Energy storage projects highlight value of Concentrating Solar Power

In October 2012, the California Energy Commission approved a USD$1 million research grant for Pacific Gas & Electric (PG&E), a utility that serves two-thirds of the West Coast state, to demonstrate a compressed air energy storage (CAES) plant.

CAES comes in a variety of flavours but essentially relies on the fact that air generates heat when it is compressed and looses heat when it expands.

According to the California Energy Commission: “The project will use excess wind energy to compress air into depleted natural gas reservoirs within PG&E’s territory. The stored compressed air will be used to generate electricity during high demand periods.”

It is fair to say $1 million is not a lot in the grand scheme of things. And this project is clearly linked to wind energy. So what has it got to do with CSP?

Kelly Kell, public information officer at the California Energy Commission, confirms: “The current grant with PG&E seeks to demonstrate a CAES facility in close proximity to wind generation resources to store energy in periods of high production and low demand.”

However, she adds: “The energy used for compression could be from a wind generation resource or any other source of electricity, including solar thermal turbines, solar photovoltaic, or conventional gas-fired turbines.”

This is significant since California has one of the most ambitious carbon reduction targets in the world. California’s lawmakers have agreed that a third of the state’s energy must come from renewable sources by 2020.

Carbon-free energy

Not only that, but by 2050 the state is planning to cut emissions by 80% below 1990 levels. That means a lot of carbon-free energy.

And since Californians remain staunchly anti-nuclear and do not have access to large hydro reserves, most of this power will presumably have to come from intermittent sources of energy such as solar and wind. The challenge does not stop there, either.

The state aims to achieve this transition at a time when its population is mushrooming. By 2025, 15% of the American population will live in California, up from just over 11% today, according to sources at the US Nuclear Energy Institute.

And by 2050 the population will hit 55 million, requiring roughly double the amount of energy as the state consumes at the moment, according to a report last year called California’s Energy Future, by the California Council on Science and Technology.

On top of this, the state also needs to cut the greenhouse gas emissions from passenger vehicles 80% by 2050.

Calculations by the California Air Resources Board indicate this may require putting half a million zero-emissions vehicles on the road every year by 2025, building up to 100% of all new car sales by 2040.

This all adds up to a lot of demand on a grid that will be pulling much of its power from sources it cannot control, including the Solar Energy Generating Systems CSP plants at Daggett, Kramer Junction and Harper Lake, Kimberlina at Bakersfield and Sierra SunTower at Lancaster.

Smart grids that can match supply and demand intelligently will no doubt solve part of this problem. But California will also likely need a lot more energy storage before it can significantly embrace solar power, including CSP.

Storage capacity

At the moment, says Kell: “The Energy Commission does not track the energy storage capacity of California. According to the Western Electricity Coordinating Council, there is about 3,951MW of pumped hydro storage in California.

“There are battery and other energy storage systems used as back up, and uninterruptible power in buildings and businesses, but the exact energy storage capacity of such systems is not known at this time.”

What is certain is that projects such as the one being funded by the California Energy Commission will be important in giving higher priority to energy storage, which in turn will be good news for CSP and solar in general.

Besides the PG&E pilot, there are a number of other energy storage initiatives across the state, including projects by the Lawrence Livermore National Laboratory, Transportation Power, Amber Kinetics, Primus Power Corporation, EnerVault, Seeo and the Sacramento District.

Furthermore, this increasing focus on storing power could help raise the profile of CSP with storage as a unique form of dispatchable renewable energy.

Monique Hanis, director of communications at the US Solar Energy Industries Association, says: “I think we do see interest in storage, in particular for CSP technology.

“People are looking forward to the completion of two major projects, in Arizona and California, that will include storage. It is exciting to see these projects come to fruition. There is a growing interest in the added value of storage to increase peak production and delivery of solar energy.”