Solar News

The base-load myth

2 May 2011
Category: Renewable Energy

To every complex problem there is a simplistic response, which is usually wrong.

For instance, to the challenge of generating all of Australia’s electricity from renewable energy, the deniers and scoffers repeatedly utter the simplistic myth that renewable energy is intermittent and therefore cannot generate base-load (that is, 24-hour) power.

Detailed computer simulations, backed up with actual experience with wind power overseas, show that the scoffers are wrong. Several countries, including Australia with its huge renewable energy resources, could make the necessary transition to an electricity generation system comprising 100 per cent renewable energy over a few decades.

Firstly, the demand for power during the night is generally low and could be reduced substantially by improving our efficiency of energy use and by the forthcoming phase-out of electric off-peak hot water. This is the reverse of the previous policies, which deliberately encouraged an increase in night-time demand to allow our inflexible coal-fired stations to generate 24/7. Under the present circumstances, where coal-fired generators must be phased out, we can reduce base-load demand and supply.

Secondly, some renewable energies are just as reliable sources of base-load electricity as coal, while being 50 times less greenhouse polluting. These include bio-electricity generated from burning the residues of crops and plantation forests, concentrated solar thermal power with low-cost thermal storage, and hot-rock geothermal power.

Bio-electricity is ready for rapid mass production. Several different types of concentrated solar thermal power are already at the pre-commercial stage (that is, in limited mass production) in Spain and California. However, we still need several years of experience with different types of collectors, heat-storage and heat-transfer systems before choosing a second-generation system for mass production. Meanwhile, it would make sense for Australia to implement a feed-in tariff for large-scale solar, so that we can gain experience and then move into local manufacture of the best designs.

Hot-rock geothermal power is being demonstrated on a small-scale in France, Germany the USA and will soon be demonstrated in Australia.

Until solar thermal power with thermal storage is ready to be rolled out rapidly, the cheapest renewable electricity option for replacing several coal-fired power stations is one of the so-called ‘intermittent’ sources, wind power, a fully commercial technology. Wind supplied the biggest contributions to new generating capacity in Europe in 2008 and 2009. It provides 24 per cent of Denmark’s electricity and over 14 per cent of Spain’s and Portugal’s. It has been undergoing enormous growth in China, which doubled its wind generating capacity each year over 2006- 2009.

So, what about intermittency? There is no doubt that the output from a single wind farm can fluctuate greatly. However, the fluctuations in the total output from a number of wind farms, which are geographically distributed in different wind regimes, are much smaller and partially predictable. Then it is relatively easy and inexpensive to lift the reliability of the whole wind output to a level equivalent to a coal-fired power station by adding a few peak-load plants that are operated infrequently.

Even in the absence of renewable energy power stations, electricity generating systems are designed to handle fluctuations in supply and demand. A power station or a transmission line may break down. An advertising break in a popular TV show may result in millions of kettles being switched on. These fluctuations are handled by peak-load plants, such as hydro and gas turbines, that can be switched on and off quickly, and by reserve base-load plants. Up to a point, these existing back-up systems can also handle fluctuations in wind and solar power without storage.

With large amounts of wind and solar photovoltaic capacity in the grid, some additional peak-load plants may be required. Gas turbines (essentially jet engines) are suitable because they are flexible, have low capital costs and, provided they are not operated a lot, have low fuel costs. They are reliability insurance with a low premium. They are fuelled by gas or biofuels produced sustainably.

Feasibility has been established by computer simulations of electricity generation systems by several research groups around the world, including my own in CSIRO in 1980s. Recent detailed studies funded by the National Renewable Energy Laboratory in the USA found that wind power could supply 20-30 per cent of electricity, given improved transmission links and a little low cost flexible back-up.

So a plausible scenario for the next decade is a phase-out of several coal-fired power stations simultaneously with a rapid growth in efficient energy use, solar hot water, wind power and bio-electricity. These clean technologies would buy us time to build up solar thermal and geothermal power and then manufacture and integrate them on a large scale in the 2020s as the remaining coal stations are shut down. Thus Australia could achieve a sustainable energy system.

Associate Professor Mark Diesendorf is Deputy Director of the Institute of Environmental Studies at UNSW. His latest book is "Climate Action: A campaign manual for greenhouse solutions".

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