Batteries, pumped hydro, more transmission lines, hydrogen, ammonia?

Introduction In 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: Increased interstate power transmission capacity; Large-scale storage of electricity in batteries; Large-scale storage of energy in pumped hydro facilities; Large-scale storage of energy as heat; Using excess electricity to produce hydrogen and ammonia; Development of demand response flexibility. The likely options for overseas export of energy seem to be with hydrogen or ammonia although export through undersea cables seems to be another possibility, although a remote one. 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

Import and export of power in South Australia in one day The record of the importing and exporting of power in South Australia over one 24 hour period, 2020/05/01 Click on the image to see in high definition. Source Open NEM The graph on the right shows that my state, South Australia, relies heavily on exporting power to the eastern states (when wind and solar power is cheap and plentiful within the state) and importing power from the eastern states (when expensive gas power is being used within SA because insufficient wind and solar power is being generated). 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. Home Top Index   Battery use in South Australia in one day The record of the usage of utility-scale batteries in South Australia over one 24 hour period, 2020/05/01; the same day as the import/export record above. Source Open NEM The record on the right of utility-scale battery use in South Australia was copied at the same time as the above record of importing and exporting power. Maximum discharging was 45 MW, the maximum charging was 40 MW. The Hornsdale battery capacity is 150 MW power and 193.5 MWh energy. The second battery, at Dalrymple on Yorke Peninsula is 30 MW/8 MWh; the third battery at Lake Bonney is 25 MW/52 MWh. 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. Home Top Index Sometimes there is too much renewable energy being generated in SA, sometimes there is not enough. What are the options? Where to from here?   Curtailment of wind+utility-scale solar in SA This graph shows that wind plus utility-scale solar (green and dark yellow) are being curtailed to a maximum of 1,300 MW. The graph covers the period 2020/04/26 to 2020/05/03. Source Open NEM The average daily energy consumption in SA is around 36,000 MWh (that's a power demand of about 1,500 MW). The flat top to the combined wind and utility-scale solar power generation in the graph on the right shows that the generation from these two sources is being limited to about 1,300 MW; another indication that renewable energy generation capacity is going to waste at the time of writing (May 2020) in SA. 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. (Update September 2023; construction started in 2022. It is expected to be completed in 2025/26.) Half a dozen or so pumped hydro power stations have been proposed in SA. None of these had reached financial close by September 2023. 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. CAES seems to have much the same advantages and disadvantages as does pumped hydro energy storage, although I believe 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. Home Top Index The advantages and disadvantages of the options   The Hornsdale Power Reserve, AKA Tesla big battery At the Hornsdale Wind Farm north of Jamestown in northern SA Photo taken 2018/01/14 by my Phantom 3 Advanced drone Advantages Lithium batteries Very quick response to demand Quick to build Lowest price to build High 'round-trip' efficiency (nearly as much power is got back as was put in) Flow batteries (as an alternative to lithium batteries) Can use more common and less environmentally damaging elements More amenable to recycling High 'round-trip' efficiency Pumped hydro The water is used repeatedly, unlike in conventional hydro power Long life Requires mainly conventional materials High 'round-trip' efficiency Sustainable: all the materials involved can be easily and fully recycled Interstate interconnectors (transmission lines) The materials are fully and easily recyclable Long life Requires only conventional materials The excess power in one place becomes available in another place Using excess power to produce 'green' hydrogen Hydrogen can be used to power fuel cell vehicles Hydrogen can be mixed with natural gas (at levels up to about 10%) and used for the same purposes as natural gas Hydrogen can be burned to generate electricity There is a growing world-wide demand for green hydrogen Hydrogen can be combined with nitrogen to produce ammonia, which has many industrial uses and is easily shipped Home Top Index Demand response Little additional infrastructure is needed Can be developed quickly   Turbines of Clements Gap Wind Farm Clements Gap Wind Farm is about 15km from my home in Crystal Brook. My region, Mid-North SA, is leading Australia in renewable energy development. Disadvantages Lithium batteries Relatively short life (compared to transmission lines and pumped hydro stations) There are environmental costs in lithium mining. (For example see The spiralling environmental cost of our lithium battery addiction.) There are environmental costs in cobalt mining (substantial amounts of cobalt are required for lithium batteries) The recycling of lithium batteries is not settled. "No recycling technology exists today that is capable of producing pure enough lithium for a second use in batteries"; Recycling batteries. This seems to be the least sustainable of the available options Flow batteries (as an alternative to lithium batteries) Too bulky to be suitable for vehicles? Further from achieving the economies of scale than lithium batteries Pumped hydro Water is lost to evaporation from both the upper and lower storages. This could be a significant problem in warm, dry climates. If seawater is used there are problems with corrosion and fouling by marine organisms or there are contamination issues if antifouling chemicals are used. Slower to design and build than batteries. Slower response to demand than batteries (the response time largely depends on the length of the pipe between upper and lower reservoirs – Snowy 2 will be very slow due to its 20 km+ tunnel). 'Green' hydrogen and/or ammonia High cost (but the cost is declining and may be competitive in a decade or two) The process of generating green hydrogen is not energy efficient (but may be viable when the wholesale price of electricity is very low) Burning hydrogen to power electricity generation is no more efficient than burning any other fuel (about 60-70% of the energy is lost) Interstate interconnectors (transmission lines) Collision with power 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) Very expensive to build Susceptible to storm damage Demand response Electricity consumers would have to accept some control over their time of use from the grid controller New metering would be needed if used on the domestic scale Would require control protocols developed on the Internet if used on the domestic scale There are losses of power in the charging and discharging of batteries, in the pumping of water and in hydro turbines, and from long transmission lines. The losses in converting electrical energy into hydrogen and in converting hydrogen into useful forms of energy are greater.

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.

This section added 2021/12/31 The need for medium-term energy storage   Graphic credit OpenNEM The two graphs in this section were downloaded from Open NEM on the last day of 2021. They show a period when there was a big excess of renewable energy generation in South Australia followed by a day of very high power demand that happened to coincide with very high temperatures (maximum temperatures in the settled areas were around 40°C) and low wind generation. 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).   Graphic credit OpenNEM The second graph shows that in the 24 hours up to 4am 2021/12/31 16.4GWh of gas-fired electricity and 0.7GWh of distillate-fired electricity was generated in the state and 8.5GWh was imported; a total short-fall in renewable generation of 25.6GWh. The 0.2GWh of utility-scale battery storage was able to provide only a tiny part of the shortfall (it wasn't designed to, it is for short-term uses). 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.)

The graph above was not selected as being special in illustrating this point, it was one I had used elsewhere on this site for another purpose. It is typical in showing the variability of wind power in South Australia, and probably many other places. The graph above, which covers the period from 2019/08/04 to 2019/09/02, shows that while there were periods of a number of days of abundant wind power there were also two notable periods of limited wind power, the first being of two days, 11th and 12th of August, the second being of five days, 24th to 29th of August. 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 maximum reserve of 350GWh of energy and a maximum power output of 2GW. (In practice only a fraction of the stated 350GWh maximum energy will be available at most times, a practical maximum could be much closer to 40GWh, see Snowy Hydro 2.0: More Expensive Than Battery Storage by Ronald Brakels, 2021/03/22.) Also see my page Snowy 2 or not?. 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.