In latest episode of Cleaning Up: Leadership in an age of Climate Change, Michael explored the pressing issue of energy storage for resilience with one of the world’s pre-eminent physicists, Professor Sir Chris Llewellyn-Smith. As a theoretical particle physicist and Director of CERN, Chris proposed the existence of the Higgs boson, helped develop the Standard Model, and steered funding of the Large Hardon Collider.
At present Chris is leading a substantial Royal Society study into the role of energy storage in a decarbonized UK, and he shared some essential findings from the yet-to-be published piece with Michael. After hearing from Chris, Michael concluded:
“The bottom line here is that it can be done: we can have a clean electric supply, that is of a scale that can decarbonize the whole of the UK economy, and the outside number that you've come up with is £90 per megawatt hour. Which is, of course, expensive, but it's not off-scale.”
Below are edited highlights from the conversation, condensed for brevity.
Michael Liebreich Chris, can you start by talking about the terms of reference for the Royal Society study you’ve been working on?
CL-S Our underlying assumption was that as we go to 2050, we think by then a very large part of our electricity will come from wind and solar, because they're cheap. But of course, if you have a lot of wind and solar, there will always be times when there's not enough. So, there's basically two things you can do. There are times when there's too much wind and solar; so, you can store the excess, and use it when there's a deficit, and / or you can find other flexible sources of supply. So, we've studied the storage option - and we did compare with some of the other options - and we think storage is the cheapest option.
ML Straight away, you're into the land of trade-offs, aren't you? Because you can have over-capacity on generation, and then that enables you to have less storage, or, you can have no over-capacity, and then store everything extra, right?
CL-S There is a trade-off, and there's a minimum in the cost. You can't get everything from wind and solar; there are periods, maybe even weeks occasionally, when there's no wind and solar. We find that somewhere between about 25% more wind and solar being generated than electricity demand, and something like 60%, 70%, there is a sort of flat minimum in the cost; you need less and less storage as the wind and solar supply goes up, but you're paying more and more for the wind and solar. So, one's cost is going down, the other's going up, there's a large flat minimum.
ML One of my key takeaways is that you don't actually have to get it exactly right, as long as you are somewhere in that zone. Let's probe some of the boundary conditions, because not everybody would agree that it's only going to be wind and solar: we’ve got nuclear, we've got biomass, we've got interconnections…
CL-S As our benchmark, we asked, could you do it without those things? What would it cost? As far as interconnectors are concerned, the difficulty we face is that you get wind droughts. And if that's true in the UK, it's going to be true across Northern Europe. So, we think it will be not prudent to build a system which couldn't work if we couldn't import. So, we haven't concluded interconnectors. On nuclear, first of all, you don't want to operate nuclear flexibly. Secondly, if you add nuclear, you've effectively removed part of demand. So, the thing that you're left to deal with - the difference between wind and solar supply and demand - has become more variable, so, the cost of meeting that from storage goes up. So, you shouldn't add it unless it's cheaper than what you started with. And it's probably not going to be. As for demand response, that will help, but the difficulty is, you get these periods, successive periods of very low supply. Now, we can reduce our electricity demand for a few hours; we could reduce it for a few days. But we're talking about having to lose half our electricity supply for weeks. That's why we put contingency in.
ML Chris, let's get back to the model that you've run, because it's got such powerful learnings.
CL-S So, to discover what you need in the way of flexible generation from storage, you have to look at demand hour by hour. We have a model of what we think the level of demand will be, and a model of wind and solar supply, based on real wind and solar data, treated as if we'd had all this generation going back over 37 years. And of the major messages from this study is that a lot of people have looked at storage and said, oh, we'll look at a couple of typical years, maybe a bad year. That's not enough; you will get the wrong answer by a very, very large factor. So, we said, let's make the store 20% bigger than we thought we needed. Now, the interesting thing is, that only adds £1 a megawatt hour to the cost. In our system, storage is only providing something like 15% of the power, so you can add 20% of it, and it doesn't have a big effect.
ML We should move back to the core of the study, and the terawatt hours of storage that we need.
CL-S I'm always being asked, what volume of storage we need? First of all, it depends: there's this trade-off between how much you're prepared to build of wind, and how much storage. We need, with just hydrogen, we need between about 60 and 100 terawatt hours. Now, to put that in context, the UK today is using about 300 terawatt hours a year of electricity. So, the energy that's got to be the capacity has to be about a third of the annual electricity generation in this country.
ML The crucial question then is: what is the cost of power per megawatt hour?
CL-S So, if we have wind and solar 33% bigger than demand, assuming that wind and solar costs £35 per megawatt hour, then I've got to pay 1.33 x £35 for the wind and solar. Then there's 15% has to come from storage. Now, the storage that will deliver 15% costs me about - in our middle case - £80 per megawatt hour. So, I've got 1.33 times £35 plus 15% of £80. So, I end up with a cost of about £60 a megawatt hour. Then I add a bit of contingency, I add about £4 for transmission. So, in that simple model, I end up at £64 per megawatt hour. But that’s a central case. We then we had to assume a discount rate, and different costs of storage. So, we got a range, including the contingency and the extra transmission, from about £52, up to just over £90. That's with the top storage costs.
ML How many billions are we talking about if you do it, instead of on a per megawatt hour, in actual total billions?
CL-S So, if you take the wind and solar that we'll need, that would have to get up to about 300 gigawatts. If I take that figure, it's of order £100 billion in wind and solar. So, it's a lot, but not impossible. In storage, it also comes out around £100 billion. We have not studied the grid, but I have looked at the National Grid, and they say between now and 2050, we're gonna have to put £100 billion in the grid.
ML To what extent is the hydrogen that you're going to be putting in these stores surplus? Because there's a lot of concern about curtailment.
CL-S In order to minimize the cost, you've always got to generate more electricity than you would literally need. I mean, there's a minimum value where you just have enough electricity to store and meet demand. But then you're storing every damn bit of wind, you have to have colossal power, you have to have huge stores, it bankrupts you. So, the case we looked at, with 570 terawatt hours of demand a year, you can get a system that works with 703 terawatt hours of wind, but it would be hideously expensive. If you just go up 10% above that, the cost drops, and then we get this broad minimum.
ML I just want to touch on salt caverns, before I leave you. Where are they? What are they? Have we got enough salt cavern space?
CL-S In the UK, supposing just for a round figure, we needed 100 terawatt hours of hydrogen storage: in East Yorkshire, there is a capacity - I have this from the British Geological Survey - to build over 100 times that. There's enough to do it all in Cheshire, all in Wessex. So, there are three regions, which between them, can produce over 100 times what we need. So, there's no question about the capacity. They are called solution-mined salt caverns; you drill a hole down about a mile underground, and then you pump in water, it dissolves the salt, and then you pump out brine. The reason it's deep, by the way, is you want to be able to put high pressure on it; you've got to have a lot above it, or it'll blow the top of the thing.
ML There's so many great takeaways here, but the bottom line is that it can be done: we can have a clean electric supply, that is of a scale that can decarbonize the whole of the UK economy. And the outside number that you've come up with is £90 per megawatt hour, which is, of course, expensive, compared what we've been used to with polluting power, but it's not off-scale. And if we can bring it in for £50, £60, £70, then it's certainly a perfectly viable future.