Monday, August 19, 2013

Hawai`i Energy Storage 5: Energy storage solutions without chemical batteries

Chemical batteries are a traditional energy storage medium, but batteries are hardly alone.

In this installment of our energy storage series, we'll be talking about water, air and spinning metal as energy storage media.

Three of the storage sources that are not chemical batteries are pumped hydro, compressed air and flywheels.

Pumped hydro has been used across the United State and the world for the last century. It’s reasonably priced, but currently difficult to get permitted.There are several folks on several islands in Hawai`i discussing pumped storage projects.

In essence, here’s how it works. You have two reservoirs of water, separated by vertical distance.  When power is cheap, you pump water from the lower to the upper reservoir. When you need the power, you run the water downhill through a hydroelectric plant into the lower reservoir. Either reservoir can be man-made or can be a natural reservoir, like a lake or even the ocean.

The Sandia-EPRI-NRECA Electricity Storage Handbook for 2013 estimates a levelized cost of energy for pumped storage in the neighborhood of $200 per megawatt hour. These systems have lifespans in the many decades, so that cost may look low when adjusted over time for inflation.

Compressed Air Energy Storage (CAES) systems in place today are based on pumping air into deep underground caverns. Our Hawaiian geology may be too porous for that application, but there have been suggestions we could install massive bladders in the ocean, and use the weight of the water to maintain compression. 

When you need the power, you open a valve and let the compressed air spin a turbine.

Based on the existing cavern systems, the handbook estimates levelized costs also in the $200 per megawatt hour range , but a different storage mechanism likely would raise the cost.

A lot of folks like the whole concept of flywheel storage. Flywheels have been around for ages in all kinds of applications. Old (and some modern) diesel engines use flywheels to create rotational inertia, translating the periodic firing of the diesel cylinder into a steady force.

You can store solar power, wind power, any kind of power in flywheels, and then later convert it back to electricity. In the words of the handbook: “Flywheels store energy in the form of the angular momentum of a spinning mass, called a rotor. The work done to spin the mass is stored in the form of kinetic energy. A flywheel system transfers kinetic energy into A/C power through the use of controls and power conversion systems.”

The handbook concludes that this form of storage is more useful for short-term grid stabilization applications than bulk energy storage. It puts the levelized cost of energy in the $375 per megawatt hour range.

Learn more about flywheel systems this company’s site.

Pumped storage and CAES tend to be priced for economies of scale. They need to be very big to have good pricing. Flywheels don’t scale up so well—you’re better off building lots of smaller flywheels than one big one, and as we said, they’re not recommended for bulk storage.

NEXT: We’ll discuss some chemical battery storage ideas next.

© Jan TenBruggencate 2013

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