Solar battery installation, and what it will actually run

Decide the job: backup, self-consumption, or rate arbitrage

Backup sizing is driven by how long you need to run a small number of critical circuits. Self-consumption sizing is driven by how much production you currently export and later re-buy. Rate arbitrage is driven by the gap between your peak and off-peak prices. The same battery capacity serves these very differently.

Watch for: A quote that promises all three without stating which one the design is optimised for. A battery reserved almost entirely for outage backup is not available to shave your evening peak, and a battery cycled hard every day is not full when the storm arrives. Ask what reserve percentage the system will hold and who controls that setting.

Choosing the backup circuits and the subpanel

Most installations feed a dedicated backup subpanel. Selected circuits — refrigerator, some lighting, internet, well or sump pump, a couple of outlets, sometimes the furnace fan — get moved onto it. Everything else goes dark in an outage regardless of how much energy is in the battery.

Watch for: The circuit list being decided on installation day. Walk the panel with the installer beforehand and name each circuit. Large loads such as electric ranges, resistance water heaters, well pumps with hard starts and central air are the ones that get quietly left off, and they are usually the ones people assumed were included.

Inverter architecture and whether your existing system can take a battery

Storage needs either a hybrid inverter that handles panels and battery together, or an AC-coupled battery with its own inverter working alongside your existing one. Retrofits to an older array frequently land on AC coupling because replacing a working string inverter is wasteful.

Watch for: An assumption that your current inverter is battery-ready. Many are not, and finding out after deposit turns a straightforward retrofit into an inverter replacement. Ask for the specific make and model of your existing inverter to be checked against the proposed battery before anything is ordered.

Siting, temperature and clearances

Batteries are heavy, need structural support, and have manufacturer requirements for ambient temperature, ventilation and clearance from doors, windows and living space. Garages, utility rooms and shaded exterior walls are the common locations, and local fire code has a say in all of them.

Watch for: An unconditioned garage in a climate with severe summers or winters. Sustained heat shortens battery life and extreme cold reduces available capacity when you are most likely to need it. Ask what the manufacturer specifies for operating temperature and whether the proposed location stays inside that range year-round.

Permitting, inspection and utility notification

Storage adds its own permit scope on top of any solar permit — electrical, sometimes structural, and in many jurisdictions a fire-department review of location and clearances. Your utility also needs to know that storage has been added to the interconnection.

Watch for: Storage being added to an existing system without re-notifying the utility. Undisclosed changes to an interconnected system can put you in breach of your interconnection agreement, which is a genuinely awkward position to be in if you later need a claim honoured.

Commissioning, transfer testing and control settings

Commissioning includes deliberately dropping the grid connection to confirm the transfer works, that the backed-up circuits energise, and that the system islands safely. The control app is configured for the mode you chose, with a reserve level set aside for outages.

Watch for: No witnessed outage test at handover. If nobody has actually cut the supply and watched the house transfer, nobody knows it works. Insist on seeing it, and note how long the changeover takes — brief interruptions matter for computers and some medical equipment.

Monitoring and knowing what normal looks like

You should leave with app access showing charge state, what is charging the battery, what is discharging it, and how much you are still importing. Storage failures are usually silent — a battery that has quietly stopped cycling looks identical from the driveway to one that is working.

Watch for: Not learning your own baseline in the first month. Note what state of charge you normally reach on a clear day and how far you draw down overnight. Without that, a degrading pack or a failed communications link can go unnoticed until an outage proves it.