The increasing number of solar panel installations in households around Australia is providing a new market opportunity for energy storage. Large batteries or multiple batteries joined together in battery banks can store the energy produced by solar panels. The household can then use that stored energy at a later time or sell it back to the electrical grid. For home owners, there are three main benefits of storing energy:

• maximise energy savings (by being able to store solar energy and thus use it more effectively)
• offset consumer feed-in tariffs (by being able to avoid using the grid at peak times when electricity is more expensive)
• provide continuity of supply (if the site has unreliable grid supply).

Battery storage is perfectly safe if it is used properly and is well looked after. There are potential risks, but these are no different to the many electrical hazards already present in the modern home. However, it is important to be aware of the risks so they can be properly managed.

Safety aspects of battery storage to consider include:

• general hazards of electrical wiring (as are already present in your premises)
• chemical and fire or explosion hazards (these are similar to the hazards associated with bottled gas or a natural gas service)
• possible escape of non-flammable gases when charging or discharging lithium batteries (which may cause risks of inhaling noxious gas that are similar to those of a natural gas leak if there is no ventilation)
• production of chemical leakages (like those from the corrosive fluid of a car battery or household chemical cleaning products).

The main options currently available for household energy storage are lithium-ion and lead-acid batteries. Both types are described in the question ‘Which type of battery is right for me?’.

Other less common options include nickel-cadmium, nickel-metal hydride and flow batteries. The latter may be more costly, but can still offer value, depending on how much energy you want to store and how you want to store it. The best battery storage for a given situation will depend on a number of factors. To work out which option is right for you, it is best to work with an CEC approved solar retailer and accredited installer.

Installing battery storage in your home does not necessarily mean that you can disconnect completely from the electricity grid. Generally speaking, going off-grid is not practical for the average urban consumer because:

• it might be difficult to store enough energy to reliably cover your use during cloudy days in winter and at night
• you would not be able to sell any surplus energy back to the grid
• there are likely to be significant extra costs, for example, you may need special additional equipment like the installation of an air-conditioning system for the battery enclosure.

Battery storage uses a chemical process to store electrical energy (for example, the electrons generated from solar panels), which can then be used at a later time.

When the energy is required, an electrochemical reaction releases the flow of electrons to be used as electricity.

Different battery types (e.g. lead-acid and lithium batteries) store and release electrons in different ways. Hence, the various types of batteries need specific kinds of treatment to ensure they work properly in a household or commercial situation.

A battery has three basic components, as shown in the figure below:

• anode (negatively charged electrode)
• cathode (positively charged electrode)
• electrolyte (the medium through which ions move).

Wires and devices (loads like lighting) external to the battery completes a circuit, allowing the electrons to flow from the anode to the cathode, providing electricity as the battery discharges. When the battery is charging, the electrons flow in the reverse direction. Once the anode and cathode have returned to their original state, the battery is fully charged.

As shown in the figure below, the power that comes from a grid power station and is available at your household power point is called alternating current (AC). Batteries and solar panels produce direct current (DC).

In a typical household system of solar panels and batteries, your solar array will produce DC power. This DC power is then converted to AC by the solar inverter, to make it compatible with the AC mains power coming into your house from the grid.

A battery system also uses DC. The batteries are usually connected to the AC mains power in a similar way to that used for the solar panels. An inverter converts DC power from the batteries to AC power. This makes the system suitable for connection to the grid and allows the batteries to charge and discharge depending on your household usage.

The capacity of a battery is the total amount of charge that it can deliver, and it is expressed in the units of ampere-hours (Ah). The energy stored by a battery is defined by the charge it can deliver at a given voltage. A battery’s stored energy is the product of Ah and V (volts), which is equal to watt-hours (Wh). Typically, household energy demands are of the order of several thousand Wh; therefore, kilowatt-hour or kWh is the common unit of measurement.

The battery capacity quoted by the manufacturer is an ‘ideal’ number that is useful for comparing batteries. In reality, once installed in your home or commercial premises, the capacity will be somewhat less when the batteries are used. This is because, for the batteries to perform well over many years, they must not be completely discharged to an empty state. The management system that controls your battery storage system will prevent the batteries from being completely discharged. However, if your batteries are being charged from solar panels, they will supply less energy during times when solar generation is low, such as rainy days in winter.

Every household is different. In the same way that you match the number of solar panels to your household’s energy requirements, your battery storage capacity also needs to be matched to your needs.

Typically, residential battery storage systems range from 3 to 12 kilowatt-hours (kWh) in size. For small-scale commercial installations, the storage can be up to 200 kWh. The kWh size of your storage system will be influenced by:

• your budget
• where you live, your house orientation and type of house
• your average household energy consumption
• the time of day when household energy consumption occurs
• the size of your solar panel installation and the energy generated by those panels
• ambient weather conditions
• customer feed-in tariffs available to you
• how you intend to use your battery (i.e. to supplement your energy supply, or to allow you to become entirely self-sufficient).

An accredited NETCC approved seller and installer will be able to advise you on the most suitable size for your needs and local conditions.

Some batteries may produce gases that can be a fire hazard if allowed to build up. Batteries must therefore be installed in a well-ventilated space or enclosure away from the living areas of the house. Ideally, the battery enclosure should be located, for Australian conditions, on a south or east-facing side of the residential or commercial premises. Also, the enclosure should be purpose-built to ensure it has the right specifications for the battery size and weight, and for battery performance and safety. Battery performance is affected by temperature variations. The design of the enclosure should therefore take into account temperature stability through insulation or ventilation, or both. The enclosure:

• must be readily accessible for safety and emergency response should an incident occur, but only by authorised personnel such as emergency responders and accredited installers
• must not be accessible by children
• should be vermin-proofed
• should display appropriate signs relating to safety, warnings and shutdown procedure
• The top of the enclosure must not be used to store heavy items such as pot plants, garden tools or other household metallic equipment.

Different battery systems have different requirements. Most battery maintenance is not difficult or onerous and is very important for ensuring the best performance of your battery storage system. The maintenance should be performed by the accredited installer. In addition, it is a good idea to carry out visual checks at least once a month, to keep your system in top condition. If you notice something is not right, call your accredited installer.

Once your storage system is installed, the installer will provide you with basic information about how it operates. You will need to understand how to interpret critical system health information and recognise when your storage system needs attention. Your installer should provide you with a log sheet or table to record the system’s critical measurements.

When doing maintenance on the system, the accredited installer can provide you with feedback on the system’s performance and help you to understand your usage and the system’s limitations. If there is an internal failure in an individual battery cell, that cell can begin to perform poorly long before the system as a whole has a problem. Again, this is something that the accredited installer can identify during maintenance of the system.

The lifetime of a battery is strongly dependent on how the system is used. Poor or heavy usage may mean the product does not last as long as the manufacturer’s specifications. The lifetime also depends on ambient temperatures. All battery types should be checked during extreme hot or cold weather to see whether they are still performing as required. Batteries can be discharged over a large temperature range (-20°C to 60°C), but the charge temperature should be limited for best results.

Your electricity consumption may also change over time, which can alter the long-term performance and life of the battery system. Check with your installer when the maintenance is undertaken, in case your consumption has changed significantly (e.g. if more people are living at your property or you have purchased new appliances).