A battery sized from summer exports may spend winter partly empty. Winter planning needs both sides of the energy balance: what the home consumes and what the solar system can supply after daytime demand.
Recharge time depends on the energy being replaced and the charging power actually available. A charger rating or PV array nameplate is an upper limit, not a promise of constant charging throughout the day.
Small essential-load systems often focus on refrigeration, communications and a few lights. A compact battery can serve these loads well when energy use, compressor starting and the intended outage duration are known.
Air conditioning can be included in a home battery design, but its electrical demand must be measured or obtained from the equipment documentation. Cooling capacity is not the same as electrical input power.
Customers sometimes add battery capacity after an appliance trips the inverter, then find the problem unchanged. The limiting component may be inverter output, a battery current setting or a short starting surge rather than stored energy.
A backup reserve keeps some stored energy available for an unexpected outage. It also reduces the energy available for daily solar shifting. The best setting depends on outage exposure and the loads that need protection.
Overnight consumption is a useful starting point for solar self-consumption sizing. The most helpful data separates daytime demand, solar exports and consumption after sunset rather than reporting only a daily total.
An essential-load list makes a battery recommendation much more accurate than a monthly electricity bill alone. Begin with the circuits that must continue during an outage, then record their power and operating time.
Two quotations labelled 20 kWh may describe different amounts of energy available to the customer. Establish whether each figure is nominal DC energy, permitted battery discharge energy or energy measured at the AC output.
A 10 kWh battery can store enough energy for an evening and still be unable to start every appliance in the house. Energy capacity and power output answer different questions. Read both before comparing quotations.