Ensuring that renewables supply us with electricity when we need it
Managing renewable energy intermittency.
Renewables are great. You build them, the wind blows, the sun shines, and you generate power. No costly fuel required.
But as critics love to point out, the sun won’t always be shining nor the wind blowing. In other words, solar and wind are intermittent, or variable. And in instances of low solar and wind output, something else will need to provide us with electricity.
I tend to put possible solutions to this intermittency into 3 buckets: overbuild, flexibility and baseload.
Overbuild
Overbuilding renewables involves building so many wind and solar farms, that even when there’s only the lightest breeze or the dimmest sunshine, a meaningful amount of electricity is produced. The flip side to this of course is that on a windy and sunny day, more electricity will be generated than could ever possibly be used.
At first glance this appears wasteful. Does it make sense to accept that we’ll waste electricity much of the time, in return for knowing that we’ll always have some energy? It feels less wasteful if you think about it this way… If the cost of wind and solar continues to fall (they’re already down 70% and 89% respectively over the last decade), it may well end up cheaper to overbuild renewables than to deploy other technologies that handle intermittency.
And in reality, we wouldn’t expect to waste all the excess electricity that is produced. That’s where flexibility comes in.
Flexibility
Flexibility is a broad term that encompasses technologies or behaviours that allow us to shift electricity from one time period to another, or even from one location to another. Flexibility doesn’t involve generating additional energy. Instead it makes better use of the energy that we already generate.
For example, flexibility may involve…
- Incentivising electricity users to shift their usage to times when the wind is blowing and the sun is shining.
- Storing excess renewable electricity in batteries (either batteries dedicated for this purpose or batteries in idle electric vehicles) for use when renewables aren’t generating.
- Transmitting renewable electricity over long distances from somewhere with a surplus of electricity to somewhere with a deficit (e.g. from a windy UK to a cloudy Spain).
Regardless of which specific technologies end up playing a key role in a future net zero energy system, flexibility as a whole will be critical in matching energy supply and demand.
However for extended periods of low wind and solar output (or ‘dull lulls’), additional technologies that can generate electricity on demand will be required.
Baseload
Baseload describes technologies that can generate electricity every hour of the day and every day of the year. Coal and gas plants can both be considered baseload (as long as you have enough fuel), while nuclear is the baseload technology typically discussed in a net zero context.
We know that coal and gas are not consistent with our net zero future unless we’re able to capture and store the carbon dioxide that is produced when they’re burned (known as carbon capture and storage, or CCS). As far as I’m aware, CCS hasn’t successfully and economically been deployed at scale, and the general outlook for the technology is far from rosy. Therefore I tend to write coal and gas out of any vision of the future. (But I’d love to learn more about progress that has been made with CCS or CCUS, so please add any good articles or reports to the comments).
Nuclear is also challenging. First of all it’s expensive — the UK government has agreed to pay £107 (in today’s prices) for every MWh of electricity delivered by the Hinkley Point C nuclear plant that is currently under construction. This is 2.5 times the £43 per MWh that the government recently agreed to pay for electricity from several offshore wind farms. You could argue that this is a fair price to pay for the reliability and consistency that nuclear provides (i.e. that nuclear is receiving a “reliability premium”). You could also argue that even with this reliability premium nuclear is too expensive, especially given nuclear’s other limitations.
Secondly, nuclear is inflexible. It’s good at churning out a consistent amount of electricity day in, day out. But nuclear is not good at ramping its output up or down. And it’s this lack of flexibility that may prevent nuclear from being the perfect complement to renewables that many like to claim it is. The perfect complement to renewables will be able to increase or decrease its output in seconds (or less) in response to clouds passing over solar farms in Devon, or strong gusts of wind in the North Sea. There are companies working on smaller, cheaper and more flexible nuclear reactors that may allow this, but they always seem to be another 5–10 years away (although this is another area I’d like to learn more about).
Last but not least, nuclear has an image problem. Whether or not you are worried about nuclear safety (I’m not), nuclear waste (I am) or proliferation of nuclear weapons (I’m not sure), enough people are worried. And this means that building new nuclear is always going to face some resistance. As we’ve seen with onshore wind in the UK, a small but vocal minority can have an outsized impact on what does or does not get built.
There’s a slim possibility that we’d be able to get away without any baseload, instead relying on lots of renewables and flexibility. This would require us to solve the rather thorny problem of long duration energy storage. And by long duration, I mean storage of electricity for at least 24 hours and maybe as long as several months (‘seasonal’ storage). This sort of storage would allow us to shift solar energy from a sunny day to a cloudy one and to shift wind energy from a windy winter to a still summer.
There are several companies working on this challenge using new types of batteries (e.g. Form Energy), hydrogen or even concrete blocks to store energy. These technologies are at early stages and there’s no guarantee that they’ll make economic sense at the scale we require. So we can’t bet on them yet.
Another game-changing technology that would allow us to reduce nuclear’s role in all this is another form of baseload, ideally cleaner and cheaper than nuclear. There’s no mature technology that would work well in the UK, given we don’t have significant potential for hydropower.
Geothermal is a technology that I’ve had my eye on for a little while and find interesting. Geothermal has the potential to offer clean and flexible baseload power. And if the touted technological developments can be achieved, it could be deployed almost anywhere around the world. It’s not likely to be a silver bullet, but geothermal could be another tool that helps us decarbonise the electricity system without compromising on affordability or security of supply. (I’ve written a separate deep dive into geothermal here)
All of the above
As is hopefully becoming clear, none of these solutions on its own is going to solve the problem of intermittency.
To deploy renewables in a cost effective way, we’ll need a combination of technologies from each of the three buckets. For example, a vision of the energy system in the UK might involve the following…
- Lots of wind and solar farms, and maybe even tidal, will generate as and when they can
- Flexibility technologies such as demand side response will shape electricity demand to match electricity generation; excess electricity will be stored in batteries or as hydrogen for use at a later stage
- Baseload technologies such as nuclear, hydro and geothermal will step in to provide power when renewables aren’t generating (alongside the electricity stored in batteries, hydrogen, etc.)
There’s an awful lot of work required in each of these areas. But we already have much of the technology that we need. The key challenge is likely to be ensuring that we accelerate the rate at which we deploy proven technologies, while taking reasonable bets on newer technologies with the potential to play a key role themselves.
To do this, we’ll need to make sure that markets and government support programmes provide the incentives required to support investment in, and continued operation of, these technologies. But that’s a big thorny topic in its own right, and one for another day.
