Hasten slowly into renewable energy

This situation is not quite as bleak as it seems. As the sources have different cycles, when one is unavailable another may be available. For example, solar power will not work at night but the wind may be blowing. By using a broad mix of renewable technologies we can reduce the variability problem. Although the wind does not always blow strongly in one location it may be blowing somewhere else. By distributing the wind turbines over a wide geographic area we can smooth out the variations in supply from each turbine. But we can never eliminate the problem completely.

The existing electricity networks in Australia have been designed to handle a relative small number of large coal fired generators, mainly located near the coal mines, with some dispersed gas plants all connected by a large grid on the eastern and southern seaboards and a separate grid in the west. Renewable generators like wind farms will generally produce much less power than a coal plant and be more widely distributed and, as discussed, not always available when needed. This means costly upgrades to the existing electricity infrastructure to interconnect and manage all these disparate, smaller renewable energy generators to improve the chance of getting a continuous, uninterrupted supply of renewable electricity everywhere.

Australia’s renewable energy will largely rely on wind and solar power in the short term with some existing hydropower. Even distributing the renewable generators and investing in a more sophisticated electricity network system will not provide the current level of availability of supply that we have grown to expect. With fossil fuels, we are protected against the occasional power station shutdown due to maintenance or unexpected problem by having spare capacity in the network. We can have spare capacity in a renewable network but solar power never works at night and works poorly in very cloudy conditions and wide area wind calms could incapacitate a significant part of the wind supply so our protection against blackouts is substantially reduced.

So how do we deal with this problem if we need to shut down the fossil fuel generators?

We need either gigawatt scale electricity storage or non-renewable reserve capacity. The only proven technology for gigawatt electricity storage is pumped storage where surplus electricity is used to pump water from a large lower reservoir to a higher reservoir. When there is an electricity shortage, the water can be released back into the lower reservoir through a hydroelectric plant. Given Australia’s water supply problems, it seems unlikely that we will build more hydro dams or new large pumped storage systems.

The CSP industry is working on ways to achieve the same thing by storing surplus heat to generate electricity during the night or cloudy days. So far only small plants with eight hours of storage have been demonstrated. Both the wind and the CSP industry recognise that they need fossil fuel reserve capacity (preferably gas) to reliably produce baseload electricity. Even with distributed wind farms, the reserve gas capacity may need to be as much as 25 per cent of the power output of the wind farms.

Any transition to renewable electricity will require the continued use of fossil fuels for some time. Technology improvement to renewable energy continues, so the longer the transition takes, the better the outcome for electricity generation if not the environment.

For example, hot dry rocks - where water is pumped into hot underground granite and the steam brought to the surface to produce electricity - is still in the development phase with demonstration plants being built in Australia. It may take a further two decades to bring this technology to maturity but it has the big advantage of low variability (in the order of decades as the hot rocks cool down) and doesn’t need electricity storage or fossil fuel backup. It has relatively low land use and environmental impact and could save thousands of wind turbines, CSP mirrors and gas reserve plants. Unfortunately, the hot rocks tend to be in regions well away from the electricity demand (like the Cooper Basin) so extensions are still needed to the grid.

Hasten slowly into renewable energy. The technology has a long way to go and there are other ways of reducing greenhouse gas emissions from electricity generation such as carbon capture and storage and nuclear power. Neither of these technologies are ideal but they could buy us time to get sustainable energy right.