Battery Backup Calculator for Gardens

• Daily energy per load (Wh/day): Watts × Hours/Day × Quantity.
• Total daily energy (Wh/day): Sum of all load energies.
• Autonomy energy (Wh): Total daily energy × Autonomy days.
• Adjusted energy (Wh): Autonomy energy ÷ (Inverter eff × Battery eff) ÷ Temperature factor.
• Nominal bank energy (Wh): Adjusted energy ÷ Depth of discharge.
• Required bank (Ah): Nominal bank energy ÷ System voltage.
• Series batteries: ceil(System voltage ÷ Unit voltage).
• Parallel strings: ceil(Required Ah ÷ Unit Ah).
• Suggested inverter (W): max(Peak load × 1.25, Peak load × Surge factor).

1. Add each device you want to run during an outage.
2. Enter watts, daily hours, and quantity for each device.
3. Set autonomy days for your preferred backup duration.
4. Select the system voltage that matches your inverter plan.
5. Adjust efficiency, discharge depth, and temperature derate values.
6. Enter your battery unit voltage and capacity rating in Ah.
7. Press calculate to see capacity, wiring counts, and inverter size.
8. Use the download buttons to save results as files.

Load profiling for garden equipment

Start by listing every device that must run during an outage. Include pumps, timers, grow lights, fans, sensors, secure, and Wi-Fi gateways. Use nameplate watts or measured values, then enter realistic daily hours and quantity. The calculator totals peak watts and daily watt‑hours, giving a clear demand baseline for backup planning.

Autonomy and usable energy planning

Choose autonomy in days based on how long you expect limited charging, storms, or grid work. The tool multiplies daily energy by autonomy to get required watt‑hours. It then adjusts for inverter efficiency, battery efficiency, and temperature derating. This prevents undersizing when cold conditions reduce capacity or when conversion losses are significant. If you can recharge with solar, model shorter autonomy, but still size for cloudy days and prioritize critical circuits using separate switches or breakers to avoid overloads at night.

Depth of discharge and battery life tradeoffs

Depth of discharge controls how much of stored energy you regularly use. Higher discharge reduces the needed bank size but can shorten cycle life, especially for lead‑acid. For lithium, 70–90% is common, while lead‑acid often performs better near 50–60%. The calculator converts the adjusted energy into nominal bank energy using your chosen discharge limit.

Voltage, series strings, and wiring logic

Select 12, 24, or 48 volts to match inverter and cable distance. Higher voltage lowers current, reduces cable losses, and can simplify long runs in greenhouses. The calculator computes series batteries to meet system voltage, then parallel strings to reach required amp‑hours. It reports total batteries and the effective bank voltage used for sizing.

Inverter sizing, safety margin, and reliability

Motors and compressors can surge at startup, so inverter sizing must cover peaks. The tool applies a surge factor and a continuous margin to recommend an inverter rating. Use fuses, proper wire gauges, and ventilation for battery enclosures. Recheck loads seasonally, and keep a reserve to handle battery aging and unexpected run time needs.

1) What watt value should I enter for a pump?

Use the running wattage from the nameplate or a power meter. If only amps are known, multiply volts by amps for an estimate, then add a surge factor for startup.

2) Should I size for all loads or only essentials?

Start with essentials like watering, ventilation, and control electronics. Add noncritical loads later. Smaller banks cost less and recharge faster, while essential-only sizing improves reliability during extended outages.

3) Why does the calculator ask for efficiencies?

Energy is lost in conversion and charging. Including inverter and battery efficiency reduces the risk of undersizing, especially when run times are long or loads are near the inverter’s limits.

4) How do I choose depth of discharge?

Select a lower value for longer battery life. Lead-acid usually benefits from 50–60%, while many lithium systems can use 70–90% depending on the manufacturer’s guidance and temperature.

5) What does series and parallel mean in the results?

Series increases voltage by wiring batteries end-to-end. Parallel increases amp-hours by wiring strings side-by-side. The calculator reports both counts so you can plan a practical bank layout.

6) Can I use this for solar-charged garden systems?

Yes. Size the battery bank with your desired autonomy, then ensure your solar array and charge controller can replace daily watt-hours. Keep extra margin for cloudy periods and battery aging.