How rooftop solar and battery storage actually works

For those not so technically minded, this is a guide to solar plus storage.
The output of a solar PV systems (solar panels plus inverter) produce power proportional to the solar energy coming from the sun. This energy is instantly converted into electricity that can be used in the home or business.
 
morris zeroAs appliances use power the solar power system contributes to their demand. If the solar system produces more than the appliances need then the surplus is exported to the utility grid – if you’re lucky – for some financial reward but for most solar customers – next to nothing!
This means that unless you use your solar energy as it is produced you “give it away” to the grid.
morris 1By adding somewhere to put this surplus energy (batteries) the excess production can be stored till it is needed (usually at night or when there is little solar input). The inverter can manage the flow of power to ensure that you maximise the use of your free solar energy and not wastefully “gift” it to the grid.
That was the simple explanation: in reality there are many products with different features that can be used to store and release energy.
Here are some scenarios.
morris 2
Scenario one: maximise self use of solar energy. This configuration requires a device installed in your main switchboard to monitor the energy flow to and from your home. The inverter can then decide if there is surplus solar energy being produced (relative to your use) and send the surplus to the batteries. Once the batteries are fully charged then the surplus energy is either exported to the grid or simply not produced.
Scenario two: optimise the price of electricity. By placing the inverter with batteries inbetween the connection to the grid and the circuits that supply power to the home, the inverter can make decisions about what is the cheapest source of electricity.
morris 3Typically this would be to use solar power first, store surplus, use stored energy at night, and if there are cheap off-peak grid tariffs – partially charge batteries at off-peak time. Some systems have weather forecasting connected to the inverter smarts and decide the night before whether to charge batteries from cheap night rate power or to charge from the sun the following day.
There are many more configurations but the important question is to know what you want the solar + storage system to do and communicate that with your design/installer.
Glen Morris is the Vice President of the Australian Solar Council, has been running his renewable energy solutions company, SolarQuip, for ten years, a member of Standards Australia committee that helps write the renewable energy standards, runs renewable energy training for hybrid and off-grid at his training facility near Melbourne and lives with his partner and two children on one of Australia’s oldest off-grid communities.

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