Off-Grid Solar System Design: Battery and Panel Sizing

Off-Grid Solar System Design: The Complete 2026 Guide

Designing an off-grid solar system is both a science and an art. The science lies in calculating energy requirements, sizing components, and accounting for seasonal variations. The art lies in balancing technical requirements against budget constraints, available space, and future expansion needs. This guide walks you through the complete process, with particular focus on battery and panel sizing.

Step 1: Calculate Your Energy Requirements

Before sizing any component, understand exactly how much energy you consume. List every electrical load and estimate daily usage hours. Example daily calculation: Lights (6 x 10W x 5 hours = 300 Wh), Refrigerator (150W x 24 hours x 0.4 duty cycle = 1,440 Wh), Laptop (50W x 4 hours = 200 Wh), Water pump (200W x 1 hour = 200 Wh), Total: approximately 2,500 Wh/day (2.5 kWh/day).

Step 2: Determine System Voltage

12V: Small systems under 1kWp, camping/RV applications. 24V: Medium systems 1–5kWp, common in residential off-grid. 48V: Large systems over 3kWp, preferred for efficiency and reduced current. For most residential off-grid systems, 48V provides the best balance of efficiency, component availability, and safety.

Step 3: Size Your Battery Bank

Battery sizing determines your days of autonomy — how many days of power you can sustain without solar generation. Formula: Battery Bank Capacity (Ah) = (Daily Energy Use x Days of Autonomy) / (System Voltage x Maximum Depth of Discharge). Example for 48V system, 2.5 kWh/day, 2 days autonomy, 50% DoD: Capacity = 2,500 x 2 / (48 x 0.50) = 208 Ah. Battery Type Selection: OPzV Tubular GEL is best for daily cycling with long design life. Flooded Lead-Acid offers lower cost but requires maintenance. AGM is maintenance-free. Lithium offers highest performance at premium cost.

Step 4: Size Your Solar Array

Formula: Array Size (Wp) = Daily Energy Use / Peak Sun Hours / System Efficiency Factor. Example: 2,500 Wh / 5 hours / 0.65 = 769 Wp — round up to 1,000 Wp minimum. Always oversize by 20–30% to account for panel soiling, aging, temperature effects, and battery charging inefficiencies.

Step 5: Select Your Inverter and Charge Controller

Inverter Sizing: Continuous rating should exceed your total simultaneous load by 25%. Surge capacity must handle motor starting loads (typically 2–3x continuous rating). For a 2.5 kWh/day home with 1.5kW peak load, a 3kW inverter provides comfortable headroom. Charge Controller Sizing: PWM: Controller amps = Array watts / Battery voltage. MPPT controllers are more efficient — for 48V systems, 60A MPPT controllers are common for 2–5kWp arrays.

Step 6: Plan for Seasonal Variation

Never design an off-grid system for average conditions — design for the worst month. In many regions, winter produces only 30–50% of summer solar output. Solutions: larger battery bank, oversizing the array, backup generator, or hybrid grid connection.


About CHISEN Battery

CHISEN Battery is a professional lead-acid battery manufacturer with 8 global production facilities and an annual output capacity exceeding 70 million kVAh. Our product range includes OPzV tubular GEL batteries, VRLA batteries, and cadmium-free industrial batteries — all certified to CE, ISO9001, and TUV standards. Trusted by distributors and system integrators in over 60 countries, CHISEN supports projects from residential off-grid systems to utility-scale energy storage installations.

Jack Chen | General Manager | CHISEN Battery
Tel: +86 131 2666 8999 | Email: jack@chisen.cn | www.chisen.cn