4 ms·

But heat based power always leaks energy? Why not lift something REALLY heavy and let gravity spin a gearbox on the way down? Like say lift a silo of sand? Up

by ck2 4y ago

But heat based power always leaks energy? Why not lift something REALLY heavy and let gravity spin a gearbox on the way down? Like say lift a silo of sand? Up the side of an existing hill on a rail/track? Alternately pump water uphill but in cold/hot climates that would be a problem and microbes, etc. Gravity isn't going to leak or fail. And enough of an angle that weight is always coming down regardless of weather.

elil17 4y ago
You're balancing the cost of energy leaking vs. the difference in capex vs. other inefficiencies of the gravity based system (e.g. heat loss due to friction)
burkaman 4y ago
Those methods are good and already in use, and this is one more additional energy storage method for places where those are expensive or impractical. This method also has the additional benefit of directly providing heat, so if you need heat more than you need power then this seems like a great choice.
rjmunro 4y ago
This unit stores 8MWh of energy with 100 tonnes of sand. Gravity is about 9.8m/s*2. If you put the calculation into google "8MWh / 9.8m/s*2 / 100 tonnes", it tells you that you need lift those 100 tonnes 29.39km up, which is over 3 times the height of Everest. And the mechanics of the system are much more complicated, more expensive to build and maintain. However, pumping water uphill is done in many places, and is more practical because a lake of water can easily weigh millions of tonnes. The problem is finding places with suitable hill top lakes. Also, if you are using it for district heating output, storing it as heat is convenient. There might scope to increase efficiency by using some sort of heat pump, but getting a heat pump to go up to 600°C is quite hard.
- kwhitefoot 4y ago
  > The problem is finding places with suitable hill top lakes. And a similar capacity lake at the bottom of the station to hold the water that you are going to pump up to the top.
Someone 4y ago
> Why not lift something REALLY heavy and let gravity spin a gearbox on the way down? Because lifting something that’s heavy doesn’t store much energy (or, stated alternatively, 1kWh is a lot of energy, compared to human muscles) https://www.quora.com/How-much-mass-in-kg-can-I-lift-to-1-m-height-with-1-kWh-of-energy https://www.quora.com/How-much-mass-in-kg-can-I-lift-to-1-m-...: Q: How much mass in kg can I lift to 1 m height, with 1 kWh of energy? A: Let x kg be the mass to be lifted. The energy required = mgh x * 9.8kgm²/s² or 9.8x Joules 1 KWH = 3.6 million Joules. 9.8x = 3.6*10⁶ => x = 3.6*10⁶ /9.8 = 3.67*10⁵ kg. So, that’s about 360,000 kg. The great pyramid of Giza weighs about 6 billion kg (https://www.egyptabout.com/2019/02/facts-16-fun-facts-about-great-pyramid.html https://www.egyptabout.com/2019/02/facts-16-fun-facts-about-...), so lifting that by a meter would store less than 20,000 kWh.
AtlasBarfed 4y ago
I believe pumping water up a mountain is the only economical energy storage battery based on current economics. Lifting heavy weights requires such a big facility that it won't beat other simpler means. I think pumped hydro is something like 70-80% efficient, which is really good. I believe sodium ion batteries (CATL alleges mass production of 160 wh/kg) will be the killer app battery of grid storage that doesn't have pumped hydro as a geographic possibility, although that's probably 5 years out. A 160 wh/kg sodium ion battery (which should have superior cell-to-pack density than nickel/cobalt chemistries similar to LFP chemistry) can power a standard range model 3.
- hedora 4y ago
  There is a company that uses electric trains to drive the heavy weights to the top of mountains. They claim 90% round trip efficiency: https://aresnorthamerica.com/gravityline/ https://aresnorthamerica.com/gravityline/ which sounds plausible, since rail freight companies have spent 200 years micro-optimizing train efficiency.
jaclaz 4y ago
Already thought of and also partly tested experimentally, cranes: https://news.ycombinator.com/item?id=17789456 https://news.ycombinator.com/item?id=17789456 https://news.ycombinator.com/item?id=32240546 https://news.ycombinator.com/item?id=32240546 https://news.ycombinator.com/item?id=29910248 https://news.ycombinator.com/item?id=29910248 Rail loop: https://aresnorthamerica.com/gravityline/ https://aresnorthamerica.com/gravityline/

by ck2 4y ago

elil17 4y ago

You're balancing the cost of energy leaking vs. the difference in capex vs. other inefficiencies of the gravity based system (e.g. heat loss due to friction)

burkaman 4y ago

Those methods are good and already in use, and this is one more additional energy storage method for places where those are expensive or impractical. This method also has the additional benefit of directly providing heat, so if you need heat more than you need power then this seems like a great choice.

rjmunro 4y ago

This unit stores 8MWh of energy with 100 tonnes of sand. Gravity is about 9.8m/s*2. If you put the calculation into google "8MWh / 9.8m/s*2 / 100 tonnes", it tells you that you need lift those 100 tonnes 29.39km up, which is over 3 times the height of Everest. And the mechanics of the system are much more complicated, more expensive to build and maintain. However, pumping water uphill is done in many places, and is more practical because a lake of water can easily weigh millions of tonnes. The problem is finding places with suitable hill top lakes. Also, if you are using it for district heating output, storing it as heat is convenient. There might scope to increase efficiency by using some sort of heat pump, but getting a heat pump to go up to 600°C is quite hard.

kwhitefoot 4y ago
> The problem is finding places with suitable hill top lakes. And a similar capacity lake at the bottom of the station to hold the water that you are going to pump up to the top.

Someone 4y ago

> Why not lift something REALLY heavy and let gravity spin a gearbox on the way down? Because lifting something that’s heavy doesn’t store much energy (or, stated alternatively, 1kWh is a lot of energy, compared to human muscles) https://www.quora.com/How-much-mass-in-kg-can-I-lift-to-1-m-height-with-1-kWh-of-energy https://www.quora.com/How-much-mass-in-kg-can-I-lift-to-1-m-...: Q: How much mass in kg can I lift to 1 m height, with 1 kWh of energy? A: Let x kg be the mass to be lifted. The energy required = mgh x * 9.8kgm²/s² or 9.8x Joules 1 KWH = 3.6 million Joules. 9.8x = 3.6*10⁶ => x = 3.6*10⁶ /9.8 = 3.67*10⁵ kg. So, that’s about 360,000 kg. The great pyramid of Giza weighs about 6 billion kg (https://www.egyptabout.com/2019/02/facts-16-fun-facts-about-great-pyramid.html https://www.egyptabout.com/2019/02/facts-16-fun-facts-about-...), so lifting that by a meter would store less than 20,000 kWh.

AtlasBarfed 4y ago

I believe pumping water up a mountain is the only economical energy storage battery based on current economics. Lifting heavy weights requires such a big facility that it won't beat other simpler means. I think pumped hydro is something like 70-80% efficient, which is really good. I believe sodium ion batteries (CATL alleges mass production of 160 wh/kg) will be the killer app battery of grid storage that doesn't have pumped hydro as a geographic possibility, although that's probably 5 years out. A 160 wh/kg sodium ion battery (which should have superior cell-to-pack density than nickel/cobalt chemistries similar to LFP chemistry) can power a standard range model 3.

hedora 4y ago
There is a company that uses electric trains to drive the heavy weights to the top of mountains. They claim 90% round trip efficiency: https://aresnorthamerica.com/gravityline/ https://aresnorthamerica.com/gravityline/ which sounds plausible, since rail freight companies have spent 200 years micro-optimizing train efficiency.

jaclaz 4y ago

Already thought of and also partly tested experimentally, cranes: https://news.ycombinator.com/item?id=17789456 https://news.ycombinator.com/item?id=17789456 https://news.ycombinator.com/item?id=32240546 https://news.ycombinator.com/item?id=32240546 https://news.ycombinator.com/item?id=29910248 https://news.ycombinator.com/item?id=29910248 Rail loop: https://aresnorthamerica.com/gravityline/ https://aresnorthamerica.com/gravityline/