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Your Electricity Usage
Average monthly bill before solar
Check your bill or use 0.14 average
80% offsets most usage while keeping costs reasonable
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System Preferences
South-facing in N. hemisphere, North-facing in S. hemisphere
Check your main panel; most US homes are 240V
Only used if System Type is hybrid or off-grid
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Your Daily Power NeedsAdd each device you plan to run. Check the Simultaneous box for every device that might run at the same moment as another. This drives inverter sizing.
| Device | Watts | Hrs/Day | Simultaneous? | Wh/Day |
|---|
Total: 0 Wh/day • Simultaneous peak: 0 W
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System Configuration
From panel spec sheet; 200W ~ 11A, 400W ~ 14A
Panels to controller; used for voltage-drop sizing
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Peak Sun Hours by RegionAnnual averages. Your actual production depends on season, local weather, shading, and panel angle. Southern hemisphere: swap summer/winter expectations. For US addresses, NREL's PVWatts tool at pvwatts.nrel.gov gives location-specific values.
United States
6.5-7.5 Arizona, Nevada, SoCal desert
5.5-6.5 Texas, Florida, SoCal coast
4.5-5.5 Mid-Atlantic, Southeast, Colorado
4.0-5.0 Midwest, Arkansas, Tennessee
3.5-4.5 Northeast, Great Lakes, Oregon
3.0-4.0 Pacific NW, Alaska, upper Midwest
Australia & New Zealand
6.5-7.5 Northern Territory, inland QLD/WA
5.5-6.5 Perth, Brisbane, Adelaide, inland NSW
4.5-5.5 Sydney, Canberra, coastal QLD
3.5-4.5 Melbourne, Hobart, New Zealand
Europe
5.5-6.5 Southern Spain, Greece, Sicily, Cyprus
4.5-5.5 Portugal, southern France, Italy, Croatia
3.5-4.5 Northern France, Germany, Poland, Austria
2.5-3.5 UK, Ireland, Netherlands, Scandinavia
Canada
4.5-5.5 Southern Alberta, Saskatchewan prairies
3.5-4.5 Ontario, Quebec, southern BC
2.5-3.5 Coastal BC, Maritime provinces, northern
Central & South America
6.0-7.5 Mexico (Sonora, Baja), Atacama, NE Brazil
5.0-6.0 Central Mexico, Colombia, Argentina plains
4.0-5.0 Southern Brazil, Chile coast, Central America
Africa & Middle East
6.5-8.0 Sahara, Arabian Peninsula, Namibia
5.5-6.5 South Africa, East Africa, Morocco
4.5-5.5 Coastal West Africa, Israel, Turkey
Asia & Pacific
5.5-7.0 India (Rajasthan, Gujarat), Thailand
4.5-5.5 Central India, Philippines, Indonesia
3.5-4.5 Japan, South Korea, eastern China
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How This Calculator Works
Every formula in this tool comes straight out of the Solar Panel Sizing Guide. If you want the full teaching on why any number below is what it is, read the companion article.
- Design Load (25% margin): Daily watt-hour use × 1.25. Covers system losses, day-to-day usage variation, and occasional cloudy days.
- Panels: Design Load ÷ (Panel W × Peak Sun Hours × System Efficiency). System efficiency is 0.78 for battery-based systems and 0.83 for grid-tied. The 0.78 factor already includes inverter efficiency losses; the calc does not double-count them.
- Inverter (van/RV): Sum of simultaneous-load watts × 1.20 headroom. Surge capacity must handle motor-startup loads (typically 2-3× continuous). Sizing to a single max appliance would be wrong.
- Battery bank: Daily Wh × autonomy days ÷ depth of discharge. LiFePO4 80% DoD, AGM 50%.
- Charge controller (cold margin): (Array W × 1.25) ÷ battery V. The 1.25 accounts for cold-weather conditions when panels can exceed rated output by 10-25%. If calculated amps exceed 60A, the calc recommends splitting into multiple controllers.
- Wire gauge battery to inverter: Current = inverter continuous W ÷ battery V. This is the inverter max input current, not daylight-average current. Under fault the full inverter load pulls through this cable.
- Wire gauge panels to controller: Isc × 1.25, then checked against voltage-drop at your actual wire-run length. 3% drop target for main runs.
- Array fuse: Isc × 1.56 (NEC 690.8 x 690.9 stacked: 125% for continuous current plus 125% for overcurrent protection). Next standard size up.
- Battery-to-inverter fuse: Class T, sized to inverter max input current. Required for LiFePO4 systems. A standard ANL fuse in this position is a fire hazard.
- Rapid shutdown (NEC 690.12): Roof-mounted systems on buildings need rapid-shutdown devices reducing array-boundary voltage to 30V within 30s. Microinverters and power optimizers meet this natively. String inverters need module-level shutdown devices.
- All estimates are conservative. Real-world conditions vary. The sizing math is universal; product links point to US retailers. Consult a licensed electrician for home installations.