Backup power for clinics and small businesses: inverters, batteries and what to size

Most backup systems are bought in a hurry after a bad outage and sized by guesswork. Spending an hour on the load list first usually produces a smaller, cheaper and longer-lasting system.

Separate critical loads from the rest

Backing up an entire building is expensive. Backing up the loads that must not stop is not. For a clinic that typically means refrigeration for vaccines, lighting in treatment areas, monitors and the server; for a business it might mean point-of-sale, security and a few workstations.

Size the inverter to peak, the battery to duration

The inverter must handle the highest simultaneous demand, including motor starting surges from fridges and pumps. The battery bank is sized separately, from the energy those loads consume over the hours you need to cover.

• List each critical load in watts and hours per day
• Add the largest motor's starting surge to the peak figure
• Decide the required autonomy in hours
• Allow for battery depth of discharge and inverter efficiency
• Decide whether solar will recharge the bank during the day

Adding solar later

If solar is likely within a year or two, choose a hybrid inverter now. Retrofitting a solar array to a battery-only system usually means replacing the inverter.

Send us your critical load list and desired backup hours and we will specify the inverter, battery bank and, if wanted, the solar array.