Solar Controllers

Introduction

This knowledge article discusses what to look for when selecting a solar controller.

Two Main Types of Solar Controllers

Solar controllers are divided into two primary categories:

1. PWM controllers
2. MPPT controllers

1. PWM Controllers

What is PWM?

PWM stands for pulse width modulation. This is a common modulation technique used in various control circuits, including motor speed controllers and temperature controllers. Despite its technical name, pulse width modulation is simply a square wave in which the pulse width is varied.

How PWM Controllers Work

PWM controllers regulate power to the battery by applying a varying-width pulse between the solar panel and the controller. When the battery requires more current, the pulse width increases. When less current is needed, the pulse width decreases.

Efficiency Concerns

PWM controllers are affordable but suffer from efficiency limitations. Efficiency is typically between 8 and 30 percent less than an MPPT controller. The efficiency decreases as solar irradiance increases. For example, sunny conditions result in approximately 20% power loss, while shady conditions cause about 8% loss of already-reduced power.

LUX Solar Recommendation

LUX Solar recommends using PWM controllers when attempting to top up batteries or when able to oversize the solar panel array. PWM controllers are used exclusively in LUX battery top-up kits.

2. MPPT Controllers

Superior Efficiency

Compared to conventional PWM chargers MPPT chargers are significantly more efficient. In comparative testing using identical operating conditions, the LUX Solar LSC series demonstrates substantially better power conversion than standard PWM chargers.

Performance Range

LUX Solar kits operate primarily in a region where efficiency rarely drops below 90%. This contrasts sharply with "high quality" PWM controllers, which show considerably worse efficiency across their operating range. Most manufacturers specify maximum controller efficiency (MPPT chargers achieve up to 98% maximum efficiency).

Visual Comparison

The page includes an efficiency comparison chart showing the LSC MPPT controller significantly outperforming PWM technology across various operating conditions.