Researching renewables

Can renewable sources meet electricity demand 99.9% of the time?

Over recent years, many letters have been published in PE suggesting that renewables are unable to provide a credible alternative to thermal power generation. I recently stumbled upon a research paper (Cost-minimized combinations of wind power, solar power and electrochemical storage, powering the grid up to 99.9% of the time – C. Budischak et al – Journal of Power Sources, to be published in March, 2013 (http://dx.doi.org/10.1016/j.jpowsour.2012.09.054) that appears to demonstrates that, with the right energy mix, renewable sources can meet electricity demand 99.9% of the time!

The research used a computer model to simulate a variety of energy mixes to meet the energy demand of a large area of north east USA over a four year period. The models used actual historic weather records to estimate the output of the renewable power sources and historic load data as the target output. Only current renewable and storage technologies were used to find the minimum cost option for power generation over the four year period. Surprisingly, wind and solar photovoltaics, together with storage from hydrogen fuel cells, static batteries and light vehicle batteries provided the minimum cost option, with only minimal use of thermal power stations to cover any shortfall in output.

The costs assume no subsidy for renewable energy, but do include the hidden subsidies for fossil fuel systems that cover the cost of the associated public health impacts.

To achieve the required output, the installed capacity of the renewable energy sources needed to be 300% of maximum demand, although this seems to be very high, the authors make the point that the best thermal plant has a fuel input of about 250% of electrical output.

I would be interested to hear reactions to the paper from those who assert that renewables have little value as a source of electrical power.

Robin Trow, Snodland, Kent

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