This blog is part of a series of interviews on our Emerging Technologies 2014.
What do we mean by “grid-scale electricity storage”?
We are talking about a spectrum of technology options for storing electricity. It’s odd that we are in the 21st century and still don’t have the potential to store electricity effectively given how essential it is. The way an electricity grid works is that the generators need to feed in exactly the same amount of electrical power as is being consumed at any point in time. Supply must always match demand.
Obviously, with the increasing supply from intermittent sources such as wind, solar and other renewables, that’s not possible. Meanwhile, nuclear is predominantly supplying a large amount of baseload rather than following peaks of demand. The challenge is how to run a grid where you have a diminishing amount of dispatchable electrical power from generators. So, storage is the sort of pot of gold, which everyone is looking for.
You have described this as a suite of technologies. What does that include?
There are a few ways to store energy: you can store energy chemically, you can store kinetic energy, and you can store potential energy. The only large-scale energy storage technology at the moment is pumped storage of water. In Wales, there is a big facility where water is pumped uphill during the excess of supply and let back downhill through large turbines to meet sudden peaks. It can deliver an additional two gigawatts or so within 16 seconds, so it can ramp up very quickly. But, obviously, when the top lake drains out, there’s no more available and these kinds of facilities are expensive to build because they require mountain topography and a lot of water. If you rely on renewable energy sources for a large portion of your energy then storing excess energy becomes a more pressing challenge.
Would enormous batteries that we can charge and use at a later date be a solution?
Batteries are one of the favourites because, obviously, they are the way which electricity has been conventionally stored on a small scale. However, with batteries the problem is volume. You have to have a gigantic battery to store enough power to deliver megawatt or even gigawatt-hours of supply. One of the options is what’s called flow batteries, where the energy is stored in the chemistry of the liquid, which you can then keep in big tanks and run it through the battery only when required. You don’t have to have a huge battery to store the power; you just have to be able to store the liquid that flows through it.
Another option is compressed air. That’s storing potential energy which then converts to kinetic energy within the turbine when it’s released. ConocoPhillips in the United States is trialling a plant where air is pumped into underground salt caverns, which is how natural gas is stored in large quantities in many countries. The air is pressurized to 100 bars and when it is released it comes back through a turbine and spins the turbine to generate electricity.
Fly wheels are a third option. They are made to spin with electricity when there is an excess supply and the spin generates power. The flywheels run down over long periods. That is actually storing energy as kinetic energy. Another option is what’s called isentropic storage of heat via reversible heat pumps. There’s a small company in Cambridge, United Kingdom, called Isentropic, which has two buildings full of gravel – with very hot gravel in one building and very cold gravel in the other. The temperature difference between the two is used to generate electricity.
You can use excess electricity to electrolyze water. You can split water into hydrogen and oxygen, then use the hydrogen to create methane, which you can feed into the gas grid. Obviously, storing gas is already a well-used technology. The gas is stored for days and weeks and then that gas can either be burned to generate electricity or it can be put into the existing gas grid. So, that would be a way of storing energy chemically.
What are the obstacles facing these technologies?
The big challenge is cost, which comes with scalability. If it’s too costly, you can’t scale it. Another component of the cost issue is the round-trip efficiency. If you’re throwing away 60% of your energy by going through the process, that’s a large waste of energy.
Are all the competing technologies at about the same stage of development?
I don’t see a frontrunner. Some are at the trial stage and others are prototypes. Some, such as the flow battery, are still at the laboratory stage. The only one that has been working for decades, of course, is pumped storage water. In Germany, where this is an urgent problem given that the country plans to run on large amounts of intermittent renewable power within the next decade or so, one of the frontrunners is the methanation technology. This process is where excess electricity is used to generate hydrogen and then methane, which is either stored or fed into the gas grid. I don’t think there’s going to be any particular technology leaping ahead, but we would expect a frontrunner to emerge by the end of the year.
Is this just about solving the problem of the efficiency of renewable energy sources?
It is about the shift away from fossil fuels in general. Fossil fuels represent dispatchable power and are extremely convenient in a sense. You can stockpile large amounts of coal or gas and you can burn it exactly when you need to generate electricity. What we’re talking about now is intermittent sources of renewable power, which are there when the weather conditions are right, or nuclear power, which is on 24/7. It can’t be ramped up to meet a peak or shut off to meet the slump in demand. So if you can shave off the peaks and fill in the troughs with nuclear, you need storage to be able to shift, in time, the amount of electricity which is available to the grid.
At what point are we likely to see these technologies make a difference to energy supply problems?
By the latter half of this decade, these technologies have to be up and running at an increasingly large scale for the move away from fossil fuels to work. Germany, which is closing down its nuclear plants and seeking to operate more renewables, is burning more coal to keep the grid stable. If the countries that are trying to shift away from fossil fuels to renewables are not to fail, these technologies have to be up and running at a large scale as the renewables penetration increases.
Author: Mark Lynas is a visiting research associate, School of Geography and the Environment at Oxford University, a former adviser on climate change to the President of the Maldives and a frequent speaker on climate science and policy. Reporting by Shane Richmond.
Image: The art installation “CLOUD”, made up of 5000 new and recycled lightbulbs, is seen in Singapore March 5, 2014. REUTERS/Edgar Su