3 Things You Need To Know About Solar Charge Controllers

By Mark Cerasuolo, Senior Marketing Manager at OutBack Power

Most professionals working in clean energy know plenty about solar charge controllers. However, the solar charge controllers we see in the market today are markedly different from their predecessors. Below are three things you need to know about recent advances in this technology:

1. The opportunity for improvement was rooted in the first solar charge controllers. When this technology first emerged in the early 1980s, solar charge converters came in one- or two-stage designs. They weren’t particularly efficient or complex, but these early controllers were more or less reliable. The problem was in how they affected battery health. Their on/off charging style rapidly damaged batteries from  either excessive heat or undercharging. Since the back-up batteries are  one of the most expensive parts of the energy system, this was a serious matter.

Within a decade, the market had addressed this problem with a “smarter” three-stage pulse width modulated (PWM) design controller.  Because these designs had a more effective and efficient charging algorithm, they “shifted” voltage modes more smoothly from constant current to constant voltage and then to lower constant voltage.  Solar panels connected to these second-generation controllers could harvest more energy, and batteries lasted longer. However, there was still room for improvement.

2. Maximum power point tracking (MPPT) controllers extract more energy from PV arrays. The latest evolution of charge controllers builds on earlier advances to locate the highest point of operating efficiency in a PV array, and then convert that power to increased current at the lower battery voltage. The result is the release of the most energy possible from the array, leading to smaller, less expensive arrays with superior performance when compared to earlier generations.

The MPPT controllers we see today are sophisticated DC-to-DC converters with the ability to continuously track and respond to changing conditions. Regardless of variations in sunlight intensity (irradiance) and output voltage based upon load and temperature, MPPT charge controllers can adapt dynamically through active software algorithms which also help controllers keep PV modules fully optimized even under the most extreme atmospheric and radiation changes.

3. MPPT technology solves the problems of earlier controllers while cutting costs.

Solving the shortcomings of early generation controllers is an important benefit of today’s MPPT technology, but the cost savings involved are also compelling. Previous charge controllers were limited to PV voltages that matched the battery bank. For instance, a 12-volt battery bank would require a 36-cell “12-volt nominal” PV module and a 48-volt battery would require an array with 144 cells in series. Sixty cell modules are now an industry norm, as module manufacturers have retooled their lines to optimize cell utilization for increased manufacturing efficiencies and reduced costs. Thirty-six and 72-cell modules are increasingly rare and command a higher cost per watt.

However, a designer using an MPPT controller can configure multiple 60-cell modules per string to charge a 12, 24 or 48-volt battery. Higher voltage and fewer parallel connections also allow the installer to save on wiring and other balance-of-system component costs.

The installer also saves money on higher voltage and fewer parallel connections also allow the installer to save on wiring and other balance-of-system component costs, since the voltage is higher and there are fewer parallel connections.

Modern charge controllers can also evaluate system performance and offer integrated communications capabilities for remote troubleshooting.

These are three important factors to understand about today’s solar charge controllers, but we can simplify the main takeaway even further: The modern controller captures maximum solar power for applications of every size.

Cerasuolo manages strategic brand marketing at OutBack Power, a designer and manufacturer of balance-of-system components for renewable and other energy applications.