Friday 17 July 2015

Energy storage - our salvation ?

 Professor Win Rampen’s inaugural lecture for the Chair in Energy Storage sums up the key energy challenges facing the world, and the UK in particular:
  • Baseload electricity is presently covered by nuclear and coal, which can’t come on and off quickly (see Supply graph from Gridwatch above).
  • The main job of balancing variations in daily demand and renewable supply (wind and solar), is done by gas. The contribution from hydro is relatively small.
  • Solar photovoltaics are on the rise. Over the last few decades prices have plummeted while efficiency has crept up. Recently new cheaper materials have had rapid efficiency improvements; these may soon overtake silicon PV. Cheap PV raises the question of how other forms of generation will be able to compete for finance.
  • Photovoltaics, which count as negative demand rather than supply, is highly variable: passing clouds cause sudden generation dips. Already there is so much solar that on sunny days there is a dip around noon (see Demand graph below).
  • Prices paid by the National Grid to generators can vary by a factor of three during one day due to this variability.
  • Demand-side management is one way to deal with variability: already big companies have agreements with the grid to switch off during peak demand. In the future we will use the internet to control household appliances.
  • We need to drop fossil fuels, but how can we provide the flexibility that gas provides, given that more renewables will require even more flexibility?

This summary of the UK’s energy prospects makes the economic case for large scale storage for grid balancing.

Competing technologies were compared on the basis of potential capacity and economics. The potential capacity of pumped storage hydro is dictated by the availability of suitable sites. The capacity of other forms of storage depends on the availability of the materials they use, hence the adage that, if you want it dirt cheap, you must make it from dirt. The economics can be described by embodied energy and cycle efficiency (the percentage of energy put into storage that can be recaptured). Batteries are unlikely to be suitable for grid storage due to their use of rare elements and their high embodied energy.

Prof Rampen started his career at the Edinburgh Wave Power group, where he worked on two technologies that had been identified as important to wave energy: short term energy storage, and large hydraulic machines with high efficiency at part load. The company Artemis was spun out of his work on hydraulic machines. Artemis later went on to do some projects on grid scale energy storage using compressed gas, which recharged his interest in storage.

The lecture finished with a reminder of the obligation that developed nations have in taking the lead in decarbonising. Prof Rampen called for our generation to take action where his had been complacent. He reminded us that the wind energy industry was built by amateur enthusiasts, and there is now so much wind installed that there were times last month when more of Scotland’s electricity was generated by wind than anything else.

Image credits
Screenshots from Gridwatch were accessed on 17 July 2015

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