the long term storage challenge

Once again fuel cells get a mention here to balance out the power fluctuations created by wind and solar.

http://reneweconomy.com.au/2013/the-long-term-storage-challenge-batteries-not-included-73186

"Battery storage technologies seem to be the hot topic wherever you look in the energy industry. Germany is investing heavily into domestic storage, California has a huge mandate, and the market for peak shifting and storing production is gaining the interest of consumers, pro-sumers and network operators alike.

But can battery storage really solve some of the issues faced by the growing penetration of intermittent solar and wind technology? In the short term, it probably can, but as the penetration of renewables starts to grow in major economies, many think that battery storage will at such scale either simply be too expensive, or not have enough capacity to solve some of the long term issues.

Three new technologies are now emerging as potential long term solutions, and all argue that they will be cost competitive and even displace some of the gas generation that is normally assumed to fill the gaps.

Here’s a brief look at three of them:

Chemical Energy Storage

In Germany, there is a view that the only way to provide the amount of storage needed for a nearly fully renewable grid in the long term is through chemical means – and right now there are a bunch of projects that are looking how to apply electrolysis to turn excess output from wind and solar and other generation into hydrogen and methane.

At the Fraunhofer Institute for Solar Energy Systems in Frieburg, Dr Gunter Ebert says hydrogen and methane is the only option for large scale “season storage”. Battery can provide some short term storage capacity, maybe up to 50GWh – and so can pumped hydro (60GWh) – but he says the options are limited in Germany.

“We need a tremendous amount of long term storage – up to 70TWh,” Ebert told RenewEconomy in Frieburg last month. “That can only be done with hydrogen and methane.”

Ebert’s plan is to use caverns to store hydrogen, which can then me used for vehicles, or in fuel cells, or it can be converted into methane for use in the gas grid. Or it can be used for direct heat and power generation, as this rather complicated graph shows."

The energy revolution is gaining momentum. All aboard