The Australian government is launching an inquiry into the possibility of building a nuclear power industry in Australia. Some will see this as a good thing – another low-carbon tool in the toolbox that we need to combat climate change; others will see it as a dangerous path to go down with the (difficult to quantify) risks of a nuclear accident and issues around dealing with radioactive waste.
There are questions about how long it might take to get a nuclear power station planned, built and operational (maybe as long as 20 years), not to mention that a change of legislation is required before a nuclear plant can even begin to be built. And then there’s the question of cost.
Assuming these issues can be resolved, is nuclear energy the right technology for the transitioning Australia’s energy market?
A key issue for nuclear power is that it's relatively inflexible compared to gas or hydro power. The technology is similar to a coal-fired power station, but with the heat source coming from the radioactive material instead of burning coal. The plant still needs to generate high-pressure steam to run a Rankine cycle turbine, and this takes time.
If we look at how nuclear power is dispatched in Germany (below), where it makes up about 10 per cent of generation, the output is more or less constant. This is partly due to the long time it takes to start the plant, and because high thermal inertia makes it difficult to ramp up and down. It’s also because, to be profitable, the power stations need to run at close to maximum capacity to produce as much electricity as possible. These factors combined means they don’t ‘load follow’ very well.
Electricity mix for Germany. Source: Fraunhaufer Institute
In the pre-renewables world, this wasn’t a problem. In fact, this kind of generation was perfect for providing the ‘baseload’ needs – that is, the minimum demand (typically occurring overnight).
But with the penetration of wind turbines and solar photovoltaics (PVs) continuing to increase (below), the concept of baseload is disappearing.
Source: Australian Energy Market Operator and Clean Energy Regulator
Australia is currently just shy of 20GW of wind and solar generation. As we approach the 2020 renewable energy target of at least 33,000 gigawatt-hours, we can expect a rush of projects. After that, most of the states have renewable targets of 50 per cent or more that, combined with the continuing falling prices of PV, should lead to a continuation of the trend.
A key feature of wind and solar technologies is that their output is dependent on the weather and the diurnal cycle. If the wind isn’t blowing or the sun isn’t shining, they don’t produce power. The demand for power also varies over the course of the day, and also depends a lot on the weather, with hot days driving demand up. But when the wind blows and the sun shines, it can meet all of our demands, making baseload generators redundant.
South Australia is a great case study for high-penetration renewables, currently providing about 50 per cent of electricity requirements using wind and solar.
The graph below shows the past seven days of generation from wind, solar and gas (labelled ‘Residual’ – that is, the power required after considering the variable wind and solar output).
Electricity generation in South Australia for the past week. Source: opennem.org.au
The residual demand varied from zero to all of the demand in a short period. South Australia used to have coal-fired power stations, but the increasing share of renewables reducing the requirement for baseload, coupled with their age, made them unviable, and so they've been shut down and dismantled.
To go to a low or zero-carbon energy system, the residual generation needs to be replaced with non-fossil technologies. That technology needs to ramp up and down rapidly in a short period of time.
Natural gas currently does this very well, especially open-cycle turbines (much like jet engines – very capable of going from low to high power in a very short period).
One option to do this with low net carbon emissions would be to use biogas, although producing enough biogas may prove challenging.
We've been able to show that 100 per cent renewable systems are technically achievable, cost-effective and reliable, without having to resort to nuclear power.
Other technologies that could work are conventional hydro power (where available), pumped hydro energy storage, and batteries.
Another approach that can also be used is demand side management – where electricity consumers (residential and commercial) are given incentives to reduce consumption when the system struggles to meet demand.
Fortunately, we've been able to show (many published studies now) that 100 per cent renewable systems are technically achievable, cost-effective (possibly cheaper than maintaining a fossil fuel system, depending on cost assumptions) and reliable, without having to resort to nuclear power. Strategic placement of wind and solar plants to take advantage of synoptic weather patterns, combined with pumped hydro energy storage, will require significant investment, and more importantly, intelligent long-term energy and climate policy.