Going off-grid can be a tempting proposition. For some, it’s the thought of completely cutting out the electricity companies and never receiving another bill. For others, its the planet-friendly idea of reducing your household carbon footprint to practically nothing.
With energy-dense lithium-ion battery storage and smart energy management, going off-grid could be up to 80% cheaper than previous estimates based on older systems predicted. At these levels, off-grid solar and battery storage is close to competitive with diesel generation over the whole system lifetime.
The first step in setting up an off-grid renewables system is to minimise your electricity use. This is important for all home renewables systems, but if you’re off the grid it’s vital.
To reduce the electricity you need and therefore the size and capital cost of any renewable energy systems for electricity, tasks such as water and space heating can be done by using dedicated renewables such as biomass boilers, ground and air source heat pumps or solar water heating. Surplus wind and PV electricity can be used to complement these systems once appliance demand is met and your batteries are full.
While many Australian buildings use solar-plus-storage to produce most of their own electricity, the majority of them still maintain a grid connection. There are two key benefits – income from feeding excess electricity back into the grid and continued power when the sun doesn’t shine.
When going off-grid, it’s not enough to just have enough solar and battery storage to meet your household’s daily energy needs. Without grid backup, prolonged rainy periods and winter weather could leave your building in the lurch. If your household has a daily energy consumption of 10 kWh (quite low for a modern family home!), you would need around 30-40 kWh of energy storage to be safe off-grid.
Consider also the size of PV system that your property can support. While more expensive upfront, larger solar panel arrays keep your batteries topped up and ready to provide power. If you have limited roof space, outbuildings and sheds can be used to mount additional panels.
Electricity from the batteries can be used directly to run low-voltage lighting and perhaps other direct-current (DC) appliances. However, most systems include an inverter to produce mains voltage alternating current (AC), which can be used to run standard appliances.
The inverter may act as a battery charger, as well as looking after the batteries and controlling the system, or you may have several separate boxes for these different functions.
Some places are just easier to be grid independent than others. Darwin naturally gets more hours of sunshine than Melbourne, and mounting your solar panels on a large open north-facing roof will produce far more juice than tree-crowded southern-facing property.
If you get a lot of sunshine and consume most of your electricity during the day, you won’t need as much storage capacity to go off-grid. Another factor to consider is seasonal variation. Some cities, such as Brisbane, have very similar levels of sunshine hours in both winter and summer. In comparison, Adelaide has over 50% less sunshine in winter. In the first case, your solar and storage system would be suitable year-round – in the second, the system would need to have extra capacity for the winter that would not be used in summer.