Renewables are cheap but not always available: storage hurdles

Chief Europe Correspondent

The world is rapidly scaling up wind and solar electricity, but technology to store these variable forms of energy is lagging.

A race for commercial solutions is now underway to store renewable energy for long periods of time—think numerous hours and even days or months. This is known as long duration energy storage (LDES). This week, we look at current limitations in storing renewable power. Next week, we’ll examine possible solutions.

Governments have been pushing wind and solar power for many decades, but a parallel focus on energy storage has only emerged in the past several years.

The reason for this mismatch? We didn’t need to. Grid operators in Europe and in the United States could rely on natural-gas-fired power plants to fill the supply-demand gaps that renewables couldn’t, which have historically generated a small share of electricity.

“When they said it’s easier to buy cheap gas and generate electricity instead of storing the extra energy, it was correct in the past,” said Patrick Clerens, secretary general of the European Association for Storage of Energy, a Brussels-based advocacy group.

That won’t be sustainable anymore given the war in Ukraine, which is driving up natural gas prices to exorbitant levels, and more ambitious greenhouse gas emissions targets discouraging gas dependence in the European Union.

“Unfortunately, we have a bit of a crisis-driven process to come up with new storage technologies,” said Ramya Swaminathan, CEO of Malta, Inc., a U.S.-based thermal energy storage company. She also serves on the U.S. Energy Department’s Electricity Advisory Committee. (We’ll learn more about thermal and other types of storage in our next article).

Renewables are the cheapest form of generating electricity today, making fossil-fuel-based generation less economical amid a growing push to cut greenhouse gas emissions.

But that cost doesn’t account for the variability of wind and solar power. That variability can be as brief as seconds, when a cloud covers the sun, or as long as weeks or months during certain seasons.

To keep our lights on without interruption, we need to generate as much electricity as we consume at any given point, a sometimes precarious effort to match supply with demand instantaneously.

The sun’s peak shine often does not match the peak of electricity usage. That’s normally in the evenings, when the sun is going down and when people come home from work.

As the share of renewables grows, that supply-demand balance gets trickier to match, putting additional stress on our grids.

In countries or regions with a lot of renewables, generators sometimes must reduce the production of wind or solar energy in case of excessive supply because it can’t be used immediately. This “curtailment” essentially means wasting green power.

For example, Germany, which met almost half of its electricity needs with renewables in the first half of the year, had to curtail power generation (mostly from wind) in recent years.

Long duration energy storage could significantly reduce this phenomenon by storing the surplus for later use and help cut reliance on fossil fuels.

Lithium-ion batteries—the same type found in electric cars—are probably the most well-known form of energy storage. Think of homeowners storing excess power from their rooftop solar panels in their backyard battery packs for a few hours.

These will continue to play a role in the future, including for utilities, but they are not cost-effective for longer durations, which is what our increasingly decarbonized power system needs, according to Swaminathan.

Long duration energy storage as a concept is not new, but it’s limited. Pumped hydro storage, a century-old technology, represents 95 percent of all LDES capacity installed globally today.

It uses excess electricity to pump water from a lower elevation reservoir to a high elevation reservoir where it’s stored. When the power is needed, the water is released, generating electricity through turbines on its way down.

Pumped hydro storage was first developed in the 1890s in Italy and Switzerland. It became widely used over the last decades to tackle excess capacity from nuclear power plants, which cannot be easily turned up or down, said Swaminathan, who previously led a hydropower company.

While it’s a proven technology, building it to the scale needed to back up massive amounts of wind and solar power would be challenging, Swaminathan said. Geographical limitations, such as vicinity to water, environmental concerns and long construction periods are significant barriers.

Editor’s note: Malta’s investors include Breakthrough Energy Ventures, a venture capital fund within the Breakthrough Energy network, which also supports Cipher. Breakthrough Energy also has a partnership with the European Association for Storage of Energy.