Sizing a battery for home storage

Start with the loads that must not stop

Before anyone talks about battery capacity, write down what has to keep running when the grid goes down. Walk the house room by room and list the loads by name: lighting in the rooms you actually use after dark, the refrigerator and freezer, the router and modem, phone chargers, a few power outlets for a laptop or a radio. Those are your critical loads.

Then write a second list: what can wait. The oven, the clothes dryer, the air conditioning, the workshop tools, the car charger if you have one. Most households find the second list is far longer than the first. That is the point of the exercise. A battery sized for everything is a battery sized for habits you can pause during an outage.

Finally, note how each critical load is used: always on, on in the evening, or on only when someone is home. That habit pattern, not a wattage, is what you take to a supplier.

Overnight shifting is a different brief from backup

Two goals get mixed up in home storage conversations, and they size very differently. The first is solar self-consumption: you charge from your own array through the day and draw from the battery in the evening, so you buy less from the grid. That battery works every day. It cycles shallowly and often, and it is sized around your evening habits against your daytime solar production.

The second is outage backup: the battery sits mostly full and is called on rarely, but when it is called on it may be asked to run deeper and longer. Sizing here is about how long the critical list must run, not about the evening routine.

A house optimized for daily shifting may be undersized for a long outage; a house optimized purely for backup may carry capacity that rarely gets used. Decide which brief leads before you discuss models. The supplier describes wall-mounted, stackable, floor-standing and all-in-one formats, and the right format follows from the brief.

Think in blocks, then map to formats

Rather than jumping to a number, plan in blocks: a small household block, a medium household block, a large household block. Each block is a planning device — a way to group your critical loads and your backup-hours ambition into a rough size class before you ever discuss capacity with a supplier. Think of it as small, medium or large, and let the supplier translate.

Once you know your block, map it to a format. Wall-mounted suits a compact block with limited floor space. Floor-standing suits a larger block where the equipment can sit in a utility area. All-in-one bundles the pieces into one unit for simpler installation. Stackable formats let you add modules over time; parallel formats let units work together. Both leave room to grow, so a growth plan can start at one block and expand later.

The questions to take to a supplier

Bring a short checklist to the conversation. First, your critical-load list, with the habit notes from earlier. Second, your backup-hours ambition in words: overnight only, a full evening and night, or longer. Third, whether you already have a solar array and how it is wired. Fourth, your inverter situation: existing, planned, or none yet. Fifth, the installation space: wall, floor, utility room, garage.

Ask the supplier to match those answers to a format and a block size, and to explain what happens if your needs grow. Ask for the test reports and certificate documents your market requires for the exact model before you order. Then look at the home storage range and send the inquiry form with your application and model details so the reply is specific to your house.