2012/05/29

Intermittency


The Cellcube battery by Gildemeister Energy Solutions
Renewable energy is often dismissed because of two major drawbacks. First, there isn’t enough capacity to meet even the present demand that is fulfilled by hydroelectric, carbon and nuclear fuels. There is only a fixed amount of sunlight falling on the earth, and there are competing demands on the use of lands and oceans for solar panels and wind farms. Second, renewables don’t provide a steady supply of base load electricity that can meet fluctuations in demand throughout the day. We don’t constantly get sunny days and windy nights.
The first problem is explained well in a book by David Mackay called Sustainable Energy without the Hot Air (this link is a video summarizing the book). The only solution for the first problem is the grim conclusion that no future growth of our energy needs is possible. In fact, global energy consumption will have to decline a great deal in order to avoid future nuclear accidents and stop the rise of atmospheric carbon above catastrophic levels (which were just measured for the first time to be above 400ppm).
The second problem might be much easier to solve. Vested interests in the coal, oil and nuclear industries have been reluctant to learn about the good news and report it, but if you search for the information you can find some promising developments in batteries that could store energy created by renewables and deliver up to 2 megawatts on demand.
Donald Sadoway at MIT has developed a battery, with cheap and abundant materials, with which “… we’d be able to address the problem of intermittency that prevents wind and solar from contributing to the grid in the same way that coal and gas and nuclear do today.” With investors and support from MIT he has established Liquid Metal Battery Corporation. Modules of batteries could be built up to the size of a shipping container, and these could provide 2 megawatts, the amount consumed on average by 200 American homes.
Another battery technology already in use is the vanadium redox battery that has been commercialized by the German company Cellstrom GmbH. Other applications are in wind farms in Hokkaido, Japan and Tasmania, and a semiconductor factory. Output of these batteries, also called output balancers, range from 5 kilowatts to 1.5 megawatts.
The plan to have a localized supply of electricity for a small number of homes fits with the vision of distributed generation that is being proposed as the solution to the traditional large grids with expensive gigawatt generating stations located far from population centers. In a distributed generation scheme, a population of a few thousand people could be serviced by a gas generator, with this local grid fitted with batteries and supplemented by residential solar panels that sell their excess capacity. Each local system could still be connected to the older larger grid for back up supply, and for a place to offload power at times of oversupply.
Solving the problem of intermittency is a huge step in energy innovation that demolishes the most common defense of dirty and dangerous ways of generating electricity. It provides some hope that, if we are smart, we can avoid a bleak future of Canadians freezing in the dark, and Qataris dying of thirst when their water desalination plants run out of fuel. But this solution doesn’t solve the supply problem, the really difficult challenge of devolving to a less energy intensive way of life. How could the human race go back to a pre-industrial age without rediscovering quaint traditions like serfdom, slavery, sexual inequality and constant war? Even to ask such a question seems far-fetched, but in the film Into Eternity – a film about the construction of a nuclear waste depository – the experts assume that the people of the future won’t be technologically literate enough to understand the danger of what we have left for them down in the hole... but come to think of it, most people alive today don't understand the danger either.

1 comment:

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