Calculated Results
Calculator Inputs
Formula Used
1) Resolve device watts
If you enter power, that value is used. Otherwise: Watts = Current (A) × Device Voltage (V)
2) Daily energy demand
Wh/day = Watts × Hours/Day × Quantity
3) Overall performance factor
Factor = Inverter × Controller × Battery × (1 − MiscLoss) × Derate
Each efficiency is entered as a percent and converted to a decimal.
4) Required solar array wattage
Array W = (Wh/day) ÷ (PeakSunHours × Factor)
How to Use This Calculator
- Enter your device power in watts, or enter current with device voltage.
- Set quantity and daily run time based on typical garden schedules.
- Provide peak sun hours for your season and location.
- Adjust efficiencies and derating to match real-world conditions.
- Click calculate, then export results as CSV or PDF.
Example Data Table
| Scenario | Device Watts | Hours/Day | PSH | Factor | Estimated Array (W) | Panels @ 100W |
|---|---|---|---|---|---|---|
| Irrigation pump, small bed | 120 | 2.0 | 5.0 | 0.65 | 74 | 1 |
| Pond aerator, daily | 60 | 8.0 | 4.5 | 0.62 | 172 | 2 |
| Grow lights, short cycle | 200 | 3.0 | 4.0 | 0.58 | 259 | 3 |
Daily energy demand ties directly to watering schedules
Garden solar sizing starts with watt-hours per day. A 120 W pump running 2 hours uses 240 Wh/day. Two identical pumps double the energy. Short bursts can look small, but frequent cycles add up, especially when drip zones run sequentially. For pumps, include startup surges by adding a 10% safety margin to the wattage.
Peak sun hours drive realistic array output
Peak sun hours translate sunlight into usable charging time. Many regions see 3–4 PSH in winter and 5–7 PSH in summer. Using a conservative PSH helps prevent undersizing during cloudy weeks. If you irrigate most in hot months, you can also compare seasonal PSH scenarios. When panels face east or west, reduce PSH by about 10–20% to reflect lower midday intensity.
Losses and derating can change wattage by 30–50%
Real systems rarely deliver nameplate output. Panel temperature, dust, wiring, and conversion losses reduce production. A practical derate range is 75–85%. Add wiring and connector losses of 3–8%, then apply controller and inverter efficiency. These adjustments often push a “200 W” need closer to 300 W.
Panel count and area planning help with garden layouts
Once array watts are known, select a panel rating to estimate how many modules fit your space. A small off-grid garden setup might use 100–200 W panels, while larger irrigation or greenhouse loads can use 300–450 W modules. As a rough check, 200 W per square meter provides a quick footprint estimate for ground mounts or shed roofs.
Battery sizing adds resilience for early mornings and cloudy days
If you run loads at dawn, dusk, or during intermittent shade, batteries smooth operation. The calculator estimates amp-hours from autonomy days and depth of discharge. For example, 240 Wh/day at 12 V is 20 Ah/day before losses. With one autonomy day and 50% discharge limit, recommended capacity roughly doubles to protect battery life and maintain consistent watering. Size up further for winter shade.
FAQs
1) What are peak sun hours and why do they matter?
Peak sun hours represent equivalent full-sun hours per day. They convert sunlight into charging time, so array wattage increases when PSH is low or seasonal.
2) Should I enter device watts or current?
Either works. Use watts if you have a label. If you only know current, enter current and device voltage; the calculator resolves watts as A × V.
3) Why does the required array look higher than my load wattage?
Solar must cover daily energy plus real-world losses. Inverter, controller, battery inefficiency, wiring loss, and panel derating can raise the required array by 30% or more.
4) Do I need a battery for garden systems?
Not always. Direct solar can work for daytime loads. Batteries help when you need early-morning watering, stable pump pressure, or consistent runtime during passing clouds.
5) How do I pick a system voltage?
12 V is common for small loads. 24 V or 48 V reduces current, which can cut cable losses and improve performance for longer wire runs or higher power devices.
6) Are the panel area and current estimates exact?
They are planning estimates. Panel area depends on panel efficiency and size. Current depends on real operating voltage. Use these numbers to compare options, then confirm with equipment datasheets.