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Friday, January 2, 2015


Because solar and wind power is intermittent, the ability to store power when the sun is shining and the wind is blowing for times when the opposite is true is still vital.  The distributed nature of the grid helps--the sun may be shining in one place but not another; the wind may blow strongly in one district but be weak in others; and the sun may shine when wind is absent and vice versa.   But still, the electrical grid (unlike the gas grid which has substantial integral storage), currently provides limited effective storage.

One tends to think of batteries as the obvious storage devices, with the batteries being recharged when power is produced and discharged when it is needed..  But there is an alternative.  Natural gas, or strictly speaking, synthetic natural gas in other words, artificially produced methane/butane.  Surplus electricity can be converted into natural gas which is then burned to heat homes or fire electricity generators.  Via the Sabatier reaction, hydrogen, generated by the electrolysis of water, is combined with carbon dioxide at high temperatures and pressures to produce methane.

From the Wikipedia article:

The Sabatier reaction or Sabatier process was discovered by the French chemist Paul Sabatier in the 1910s. It involves the reaction of hydrogen with carbon dioxide at elevated temperatures (optimally 300–400 °C) and pressures in the presence of a nickel catalyst to produce methane and water. Optionally, ruthenium on alumina (aluminium oxide) makes a more efficient catalyst. It is described by the following exothermic reaction:
CO2 + 4 H2 → CH4 + 2 H2O + energy
∆H = −165.0 kJ/mol
(some initial energy/heat is required to start the reaction)

The article says that most countries have 1 to 2 years' worth of gas storage,  but other pieces I have read say 1 to 2 months, not years, and the calculations I did for the US came out at about 1.4 months.  Either way, that is more than enough to fill gaps in wind and solar electricity production.  The beauty of it is that in many countries, gas peaking plants are already being used to keep the grid stable when demand peaks or renewable power temporarily declines.  In future, these gas peaking plants could be fired with methane produced via renewable electricity.  There is a gas grid with extensive gas storage facilities which can be quickly adjusted to use synthetic natural gas along with natural gas to heat homes and generate electricity.   The infrastructure already exists: national and international gas grids, gas storage, gas peaking power stations, vehicles which run on LPG (producible from SNG), gas-fired  building- and water-heating.

As the cost of solar power falls, we are going to see more and more 'natural gas' and LPG produced from renewable power.  Even without that, batteries are in any case falling in cost, and will become ubiquitous in electrical grids.   The need for storage will not stop the renewables revolution.

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