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Retrofit Battery Storage

There are approximately 1.2 million residential scale solar photovoltaic (PV) installations in Australia currently. The majority of these are grid tied PV systems, meaning that they can use power from the electricity network as necessary to supplement that generated by the PV system to meet the load requirements of the dwelling.  A grid tied solar inverter supplies power from the PV panels to the home and injects any excess power into the electricity network. It also shuts down the PV system in the case of a network outage. This is a safety feature to ensure that no power is exported to the grid during a blackout, potentially endangering the lives of people in the vicinity of downed power lines for example or those trying to restore the network to operation. However, it also means that the residential PV system is unable to supply any power to the home during a grid outage.

Adding battery storage to an existing PV system is considered a retrofit installation. Generally, the most cost effective and least time consuming means of achieving this is by using an AC coupled configuration. This involves installing an inverter-charger in between the existing solar inverter and the main switchboard (MSB). The electricity network then interfaces with the inverter-charger rather than the solar inverter. The inverter-charger is wired to a battery bank and charges the bank with any excess power generated by the PV system rather than injecting it into the grid. Depending on the choice of components used, additional features such as charging the battery bank from the grid and supplying power to the home during a blackout (uninterruptable/emergency power supply) can also be incorporated. With the addition of storage, the PV system becomes a hybrid system. It can be programmed to maximise self-consumption of the solar power generated on site or maximise electricity cost savings (tariff optimisation) among other things.

Evade network restrictions

Network operators impose limits on how much PV capacity can be installed at a site without the need for undergoing lengthy and costly approval processes. In cases where there is an extant PV system at a site but more solar power is desirable, battery storage provides a means of getting around network restrictions on adding capacity.

The additional capacity can be wired up to be completely separate from the grid, supplying power to dedicated load circuits on site. The battery bank can be sized up to meet the energy and power requirements of the loads. There is also the extra benefit that these loads will keep running even if there is a grid outage. Connecting only essential loads (which excludes power hungry appliances like washing machines, dryers, electric ovens and dishwashers) means that the battery bank can be relatively small and in conjunction with an appropriately sized PV system, virtually ensures an electricity supply for extended grid outage events.

The battery storage can even be done away with in certain cases, where the loads are non essential. A perfect example of this would be a pool pump.

dedicated-load_PV_system

 

Many households in Australia include swimming pools. Swimming pool pumps draw large amounts of power to provide the filtration required to keep pools hygienic. This can add considerably to the electricity bill. Running the pool pump only while the sun shines using an off-grid PV system can provide a very attractive savings on investment.

Swimming pool pump schematic without solar and battery storage

 

SSS has years of experience in the design and installation of stand-alone power systems utilising battery storage. With the ever increasing interest in battery storage for grid tied PV systems, we are now utilising that expertise to cater to retrofitting existing PV systems with battery storage. This is a market where the Tesla Powerwall will play an insignificant role in the near to medium term.

 

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