Solar Battery Charger: MPPT Controller with Arduino

Pairing solar panels with lithium batteries requires an intelligent charge controller. MPPT (Maximum Power Point Tracking) controllers extract up to 30% more energy from solar panels compared to simple PWM controllers. This guide covers building an Arduino-based MPPT charger and using ready-made MPPT modules available in India.

MPPT vs PWM Charging

A solar panel’s output voltage varies with sunlight intensity and temperature. A PWM controller simply connects the panel to the battery through a switch, wasting energy when panel voltage is higher than battery voltage. An MPPT controller uses a DC-DC converter to transform excess voltage into additional current, harvesting maximum power regardless of conditions.

How MPPT Works

MPPT works by continuously adjusting the load on the solar panel to find its maximum power point (the voltage-current combination that produces maximum watts). The algorithm (Perturb & Observe or Incremental Conductance) slightly adjusts the operating point and measures whether power increased or decreased, then continues in the beneficial direction.

CN3791 MPPT Charger Module

The CN3791 is a single-chip MPPT solar charger IC available on breakout modules in India. It supports 6V, 9V, or 12V solar panel inputs and charges a single lithium cell with true MPPT. No microcontroller programming required – it is a complete hardware solution.

Arduino MPPT Controller Project

For a more flexible MPPT controller, use Arduino with an INA219 sensor and a buck converter:

1. INA219 monitors solar panel voltage and current
2. Arduino runs P&O algorithm to find maximum power point
3. PWM output controls a buck converter’s duty cycle
4. Second INA219 (optional) monitors battery charging current

This approach lets you handle any panel voltage and battery configuration, with full data logging via Serial or WiFi.

Solar Panel Selection for Battery Charging

Match your solar panel to your battery and application:

Complete Solar Battery System

A complete solar battery charging system for an IoT node:

• 6V 1W solar panel → CN3791 6V MPPT module → single 18650 cell → ESP32 sensor node
• Total cost: ₹130 (panel) + ₹223 (CN3791) + ₹72 (cell) + ₹500 (ESP32 + sensors) = under ₹1,000

This system can run indefinitely in Indian conditions, as even 4-5 hours of partial sunlight generates enough energy for an ESP32 that wakes, reads sensors, sends data over WiFi, and sleeps for 5 minutes between readings.

Indian Climate Considerations

India’s solar potential is excellent – most regions receive 4-6 peak sun hours daily. However, dust accumulation on panels reduces output by 20-40% within weeks. Clean panels monthly. During monsoon, output drops significantly. Size your battery for 2-3 days of autonomy to handle consecutive cloudy days.