Recently on BNC, I ran two guest posts on the economic and technical challenges of supplying an energy-intensive, developed-world market using 100% renewable sources (under a situation where large hydro and/or conventional geothermal can provide little or no contribution). The case study was the national electricity market of Australia, with an average demand of 25-30 GWe.
and the response, from one of the authors of the original simulation study:
Below is a further commentary, by Ted Trainer of UNSW, which focuses particularly on the issues of supplying winter demand, the feasibility of the biomass option for the gas backup, and the “big gaps” problem (i.e., long-run gambler’s ruin). Ted asked me to post it here on BNC to solicit constructive feedback (and has promised me he will be responding to comments!).
“Simulations of scenarios with 100% renewable electricity in the Australian National Electricity Market” Solar 12011, 49th AuSES Annual Conference, 30 Nov – 2 Dec., By Ben Elliston, Mark Diesendorf and Iain Macgill, UNSW.
Ted Trainer; 21.3.2012
The paper outlines a supply pattern whereby it is claimed that 100% of present Australian electricity demand could be provided by renewable energy.
The following notes indicate why I think that although technically this could be done, we could not afford the capital cost. This is mainly because the analysis seems to significantly underestimate the amount of plant that would be required.
I think this is a valuable contribution to the discussion of the potential and limits of renewable energy. It takes the kind of approach needed, focusing on the combination of renewable sources that might meet daily demand. However it is not difficult to set out a scenario whereby this might be done technically; the problems are what quantity of redundant plant would be needed to deal with fluctuations in renewable energy sources, and what might the capital cost of this amount to?
Two of the plots given set out the contributions that might be combined to meet daily demand over about 8 days in 2010, in summer and winter. It seems to me that when these contributions are added the total capacity needed is much more than the paper states.
The task is to supply 31 GW. The plots given show that at one point in time wind is contributing a maximum of 13.5 GW, but at other times its contribution is close to zero, meaning that other sources are backing up for it. The corresponding peak inputs from the other sources are, PV 9 GW, solar thermal 27, hydro 5 GW and gas from biomass 24 GW. Thus the total amount of plant required would be 75.5 GW of peak capacity… to supply an average 31 GW. (in his response to Peter Lang, Mark Diesendorf says their total requirement is 84.9 GW.) That’s the magnitude of the redundancy problem and this is the major limiting factor for renewables; the need for a lot of back up plant, which will sit idle much of the time.