Exactly how much storage and back-up does renewable energy need? It’s a question at the heart of electricity planning and the subject of many of the myths peddled by vested interests in the fossil fuel lobby and the gullible media. The answer is: not nearly as much as the naysayers would have you think.
According to the CSIRO and Energy Networks Australia, which own the local and interstate grids, a level of between 30 and 50 per cent share of variable renewable energy sources such as wind and solar can be easily accommodated without any further back-up.
That’s because there is so much back-up built into the system already to support coal and gas-fired generation, either to meet peaks in demand, or to fill in gaps when coal and gas plants fail, as they do quite regularly, particularly in hot weather.
The estimate also reflects the changing view of technologies and how grids are managed. It was not so long ago that most engineers would have thought 10 per cent was the absolute maximum. The Murdoch media has been misquoting an old report saying that 20 per cent is the level at which problems occur. Some network operators think 60 per cent is the level.
The CSIRO and ENA says the amount of storage needed beyond that 30 to 50 per cent continues to be minimal until much greater levels of renewable energy are introduced, and then the extent of that back-up is largely dependent on local weather and climate, and their natural renewable energy sources.
The roadmap released by CSIRO and ENA on Friday, following nearly three years of work, includes an appendix on the levels of storage and/or peaking plant back-up needed, and how this might affect individual states.
By their own admission, the estimates are on the conservative side – because they have not allowed for greater network links between the states, and because some of the estimates do not include a mix of options. But you can get the drift.
“(Our findings) indicate that battery storage is generally not required until high levels of renewable energy share are achieved and may form part of an optimised system when renewable share reaches 30-50%,” the report says.
Even approaching 100 per cent renewable energy, the amount of storage in some states is only around five hours. In other states, it could be much higher (see table above).
As the renewable energy share approaches 100 per cent, the amount of battery storage increases non-linearly and approaches an average ratio of 1:1 with installed capacity of variable renewables.
Again, however, there is significant variation, and it will depend on how much alternative dispatchable energy there might be: biogas peaking plant, solar thermal, pumped hydro and the like.
Tasmania, for instance, will require a much lower ratio due to its large existing hydro power capacity, and there are circumstances where New South Wales and South Australia may be able to deploy a lower ratio of batteries.
Queensland and Victoria, however, may require a higher ratio, due to poorer wind resources in the former and poorer solar resources in the latter.
The analysis indicates that up until 80 per cent wind and solar share, less than five hours of battery storage at average state load is required to support energy balancing working together with the existing dispatchable technologies such as hydro and gas.
It notes that gas or biogas peaking plant will be more cost effective than adding additional storage capacity in circumstances where a substantial renewable generation shortfall extends for more than a third of a day – underlining the point that battery storage is best for short periods.
And if the reliance does fall on peaking plant, then there will not be a need for 1:1 back-up, because that will likely be required in mild, cloudier winter days rather than the heatwaves in mid-summer, when there should be enough solar and storage to cater for the peaks. In winter, the peaking capacity would be around 60 per cent of peak demand.
“While variable renewable generation creates a need for additional battery storage it may not necessarily be installed via a formula relating to installed capacity. Rather the total battery requirement more strongly relates to being able to meet average state load for an increasing number of hours.”
But the need for storage and back-up will be reduced if more interconnectors are built linking the renewable energy sources in one state with another.
“Solar provides a relatively economic and predictable daytime supply in all states,” it says. “However, a significant contribution from wind power is crucial to fill in the supply gaps at night together with storage and dispatchable gas capacity.”
But it is the sheer volume of rooftop solar and consumer-installed battery storage that will play a critical role in managing the grid.
This graph below illustrates the phenomenal amount of rooftop solar that will be installed in each state over the next few decades – a total of 85GW across the country. By 2030 in Queensland, there will be more solar capacity than current coal capacity. The same will be true of NSW a few years later.
Even more dramatic is the amount of battery storage that is installed – nearly 100GWh across the country – as customers seek to maximise the value of their solar panels, and to lessen their dependence on the grid.
The collection of installation data is in its infancy, however, it is widely reported that existing rooftop solar owners, seeking to get greater value from their existing investment are the primary early adopter group. Battery storage also represents an opportunity for customers
“It is anticipated that battery owners may allocate control of their battery to other agents who can fine tune and aggregate battery operation to maximise the rewards they receive for assisting with energy balancing for both the local network zone substation and the state generation node,” the report says.
“This wide ranging and very important role envisaged for battery storage means that the factors that will play into state level adoption include existing and future solar installations, the specific critical peak and daily peak prices offered in each state, the state opportunities for avoided network augmentation and the relative need for wholesale market energy balancing or variable renewable penetration.”
One of the key challenges for the growing installation of rooftop solar was the stress on substations, which began to experience “reverse flows” when the penetration reached more than 30 to 40 per cent.
High shares of rooftop solar will hollow-out the load during the middle of the day, leading to rising voltages on the local distribution system, but the addition of storage allows a zone substation to potentially absorb a higher penetration of solar without running into issues.
“However, this requires coordinated action to provide incentives or rewards for a useful level of storage to be installed, and for the available capacity to be operated in a way that addresses zone substation level needs and local congestion,” the report says.
