I read a paper recently which examined the possible UK electricity generation mix by 2030 and whether it could achieve the required carbon reduction targets. The aim of the paper was to consider the extreme conditions faced by the electricity grid with different energy mixes.
The target for carbon reduction for the UK is 80% of 1990 levels by 2050. In order to meet this it is necessary to reduce carbon emissions arising from electricity generation from the current value of 560 gCO2/kWh (CCC, 2008) to 70 gCO2/kWh by 2030. Two scenarios were modeled to assess whether this could be achieved: one with a high penetration of renewable energy, predominantly wind power, and the other with a high proportion of renewable energy, tidal energy from a Severn Barrage, Carbon Capture and Storage schemes on 80% of coal and gas power stations and an increase of approximately 20% in nuclear generation.
The authors found that only the latter option could achieve the required reduction in carbon emissions and that the former required more fossil fuel back up due to variability of the wind. This raises a few issues:
Severn Barrage: If built this could generate 8GW, approximately 5% of the UK's electricity requirements, and unlike wind it would be totally predictable: we would know with certainty when it would and would not generate electricity. With a £33bn price tag, major ecological issues caused by changing the pattern of tidal flows in the Severn Estuary and lack of Government support, it is unlikely to be built.
Carbon Capture and Storage(CCS): There are no full scale CCS schemes in operation, only trial schemes, therefore it is rather ambitious to assume that the majority of power stations will be retrofitted with CCS over the next twenty years at a substantial cost. Furthermore, depending on the techniques employed to capture the carbon and the storage location and methods, the process can be fairly energy intensive in its own right.
Nuclear Waste Management: Even if all the safety and security concerns regarding construction and operation of new nuclear power stations can be overcome - which will be particularly difficult in the wake of Fukushima, there are still no permanent solutions for dealing with the spent fuel and ancillary radioactive wastes.
The paper does look at extreme demand scenarios so the carbon reductions for the scenario without the Severn Barrage, CSS and new nuclear may perform better on average. Both scenarios modeled had 25% greater installed capacity than we currently have, to allow for lower efficiency (load factor) of wind energy, and assumes that demand will be the same as current demand.
It is likely that the energy mix that develops over the next twenty years will include some CSS and some increases in wave and tidal energy (although not on the scale of the Severn Barrage), which will result in an outcome somewhere between the two scenarios studied. If energy storage schemes and demand side management systems can also be developed to smooth out the worst disparities between supply and demand then further emission reductions could be achieved.
My conclusion is that developing more renewable energy sources will not be enough in itself to reduce Britain's carbon emissions in the medium term and that a significant reduction in demand will be required.
The paper is available for a limited time from the publisher, Thomas Telford
Gerber, Awad, Ekanayake & Jenkins, Operation of the 2030 GB power generation system, Proceedings of the ICE - Energy, Volume 164, Issue 1, January 2011 , pages 25 –37