A cheaper path to 100% renewables

While a fierce debate rages about the environmental impacts of coal seam methane, coal mining and coal combustion, research has been progressing on the challenging problem of cutting greenhouse gas emissions by replacing most fossil fuels by renewable energy.

In Europe, political commitment to this sustainable pathway is growing. The government of Germany has committed to an 80 per cent renewable energy target by 2050, has modelled a system based on 100 per cent renewable electricity and, in the wake of Japan's Fukushima disaster, has passed legislation to phase out nuclear energy by 2022.

Scenarios for 80-100 per cent renewable energy have also been developed by government agencies, academics and NGOs for Denmark, the UK, Japan, New Zealand, Ireland, northern Europe, the European Union and the world.

Australia has enormous renewable energy resources in the form of sunshine, wind, biomass (organic) residues, hot rocks and waves. But is a transition to 100 per cent renewable energy technologically and economically feasible here?

Last year, a ground-breaking study, "Zero Carbon Australia Stationary Energy Plan," claimed that 100 per cent renewable energy is technically possible and would cost about $370 billion.

The core of the ZCA study was an hour-by-hour computer simulation, by Jack Actuarial Consulting, of Australian electricity demand in 2008 and 2009, supplied mostly by concentrated solar thermal power (CST) with thermal storage, and by wind power.

As is inevitable in a first-of-a-kind study of a revolutionary new energy system, some simplifying assumptions were made:

– Western Australia was connected at great expense to the eastern states with new transmission lines;

– Second-generation CST power stations, for which there is little operating experience, were chosen as the principal energy source. These solar stations were given thermal storage equivalent to 17 hours of full power output and so can, in theory, run through the night;

– A daily average was taken for solar energy inputs, although hourly data are much more accurate;

– To compensate for the reduction in sunshine in winter, a vast excess of CST generating capacity was introduced;

– Also for winter, biomass residues were shipped out to the solar power stations to be burned under the thermal storages when necessary.

At the University of New South Wales, PhD candidate Ben Elliston, Associate Professor Iain MacGill and I initiated an independent research project based around some different assumptions, to remove the above assumptions of the ZCA study.

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. We chose a broader energy mix than ZCA: first-generation CST with thermal storage, wind, solar PV, gas turbines and existing hydro – all commercially available technologies. Gas turbines, which are like jet engines, are highly flexible generating plants ideally suited to supporting fluctuating renewable generation. Some are already being deployed in Australia. They could initially be fuelled on natural gas, however this could be replaced with liquid biofuels produced sustainably from the residues of existing crops.

We found that it is, indeed, technically feasible to supply current electricity demand by 100 per cent renewable energy with the same reliability as the existing fossil fuelled system.

The key challenge is meeting demand on winter evenings. At sunset on overcast days, the thermal energy storages are not full and sometimes wind speeds are low. In our initial simulations, to be presented in a peer-reviewed paper at the forthcoming Australian Solar Energy Society’s annual conference, 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, which would not be used in summer.

However, the UNSW study proposes an even cheaper solution than lots of gas turbines or CST: namely a revitalised energy efficiency program to reduce electricity demand on winter evenings. Furthermore, in a ‘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 sceptics that renewable energy cannot replace baseload (24-hour) coal-fired power. ZCA interprets its results by concluding that CST with thermal storage is baseload.

We interpret the simulation results differently, concluding that although CST can perform in a similar manner to baseload in summer, it does not in winter. However, we maintain that it doesn’t matter. The important result is that our renewable energy mix gives the same reliability of the whole generating system in meeting demand as the existing polluting system.

Although the UNSW study has not yet performed an economic analysis, our scenarios have the potential economic advantage over ZCA’s that they don’t require transmission links between WA and the eastern states and they have a smaller percentage contribution from CST, currently the most expensive component of the energy mix.

It should be emphasised that neither the modelling of ZCA nor UNSW establishes a timescale for the transition to 100 per cent renewable electricity. However, the ZCA study claims that the transition could be made in a decade. That claim is 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 claim for 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.

Dr Mark Diesendorf is Associate Professor and Deputy Director of the Institute of Environmental studies at UNSW