Section 6: Planning your solar battery system

What size battery do I need?

Choosing the right battery size for your needs will mostly depend on the size of your solar electricity system, how much energy you typically consume overnight and whether you want backup during a power outage.

To save the most on electricity bills it is generally best to buy a battery that you will regularly charge and discharge to the recommended level. You want to be able to store any excess solar electricity generated each day and ensure that the majority of that stored energy is used later on.

At the same time, it is wise not to overuse a battery, for example by fully charging and discharging two or three times a day. Doing this might shorten its lifespan.

You can usually set this up in an Energy Management System or similar app that helps to optimise the system.

You should also consider any changes you might want to make further down the track, such as switching from gas hot water to electric heat pump, for example, or adding more PV panels in the future to cover the needs of a growing family.

The best way to choose the right battery for your needs and budget is to get an independent assessment from an energy expert or accredited installer or supplier. Renew’s advice services can help with determining system size and the payback time.

Planning upgrades or system expansion

Some battery systems are modular, allowing you the option to increase your system’s capacity later, for example, when your energy use increases or when funds become available. This is typically harder in a DC-coupled arrangement. The ability of your existing battery to be upgraded needs to be confirmed with your installer prior to purchase.

Designing a system that provides backup during a power outage

A home battery system can be designed to provide backup during a power outage, however, not all storage systems are designed to provide energy when the grid is down, and this may depend on the storage system, the system design and inverter used.

Your installer will be able to provide you with more guidance; just make it clear what your requirements are when looking for a system. See Will adding a battery ensure I have power during a power outage?

A pre-approval from your Distribution Network Service Provider is an eligibility requirement for a battery rebate to ensure that the battery can be safely connected to the network.

Unfortunately, not every household may be able to receive a pre-approval for various reasons; including the strength of the local grid. It is also possible connections approval provided by the DNSP are subject to export constraints. The Victorian Distribution Code regulates the distribution and connection of electricity to customers, and safety of community is a key priority.

Planning a system that is Virtual Power Plant ready

All batteries on Solar Victoria’s products list are aggregation and VPP ready and comply to Australian Energy Market Operator’s (AEMO) minimum specifications. This is to enable your household to participate in Virtual Power Plant Trials, where many households are linked via cloud-based systems to work like a small power station.

Benefits of participating in aggregation projects or a VPP program

• receive compensation for sharing your stored solar energy with the VPP network
• make the most of the solar power you generate
• balance the supply and demand of energy for fewer disruptions
• reduce network costs for all Victorians
• increase grid resilience
• enable greater uptake of Distributed Energy Resources (DER)

Most aggregation and VPP programs have specific product requirements, so you will need to review these to ensure the system you are installing is capable of participating in the VPP you want to participate in.

Your system needs certain features to be aggregation and VPP-ready, including:

1. Being able to respond to remote requests to charge/discharge the battery

Examples include requests to charge the battery at peak solar PV generation time. During periods of high solar generation and low electricity demand (e.g. sunny, mild afternoons in summer, autumn and spring), neighbourhoods with high numbers of rooftop solar systems will export significant amounts of solar electricity to the grid and may push network voltage above acceptable levels.

Delaying the charging of any household batteries until around midday, so that they charge for most of the afternoon, will reduce exports to the grid and help alleviate high voltage issues for the network.

2. Being able to communicate state of charge and voltage

This functionality is important for communicating to the AEMO regarding battery charge level to assist with energy forecasting. AEMO is constantly planning to ensure all system generation can meet the required demand from homes and businesses, particularly on very hot days in Victoria.

Having visibility of how much stored electricity is available from household batteries, prior to peak demand events, can be very helpful for managing the overall electricity system.

3. Being able to assist network security and reliability

This includes advanced settings to support system security in the event of unscheduled outages in the grid. This means that the system can stay connected when the grid voltage is below specification, to prevent a complete outage. Your retailer should be aware of these VPP system features, and they are essential to receive the rebate.

Siting considerations

Most home batteries can be installed outdoors, however, their lifespans will be improved by a stable, cool temperature, so try not to locate them in direct sun or in an uninsulated, unshaded metal shed.

It’s also important to make sure that any enclosure is vermin-proofed, cannot be accessed by children and displays appropriate signs relating to safety, warnings and shutdown procedures.

Installation and safety considerations

1. Like most electrical equipment, batteries are generally safe if they are installed correctly.
2. Make sure there is appropriate space around the battery unit and position the battery away from any potential hazards.
3. It’s important not to store heavy household equipment on top of a battery and keep the area clear of obstacles.
4. Note that batteries cannot be installed in domestic habitable rooms in Australia as required by regulatory safety standards, including Australian Standard AS/NZ 5139 2019.
5. Don’t put flammable objects or those that could conduct electricity in or on the battery enclosure.
6. Make sure the battery is maintained according to the guidelines given by your installer.
7. The safety risks associated with actual cell chemistries differ depending on the chemistry. Discuss any potential risks with your installer so they can be mitigated.
8. Your CEC-accredited installer will be aware of these installation standards. These guidelines are discussed further in Section 7 Finding the right retailer.

Insurance

Solar panels and batteries are high value items so include them in your home insurance policy and check any insurance clauses and requirements for solar battery related issues prior to installation.