February 6, 2017
A Hybrid Future
By Nigel Brandon
Chair of Sustainable Development in Energy at Imperial College London

As renewable energy grows in importance, a challenge will be hanging on to all that electricity created by wind turbines or solar panels. Already, innovations are being developed to store surplus power for when demand peaks.

As renewable energy grows in importance, a challenge will be hanging on to all that electricity created by wind turbines or solar panels. Already, innovations are being developed to store surplus power for when demand peaks.

The lack of available and low cost energy storage is often cited as a major barrier to the development of a much more renewable energy system. But is this the case? Is it a barrier today or a challenge for tomorrow?

We are all familiar with some form of energy storage, mainly through the batteries that are endemic in our phones, laptops and household appliances.  Almost all of these are based around lithium ion battery technology, which is also increasingly finding its way into mobile applications in the form of hybrid and battery-electric vehicles.

But there are other forms of storage to help us manage our energy systems today. Stockpiles of coal and natural gas are essentially a form of energy storage, capable of dealing with the large swings in energy demand between winter and summer experienced in many parts of the world. But, of course, these are fossil fuels, and we will want to reduce our dependency on them if we wish to develop an all-renewable future.  Pumped hydro-electricity energy storage is by far and away the most common form of energy storage today in electricity systems.  This involves constructing two large bodies of water, one higher than the other; water is pumped to the upper lake when energy is needed, and then allowed to fall to the lower lake, powering large turbines to generate electricity.

So why might we need more energy storage than pumped hydro-electricity can provide in the future?

Well, it is clear that we still need a way of delivering electricity when renewables, such as wind and solar, are not delivering energy.  But perhaps less obvious is the need to balance the supply and demand of electricity on a second-by-second, minute-by-minute and hour-by-hour basis, to ensure that we have a reliable supply, at a set voltage and frequency.  If we do not do this, then the system becomes unstable and trips, resulting in blackouts.

This is more difficult to do as more renewables come onto the system, meaning that some form of buffer, such as an energy store, helps maintains a stable electricity grid.  As we seek to use this electricity to displace fossil fuels – for example driving electric rather than gasoline vehicles, or heating homes with electric heat pumps rather than gas boilers – it will prove very expensive and intrusive as we build more wires and cables to carry this extra electricity.  In some countries, such as Britain, this might mean doubling the capacity of the electricity system.  However, access to technologies that help us manage the size of peak electricity demands means that we do not need to build as much new grid infrastructure, significantly lowering the cost keeping the grid afloat.

It is common knowledge that the economic value of energy storage will significantly increase as more renewable electricity is produced, and as more of it is used for transport and heat; hence, the need for more energy storage to be installed in the coming decades.

To help get ready for this change, a large number of new technologies are being developed and tested.

Many of these projects involve large lithium ion batteries.  In Britain, a 6MW/10MWh Li-ion battery is being tested by UK Power Networks to relieve constraints on local electricity systems.  Located in a residential area and adjacent to a school, care has been paid to minimizing any noise – associated with cooling of the battery – and visual impact; the unit sits quietly doing its job.

Another interesting approach is being developed by Highview Power Storage, which produces very cold liquid air through compression, and then expands this to drive electrical turbines.  This liquid air energy technology can be deployed at large scale, sufficient to store the energy for a whole town or even a small city.

But can these innovations provide very large scale storage for weeks or months, if communities do indeed plan to replace those stockpiles of coal?  One option under consideration is to produce hydrogen gas by electrolysis, using renewable electricity, and then store this gas in large underground caverns.  Another approach is to store compressed air underground, then releasing it to drive an electrical generator when energy is needed.

Energy storage is a technology that will play an important role in enabling us to generate and use more renewable electricity – to decarbonize our lives.  While we need some energy storage today, we will need lots more in the future.  So it is vital that we carry on developing and testing the technologies we need, so that they are ready at scale when we all need them.

Nigel BrandonProfessor Nigel Brandon OBE is Chair of Sustainable Development in Energy at Imperial College London. Following a 14 year career in the energy industry, he has been an academic for the past 18 years. He is Director of the UK's Energy Storage Research Network, Co-Director of the Energy SuperStore Hub, and Director of the Sustainable Gas Institute. He is a founder of the fuel cell company Ceres Power.