Off Grid Solar Calculator (Daily Load kWh)
Instant off grid solar calculator for load roll-up: enter appliance watts × hours → daily kWh. This page sizes load only—not a full kit (array + battery + inverter) on one page.
Quick answer
Daily kWh ≈ Σ(Watts × Hours) ÷ 1000 (± contingency). Example: 800 W × 10 h + 200 W × 5 h → 9.0 kWh/day base. Cabin / RV: use Remote cabin or RV / van presets below (no separate scenario page). Next: solar panel calculator, then solar battery bank calculator. Hub: Solar Applications.
Quick Off Grid Load Calculator
Defaults: one continuous load 800 W × 10 h.
800 W × 10 h ÷ 1000.
Advanced Off Grid Load Calculator
Presets
Up to three appliance groups (name + W × h/day). Contingency margin adds spare.
Off Grid Load Results
Engineering disclaimer
Planning estimate only. Confirm nameplate watts, duty cycles, and startup surges on site before array or battery procurement.
Daily kWh by contingency
| Margin | kWh/day |
|---|
People also ask
- How do I calculate off-grid load? Sum watts × hours, divide by 1000.
- Next after daily kWh? Size the PV array, then autonomy days.
- Same as factory load? Similar roll-up, but off-grid duty cycles and no utility diversity.
Planning guidance
Daily kWh drives array and battery screens. Keep running energy separate from surge watts for inverter peaks.
- Array next: Feed daily kWh into the solar panel sizing calculator. Method: how to size a commercial solar array.
- Autonomy: Size storage with the Solar Battery Bank Calculator—not UPS runtime tools.
- PSH: Confirm resource with peak sun hours.
- Hub: Solar calculator.
Last updated: 2026-08-07. Planning estimate only—confirm nameplate watts and duty cycles on site.
Typical scenarios
- Telecom hut: Continuous radio + intermittent cooling—watch 24 h loads (use Telecom preset).
- Remote workshop: Day-heavy tools—hours often 6–10 h, not 24.
- Winter worst-month: Longer lighting/heating hours when PV production is lowest—prefer this for sizing.
- Hybrid site: Partial generator cover—still size PV for critical kWh first.
Surge vs running watts
Motors and compressors draw 3–7× running watts at start. Use running watts × hours for daily kWh in this calculator; sum surge watts (and coincidence) when selecting inverter peak capability.
| Appliance (typical) | Running W | Surge W |
|---|---|---|
| Refrigerator | 100–200 | 600–1200 |
| Well / transfer pump | 750–1500 | 1500–4500 |
| Window AC / mini-split | 500–1500 | 1500–3500 |
| Microwave | 800–1200 | ≈ running |
| LED lighting (string) | 10–60 | ≈ running |
Values are planning ranges—use nameplate data. OEM curves override this table.
Load priorities: critical / convenience / luxury
- Critical (cover 100%): refrigeration for medicine/food, lighting, radios/comms, controls.
- Convenience (~80% coverage planning): computers, microwave, tools used part of the day.
- Luxury (shed first): space AC, laundry, recreational loads.
Size the PV/battery stack for critical + agreed convenience kWh. Luxury loads drive oversized arrays—shed them in the autonomy policy instead of forcing 100% coverage.
Seasonal load variation
Winter often raises lighting/heating hours while peak sun hours fall. Prefer worst-month daily kWh for array and bank screens (use the Winter preset above).
| Season (example cabin) | Daily kWh trend | Notes |
|---|---|---|
| Summer | ~6–9 kWh/day | Fridge/AC up; PV production usually higher |
| Winter | ~9–12 kWh/day | Lighting/heat up; PV production usually lower |
Off-grid load calculation worksheet
Print this table to inventory appliances on site, then enter three roll-up groups in the Advanced calculator (or sum offline and put the total into Quick).
| Appliance | Qty | Running W | Surge W | Hours/day | Priority | Wh/day |
|---|---|---|---|---|---|---|
| C / Conv / L | ||||||
| Sum Wh → ÷ 1000 = base kWh/day | ||||||
Formula (quick reference)
Daily kWh = Σ(W × h) ÷ 1000 × (1 + margin%)
Next funnel: how to size a commercial solar array → panel sizing.
Formula and sources
Energy roll-up is engineering bookkeeping; site duty cycles and OEM nameplates govern procurement.
- NREL System Advisor Model (SAM) — off-grid / storage simulation reference
- NREL PVWatts — production context after daily kWh is set
- NFPA / NEC (NFPA 70) — wiring and listing context for installed systems
Frequently Asked Questions
How do I calculate off-grid solar load?
Multiply each load’s running watts by hours per day, sum watt-hours, divide by 1000, then apply contingency margin. Example: 800 W × 10 h + 200 W × 5 h = 9.0 kWh base; +15% ≈ 10.35 kWh/day.
Is this an off-grid solar system sizing calculator?
This step sizes daily energy (kWh). Use the result in the solar panel sizing calculator and Solar Battery Bank Calculator for full off-grid system sizing—not camping kit shopping pages.
What is the solar load calculation formula?
Daily kWh = Σ(W × h) ÷ 1000 × (1 + margin%). Energy uses running watts × hours; inverter peak uses surge watts separately (see the surge table above).
Should I include surge loads in daily kWh?
No. Short motor starts barely change daily energy but dominate inverter surge rating. Keep surge watts out of this roll-up; list them for inverter selection.
Should I size for summer or winter load?
Prefer the worst month—often winter (higher lighting/heat hours, lower PV). Use the Winter worst-month preset, then size array and battery for that daily kWh.
What is the difference from the factory load calculator?
Factory load targets plant demand and diversity for utility/transformer planning. This tool targets off-grid daily energy for PV and battery screens.
What is the next step?
Size the PV array from daily kWh, then screen autonomy days and MPPT current.
Is this for camping kits?
No—industrial/remote-site planning. Avoid portable power-station shopping intents.
Can I size solar for a cabin or RV here?
Yes for daily load roll-up: use the Remote cabin or RV / van presets, then continue to panel sizing and battery autonomy. We do not sell kits and do not maintain a separate cabin/RV landing URL—see Solar Applications.
How it works
Off-grid daily energy is the sum of watt-hour contributions from each load group, with an optional contingency margin for growth and measurement error. Surge watts are tracked separately for inverter peak checks—not mixed into kWh/day.
Worked examples
- 800 W × 10 h + 200 W × 5 h, 15% margin
Base 9.0 kWh → with margin ≈ 10.35 kWh/day.
- Telecom hut preset
600 W × 24 h + 1500 W × 4 h = 20.4 kWh base; +20% ≈ 24.5 kWh/day.