Build your energy budget, size your battery bank, and plan your solar array with real-time calculations. Add appliances, see daily Wh, peak surge, and system losses — all in one dashboard.
Add each device that will run on your off-grid system
No appliances yet
Click "Add Appliance" to start building your load profile.
Use December/rainy season value for off-grid reliability
How many cloudy days should the battery cover?
12V (small) / 24V (medium) / 48V (large)
Daily Consumption
0
Monthly Consumption
0
Peak Running
0
WPeak Surge
0
W0
kWh usable capacity
≈ 0 Ah @ 24V
Sized for 2 days autonomy at 80% depth of discharge.
0
W minimum array size
0
× 400W panels
Assumes 75% system efficiency including wiring, conversion, and temperature losses.
0 W
Continuous
0 W
Surge (5s)
Includes 25% headroom for future loads and safe operation.
Off-grid solar design starts with your energy budget — the total watt-hours you consume per day. Every appliance contributes: watts × hours × quantity. Once you know your daily Wh, you can size the battery bank for autonomy, the solar array to recharge it, and the inverter to handle peak demand.
Watts measure power — how fast energy flows. Watt-hours measure energy — how much total work is done. A 100W device running 10 hours = 1000Wh.
Sum of (watts × hours × quantity) for every load. This is the foundation of all off-grid sizing.
Peak running load = sum of all simultaneous watts. Surge load = startup spike (2–7× running for motors). Inverter must handle both.
Battery kWh = Daily Wh × Autonomy Days ÷ (DoD × Efficiency). Lithium allows 80% DoD; lead-acid only 50%.
Array W = Daily Wh ÷ (Peak Sun Hours × System Efficiency). Always use worst-month PSH for year-round reliability.
Continuous rating = Peak running load × 1.25. Surge rating = Highest startup spike × 1.25. Pure sine wave for sensitive electronics.
Off-grid systems are less efficient than grid-tied installations because energy passes through more conversion stages. The calculator uses a 75% overall efficiency factor, which accounts for:
| Loss Source | Typical Range |
|---|---|
| Inverter conversion | 5–10% |
| Battery round-trip | 10–15% (lead) / 5–8% (lithium) |
| Wiring / cable | 2–5% |
| Charge controller | 5–15% (PWM) / 1–5% (MPPT) |
| Temperature derating | 10–20% (cold climates) |
For critical systems, reduce the efficiency factor to 70% or lower. For mild climates with lithium batteries and MPPT controllers, 80% may be achievable.
Common questions about off-grid solar sizing
Watts (W) measure instantaneous power — the rate at which an appliance uses electricity. Watt-hours (Wh) measure energy over time. A 60W bulb running 5 hours uses 300Wh (60 × 5).
Peak load determines minimum inverter size. Running a microwave, kettle, and heater simultaneously must stay within your inverter's continuous rating.
Surge is the brief spike when motors start — often 2–7× running watts. A 150W fridge might surge to 600W. Your inverter must handle this without shutting down.
Battery kWh = Daily Wh × Autonomy Days ÷ (DoD × Efficiency). Lithium allows 80% depth of discharge; lead-acid only 50%.
Inverter 5–10%, battery 5–15%, wiring 2–5%, charge controller 1–15%, and temperature 10–20%. Total system efficiency is typically 70–80%.
Off-grid must work year-round. December has the lowest peak sun hours. Sizing for annual average means your battery runs flat every winter.
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