I've been involved in an email discussion about the best way to store electricity recently, and I thought I'd throw the discussion out via the site and see what comes back.

It started as a discussion about the potential for a future hydrogen economy. The protagonist of a hydrogen economy argued that hydrogen is one of the only methods to store electricity - electricity is used to electrolyse water into hydrogen and oxygen. The hydrogen can then be stored and run through a hydrogen internal combustion engine or fuel cell to produce electricity when required.

The antagonist argued that the efficiency losses in electrolysis, storage and subsequent electrical generation rendered hydrogen impractical as a method of electricity storage and that a hydrogen economy could never come about due to these inefficiencies, and that alternative methods of electricity storage would be used instead.

As a group, we came up with the following methods of ‘storing’ electricity:
- Batteries - http://www.desmogblog.com/canuck-megabattery-cleans-up-wind-power

- Hydrogen - http://www.lowcarboneconomy.com/community_content/_low_carbon_news/

- Compressed Air (especially for wind turbines) – http://www.isepa.com/index.asp

- Flywheels - http://www.carbonfree.co.uk/cf/news/wk19-08-0002.htm

- Molten Salt (especially for Concentrated Solar Power plants) - http://www.reuters.com/article/scienceNews/

- Hydro storage (particularly useful where you have an existing hydro-electric power plant and a nearby wind turbine: in times of surplus generation, the electricity can be used to pump water back up to the top of the damn)

- Some kind of pressurised boiler or storage heater
I believe that what we’ll end up with in the future is an energy mix where different requirements have different optimum solutions, as you can start to see from the preferred energy storage solutions for wind in contrast to concentrated solar power above. Thus, large- and small-scale electricity generators both need solutions for storing renewable energy.

From a sustainability perspective, I believe that local generation meeting local demand within a decentralised but contiguous national grid network MUST be the most resilient and secure electricity network paradigm. The factors that pull in the centralised power generation include:

1. efficiency of generation

2. load balancing

3. commercial interests

4. health and safety management

5. energy storage

6. overall 'well to wheel' efficiency

I think that hydrogen is likely to come into the equation at large-scale - commercial and industrial - levels to start with and then filter through as certain commercial barriers are overcome, but where the dividing lines between the components of the energy mix will fall is still unclear to me at this stage.

So, in the meantime, what are the best community-scale energy storage solutions? Does anyone know of a solution that could, for example, buffer a community of ~100 houses against supply/demand variations for electricity. If every house nominally had a wind turbine and photovoltaic panels enough to supply it’s own electricity demands (on average), what solution would allow those houses to pool their surplus electricity in times of plenty, and draw on a reserve in times of need? How long could each of these storage solutions store electricity efficiently for?

Any ideas – I’d love to hear them.