This domestic installation was designed to run as a grid minimisation installation. Although the grid remains connected it is rarely used.
This is an area with frequent power outages, often for many days so the ability to have power in an off-grid installation when the grid wasn’t available was a major requirement.
Sodium Nickel Chloride (SoNick) batteries were selected as they have the highest energy density of any batteries and are completely safe with no off-gassing or fire risk, meaning there are no safety issues with installing the batteries. As the SoNick batteries operate with no temperature effects and no degradation from -20°C to +60°C there are no issues with either heat or freezing temperatures that are often experienced and the batteries don’t require air conditioning to keep them cool or heaters to heat them enough for them to work.
Lithium-ion batteries weren’t considered due to the difficulty in recycling lithium batteries at end of life and to their inherent fire risk.
A 6.75 kW PV solar array was installed on a north facing roof. This is in 3 strings and goes into a Victron MPPT, then into a 5kVA Victron Multiplus-II inverter. A changeover switch was also installed so that if there were ever any issues with the battery system the house would then revert to mains power. A Victron Cerbo allows the whole system to be monitored remotely and any changes to the system can also be done remotely.
With the installation of the battery system came a change in how power was used to maximise the usage of the solar PV as it was produced. Instead of using appliances like washing machine and dishwasher overnight using off peak power all appliances are now used when the sun is shining if at all possible. Excess power is then put into the battery. As this system is running as an off-grid system no power is sent back to the grid for a feed in tariff. However, this is more than offset by not having to purchase electricity from the grid
Installation of the PV system reduced power purchased from the grid from an average of 85% in summer of previous year up to 50% in winter of previous year. It was realised that to become completely independent from the grid two batteries would be needed.
The house is a rural property and is completely electric so electricity usage is higher than it could be for a normal suburban house. Water pumps, electric fences and all electric cooking can use a lot of electricity. Although the hot water uses evacuated tubes to heat with solar, the booster is electric so a heat pump is being considered to further reduce electricity usage which would further support the battery system.
During a power outage that lasted for over a week the battery system enabled the house to keep running when surrounding properties were without power. Electricity was conserved with all non-essential items being switched off and even though the weather was not good the batteries were able to supply the house with essential power.
Another advantage of the battery system was the elimination of brownouts or power that goes off for a couple of seconds to a few minutes. This used to happen on a fairly frequent basis which can produce quite a lot of wear and tear on appliances. Theses brownouts no longer occur as the battery system takes over as soon as an interruption in power is detected.
Application – independent domestic power supply
System Objective – to provide grid minimisation installation capable of supplying off-grid backup supply during blackouts,
Commissioned – April, 2021
Installed PV – 6.75 kW
Battery storage – 19.2 kWh
If you would like to know more about getting safe, reliable, recyclable, SoNick (molten salt) battery storage for your own home, business or micro-grid application visit us at https://gridedge.com.au/