Last week, Bill Gates mentioned that he’s involved with an energy storage company that was basically “gravel on ski lifts” at the Eco:nomics Conference organized by the Wall Street Journal. (Thank you, Katie Fehrenbacher, for attending.) (See video, minutes 19:15 to 20:10).
Ski lift storage has been one of those topics discussed in the hallways of energy storage conferences for years. Someone was out there, the conversation went, that wanted to use a solar- or wind-powered ski lift apparatus as a pump. It would pump gravel or water up a hill during sunny periods. At night or during peak power emergencies, the gravel or water could be released. The system essentially artificially supplies the elevation that nature left out.
Such a system could even harvest regenerative power on the way down. It’s part of a segment I call macro or terrestrial storage, i.e. large mechanical devices that store power through the power of geography and gravity. Bright Energy Storage Technologies, for instance, wants to put giant plastic bags shaped like sea cucumbers connected to air hoses in the ocean. Seawater will contain and pressurize the water for free. It sounds strange, but the device could deliver power for 2.5 to 6 cents a kilowatt-hour, say the backers of the technology.
Research and project management company Escovale Consultancy Services talks about using a 100 million ton stone in a cavern to pressurize water, similar to an idea being pursued by Gravity Power. Think Stonehenge for the grid.
Then there are the micro-macro storage ideas: SustainX (compressing air in large tanks with water vapor), Isentropic (big tanks of hot gravel) and LightSail Energy (founded by an entrepreneur who entered college at age twelve.)
I scribbled down the name of the ski lift guys once at the Energy Storage Association conference in 2011, but I subsequently needed a paper towel and lost it forever.
So who is that company? I am going to guess it is Energy Cache. Energy Cache wants to create a solar-powered pump for delivering materials to the top of mountains that can be released to produce energy. Here is one of their patents — note that one of the inventors is Bill Gross, the energetic dervish behind Idealab.
Here’s a video of how the system works:
It’s an interesting idea, but one with many caveats. Terrestrial storage isn’t cheap. Compressed air energy storage, pumping megawatts of air into underground caves, has been around since the 1970s, but only a few trial systems have been built. Big projects take a lot of cash, and almost anything — geological surprises, changing world economics — can go wrong in the ten to fifteen years it can take to complete a project.
Environmental review can bottle up projects for years. Gridflex Energy has talked about building multi-megawatt hydro storage systems in Hawaii — the ocean would act as a free reservoir — and large systems in Montana. But good luck getting through the review process.
Some of the energy ideas from Idealab have stalled on the way to commercialization. Energy Innovations, a startup building concentrated solar photovoltaic technology, has reportedly put itself up for sale after struggling. Idealab also invested in Aptera, the three-wheeled electric car. The lightweight material Aptera used to build its car was fantastic — the car didn’t do so well.
Image courtesy of Andrew Miesem, Flickr creative commons and Energy Cache.