Renewable Energy and Storage – the Options

I get frustrated that any time renewable energy and net-zero get mentioned on social media, reporting a new technical breakthrough, a bigger pipeline of projects or reducing costs, someone will triumphantly reply “you know the sun doesn’t shine at night!”, or “what happens when the wind doesn’t blow?”.

As if the hundreds of companies, the thousands of scientists, entrepreneurs, and engineers committed to renewable energy had not noticed this. It is obvious, it is understood, and it is planned for. These comments are not the slam-dunk their authors suppose.

I suppose we should look on the bright side. At least I now see fewer comments stating it is ‘obvious’ that an equivalent MW of gas-fired power station must back up every MW of renewable electricity generation. These days, it is more likely to be comments that fossil fuel electricity production will ‘always’ be part of the energy mix. How much depends on how offended by renewables the objectors are.

Electricity storage is a key part of the vision for future energy systems. Some methods are already commercial and being deployed, some are in prototyping and testing, and others are still in research and early development. We have a wealth of options in front of us, and some of them will win out and solve the renewable intermittency problem. I just don’t know which.

So, as an exercise in hope over experience, I am going to write a series of posts on the many approaches to storage that are available now or in development. It is a fascinating story; just about every way of transforming energy from one form into another has been proposed for storage. Each has unique characteristics and can help solve different parts of the intermittency conundrum.

Conventional electricity generation is intermittent too

Before we dive into energy storage technologies, let me just correct one common misunderstanding. Despite what many objectors claim, conventional power stations are not available 24/7 365 days a year. They have to be taken offline for maintenance, or they drop out because of a technical problem in the power station or the grid. Planners must already allow for the temporary loss of supply from any power station, and if several are forced off the grid at the same time, you can have a serious problem.

France generates 70% of its electricity from nuclear. But problems with corrosion, mechanical failures and lack of water for cooling in the hot summer have forced half of its nuclear fleet offline. At a time of international tension and high gas prices, this is serious. An extreme case, but it shows we cannot assume that renewables are uniquely intermittent resources.

Creating resilient grids

So how did energy planners solve the problem? How did they create resilient grids that could cope with one or more power stations dropping out? The answer is geographic and technological diversity with some storage. Connect multiple power stations into a grid across a large area, use different generation technologies, have some spare capacity, and you can provide a reliable supply that copes with weather, technical faults, and demand fluctuations.

Even then, electricity storage has its place. Pumped hydro (pumping water uphill when you have spare electricity and letting it run back down when you need the energy back) was first used in 1907 in Switzerland, 1930 in the US, and my local storage station at Dinorwig opened in 1984. We have been using stored electricity to cope with fluctuating supply and demand for over 100 years.

The solution to a decarbonised electricity network is the same as for the current energy network; geographic and technological diversity with some storage. A recent report reviews all recent studies on 100% renewable energy systems, and concludes that sustainable and cost-effective renewable electricity grids are viable across the world.

Technology options for storage

Because of the characteristics of renewable electricity generators, storage must do a slightly different job in a renewable grid. We need storage that can respond rapidly to fluctuations in the grid and methods to store larger amounts of electricity over longer times. This diagram shows some of the different technologies, how much power they can deliver and how long they can deliver it for.

Power delivery and discharge times for electricity storage technologies

Among the technologies deployed or in development, these are the ones I will review in the next series of blogs:

Fundamental electricity storage technologies

• Gravity – lifting mass against gravity to create potential energy to convert back into electricity
• Mechanical – flywheels and springs
• Thermal – storing as heat, including phase changes
• Electrical – temporary storage using capacitors
• Chemical – changing oxidation state or making and breaking chemical bonds
• Power-to-X – a special case of chemical storage where you synthesise fuels with spare electricity

Next Up – Gravity Storage