Renewable energy | Ecotrope

5 ways to store renewable energy

Ecotrope | Aug. 30, 2011 1:34 p.m. | Updated: Feb. 19, 2013 1:35 p.m.

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One way for Northwest to store surplus renewable power is to use it to pump water uphill with a reversible generator that can be run in reverse to produce power later when the water flows back downhill.

One way for Northwest to store surplus renewable power is to use it to pump water uphill with a reversible generator that can be run in reverse to produce power later when the water flows back downhill.

In response to my post about the cost of delivering wind power in the Northwest, Dave Miller asked me to write about the potential for storing renewable wind and solar energy.

Storing renewables would allow us to use them when we need them – regardless of when the wind is blowing or when the sun goes down. And it would reduce the strain on the grid that comes from having wild swings in power production.

I have a few responses to share based on conversations I’ve had with Ken Dragoon, a senior analyst for the Northwest Power and Conservation Council and Carl Imhoffe, smart grid specialist for the Pacific Northwest National Laboratory.

Imhoffe said most energy storage technology right now is about twice as expensive as what would be cost effective. In other words, the cost of delivering wind power right now – even with the added cost of holding back-up power in reserve – is less than the cost of storing it.

Utilities could make cost of energy storage pay for itself, in theory, by storing the renewable power when the price is low and selling it when prices are higher. But to do that – particularly in the Northwest where the difference in price is small – the cost of energy storage would have to come down, Imhoffe said.

“Fundamentally, we’re trying to reduce the cost of energy storage technology by half,” he said. “Storage is going to be a really important tool. But we need to drive the costs of storage down.”

That said, he explained four basic ways to do it:

  1. Electrochemically in a battery (electric cars or stand-alone lithium ion, for example),
  2. Mechanically in a flywheel (which stores energy through rotation)
  3. In compressed air stored in underground basalt formations, or
  4. In water pumped up from one reservoir to a higher one at night and send downhill through a turbine later when prices are higher (commonly called pumped storage).

Dragoon said the existing hydropower system already offers the Northwest quite a bit of renewable energy storage in its reservoirs. And that means additional storage technologies are less likely to be cost-effective here.

“We have more storage than almost every other region in the U.S.,” he said, “so if storage technology becomes cost effective it will be practical here last.”

To prepare for additional wind power expected over the next few years, and to help absorb the extra power that’s generated in the spring when there’s lots of water in the Columbia, Bonneville Power Administration is adding more pumped storage capacity at Banks Lake above the Grand Coulee Dam reservoir.

BPA is also experimenting with storing energy in home hot water heaters by overheating the water at night and then turning the heater off during the day. (We’re calling that storage method No. 5)

Miller also inquired about the potential to use renewable energy to convert nearby water into hydrogen and oxygen and then pipe hydrogen to places where it can be converted into energy. “It sounds like there are some issues with pipe corrosion,” he wrote after doing some of his own homework, “but those are not insurmountable.” He wants to know the cost per mile of a high-voltage power line versus a hydrogen pipe for an equal amount of energy transmitted. I will have to get back to you on that one later, Dave. Stay tuned…

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