Storing Renewable Energy in Boxes of Air

November 20th, 2009 by Susan Kraemer

Storage is needed to harvest the full yield available from intermittent sources of energy like wind and solar. One of the options is compressed-air storage; till now only possible in underground caverns. But SustainX Energy Solutions; a Dartmouth College start-up that got $4 million in VC funding from Polaris Venture Partners and Rockport Capital this year is working on compressing and storing air in cheap off-the-shelf shipping containers.

Over the next two years SustainX will try to develop a way to cram 4 megawatt-hours worth of stored energy into each 40-foot long container and to reduce the energy that it currently takes to compress and release air by about 70%.

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The goal? A renewable energy storage system with the portability and scalability of a battery and the economy and capacity of a cave. Make that a portable cave.

Cheap storage is needed. A lot of research dollars are going into building a variety of storage options for renewable energy to extend their contribution to the grid. We have too much wind at night and too much solar in the day: but seldom overlapping in any one region.

The breakthrough better battery is being funded by ARPA-E and sought by hundreds of researchers and companies from the traditional fly-wheel manufacturers to new nanotech start-ups.

Utilities are looking into storing energy in compressed-air in caves, in gravity; by pumping water up – to let it drop when needed – or in rolling batteries; by loading up extra juice at night into electric cars – to be dispatchable back to the grid again at peak with interactive vehicle-to-grid technology.

PG&E is one public utility scouting for caves suitable for compressed-air storage capable of storing 3,000 megawatt-hours (or 300 megawatts for ten hours). There are already a few compressed-air facilities in the world where off-peak electricity is used to pump air underground for storage. During peak-demand times, the air is released and pushed through a turbine to make electricity. Utility-scale battery storage systems only deliver 1 or 2 megawatts for a few hours.

But underground limestone caverns aren’t always right where you need them; at least with the right geological attributes that make them safe as depositories. You need the portability and scalability of a battery and the economy and capacity of a geological feature.

The president of SustainX; Dax Kepshire conceived his modular scalable portable “cave” system to find that solution. Portable compressed air storage could be big simply because it is a very cheap tech. Even more so now, since Dan’s portable “caves” could be the unused shipping containers that are piling up in ports around the world.

Related stories:

Pump Hydro Underground to Store Wind

For Energy Storage Cheaper than Fossil Fuels – CAES

Image:SustainX

Source:Greentech









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