What if a wind turbine didn’t have a gearbox and electric generator in the nacelle, but instead a highly efficient air pump that sent compressed air down a pipe and into a storage network? That is the vision of General Compression, a privately held Massachussetts company that raised $8.1 million from 70 investors in April 2007.
When you consider the likelyhood of implementing utility scale electricity storage, the primary need would arise if wind power begins to take on a significant share of total electricity generating. When weather changes across an entire region that has huge wind generating capacity, it is possible several gigawatts of power can suddenly surge onto the grid. Currently this is handled quite effectively by grid management systems shutting down fossil fuel generating plants or deactivating hydroelectric turbines – so the need for massive storage solutions may be overstated. Denmark, for example, gets 30% of their electricity from wind turbines, but don’t have massive electricity storage systems. And as electric cars begin to proliferate in huge numbers, they will have smart systems that purchase electricity precisely when the wind is surging, when they can charge at a lower cost per kilowatt-hour.
Nonetheless, General Compression’s “Dispatchable Wind Power System” (DWPS) is a unique approach to buffering and storing wind energy. The conventional plan to use air storage for wind turbines is to have wind generators allocate surplus electricity to powering pumps to store air – the turbine itself is a generator. General Compression has an air pump in the wind turbine from the start, and any electricity that comes from their DWPS starts out as compressed air.
The complete scheme General Compression has come up with is rather elaborate. Each wind generator sends compressed air into a network of pipes, which then go to centralized pressure vessels, potentially augmented by using underground geologic features such as empty salt caverns or vacant hard rock mines. This compressed air is then used as grid demand requires to create mechanical or electrical energy.
According to General Compression’s website, they have “identified numerous locations around the world with outstanding wind resources but lacking local power demand and/or transmission capacity.” They believe with their DWPS system they can create not only wind power installations with the ability to store and deliver electric power onto the grid, but also create large scale off-grid industrial complexes.
The question probably comes back to cost and efficiency of the DWPS system compared to traditional wind generators. How much would all these pipes cost that transfer the pressurized air from the wind turbines to the centralized storage units and generating system? Is a General Compression’s decentralized pumping system and a centralized storage and generating system cheaper and more efficient than the conventional design consisting of decentralized generating systems and centralized pumping and storage? And will compressed air storage really be that necessary in the grid of the future?
Time will tell. General Compression expects to have operating prototypes by 2010, with commercial scale installations by 2012.