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If you overprovision the electricity production you can get away with less battery capacity. It’s a tradeoff and the cost-optimal point is not going to be the one where the production is exactly equal to the demand.

This was the most interesting finding: increasing production by 20% did more then increasing storage by 10x.

Yes that's why no one is going for 100% currently yearly production match with renewable, it will need to go higher in production :).

Then you'll get times with overproduction with very low prices, this will prop up "power to storage for power later" (liquid, gaz, whatever) with buy low sell high usual market stuff.

Note that France has currently 130 TWh of gaz storage capacity for about 473 TWh of yearly electricity consumption.

Grid storage is different from powering EVs though. You don’t provide a week of grid backup via battery. You do stuff like pump 100 million gallons of water into a dam with a hydro plant ready.

I think water is more efficient then hydrogen even.

Sure, but it's very dependant on geography, if you want to do it at scale. We're definitely going to have to adopt a mixed approach, so I'd say it still makes sense to keep the research into hydrogen, batteries, all of it.

That's 3 minutes of maximum generation at https://en.wikipedia.org/wiki/Ludington_Pumped_Storage_Power...

I guess that plant doesn't have an extreme amount of head or a particularly large reservoir.

It's about 7 minutes at https://en.wikipedia.org/wiki/Bath_County_Pumped_Storage_Sta... , which has a lot more head.

So you need a lot more pumped storage if you want to start talking about days of backup, and we already used quite a few of the best sites.

Hydrogen is not very efficient, hydro is very efficient. But the energy density for hydro is lower than people think.

m * g * h -> you either need lots of water or lots of height. Best is to have both. You only get that in the Alps and you need some special geoprgaphic features to make it work. Europe is also densely populated and the nature we have left, we want to preserve, so we can't flood all of it.

Do the math, figure out how big of damn we would need to store 3TWh.

My result: at 1000m pump height, you would need 3000 billion liters, which is cube of water with a length 1.5km. Double check this tough, I'm not sure if I did all the conversion correctly

I am not sure there is a universal value for "what people think" about pumped hydro energy density, but your numbers are quite far of: 3TWh at 1000m pump height would require 3e6Wh3600s/h/(1000m1000kg/m3*9.8m/s2) = 1.1e6m3, so a waist-high lake of one square kilometer would do.

For what it is worth, in Europe, Switzerland is doing a lot of pumped hydro powered by surplus French nuclear power in the summer time. Norway has huge amounts of hydro and only pumps a little, but it doesn't matter much: The Scandinavian grid is so well connected, that hydro will ramp down when power is available elsewhere, in effect providing on-demand provider for the whole region.

> I recently played around with the data from Germany 2020. I scaled up the existing renewables (only the ones that are scalable - wind and solar, hydro is pretty much maxed out) so that the yearly consumption can be served from 100% renewables. Then I added a battery to carry the overproduction over to the gaps. A 3 TWh battery would still lead to 50 days of empty battery and thus gaps in the power supply.

Did you use the approach outlined in https://doi.org/10.1016/j.euroecorev.2018.07.004 ? Because "50 days of empty battery" is vastly different from the results in that work. 3 TWh is roughly 0.5% of German annual consumption and should bring you to at least a 90% renewable scenario, if not to 100%.

90% is pretty close to the 50 days of empty battery. Keep in mind that on empty battery days, you still produce some energy as well.

My approach was very very simple: if production is higher than consumption, store energy. Energy storage is limited, so when the stroage is full, energy is lost. If consumption is higher then production, take the difference from the battery.

I have not considered any smart usage patterns or any advanced concepts at all.

Also keep in mind that this ignores transport an heat. Pure electricity was what I looked at and that is somewhat around one third of the total energy used in Germany.

> 90% is pretty close to the 50 days of empty battery.

That's not quite how I understood "50 days of empty battery", but fair enough. This is not something that can't be solved, though. Even the 90% estimate is the worst case estimate, since there's actually a high likelihood of 3 TWh of storage being sufficient for 100% of renewables in any given German year.

> My approach was very very simple: if production is higher than consumption, store energy. Energy storage is limited, so when the stroage is full, energy is lost. If consumption is higher then production, take the difference from the battery.

That's Sinn's approach ("waste no energy and store everything, no matter the cost"), which yields significantly higher total costs (and storage capacities) than Zerrahn's approach which actually takes costs into consideration and leads to much smaller storage capacities on the basis of throwing energy away or using it opportunistically being actually cheaper than storing it for later grid use.

> Also keep in mind that this ignores transport an heat.

Transport and heat actually simplify things significantly for the grid since charging of EVs in Europe can be shifted around by as much as several days while heat will have been largely solved by the EU's 2010 and 2012 energy efficiency directives.

Exactly, and we think ammonia is even better than hydrogen. It is easier to transport and to store (especially for places without underground salt caverns). See Https://www.airthium.com

> 3 TWh is 30 million Model S batteries

Given that Germany has 60 million cars, that sounds not just realistic, but outright easy.

My back of napkin calculation says transatlantic HVDC cable has lower LCOE than batteries, but question is capacity.