Charging into the future

Date: Apr 13, 2018

Perfecting large-scale battery technology is high on the agenda for the government. Stuart Nathan reports on the latest developments here and around the world.

An energy storage installation from UniEnergy Technologies

Energy storage is often seen as the most important missing part in the electricity infrastructure of many countries, not least the UK. The main reason for this is renewable power. Wind, solar and marine energy (wave and tidal) have the potential to generate large amounts of electricity, but being dependent on natural processes they are not predictable and sometimes occur at periods diametrically opposed to when they are needed – for example, the sun shines during the day but we switch our lights on at night. Being able to store the energy in times of plenty – when it’s windy, sunny or the tide is coming in or going out – and then release it to the grid when it’s needed would allow renewables to be used to their full potential, and further reduce our reliance on fossil fuels.

There are many ways to store energy. Pumped storage, where water held in a reservoir at a high altitude is allowed to run through a turbine flowing down to a lower reservoir, is among the most reliable and is used in the UK, Scandinavia and elsewhere. Compressed air storage is also increasingly scrutinised, as is using surplus electricity to liquefy air so that it can be allowed to evaporate through a turbine (Highview Power, a pioneer in this field, is a previous winner of an Engineer award for innovation). The so-called hydrogen economy, where surplus electricity is used to electrolyse water, and the resulting hydrogen stored to be converted back into electricity through a fuel cell, has been touted as a solution for decades. All of these systems have been covered by The Engineer.

The technology that is currently receiving the most innovative engineering attention is, however, the energy storage solution that electrified the Industrial Revolution and one we have all been familiar with from our childhoods: batteries. But these are not Triple-As. They are large and highly sophisticated devices capable of holding very high amounts of charge and releasing them in the way that is required for the grid.

The workhorse for grid-scale storage today is the lithium-ion battery; not just the same battery technology that is used to power electric cars, but literally the same battery. The best known large-scale grid storage facility in the world, built by Tesla in South Australia, is known simply as the Big Battery. This consists of a very large array of Tesla’s Powerwall units, based on the same type of battery that powers Tesla’s cars.

Properly known as the Hornsdale Power Reserve, it is rated at 100MW/129MWh and stores wind energy from the adjacent Hornsdale wind farm and solar energy from domestic photovoltaic panels across the state. According to Tesla, it stores enough energy to power more than 30,000 homes. “By allowing renewable energy to be dispatched during peak periods when the wind is not blowing and mitigating the need for expensive gas peaking generation, South Australian electricity prices will be both lowered and stabilised,” Tesla said

Tesla lithium-ion units at the Horsndale Power Reserve

Australian battery expansion

Elsewhere in Australia, in late March the Australian government announced that it would invest $25m (£13.5m), matching an investment from the State of Victoria, to fund large-scale grid-connected batteries, together providing 50MW of power and some 80MWh of energy storage. Both will be located near solar farms; one at Gannawarra, near Kerang, again using batteries supplied by Tesla, and one at Warrenheip, Ballarat, with batteries supplied by Fluence. “Both Victorian batteries will help demonstrate how large-scale batteries can provide different benefits to the electricity system, including improving grid stability and power quality, and how they can help integrate more variable renewable energy into the grid,” said the Australian Renewable Energy Agency.

But despite lithium-ion batteries being the current preferred option, according to Prof Clare Grey, a theoretical chemist and specialist in rechargeable battery chemistry at the University of Cambridge, they are not necessarily the best option for this application. “Lithium-ion is good for short-term storage,” she said. “But how are you going to store energy for the weeks and months you might need if you went for an all-wind scenario? You either have absolutely massive storage facilities or you shunt electricity around over large distances, even between countries. The other issue is whether battery packs are going to last for long enough for the really big-scale applications. Lithium-ion batteries last on average two to seven years, but a lot of utility companies work in 20- to 40-year timescales. That’s a challenge, and although it’s grossly straightforward to change out a spent battery, it will come with a cost.”

Redox flow cells

Grey pinpoints other battery technologies such as sodium-ion as a drop-in replacement for lithium-ion, even being potentially cheaper, along with so-called “beyond lithium” solutions such as lithium-sulphur. But she sees the ultimate solution as a different type of battery known as a redox flow cell (sometimes known as a vanadium flow cell). These are, in essence, a type of fuel cell rather than a traditional electrochemical battery. “They are much larger-scale batteries where you have vats of liquids of oxidised and reduced chemicals and you flow them in and out to recover power whenever you need it. In principle, they are completely scalable, but just as expensive as lithium-ion, if not more so.”

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