Renewable energy has the potential to become the basis of Australia's energy system, providing 24-hour baseload power to everyone everywhere, says Dr Mark Diesendorf.
Nowadays renewable energy deniers are almost as active in spreading misinformation as the deniers of anthropogenic climate change. One of their principal false claims is that renewable energy sources are too unreliable to form the basis of an energy system for an industrial society. In particular, they assert that renewable energy cannot replace conventional base-load (24-hour) power and is only suitable for niche markets. The research reported in this article helps to refute these claims.
In Europe, as wind and solar installations grow rapidly and perform well, political commitment to sustainable energy systems, based on 80-100% renewable energy, is also growing. The government of Germany has committed to an 80% renewable energy target by 2050 and, in the wake of the Fukushima disaster, has passed legislation to phase out nuclear energy by 2022. The Danish government has invited proposals for sourcing just over half its electricity from wind turbines by 2020 and all its electricity from renewable sources in 2050.
Scenarios for 80-100% renewable energy have been developed by government agencies, academics and NGOs for Australia, Denmark, Germany, United Kingdom, Japan, New Zealand, Ireland, northern Europe, the European Union and the whole world.
Last year a ground-breaking study, ‘Zero Carbon Australia Stationary Energy Plan’, found that 100% renewable energy is technically possible for Australia and estimated that it would cost about $370 billion. The core of this study was an hour-by-hour computer simulation, by Jack Actuarial Consulting, of Australian electricity demand in 2008 and 2009. The principal renewable energy sources chosen were concentrated solar thermal power (CST) with thermal storage and wind power. Some constraining assumptions were made:
- Western Australia was connected at great expense to the eastern states with new transmission lines with the aim of improving system reliability through geographic diversity.
- Second-generation CST power stations, ‘power towers’, for which there is little operating experience, were chosen as the principal energy source. These solar stations were given a solar multiple of 2.5 and thermal energy storage equivalent to 17 hours of full power output.
- A daily average was taken for solar energy inputs, although hourly data enable more detailed dynamic modelling.
- To compensate for the reduction in sunshine in winter, a vast excess of CST generating capacity was introduced.
- Also for winter, biomass residues were transported to the solar power stations to be combusted in order to heat the thermal storages when necessary.
At the University of New South Wales, PhD candidate Ben Elliston, Associate Professor Iain MacGill and I commenced an independent simulation project, which removed all of the above assumptions of the ZCA study. However, we still have some assumptions of our own that will be progressively removed. Ben presented the first of our projected series of peer-reviewed papers on this topic at the Australian Solar Energy Society’s Solar 2011 conference .
We performed a series of hour-by-hour computer simulations of the 2010 electricity demand in the five Australian states covered by the National Electricity Market. To meet demand we chose a broader energy mix than ZCA: mature parabolic trough CST technology with thermal storage, wind in existing wind farm locations, solar PV in the major population centres, biofuelled gas turbines and existing hydro, all commercially available technologies. Together the two types of direct solar technology provide about half the electricity generated.
Gas turbines are highly flexible generating plant ideally suited to supporting fluctuating renewable generation. Some are already deployed in Australia as peaking plant fuelled on natural gas. However, they can also burn liquid biofuels produced sustainably from the residues of existing crops. Indeed, jet aircraft on some overseas commercial flights are already flying with one or more of their engines burning biofuels.
Our research confirms that it is technically feasible to supply current electricity demand by 100% renewable energy with the same reliability as the existing fossil fuelled system. The key challenge is meeting demand on winter evenings. A large part of this demand is of course residential space heating. At sunset of overcast days, the thermal energy storages are not full and sometimes wind speeds are low as well. In our initial baseline simulations, we used biofuelled gas turbines to fill the gap. This is likely to be lower cost than ZCA’s solution of choosing a vast excess of CST power stations, many of which would not be operated in summer.
The UNSW study also proposes an even cheaper solution than lots of gas turbines or CST: namely a revitalised residential energy efficiency program to reduce peak electricity demand on winter evenings. In a second paper  we show that reducing the winter peak demand by only 16% allows us to reduce the gas turbine capacity by 27% and the biofuel combusted by 8%, while still maintaining the required reliability. Furthermore, in a future ‘smart’ electricity system it will be easier to reduce demand quickly during periods of low supply.
Both the ZCA and UNSW studies refute the claims by renewable energy deniers that renewable energy cannot replace base-load (24-hour) coal-fired power. ZCA interprets its results by saying that CST with thermal storage is base-load. We interpret the simulation results differently, concluding that although CST can perform in a similar manner to base-load in summer, it cannot in winter. However, that doesn’t matter. In a predominantly renewable energy supply mix, the concept of ‘base-load power station’ is redundant. The important result is that renewable energy mixes can give the same reliability of the whole generating system in meeting demand as the existing polluting fossil-fuelled system. Similar results and conclusions are obtained for the USA by David Mills in a paper presented at Solar 2011 .
The first UNSW paper does not consider the internal transmission requirements within the NEM region for 100% renewable electricity and so has not yet performed an economic analysis. More complex simulation models are being developed to tackle this task.
It should be emphasised that neither the modelling of ZCA nor UNSW establishes a timescale for the transition to 100% renewable electricity. However, the main body of the ZCA report claims that the transition could be made in a decade. That claim is actually an assumption based on the observations that Australia could supply the raw materials for manufacturing the systems and that solar and wind technologies are suitable for rapid manufacture.
While these observations are valid, they don’t justify the notion of a very short timescale for the transition. ZCA doesn’t consider the time needed to undertake a huge training program for engineers (especially electric power engineers) and other essential professionals, or the challenges of reversing the industry policies of many previous Australian governments that have decimated most of our manufacturing capacity, or the complex institutional reforms needed, such as changing the rules of the National Electricity Market. ZCA cites no literature on technology diffusion or even on wartime mobilisation of industry. An entirely different kind of research project is needed to investigate possible transition timescales.
 Elliston, Ben, Diesendorf, Mark & MacGill, Iain, I. (2011) 'Simulations of scenarios with 100% renewable electricity in Australian National Electricity Market', Solar 2011 Conference, Australian Solar Energy Society, Sydney, 30 Nov - 2 Dec. <http://www.ies.unsw.edu.au/staff/mark.html>.
 Elliston, Ben, Diesendorf, Mark & MacGill, Iain, I. (2012) 'Simulations of scenarios with 100% renewable electricity in the Australian National Electricity Market', Energy Policy (in press) . doi:10.1016/j.enpol.2012.03.011.
 Mills, David R. & Cheng, Weili (2011, to be published) ‘Powering the USA from wind and solar power’, Solar 2011 Conference, Australian Solar Energy Society, Sydney, 30 Nov - 2 Dec.
(Dr Mark Diesendorf is Associate Professor and Deputy Director of the Institute of Environmental Studies at UNSW. His latest book is "Climate Action: A campaign manual for greenhouse solutions", UNSW Press, 2009, http://www.unswpress.com.au/.)
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