Off-Grid Solar Calculator
Created by: Ethan Brooks
Last updated:
Size your off-grid solar system for homestead living. Add your appliances to calculate required solar panel wattage, battery bank capacity, and inverter size with cost estimates.
Off-Grid Solar Calculator
HomesteadingSize your solar system for off-grid living.
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What is a Homesteading Off-Grid Solar Calculator?
A homesteading off-grid solar calculator helps you determine the right system size for living independently from the electrical grid. It calculates the solar panel wattage, battery storage capacity, and inverter size you need based on your actual electrical usage patterns and local sun conditions.
Going off-grid with solar requires careful planning. Too small a system leaves you without power on cloudy days; too large wastes money on equipment you don't need. This calculator accounts for real-world factors like system losses, depth of discharge, and days of autonomy to give you practical recommendations.
Understanding Peak Sun Hours
Peak sun hours represent the equivalent hours of full-strength sunlight (1,000 watts per square meter) per day. This is different from daylight hours — a partly cloudy day might have 12 hours of light but only 3-4 peak sun hours of usable solar energy.
The Southwest US averages 6+ peak sun hours daily; the Pacific Northwest may see only 3-4 hours in winter. Always design your system for your worst-case scenario (typically December-January) to ensure year-round reliability.
Accounting for System Losses
Real-world solar systems lose 20-30% of theoretical output to various factors: inverter efficiency (90-95%), battery charging losses (10-20%), wire resistance losses (2-5%), dust and partial shading, temperature effects (panels produce less in extreme heat), and panel degradation over time. Always add at least 25% to your calculated requirements.
Battery Bank Sizing for Off-Grid
Off-grid battery banks should provide 2-3 days of power without sun to handle extended cloudy periods. Lead-acid batteries (AGM or flooded) should only be discharged to 50% for longevity; lithium (LiFePO4) batteries can safely discharge to 80-90%. While lithium costs 2-3x more upfront, its higher usable capacity and 10-15 year lifespan often makes it more economical long-term.
Tips for Off-Grid Success
- Reduce loads first: The cheapest watt is the one you don't use. LED lights, efficient appliances, and propane for heating/cooking dramatically reduce system size and cost.
- Use 48V systems: For systems over 3kW, 48-volt systems are more efficient with lower wire losses.
- Include a backup generator: A small propane or gasoline generator can cover extended cloudy periods and reduce battery bank requirements.
- Monitor your system: Track daily usage and battery state of charge to optimize habits and catch problems early.
Frequently Asked Questions
How do I calculate my solar panel needs?
Calculate daily watt-hours (watts × hours used per day for each appliance), divide by peak sun hours to get required panel wattage, then add 25% for system losses. Example: 5,000 Wh/day ÷ 5 sun hours = 1,000W panels, plus 25% = 1,250W minimum system.
How much battery storage do I need?
For off-grid, plan for 2-3 days of autonomy (cloudy days without charging). Calculate: Daily Wh × Days of autonomy ÷ Depth of Discharge (50% for lead-acid, 80% for lithium). A 5,000 Wh/day system needs 20,000-30,000 Wh of lithium battery storage.
What's the difference between lead-acid and lithium batteries?
Lead-acid batteries are cheaper upfront but last 3-5 years and should only discharge to 50%. Lithium (LiFePO4) costs 2-3x more but lasts 10-15 years, discharges to 80%, and is lighter. Lithium has lower lifetime cost for most off-grid systems.
Do I need an inverter?
Yes, for any AC appliances (most household items). Inverter size should match or exceed your largest simultaneous load plus startup surge (motors need 3-5x running watts to start). A 3,000W inverter handles most homestead needs; 5,000W+ for well pumps or power tools.
Can solar power a whole house off-grid?
Yes, but requires careful planning. Typical off-grid homes use 10-30 kWh/day with efficiency measures. This needs 3-8 kW of panels and 20-60 kWh of batteries. Budget $15,000-50,000+ for a complete system. Reduce loads (propane for heating/cooking) to lower costs.
Sources and References
- National Renewable Energy Laboratory (NREL), "PVWatts Calculator Documentation"
- US Department of Energy, "Planning a Home Solar Electric System"
- Home Power Magazine, "Sizing Battery Banks for Off-Grid Systems"
- Solar Energy Industries Association (SEIA), "Solar Industry Research Data"