then you still need some way of generating power to get the water pumped back up to the top.
You wouldn't lose capacity the same way a battery does, but you'd have evaporation losses and rainfall instead.
Look... if you were really desperate and there was no diesel or anything to run a REAL generator, and you were nowhere near a creek and in a solar winter... i could see the value of a gravity-fed one.
On a property you have choices - there's a US list of available turbines here: ecavo.com/best-hydroelectric-generators/
But realistically, it looks like Pumped Hydro is not really going to be a workable solution for urban/city households. If you have acreage with dams, a decent elevation drop between them and wind turbines or solar panels to pump the water back up, it might well be a thing. But a toy system with a few hundred litres in a tank and a drop less than a metre isn't going to generate enough power to do anything interesting.
As a side note, there are small generators that use ?80psi household water pressure to generate small amounts of electricity, like this one (not for sale yet/still in development) vorticaltech.com/index.html which says it can generate up to 120W at the point where water comes in from the street, *when water is being used*.
