https://en.wikipedia.org/wiki/Pumped-storage_hydroelectricit...
A standard lithium ion batter is at 87% in the worst case, when it's AC-DC-storage-DC-AC. Going direct from solar panels to storage would save one trip:
http://www.catalyticengineering.com/top-ten-facts-about-tesl...
In any case, the efficiency of storage is only one aspect; it limits how cheap the storage can potentially be, but electricity lost due to inefficiency is not the primary driver of storage cost with any of the currently used technologies.
https://www.sciencedaily.com/releases/2015/08/150801082647.h...
But I think there may be other areas that I'm not finding specifically right now... ("solar battery" is a poor search term for this research...)
- a redox flow battery coupled directly to solar charging
- super high specific energy, ~0.33kWh/kg which is right on par with traditional solid lithium ion batteries
My remaining questions are:
- Compared to PV solar + lithium ion battery, how much insolation is required to store a kWh?
- What is the cost/kWh of the lithium iodide?
- What is the cost/kW of the solar charger, discharger?
- Can the anode and cathode be used to charge the battery from standard electricity, in addition to the (more efficient) solar method?
Thanks for this pointer, this gives me even greater optimism about the future of storage!
The advantages over pumped hydro are,
The power density is much higher, 100000 joules/kg vs 300-500 joules/kg.
You can locate storage facilities pretty much anywhere that's out of shrapnel range. In case the big tank of gas and rocks blows up.
Doesn't have the environmental impact of dams. And rocks are significantly less precious than huge amounts of water.
To flip that around, there exist applications where battery storage isn't reasonable. Is it thus also bizarre to bring batteries?
You're not answering:
> To flip that around, there exist applications where battery storage isn't reasonable. Is it thus also bizarre to bring batteries?
The post I was replying to called talking about hydro storage "bizarre". I was pointing out that it isn't. The logic here seems analogous to saying that compact cars suck because you can't use them as a dump truck.
The strong part of pumped hydropower is that it scales really really well even if the baseline efficiency isn't stellar.
https://www.google.com/maps/@43.9207263,-86.3978435,18314m/d...
It's a big power station, 1.8 GW, but is only providing service to portion of consumers in Michigan.
Making it 10 times bigger would probably be doable but it wouldn't be trivial.
It's also one of the better places on the planet to build a single reservoir system (otherwise you need 2 enormous reservoirs).
I wonder if the answer to seasonal variation will be to make fuel in the summer.
It kind of reminds me of people that think that we should use the exercise bikes in gyms to power the lighting; yes, brilliant, but actually run the numbers and you realize that humans output very very little energy even at peak exercise. The amount of waste on generators would be phenomenal.
There are some cases where pumped hydro makes sense, but there's limited scalability.
I'm sure compressed air in other forms would be a good store. You could also raise and lower weights into a mine, it doesn't matter so long as you can convert between electric energy and kinetic potential of some kind.
1000L tank on a roof which is ~4m high.
E = m * g * h = 1000 * 9.8 * 4 = ~40,000J
Which is about 12Wh not taking into account any losses.
You could maybe improve this by having the water fall into a well but still nowhere near what a battery can provide for a fraction of the cost/complexity.
A standard 100Ah battery will provide 1200Wh.
For example, 1000 kilograms of water (1 cubic meter) at the top of a 100 meter tower has a potential energy of about 0.272 kW·h (capable of raising the temperature of the same amount of water by only 0.23 Celsius = 0.42 Fahrenheit).
https://en.wikipedia.org/wiki/Pumped-storage_hydroelectricit...
Given the much smaller height of a rooftop tank, every 1000 kg of water pumped would support a number of minutes of normal household usage (a decent refrigerator would need several thousand kg per hour).