IntroductionIn my home state, South Australia, there are some times when there is too much renewable energy being generated, there are many times when wind and solar power are insufficient for local demand. When there is a deficiency it is made up by expensive gas generation within the state and importing power from the largely coal-fuelled generators in the eastern states, both of which are polluting and unsustainable.
There is no hydro power at all in the state (the state has no well watered mountains). We do have what was at the time of building, the biggest battery in the world (100 MW/129 MWh) at Hornsdale and two smaller, but also utility scale batteries elsewhere in the state.
If South Australia's huge remaining potential for renewable energy is to be developed ways will have to be found to handle the variable nature of renewable energy generation. The main options that are viable at the present seem to be:
Other options will probably gradually become available in the medium to long term.
As things stand at the time of writing curtailment of generation from wind farms is used regularly, and curtailment from solar generation is becoming necessary; both are, of course, undesirable.
Part of Snowtown Wind Farm
Photographed by my drone, June 2020
This record of the importing and exporting power from South Australia to the remainder of the National Electricity Market (the eastern Australian states) on the right was copied at the time I started writing this page. I believe that it is fairly typical, although the amount of renewable generation for the day (83%) was well above average.
There are two transmission lines (interconnectors) connecting SA with Victoria, the Heywood (alternating current, nominal capacity of 650 MW) and Murraylink (direct current, nominal capacity of 220 MW).
The graph shows a maximum import of about 600 MW and a maximum export of about 475 MW on the day. Average power demand within SA is around 1,500 MW.
The long period of exporting power (0930 to 1930) was ten hours at an average of about 240 MW; that is about 2,400 MWh of electrical energy.
Maximum discharging was 45 MW, the maximum charging was 40 MW.
The total energy storage capacity of the three batteries is 254 MWh. This can be seen to be small compared to the amount of daily imports and exports to and from SA.
There is also a 'virtual power plant' in South Australia. This consists of many home batteries that can be, to a limited extent, centrally controlled to help balance the state grid. The aim is to get to 50,000 home batteries, at the time of writing (May 2020) there is a trial phase that includes 1,100 batteries. Given that a typical home battery is about 14 kWh, the trial phase capacity is 15 MWh, and the full virtual battery, if it is developed, will be 700 MWh.
Plainly there is a long way to go if energy storage is to fill in for a week or so of low wind and solar generation (which is not to say that it is impossible). It should be said that the main intention and use of the batteries is grid stabilisation rather than the supply of gross power.
A third power interconnector (transmission line between states) has been proposed; this time between SA and NSW. Its intended capacity is 800 MW and expected cost $1.5 billion.
Half a dozen or so pumped hydro power stations have been proposed in SA. To the present none of these has reached financial close. Their total energy storage capacity, if built, would be at least 6,000 MWh. (Pumped hydro is probably a better fit for Tasmania with its existing well developed hydro power and lower evaporation rates. It will require more interstate transmission interconnection, a second undersea cable across Bass Strait has been proposed.)
Compressed air energy storage (CAES) is another technology that is being developed. See, for example, Hydrostor's Angas Project, apparently under construction a couple hundred kilometres from my home. CAES seems to have much the same advantages and disadvantages as does pumped hydro energy storage, although the round trip efficiency of the former is about 60% while that of the latter can be up to 80%.
More lithium battery capacity can, and most likely will, be built. Flow batteries are an alternative to lithium batteries for some applications and seem to be more environmentally friendly.
Some excess renewably generated power could be used to produce hydrogen which has a number of uses including the production of ammonia, a substance in high demand around the world and that is easily exported. At the time of writing (May 2020) 'green hydrogen', hydrogen produced using renewable energy to electrolytically break water into hydrogen and oxygen, is not economically competitive with hydrogen produced by using fossil fuel energy, but the price is rapidly dropping. There are several pilot plants under construction in the state.
Demand response is another factor in the mix; encourage the use of more power when there is plenty of generation by low retail prices, encourage less use when there is a shortage by high retail prices. It is being used to a small extent already, but there is potential for much more. Anything the has some flexibility in time of use can be involved: storage water heaters are an obvious candidate, electric vehicle charging is another, then there's at least some short-term flexibility in air conditioning and refrigeration. On the industrial scale is aluminium smelting (there are no aluminium smelters in SA but there is one close to the Victorian end of the Heywood Interconnector) and possibly desalination (the Adelaide desalination plant produced 4925 Ml of water in April 2020 and, I calculated, used around 25 MW of power).
Electricity is easily and efficiently converted to heat, which can be conveniently stored for limited times. However, converting heat back to electricity is much less efficient.
Bungala solar farm, completed
Photo taken by my Mavic Mini drone, 2020/03/26. Click on image to view full size, 'back' to return
We visited Bungala Solar Farm on our way north to stay at Willow Springs in the Flinders Ranges at the beginning of the first outbreak of Covid-19. Bungala is, I believe, the biggest solar farm in Australia (275 MW?); we had previously seen it when it was under construction.
The first graph shows the generation record for the week from 4am 2021/12/24 to 4am 2021/12/31. Over the period 29.7GWh of electricity was exported, 18.1GWh was imported and 34.4GWh was generated by fossil fuelled stations. At the time total utility-scale battery capacity in the state was about 200MWh (0.2GWh).
There is an obvious need for much more medium-term energy storage in SA if the state is to come close to being 100% reliant on renewable energy.
A month's generation in South Australia
This graph demonstrates the need for 'deep' (or long-term) energy storage in a grid with a high percentage of renewable energy; see text below. (Click on the graph for higher definition.)
As it was late winter there was little solar power.
The energy short-fall for each of the 11th and 12th was about 30GWh. For comparison this is about 150 times the capacity of the Hornsdale Power Reserve (also known as the Tesla Big Battery), as expanded in September 2020, 194MWh.
As of the time of writing, early 2021, the biggest energy storage proposals were Snowy 2.0 and the Tasmanian 'Battery of the Nation'.
Snowy 2.0 is to link two existing Snowy Mountain Scheme reservoirs, Tantangara and Talbingo. It is expected to hold a reserve of 350GWh of energy and a maximum power output of 2GW.
The Tasmanian Battery of the Nation project is dependent on two new 750MW power cables being laid beneath Bass Strait, and at present no one seems willing to pay for these. An article published by ARENA gave 4.8GW and 140GWh as the estimated total capacity of the project.
Other proposals are much smaller, such as Kidston (2GWh) and Baroota (1.6GWh).
Batteries are good for supplying power for periods of up to four to eight hours, but pumped hydro is much better suited for supplying power for several days.
Related pages on external sites...Renew Economy's big battery storage map of Australia.
The Conversation: "Against the odds, South Australia is a renewable energy powerhouse. How on Earth did they do it?" Written by Michael McGreevy and Fran Baum, 2021/02/25.
Recycling batteries; the challenges, what can be done, what is being done.
Flow batteries; Wikipedia
South Australia's virtual power plant; combining thousands of domestic batteries to improve grid supply and demand.
Journal of Sustainable Mining; Life cycle assessment of cobalt extraction process, Shahjadi Hisan Farjana, Nazmul Huda, M.A. Parvez Mahmud
Collision with transmission lines is the biggest human-related cause of bird deaths after domestic and feral cats (for example, see 9 leading causes of bird deaths in Canada)
Australia’s first compressed air energy storage system gets development approval, 2019/07/17, Renew Economy, written by Michael Mazengarb.
Related pages on this site...Australia's energy future
Bird deaths from wind turbines collision and other causes
End of coal: why the coal industry has a very limited future.
Greenhouse/climate change: the greatest threat currently facing mankind.
Killer coal: how the burning of coal kills millions of people world-wide each year.
Power to Gas (P2G, renewable energy used to produced hydrogen gas) in Australia.
Pumped hydro energy storage.
Wind power opposition: almost universally dishonest.