| Load | Watts | Hours/day | Qty | Wh/day |
|---|---|---|---|---|
| Irrigation pump | 250 | 1 | 1 | 250 |
| Grow lights | 120 | 4 | 1 | 480 |
| Controller & sensors | 8 | 24 | 1 | 192 |
| Watering timer | 2 | 24 | 1 | 48 |
| Total | 970 | |||
- Choose total Wh/day or an appliance list.
- Set autonomy days for cloudy spells.
- Pick system voltage and battery type.
- Enter inverter efficiency for AC loads.
- Set lowest temperature and loss per °C.
- Add a margin for aging and growth.
- Press Calculate, then export CSV or PDF.
Guide
Daily load profiling for garden systems
Accurate battery sizing starts with daily watt-hours. List irrigation pumps, pond aerators, grow lights, controllers, and charging ports, then multiply watts × hours × quantity. Many gardens have short high-power pump runs plus long low-power controls. Appliance mode helps reveal the real average. If your total is 1,200 Wh/day and you later add a 60 W light for 5 hours, your load rises by 300 Wh/day, increasing storage needs immediately.
Autonomy and seasonal reliability
Autonomy is the number of days the battery must carry the garden without meaningful charging. Two days is common for small systems; three to five days suits shade-prone yards or monsoon periods. Storage scales nearly linearly: doubling autonomy roughly doubles required nominal energy. Use the calculator to compare scenarios: 1,000 Wh/day at 1 day is very different from 1,000 Wh/day at 3 days, especially when paired with efficiency and temperature adjustments.
Depth of discharge and battery chemistry
Depth of discharge (DoD) controls how much of the battery you plan to use. Lead-acid banks are often designed around ~50% DoD for cycle life, while many lithium systems are sized around ~80% DoD. A higher DoD lowers the required nominal bank size, but repeated deep cycling can shorten lifespan for some chemistries. The preset button quickly applies typical values, and you can override it for manufacturer guidance.
Temperature, losses, and design margin
Cold weather reduces available capacity, so the calculator applies a temperature factor based on your lowest battery temperature. For example, a 10°C minimum with a 0.005 loss/°C implies a 7.5% reduction from 25°C. Inverter efficiency accounts for conversion losses feeding AC loads. Finally, an aging/design margin (often 10–25%) adds buffer for battery wear, wiring voltage drop, and garden expansion like extra drip zones or longer lighting schedules.
Interpreting series and parallel recommendations
After computing required amp-hours at the chosen system voltage, the tool suggests a practical bank layout from your battery unit voltage and Ah rating. Series batteries raise voltage; parallel strings raise capacity. Keeping parallel strings modest improves current sharing and simplifies fusing and balancing. If the parallel-string count exceeds your limit, consider higher-Ah batteries, a higher system voltage, or reducing autonomy after confirming solar array capacity.
FAQs
1) Should I use total Wh/day or the appliance list?
Use the appliance list when loads vary by device and schedule. It reduces guesswork and highlights which items dominate energy use, especially pumps and grow lighting.
2) What autonomy is reasonable for irrigation-only setups?
Many irrigation-only gardens work well with 1–2 days if solar charging is consistent. Choose higher autonomy when shading, cloudy seasons, or critical watering windows are common.
3) Why does inverter efficiency change the result?
If your loads run through an inverter, the battery must supply extra energy lost as heat. Lower efficiency increases required usable Wh and therefore the nominal battery size.
4) How does battery temperature affect sizing?
Capacity drops in cold conditions, so the temperature factor increases the nominal bank requirement to maintain the same usable energy when your batteries are cool.
5) What does “required Ah” mean for a 24V system?
It is the amp-hour capacity at the selected system voltage. At higher voltage, the same energy needs fewer amp-hours, which can reduce parallel strings and cable size.
6) When should I increase the aging/design margin?
Increase it for older batteries, long cable runs, frequent deep cycles, or planned expansion. A conservative margin can prevent nuisance shutdowns during peak watering or lighting periods.