The most common question we are asked about home storage is which size to buy. It is the wrong first question. The size falls out of two other answers, and getting those clear first is the difference between a system that pays for itself and one that does not.
First: which problem are you solving?
Two goals get confused constantly, and they lead to very different systems.
Solar self-consumption. You generate more during the day than you use, and you want that surplus in the evening instead of exporting it. The battery is sized against your daytime surplus and your evening consumption. It cycles every day, so cycle life matters enormously.
Backup supply. You want essential circuits to keep running through an outage. The battery is sized against what you consider essential and how long an outage you want to ride out. It may sit at full charge for months and cycle rarely.
A system built for one is usually poor value for the other. Say which one you are solving for — or that you want both, which is legitimate but changes the sizing.
Second: what is the actual load?
An electricity bill gives monthly kWh, which is a start but not enough. For backup, what matters is a short list: which circuits, drawing roughly what, for how many hours.
Two things are worth checking specifically:
- Air conditioning. It dominates any household load it appears in. A system that will run air conditioning through an outage is a different class of system, and cost, from one that runs lights, fans, fridge, router and phone charging.
- Motor start-up. Fridges, pumps and compressors draw several times their running current for a moment at start. The inverter and the battery's BMS must both allow that surge, or the system will trip when the fridge cuts in.
The overspend we see most
Buying capacity for a scenario that has not been thought through — usually 'run everything for a long time' — and paying for a battery that spends its life at full charge. Storage is expensive per kWh. Being specific about what genuinely must stay on is the single biggest lever on the price.
What to send us
A recent electricity bill, a short list of what should stay running during an outage, whether you already have solar and its size, and whether air conditioning is on the list. We will come back with a capacity — and if storage is not the sensible spend for your situation, we will say so.
Send us the voltage, capacity, discharge current and the space you have — or a photo of the battery you are replacing. We will come back with a specification and a price.