FoxESS EQ4800 battery

Divide the usable capacity by what your home is drawing. Most households sit around 0.3 to 0.8 kW overnight and spike to 3 to 6 kW in the evening with the oven, kettle and aircon. So a battery of this size covers an ordinary evening and overnight comfortably, and far less if you are running heavy loads. We size it against your actual bill rather than an average.

Only if backup is specified and wired. A battery on its own does not do it. You need an inverter with a backup output, the backup circuits wired to a separate sub-board, and on some products an extra gateway. Most homes end up backing up essential circuits — fridge, lights, internet, a few power points — rather than the whole house, because the oven and ducted aircon alone can exceed what any home battery delivers.

Nameplate is the energy in the cells. Usable is what the battery management system will let you take out. The usable figure is the honest one and it is what the federal discount is calculated on, so it is the number shown above.

The Cheaper Home Batteries Program is delivered as certificates your installer creates and takes off the invoice up front, so you do not claim anything yourself. It is worth about $265 per usable kilowatt hour at the current rate, and it tapers: the first 14 kWh gets the full rate, 14 to 28 kWh gets 60% of it, and 28 to 50 kWh gets 15%. The rate also steps down over time, so the figure on this page is today’s.

This is set by the wiring standard, not preference. Batteries cannot go in habitable rooms, ceiling or wall cavities, under stairs or on an escape route, and they need clearance from windows, doors and vents. A garage that is not used as living space, or an external wall out of the afternoon sun, is usually where they end up. We confirm the position on site before quoting.

Only up to a point. The discount pays the full rate on the first 14 kWh and only 60% on the next band, so the value per kilowatt hour drops as you go bigger. Past a certain size you are paying close to full price for storage you may only use a few times a year. The right size is the one that gets you through your own evening, not the largest one the rebate touches.