Off-Grid Land Solar + Battery Size Estimator (Simplified)

What This Estimator Does

This tool provides a simplified estimate of the solar panel array size (in kW and number of panels) and battery bank capacity (in kWh and Ah) needed for an off-grid application. It uses basic inputs like your daily energy consumption, available sun hours, system losses, and desired days of battery autonomy to calculate approximate system sizes.

The results are meant for early-stage planning and educational purposes only. They help you understand the general scale of equipment needed before consulting with professionals for detailed system design.

How Daily Load and Sun Hours Affect Array Size

The solar array must produce enough energy each day to meet your consumption. The key relationship is:

• Higher daily load = larger array needed
• Fewer sun hours = larger array needed (less time to generate the same energy)
• Higher system losses = larger array needed (more waste between panels and usable power)

Why System Losses Matter

Real solar systems lose energy at multiple stages: wiring resistance, charge controller conversion, battery charging/discharging, inverter conversion, and temperature effects on panels. Typical combined losses range from 20% to 35% for well-designed systems.

A 30% loss factor (0.3) means only 70% of the panel's rated output actually reaches your loads. Higher losses require proportionally larger arrays to meet the same demand.

Battery Autonomy and Depth of Discharge

Autonomy days represent how long your battery bank should power your loads with little or no solar input (cloudy days, winter, emergencies). More autonomy days = larger battery bank.

Depth of discharge (DoD) is the fraction of battery capacity you actually use. Lead-acid batteries typically should not be discharged below 50% (DoD = 0.5) for longevity, while lithium batteries often allow 80-90% (DoD = 0.8-0.9). A lower DoD means you need more total battery capacity to store the same usable energy.

Typical Ranges for Planning

• Peak sun hours: 3-6 hours/day for most locations (varies by latitude and season)
• System losses: 0.25-0.35 (25-35%) for typical installations
• Autonomy days: 1-3 days for most off-grid applications
• DoD: 0.5 for lead-acid, 0.8-0.9 for lithium
• Panel ratings: 350-450 W for modern residential panels

Why Professional Design Is Still Essential

This calculator provides ballpark estimates only. A real off-grid system requires:

• Proper charge controller sizing (MPPT vs PWM, voltage and current ratings)
• Inverter selection (pure sine wave, surge capacity, efficiency)
• Wire sizing calculations for voltage drop and safety
• Overcurrent protection (fuses, breakers) per electrical code
• Battery bank wiring configuration (series/parallel)
• Grounding and safety disconnects
• Seasonal variation analysis (winter vs summer sun hours)
• Shading analysis and panel orientation

Always consult a qualified solar installer, licensed electrician, and local building/electrical codes before purchasing equipment or installing any electrical system.