Guest essay by Eric Worrall

Yet another renewable energy storage idea…

To Store Renewable Energy, Try Freezing Air

Such energy storage technology could help relieve congested transmission lines in places like Vermont

By John Fialka, E&E News on January 2, 2020

The system that supplies clean electricity to Vermont is not exactly a model of Yankee ingenuity.

In 2011, the state adopted a plan to get 90% of its power from renewable sources by 2050. That led to a surge of wind-generated power from the northeastern part of the state and an expansion of solar.

But transmission lines in this sparsely populated part of Vermont have such low capacity that much of the renewable energy is often unavailable because the lines are too congested. The state was deprived of another form of emission-free power in 2014 when an aging nuclear power plant called Vermont Yankee was permanently shut down.

So what can Vermont do?

A British company called Highview Power proposes a novel solution: a storage system that uses renewable electricity from solar or wind to freeze air into a liquid state where it can be kept in insulated storage tanks for hours or even weeks.

The frozen air is allowed to warm and turn itself back into a gas. It expands so quickly that its power can spin a turbine for an electric generator. The resulting electricity is fed into transmission lines when they are not congested.

“Vermont has transmission issues,” explained Salvatore Minopoli, vice president of Highview’s USA affiliate. “It’s a situation that many places in the U.S. are dealing with where renewable energy is being deployed more and more. It’s power that’s intermittent. They need something to balance their system out.”

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Read more: https://www.scientificamerican.com/article/to-store-renewable-energy-try-freezing-air/

Now we understand what happens when you put a humanities graduate in charge of rebuilding a power grid, what about this great new energy storage idea?

Liquid-air energy storage: The latest new “battery” on the UK grid

New energy-storage solution solves some problems but creates others.

MEGAN GEUSS –  6/13/2018, 10:00 PM

A first-of-its-kind energy-storage system has been added to the grid in the UK. The 5MW/15MWh system stores energy in an unusual way: it uses excess electricity to cool ambient air down to -196°C (-320°F), where the gases in the air become liquid. That liquid is stored in an insulated, low-pressure container.

When there’s a need for more electricity on the grid, the liquid is pumped back to high pressure where it becomes gaseous again and warmed up via a heat exchanger. The hot gas can then be used to drive a turbine and produce electricity.

Tesla’s new battery in Belgium shows value is in dispatch speed The system is called Liquid Air Energy Storage (LAES, for short), and if you’re thinking it sounds remarkably like Compressed Air Energy Storage (CAES), you’re right. LAES takes filtered ambient air and stores it so it can be used to create electricity later, just like CAES. But LAES liquifies the air rather than compressing it, which creates an advantage in storage. Compressed-air storage usually requires a massive underground cavern, but LAES just needs some low-pressure storage tanks, so it’s more adaptable to areas that don’t have the right geology.

LAES has also been compared to pumped hydro, where excess electricity is used to pump water up to a reservoir above a hydroelectric turbine. Pumped hydro and LAES both can be designed to provide power for hundreds of thousands of homes. But unlike pumped hydro, LAES doesn’t require a water system or elevation differences to operate.

On the other hand, an LAES system is only 60- to 75-percent efficient, compared to the 75- to 85-percent efficiency of lithium-ion batteries. Lithium-ion batteries can also respond to minute frequency changes on the grid almost instantaneously, whereas LAES systems deliver electricity by turbine, so their delivery response time isn’t as quick.

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Read more: https://arstechnica.com/science/2018/06/liquid-air-energy-storage-the-latest-new-battery-on-the-uk-grid/

This energy storage idea in one form or another has been kicking around the UK for several years. The original incarnation of this idea was a compressed air storage system, but liquified air has advantages of compressed air. Liquid air containers don’t have to withstand extreme pressures, and a large volume of air can be condensed into a small volume of liquid.

The manufacturers claim the system is 60-76% efficient, which with other costs likely at least doubles the cost of renewable energy stabilised via this system. Probably cheaper than a battery, but likely still hugely uneconomical compared to fossil fuel.

There are also potential problems with reheating the liquified air in adverse weather conditions. Things could get very icy around the cold end of the reheater circuit. Highview claims to have a proprietary solution to the “waste cold” problem.