The Labor Government is funding 400 community batteries as part of ‘Rewiring the Nation’. Additional funding is provided by some state governments, such as the Victorian Neighbourhood Battery Initiative. The popularity of these subventions is understandable, given that home batteries are often not economical, having typical paybacks of 12+ years. Community batteries are seen as the affordable alternative.
Community batteries can assist networks in postponing network upgrades and the associated substantial cost of excessive infeed. New transformers, new conductors, trenching for underground cables are major capital investments resulting from the growth in rooftop solar, so networks welcome community batteries as a way of mitigating these costs.
Solar systems cause voltage control problems. Australian Standard AS4777 has alleviated some of this issue by changing the requirement for inverters, but given the majority of non-complying solar inverters installed prior to December 2019, major problems remain. Community batteries are a very convenient ‘soak’ to the excess power generated by rooftop solar therefore assisting in the reduction of ‘infeed’ and substation reverse power flow.
Community batteries can be network owned, community or third party owned. If a battery is owned by a network provider, it cannot function commercially other than by reducing network charges. Community batteries and third party owned batteries can be used for energy market operations including frequency control ancillary services (FCAS).
Community batteries can also function in energy arbitrage but given their often very small capacities, typically under 300 kilowatt-hour, financial benefits for communities have to be on other than strictly commercial terms, for example by reducing use of network charges. This can be an important concession as approximately half of a typical tariff is network charge. Given the pressure on upgrading distribution networks because of the steadily increasing rooftop solar penetration, there are good incentives for network owners to provide concessions on network charges.
Community batteries come in many sizes and depend on definition of ownership and application. A 5 megawatt.hr battery connected to an 11 kV or 22 kV feeder in a distribution network will be regarded differently to a 300-kilowatt-hour battery connected to the low voltage network. Both require sophisticated management systems for safe and efficient operation.
Batteries have been around for while in rural network applications, for example in Queensland single wire earth return (SWER) networks allowed consumers to avoid the cost of rewiring as solar systems were installed. Western Power in WA has been using 460 kW.hr batteries for low voltage networks. For most applications lithium batteries are used rather than flow technology.
A peek under the bonnet of domestic battery systems is useful. There are two basic versions—the ‘in line’ and the AC type. The former utilises generally smaller capacity, high voltage batteries that are connected between the solar panels and the inverter. The AC type connects at the grid side of the solar inverter. They are low voltage batteries, typically around 48 volts. Their advantage is that they can be fitted to virtually every solar installation. Unlike the in-line systems that only charge when the sun is out, they can charge other than by solar—for example, at night rates. The AC type will charge as well when there is excess solar power to the consumers energy needs.
Community batteries are of the AC type, charging up when there is excess energy available from neighbouring solar installations. But they can also charge directly from the distribution network in the same way as individual household batteries. They are charged and discharged by a ‘power converter’, which is a device that acts as an inverter, supplying AC power while discharging and as a battery charger at other times.
The power converter is likely to be three-phase whereas AC home batteries are single-phase units. Software measures the state of the charge of the battery and therefore provides control to the power converter. Community batteries are sometimes pole mounted, next to a transformer, servicing maybe 40 or so consumer connections, or are installed next to local substation.
The economics of community batteries are not as yet solidly established. They are becoming popular for socially acceptable purposes, for example, combatting carbon emissions. There is also opportunity for establishing new rules regarding their use as network providers are likely to be major beneficiaries of installation. The provision of rules regarding their various modes of employment ought to be addressed by the AEMC as soon as possible,clarifying their economic benefit for network augmentation and aggregated services such as FCAS, virtual power plants, etc.