Stop guessing your off-grid solar needs. This comprehensive calculator walks you through every calculation needed to size your system perfectly – preventing costly oversizing or frustrating undersizing.
Whether you're planning a cabin retreat or complete grid independence, get the exact specifications for solar panels, battery storage, inverters, and charge controllers tailored to your unique situation.
Quick Solar Sizing Calculator
Step 1: Calculate Your Daily Energy Needs
Name: [] Watts: [] Hours/Day: [] Quantity: []
Comprehensive Load Analysis Worksheet
Essential Loads (Must Have Power)
Kitchen Appliances
Lighting
Electronics
Climate Control
Water Systems
Solar Array Sizing Formula
The Mathematical Foundation
Daily Energy Requirement
Total Daily kWh = Sum of all appliance daily usage Example: 15 kWh/day total household usage
System Losses Factor
Adjusted Daily kWh = Daily kWh × 1.3 (30% for inefficiencies, inverter losses, wire losses) Example: 15 kWh × 1.3 = 19.5 kWh
Solar Array Size
Array Size (kW) = Adjusted Daily kWh ÷ Peak Sun Hours Example: 19.5 kWh ÷ 5 hours = 3.9 kW array needed
Number of Panels
Panels Needed = Array Size ÷ Panel Wattage Example: 3,900W ÷ 400W panels = 10 panels
Peak Sun Hours by Location
Sun Hours by Region
Southwest USA
Southeast USA
Northwest USA
Northeast USA
Midwest USA
Battery Bank Sizing Calculator
Determining Storage Capacity
[Battery Calculator - Interactive component coming soon]
Battery Configuration Examples
Small (10-15 kWh)
4× 12V 200Ah LiFePO4 batteries in series = 48V × 200Ah = 9.6 kWh
2× 48V 100Ah server rack batteries = 48V × 200Ah = 9.6 kWh
Medium (20-30 kWh)
8× 12V 300Ah LiFePO4 batteries (2 parallel strings) = 48V × 600Ah = 28.8 kWh
6× 48V 100Ah server rack batteries = 48V × 600Ah = 28.8 kWh
Large (40-60 kWh)
16× 12V 300Ah LiFePO4 batteries (4 parallel strings) = 48V × 1200Ah = 57.6 kWh
12× 48V 100Ah server rack batteries = 48V × 1200Ah = 57.6 kWh
Inverter Sizing Guide
Calculating Inverter Requirements
Continuous Load Calculation
Add up watts of all appliances that might run simultaneously
• Refrigerator: 400W • Lights: 200W • Computer/TV: 300W • Water pump: 750W • Miscellaneous: 350W Total: 2,000W continuous
Surge Load Calculation
Identify highest starting surge (usually motors/compressors)
• Refrigerator: 3× running watts • Well pump: 3-5× running watts • Power tools: 2-3× running watts • Microwave: 1.5× running watts
Well pump surge: 750W × 4 = 3,000W
Inverter Selection
Inverter Size = Continuous Load × 1.25 Surge Rating ≥ Highest surge load
2,000W × 1.25 = 2,500W minimum Choose 3,000W inverter with 6,000W surge
Inverter Type Comparison
Pure Sine Wave
Pros
✅ Works with all appliances ✅ No interference or noise ✅ Most efficient ✅ Required for sensitive electronics
Cons
⚠️ More expensive ⚠️ Slightly lower surge capacity
Modified Sine Wave
Pros
✅ Lower cost ✅ Higher surge capacity ✅ Simpler design
Cons
⚠️ Not compatible with some appliances ⚠️ Creates electrical noise ⚠️ Lower efficiency ⚠️ Can damage sensitive electronics
Charge Controller Selection
MPPT Controller Sizing
Controller Amps = Solar Array Watts ÷ Battery Voltage × 1.25
4,000W array ÷ 48V battery = 83A 83A × 1.25 = 104A Choose: 100A or 120A MPPT controller
2,000W array ÷ 24V battery = 83A 83A × 1.25 = 104A Choose: 100A or dual 60A controllers
• Max input voltage: Usually 150V or 250V • String configuration must stay below limit • Cold weather increases voltage - add 20% margin
Complete System Examples
Example 1: Small Cabin System
• 6× 400W panels = 2.4kW • Daily production: 10.8 kWh summer, 7.2 kWh winter
• 4× 12V 200Ah LiFePO4 = 9.6 kWh • 2 days autonomy at 80% DoD
• 2000W pure sine wave • 4000W surge capacity
• 60A MPPT controller
Example 2: Full-Time Off-Grid Home
• 16× 400W panels = 6.4kW • Daily production: 32 kWh summer, 22 kWh winter
• 8× 48V 100Ah rack batteries = 38.4 kWh • 3 days autonomy at 80% DoD
• 6000W split-phase inverter • 12000W surge capacity
• 2× 80A MPPT controllers
Example 3: Large Off-Grid Property
• 24× 450W panels = 10.8kW • Daily production: 65 kWh summer, 54 kWh winter
• 12× 48V 100Ah rack batteries = 57.6 kWh • 3 days autonomy at 80% DoD
• 10kW hybrid inverter • 20kW surge capacity • Generator input capability
• Integrated with hybrid inverter
Planning Checklist
Pre-Installation Planning
Planning Checklist
Assessment (Month 1)
□ Track actual energy usage for 30 days □ Identify essential vs. optional loads □ Research local sun hours data □ Check local codes and permits □ Evaluate installation locations □ Consider seasonal variations
Design (Month 2)
□ Calculate system size requirements □ Select battery chemistry type □ Choose inverter capacity □ Plan charge controller configuration □ Design grounding system □ Plan cable runs and electrical panel
Procurement (Month 3)
□ Get 3-5 quotes from suppliers □ Compare warranties and support □ Order long-lead items first □ Schedule professional installation □ Arrange permit inspections □ Plan delivery logistics
Common Sizing Mistakes to Avoid
Advanced Considerations
Seasonal Adjustment Strategies
Seasonal Strategies
Winter Optimization
Summer Optimization
System Monitoring and Optimization
Your Custom System Plan
Daily Energy Need: [] kWh Location/Sun Hours: [] hours Days of Autonomy: [] days Battery Type: [LiFePO4 / AGM / Lead-Acid] Budget Range: $[] - $[____]
Recommended Solar Array: [] kW Number of Panels: [] × []W Battery Bank Size: [] kWh Inverter Size: [] W Charge Controller: [] A MPPT Estimated Total Cost: $[____]
Next Steps
Download our detailed load calculation spreadsheet
Monitor your actual usage for 30 days
Get professional system design consultation
Request quotes from certified installers
Join off-grid solar communities for support
Proper system sizing is the foundation of successful off-grid living. Use these calculations and tools to design a system that provides reliable power for years to come, without overspending on unnecessary capacity.
Calculations based on industry standards and real-world performance data. Individual results vary based on location, usage patterns, and equipment quality. Always consult with qualified solar professionals for final system design.