System calculator
Work out battery runtime, solar charging and the size of a complete system from your own numbers.
Battery runtime
How long a battery bank runs your load, and the bank you need for a target time.
Efficiency and other assumptions
How far the battery may be discharged.
Results
- Backup time
- 17.0 hr
- At 1,000 W
- Battery for your target time
- 283.1 Ah
- 14.5 kWh for 12.0 hours
- Stored energy
- 20.5 kWh
- 400 Ah, LiFePO4 at 51.2V
- Usable at this load
- 17.0 kWh
- 90% usable, 92% inverter efficiency
Backup time 17.0 hr. Battery for your target time 283.1 amp-hours.
Shows 48V batteries in the catalog.
Solar charging
The charge current your solar array gives a battery bank, and how long a recharge takes.
Efficiency and other assumptions
Share of rated output you expect after heat, dust and wiring losses.
Results
- Charge current
- 44.5 A
- 2,400 W into LiFePO4 at 51.2V
- Recharge time in full sun
- 7.3 hr
- 320.0 Ah to replace (80% of the bank)
- Energy from solar per day
- 9.9 kWh
- 1.6 sunny days to reach the target
- Usual charge current for this battery
- 120.0 A
- Below the ideal rate for LiFePO4 (about 0.3C). Gentle, but slower.
- Charge rate
- 0.11C
- Charge current divided by capacity.
Charge current 44.5 amps. Recharge time 7.3 hr.
Shows solar charge controllers in the catalog.
Off-grid system
The battery bank, solar array, charge controller and inverter for a daily load with no grid.
The highest draw when motors start.
Efficiency and other assumptions
Results
- Battery bank
- 23.2 kWh
- 452.9 Ah, LiFePO4 at 51.2V, for 16.0 hours of use
- Solar array
- 2.4 kW
- 5 panels of 550 W
- Inverter
- 2.5 kW
- Covers the running load and the starting surge.
- Charge controller
- 58.5 A
- Includes 25% headroom.
- Energy used per day
- 9.6 kWh
- 1,200 W for 8.0 hours
Battery bank 23.2 kWh. Solar array 2.4 kW. Inverter 2.5 kW.
Shows 48V inverter chargers in the catalog.
Grid-tied with backup
The solar array to offset your electricity use, and a battery to keep critical loads on in an outage.
Efficiency and other assumptions
Results
- Solar array
- 11.4 kW
- 21 panels of 550 W
- Backup battery
- 18.1 kWh
- 353.8 Ah, LiFePO4 at 51.2V, for 15.0 kWh of outage use
- Hybrid inverter
- 9.7 kW
- For 1,500 W of critical load and the array.
- Solar production
- 1,530 kWh a month
- 18,360 kWh a year, before shade and snow
- Estimated savings
- $245 a month
- At $0.16 per kWh, 85% covered by solar
Solar array 11.4 kW. Backup battery 18.1 kWh.
Shows hybrid inverters in the catalog.
How we calculate
Battery runtime
Lithium: capacity (Ah) × voltage × usable share × inverter efficiency ÷ load (W). LiFePO4 banks use their nominal voltage (12.8 V, 25.6 V or 51.2 V). Lead-acid runtime is corrected for discharge current (Peukert, exponent 1.25 at the 20-hour rate) and defaults to 50% usable capacity.
Solar charging
Charge current = array (W) × controller efficiency ÷ bank voltage. Recharge time also allows for charge efficiency: about 99% for lithium and 95% for lead-acid. Lead-acid needs extra time to finish the last part of a charge.
Off-grid system
Array = daily load ÷ (sun hours × solar losses allowance × inverter efficiency × charge efficiency). The inverter covers 125% of the running load or the starting surge, whichever is higher. The charge controller has 25% headroom.
Grid-tied with backup
Array = monthly use × share covered ÷ 30.4 days ÷ (sun hours × solar losses allowance). Savings use the electricity price you enter.
Before you buy
These are estimates. Shade, tilt, temperature, wiring and local rules change the result. Call us to check a design before you order.