Wind turbines in Denmark reached record level in 2014

Of course it is. The arbitrage is what makes it happen because that's what makes it profitable. If the energy so generated were labeled with the point of origin then it would count as fossil fuel and then it would yield less on the energy market. The load variations are not such that the generating capacity could not be reduced in time, but there is less money in that.

This is not renewable energy though it masquerades as such. Note that before green energy became a thing this was already happening so it is simply a re-labeling rather than that these lakes suddenly got re-purposed for renewable energy storage.

If the source of the electricity is not originally renewable energy then it is deceptive to sell it as such. People pay a pretty premium for renewable energy.

Pumped storage has the same "greenness" profile as the whole grid had when the pumping was happening, minus the efficiency loss from the round-trip conversion.

Pumping upward typically happens when the renewables are overproducing and the (controllably) variable power plants are idling. It makes no sense to run the pumps for storage when you could throttle back the gas turbines instead. But you can't adjust cloud cover, or tweak windspeed. So when the sun is shining, and the wind blowing, and the methane not burning, you store that excess for later.

That may also include relatively constant baseline power plants. But even then, the storage is often allowing those plants to run at their optimally efficient design capacity. If you idle the coal plant to 80% rated output, you may still be using 85% as much coal (made-up numbers for illustrative purposes). Trying to adjust the output of a nuclear plant is rather complicated, and may involve altering shutdown and maintenance schedules such that the output capacity several months in the future is affected by a decision made today.

So on the whole, re-generation from pumped storage is going to be greener than the baseline plants, and definitely greener than other types of adjustable peak load power plants, like natural gas turbines.

Gas turbines are not that expensive in capital. Instead they cost a lot to run, since they use gas that's much more expensive than coal. (Nevermind Uranium or wind or the sun.)

A big part of US climate strategy seems to be to install a lot of wind and solar power and fill the rest with natural gas, phasing out coal. Keep the nukes that are there. That's possible since in the USA, natural gas is cheaper than in many other places.

I visited the station a few years ago and it is the reason for my original comment, at the time this was explained in some detail by one of the people on the tour. Very impressive by the way and highly recommended if you're in the region.

As for the bookkeeping:

A certain amount of electricity is produced using renewables which is always < the current baseload. It is then (much) more profitable to sell this energy to consumers directly and then to use the reduced base load requirements to top off the lakes before reducing base load generation capacity. At night the process reverses and now the 'newly minted green electrons' get added to the green energy already being sold. This makes more money than selling the nuclear/coal/NG generated electricity directly even though there is some loss from the whole pumping operation.

Note that the scheme already made money based on the demand pricing of electricity, the 'green' aspect simply made it more profitable.

Yes, that's another use. But when it is favorable economically speaking then fossil fuels and nuclear will be used as well. The pumps don't care what color the electrons are. It's mostly a matter of bookkeeping and less one of technology. And as long as demand for electricity during peak times does not coincide with the point in the day when the peak amount of electricity is generated this is a nice way to make some money for the operators.

The owners of coal and nuclear plants are the ones that paid for the pumped storage, they had the idea of making their plant operations more efficient, not of storing renewable energy.

This is one of the early large ones, built by the local utilities:

https://www.consumersenergy.com/content.aspx?id=6985

I am not sure about coal, but you can't easily shutdown a nuclear reactor, so there are times during the day when you are overproducing. So pumping some water is a way to not totally lose the energy produced during that time.

> pumping water into high reservoirs (don't know the english name)

It's just pumped storage! :) Easy to remember.

But yeah there's a lot of things. Pumped storage is a big one, The International Renewable Energy Agency in their roadmap for 2030 for example call for just 150 GW of battery storage, but a whooping 325 GW of pumped storage.

There's other ones, too. One of them is storing thermal, heat energy in caverns, or in rocks. You can then extract when you need to, so you could take wind energy at night when there is barely any demand and use it to electrically heat up rocks, and store the energy for the next day.

Molten salts is similar but different.

Ice, same thing for air conditioning purposes. At night you use excess electricity and essentially run a big fridge on your roof to create ice, and then use that to cool the air during the day.

Those are all thermal storage. Then there's say pressure based storage, like compressing air and releasing it when you want to.

Flywheels are also a thing, you have a wheel and rotate it really fast using energy, and then just slow it down and capture the energy when you want to. It sounds pretty ridiculous but it works and there's various ways to reduce friction.

Good points, I don't really know. Germany's currently producing 10% of electricity with wind, assuming they'd triple that to 30%, and then assuming that say about 25% of the generated wind energy falls so far outside of peak demand hours that it's excess energy to-be-stored.

That'd put the daily storage at 140 gwh for Germany, or 140m kwh. (so definitely billions on a global scale).

Tesla cars might be a decent comparison point, they sell about 50k cars a year (more even this year), at an average of a 80 kwh battery per car they produce 4 gwh of storage each year.

But the Tesla gigafactory is set to produce a projected 85 gwh (of battery packs and cells combined) in a few years. Tesla's current battery products are set to last 15 years, although this may not be a reliable figure to use as it's a consumer grade, not utility grade product. But assuming it is, then every replacement cycle it can produce 1275 gwh of storage. Germany (with my crappy and quick assumptions above) would need about 140 gwh, and Germany represents about 1/16th of the world economy by the way, so a global figure with Germany's model would require 2240 gwh, about twice the projected 15 year production of the gigafactory. (which, we ought to assume, wasn't built without checking if there was enough lithium to run it :p, and given there's already talk of the next one (it's been renamed gigafactory 1, this alone probably says that lithium running out probably isn't the biggest concern).

About reserves though... well there's lots of resources, like close to 40 million tons. reserves (resources that are, today, economically and technically feasible to extract) are lower, but still a substantial 14m tons.

So how much does storage need... well for one we can look at annual production which is 36k tons for 2014. So if we capped out at today's rate, the 14m tons of reserves (the resources that can be mined at a profit), would last close to 400 years. I think it's pretty likely we'll hit a rate of usage that's 3-4 times higher than it is today at some point, so that'd drop that figure down to just 50 years. But I also think more resources will become reserves (as mining technology cheapens), and more resources are found (as exploration techniques improve, see shale gas), and I also think recycling will pick up and increase net production without reducing reserves (afaik recycling is still small for lithium, but growing).

One thing to note here is that apparently lithium is only accountable for about 1% of a battery's cost (at least a few years ago, with lithium prices not dropping and battery prices dropping the past years, it may be a few percent by now). This is generally good news as it means that you can pay e.g. (hypothetically) 5x as much for lithium while barely increasing the price of a battery by a few percent. And if lithium prices go up by 5x, then more resources become reserves, and more resources will be found through exploration due to renewed economic feasibility, meaning lithium scarcity can be sharply reduced without increasing prices of batteries much at all.

Actually I found some numbers too, about 500g of lithium metal for every 1 kwh of storage. So how much storage can we built if we exhausted the 14m reserves entirely, well almost 30k gwh. For comparison, The International Renewable Energy Agency called for 150 GW installed capacity by 2030, which corresponds to roughly 200 gwh or so.

Plus the company I mentioned is going for ridiculous amount of cycles, like 40k of them. That's a very long lifetime compared to say the 5k cycles of the new 7kwh Tesla powerwall, or the 1.5k cycles of the 10kwh version. That means production can be cut in half because batteries last longer, to sustain the same storage levels. Plus grid-scale storage I think is much easier to recycle compared to consumer storage.

So I don't think we've got a resource problem, but again all of these are back of the envelope numbers I'm just throwing out there. I also didn't mention that batteries are only about a third of total lithium consumption, so there's that, too. The other issues you mentioned though are there and definitely need to be overcome.