System design and cost

Solar battery sizing for a quotation

Author: to be added

Published 10 Oct 2026

Size a solar battery by listing the loads that must run during an outage, estimating how many hours of backup the customer wants, converting that to energy, adjusting for usable depth of discharge and system losses, and checking the result against the inverter's battery voltage and charge limits before quoting.

Start with the load and backup hours

Battery sizing begins with what the customer wants to keep running when the grid is down. List each essential appliance with its power rating and the hours it will run, add them up, and agree the backup duration with the customer. Fans, lights, a refrigerator and a router are very different from an air conditioner or a water pump, so be explicit about what is on the backup circuit.

Convert to energy, then adjust

Multiply the backup power by the backup hours to get the energy the battery must deliver. Then adjust for the portion of the battery that can safely be used, which depends on chemistry and the manufacturer's guidance, and for losses in the inverter and wiring. The result is the battery capacity to quote.

Match the battery to the inverter

A battery bank must fit the inverter's battery voltage and charge-current limits. The hybrid inverter entry explains how these units manage the panels, the battery and the grid together. Check the maximum charge and discharge current against the bank you propose, and confirm the manufacturer approves the battery model.

Start from the hybrid solar bill of materials for grid-connected backup systems, or the off-grid bill of materials when there is no grid, and add the battery rows with make, model, count and warranty.

Keep catalogue data tidy

Battery makes and models change often. Keeping them in one catalogue means each quote pulls the same names and warranty terms; the brand and battery catalog feature is built for that.

Common mistakes

• Sizing from the nameplate

  Not all of a battery's rated capacity is usable. Account for depth of discharge.

• Ignoring surge loads

  Pumps and compressors draw more at start-up. Check the inverter can handle it.

• Mismatched voltage

  A bank that does not fit the inverter input will not work however big it is.

• Promising unlimited backup

  Backup time depends on load. State the assumption on the quote.

• No battery warranty terms

  Warranty conditions differ a lot. Write them into the quote.

What to check before you send

Confirm the load list with the customer, check the energy calculation once more, verify the battery fits the inverter limits against the datasheet, state the backup assumption in the quote, and make sure warranty terms for the battery are included.