As funds flow into wind and solar power and governments around the world make progressively more optimistic commitments to the percentage of national power they will generate from alternative renewable energy, scant attention is being given to the fact these power sources are highly unpredictable and intermittent in the nature of their supply.
Supporters blithely promise a smart grid system will fix all that; indeed it would (at least in part) if a smart grid was a possibility inside of the next 20 years. The reality is it will take a decade or more to roll out anything like an integrated smart grid. So in the meantime, utilities have to find a way to store energy produced during peak periods or when power is not required, ie smooth the intermittent and largely uncontrollable nature of alternative energy sources.
An interesting review in the Guardian this week explores some of the options. If power generated by turbines on windy days or by solar panels/thermal solar could be stored in a giant battery it could be drawn on when the wind dropped or the sun went down. In fact just such a system serves the city of Fairbanks, Alaska where the world’s largest battery back-up has been storing electricity for an entire city. With its 1,400 ton nickel cadmium battery covering an area larger than a football field, it can produce 40 million watts on demand. In the two years since it has been installed, it has prevented 81 blackouts. But even a plant this size is only able to serve 12,000 or Fairbanks 100,000 residents for up to seven minutes.
One of the issues with storage is round up efficiency. Some energy is lost in storage and some when it comes back out. Lithium ion batteries have impressive round up efficiencies meaning very little is lost and they can pack high densities of energy while being able to charge and discharge thousands of times before degradation sets in. Lithium ion remains an expensive technology, some ten times more expensive than lead acid by some counts. And, that has stopped GE from installing a 2 mw storage unit in California for the usability AES. GE is pretty active in this field as we wrote back in May. They are setting up a factory in New York to develop sodium sulphur battery packs to position near renewable energy collection points.
Meanwhile IBM is developing the PolyPlus metal air lithium ion battery which promises to deliver an energy density ten times that of current technology. The only sticking point is it could take 5-10 years to develop the membranes to allow the metal part to interact with the oxygen in the air without spontaneously combusting!
There have been proposals to tap into the latent storage capacity of all these electric and hybrid plug-ins we will be buying to act as storage capacity when not in use. The problem with that is we can’t see users being too pleased to find their Tesla has just been drained by the utility when they go to take their car out.
A company in Texas called EEStor has patented ultra-capacitor technology that claims to pack four times the energy of a lithium ion battery into the same weight. Lockheed Martin has signed up with the firm to use its ultra capacitor technology in defense applications so this could be a story to watch.
The most elegant solution would be to take spare power and split water into hydrogen and oxygen that could be recombined later to power a turbine or otherwise used as fuel. The cycle produces no carbon but needed a technology advance to be economically viable. That may just have arrived with an announcement by an MIT team that using cobalt and phosphate, both relatively abundant, can kick start the electrolytic process in a similar way to how plants split carbon dioxide into oxygen and carbon. The project lead has since set up a company called Sun Catalytics to develop the idea.
Finally there are ideas to take spare power and use it to store some other power source, such as the pump storage schemes used in some parts of the world to pump water uphill during excess and use the water to drive a turbine during peak demand. The concept being developed now is taking excess power to pump compressed air into caverns, salt domes and old natural gas wells, releasing the air to help new generation natural gas turbines run more efficiently reducing the fuel used by up to 70%. The Iowa Stored Energy Park is a giant 268 mw compressed air system under development coordinated by the Sandia Power Authorities.
In practice a number of these ideas will prevail and form the basis of storage schemes to even out the peaks and troughs of renewable energy power delivery. What is certain is renewable energy does not have much of a viable future unless we develop ways of managing the variability economically, efficiently and soon.