Why is Intermittency a Problem for Renewable Energy?

Here at the GreenAge we love renewable energy. There’s absolutely no doubt that it’s the way forward, not only for the UK but for the whole world. 

That said, we think it’s important to understand how renewable energy works, and realise its limitations. Only then can we maximise its potential, and move forward with a cleaner energy system.

We’ve done a podcast on this topic, covering the intermittency issue as well as many other issues we’ll have to tackle. You can listen to it here, or scroll to the bottom of the article to watch it.

What is intermittency?

Without a doubt, the biggest problem with mainstream renewable energy is intermittency. Wind power is only generated when it’s windy, solar power is only generated when it’s sunny. This creates several fundamental issues.

We need some level of predictability with our energy generation, or we risk mass blackouts. On a windless day without any sun, we still need power.

At the opposite end of the spectrum, are the times when these forms of generation create more power than we’re able to handle. There are times at which the national grid, in its current state, cannot handle the energy we’re generating.

How does intermittency affect the grid?

So to understand how intermittency affects the grid, first we need to understand how the National Grid works.

The main problem is that in order to operate properly the National Grid has to work maintain a 50Hz frequency, and if it varies too much from that then there are big problems. It’s a demand and supply thing. If demand is up then supply needs to be high, if demand is low then we need to reduce the amount of energy going into the grid. That’s okay with controllable energy generation like gas, but is a problem for things like wind and solar. 

Take, for example, wind turbines. If the wind is blowing like crazy but the demand is low, the frequency rises too high. If the demand is high but it’s a still day, the frequency of the grid falls too low and we begin to experience blackouts. These fluctuations caused by intermittency can, if not properly managed, can cause a lot of damage to the National Grid infrastructure, which would be extremely costly to repair.

Intermittency is an expensive problem all round. Let’s stick with the wind turbine example; as we’ve said, if there’s an extremely windy day and all our wind turbines are spinning like wild, we would overload the grid and create an enormous issue. Wind turbines are privately owned and make money by selling electricity, which means that asking the wind farms to stop generating energy would cause them to lose a lot of money. Therefore we have what are known as constraint payments. It’s essentially compensation for lost revenue when we’re unable to handle energy production. Last year, we paid £124 million in constraint payments to wind farms for precisely this. Those costs are swallowed by us, in the form of higher energy bills. It’s a lot of expense for the privilege of throwing away valuable energy.

How can we combat the problem of intermittency?

At the moment, we use subsidies like the above to prevent the grid overloading from intermittent sources at times of excess generation. We also rely on other, more easily controlled sources to work in tandem with our renewable energy generation. This can’t be a baseload plant like nuclear, it has to be something that we can turn on and off at short notice. In the UK, this is predominantly gas. One of the issues with renewable power is therefore that the more renewable infrastructure we build, the more gas (or similar) plants we have to construct in order to counter-balance.

So why don’t we put the extra energy into batteries? That would solve the intermittency issue, right? Well, theoretically yes, but the problem there is simple: technology simply isn’t there yet. We do have some battery storage, but nothing on the scale that we’d need. Developing new and better batteries will be the defining feature of 21st-century energy management. We need it, and we need it now.

Think we missed something? Do you have a different opinion?

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