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%.

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.

Written by Susan Kraemer

As part of developing new energy resources that don’t emit carbon dioxide, the DOE is funding 9 trials that use supercritical CO₂ to extract more geothermal energy.

The idea started in 2000 at Los Alamos National Laboratory; when physicist Donald Brown thought of pumping geothermal fluid using supercritical CO₂ – a pressurized form that is part gas, part liquid; instead of water.  Theoretically this should flow more freely through rock than water, because it is less viscous than water.

Then, six years later; in modeling the technology Lawrence Berkeley hydro-geologist Karsten Pruess projected that not only should it perform as expected but that it would also yield a 50% hotter geothermal resource.

Now the DOE is funding this promising research with $16 million in nine trials to see if this will work in the real world.

The funding is to be shared by nine carbon dioxide-related projects led by Lawrence Berkeley National Laboratory and other national labs and universities, and the Californian combinatorial chemistry firm Symyx Technologies that screens about a million potential materials a year using advanced computer modeling.

Brown’s idea was that the density difference between the supercritical CO₂ pumped down and the hotter gas coming up would make the gas cycle better by a siphoning action, so the pumping process would use less energy.

Symyx project leader and materials scientist Miroslav Petro wants to make sure that supercritical carbon dioxide plays nicely with rock and minerals. It could form a super-dissolving “acidic soda water” that dissolves minerals from rocks.

Sequestering the carbon would be the big bonus. It could be a large amount: 70 years worth of CO₂ emissions from a 500 megawatt coal power plant.

Written by Susan Kraemer