See – http://claverton-energy.com/pipermail/claverton-group_claverton-energy.com/2009-May/000893.html

Denis,

It looks as though I did not place sufficient emphasis on the need to examine several years worth of data in order to derive reliable estimates of capacity credit, see Dale, Milborrow, Slark and Strbac, 2004, Energy Policy, Volume 32, Pages 1949-1956. (I think it is posted on Claverton).

That paper states, “analysis of a five-year time series of wind speeds…… do not provide any statistical evidence for wind variations at peak being substantially different to those at other demand levels for similar times of the year.”

In Energy Policy, Volume 35, Pages 112-127, Graham Sinden implies we were perhaps being a bit cautious………. “there is an increased probability of high wind power output…. during periods of high electricity demand; this translates into a capacity factor during peak electricity demand hours that is around one-third higher than the annual average.”

Sinden’s conclusion ties in nicely with all the other estimates of capacity credit at low wind energy penetrations that were the basis of figure 1 in the my latest paper. (Graham, do correct me if I am misquoting you!)

Best regards,

David Millborrow

Dear all

Apologies for the nth broadcast of this.

These materials show how renewable generation with back-up, storage and transmission allow for reliable electricity services. More detailed work is required, as always, but I think it clear that existing facilities plus new fossil/biomass back-up generation/storage/transmission as required will be adequate. As the modelling shows (and as Dave A says), keep fossil for low capacity factor output as required until storage/transmission replace it. CCS is not so low in carbon (about 75% reduction per kWh and we need ~100% in elec to leave room for aviation etc,) and nuclear is incompatible with high renewable and will shut it out for decades because it has to be baseload for technical and economic reasons. (This is quite apart from the security risks, ethics, politics, economics etc. of these options.), We should start the transition to 100% renewables now without recourse to the last gasps of finite fuelled options.

Note the importance of heat storage for load management. Currently about 70 GWe of connected heat storage (10 GW off peak heating, 60 GW water heating) and this will increasingly come into play as elec replaces gas.

Slide 73 of this summarises currently (~2005!) available back up capacity with public and private generation.
http://www.bartlett.ucl.ac.uk/markbarrett/Energy/UKEnergy/UKElectricityGreenLight_100506.ppt

Renewable electricity system: Feasibility of a high renewable electricity system
Barrett, M. 2007, A Renewable Electricity System for the UK. In Renewable Energy and the Grid: The Challenge of Variability, Boyle, G., London: Earthscan. ISBN-13: 978-1-84407-418-1 (hardback).
· http://www.cbes.ucl.ac.uk/projects/energyreview/Bartlett%20Response%20to%20Energy%20Review%20-%20electricity.pdf

Best wishes

Mark

Dr Mark Barrett, Principal RCUK Academic Research Fellow
Energy Institute, University College London
Room 227, Wilkins Building, North Cloister
Gower St, London WC1E 6BT
Site : http://www.bartlett.ucl.ac.uk/markbarrett/Index.html

Skype: MarkAlexBarrett (Mark Barrett)

In the region/capacity table, is there a formatting problem: could it be that the percentage figure shown for Scotland of 0.10 is actually 10%?

As you’ll know, a 20% wind penetration can reduce GHG emissions from electrical generation by over 20%, as it’s the high-carbon, dirty coal that can get taken offline first; so is it that 20% isn’t significant to you, or have you assumed some other mechanism in place?

And from the POV of reserve capacity, there’s the big question of what capacity of interconnectors the system has available: 29GW offshore wind looks like at least 29GW of potential interconnector capacity, using the North Sea Ring model. And how much on-call capacity from grid-connected gensets? Do biomass CHP plants count as “conventional capacity”? How much responsive demand is there in this particular system that can be postponed?

After all, as a lot of that peak power capacity is only needed a few hours each year, building fossil power stations for it seems a bit daft – much cheaper to use a combination of interconnectors, gensets, pumped hydro, a smart grid with responsive loads, etc.

As ever, in questions of intermittency, these partial spreadsheets are amusing diversions, but don’t really tell you how the system would behave: that’s what system models are for.

It would be wonderful if wind power were a luxury, and we didn’t need to decarbonise, and there was no global warming. But hey, that’s reality, and a large wind turbine fleet for Britain is crucial and inevitable.