Australia has some fairly ambitious goals for green energy: a renewable energy target (currently under review) of 20% of electricity from renewables by 2020, and a forecast to get 51% of electricity from renewables by 2050.
But in setting these targets, not enough consideration is being given to the difficulty of getting the job done – in terms of generating enough renewable energy, and of storing it so it can be supplied 24 hours a day.
Renewable energy sources, mainly hydroelectric and wind with a smaller amount of solar, currently provide around 13% of Australia’s power; the rest comes from fossil fuels. Increasing renewable sources to and beyond 20% will depend on being able to generate power at the right locations, and building enough storage infrastructure too.
The problem of consistency
Hydroelectric power requires reliable rainfall upstream; wind power needs consistent wind speeds; and solar energy naturally depends on sunshine. Geothermal and ocean power sources are unproven at any scale in Australia, while biomass resources will always be very limited without having a major impact on food production.
The common factor for all of these sources is irregular weather patterns, which lead to uncertain and intermittent power output. This is a big challenge for electricity generators and retailers, and it can cost lots of money.
Solar and wind, even in favourable locations, typically produce power at around 20-30% of their total theoretical capacity, compared with more than 90% for many fossil fuel plants. This means that to produce the same amount of electricity, the renewable plant must have around four times the capacity of the fossil fuel plant. For example, a 1000 megawatt wind farm would typically be needed to produce the same electricity output as a 250 megawatt coal or gas plant.
To look at it another way, while fossil fuel plants can be online 24 hours a day, we can only rely on wind or solar sources to generate electricity for an average of 5 to 8 hours each day (although the energy can potentially be stored for use later in the day, which we will come to shortly).
Australians expect that when they turn on a light switch, be it 8 am or 8 pm, the light will come on. If we depended solely on renewable energy for direct power generation, this wouldn' happen. We need baseload electric power, generated reliably around the clock, to guarantee security of supply.
Advocates for high levels of renewable electricity, such as supporters of the Bureau of Resources and Energy Economics projection of 51% by 2050, or even for 100% renewable energy, argue that energy storage can overcome this problem. In reality, however, few financially and technically viable solutions exist to store large amounts of electrical energy for significant periods of time. Pumped water storage is the favoured solution, but this requires dams and water normally near to the power sources to minimise transmission losses.
Australia has very limited capacity for growth in this area. Battery storage is typically limited to tens of kilowatt hours discharged over a few hours or days at best. Batteries will not serve the needs of most industries. Molten salt storage has been advocated for solar thermal plants, but the scale required to achieve more than a few hours' storage makes this solution unviable for most applications. An electrolysis process to produce hydrogen from water for subsequent use in a gas-fired plant or with fuel cells is possible, but unlikely on a large scale because of practicality and cost.
Weighing the options
So what options do we have in Australia to ensure security of electricity supply on a 24/7 basis? The reality is that the higher the proportion of electricity produced from renewable sources, the more we must have available standby baseload capacity from fossil- or nuclear-fuelled plants for when the wind does not blow and the sun does not shine.
Of course, it is expensive to have power stations sitting there on standby, which in turn drives up the cost to consumers. Gas-fired standby plants are favoured because of their flexibility, but the long-term security of supply and the escalating cost of gas are significant concerns.
A credible Australian energy policy must reflect the limitations on the use of renewable energy sources, and focus more on other greenhouse gas mitigation strategies. It has been proven internationally that coal-fired electricity generating plants can be around twice as efficient as most existing Australian plants. Technology also exists to capture around 90% of all the emissions from fossil-fuelled plants, but further cost reductions and incentives will be needed to help generators invest this new equipment. The other option is to build low-emitting nuclear plants, but that is another story. And consumers can also focus on trying to reduce their own power use.
More attention must be given to greenhouse gas emissions from outside the energy sector, which account for more than 60% of all Australia’s emissions. Direct fuel combustion, transport and agriculture contribute some 46% of emissions – and might offer easier ways to cut down.