Tracking the Advances in Solar Charge Controllers

10.16.12

Mark Cerasuolo, Senior Marketing Manager, OutBack Power

Recently, there has been an increase in popularity for off-grid solar systems for independence from utilities and grid-interactive systems for flexibility to easily switch from drawing from the grid when it's up or switching to off-grid power from other sources when the grid is down. This has resulted in more attention being paid to the technology providing the battery storage for backup power -- the solar charge controller. If you work in the energy industry, or more specifically, in the cleantech energy industry, chances are you have a good understanding of solar charge controllers. With recent advances, the solar charge controllers currently in the market are much different from their forerunners. Let's take a look at how this technology has transformed since its emergence in the early 1980s.

The first solar charge converters back in the early 1980s came in one- or two-stage designs. While these early controllers were more or less reliable, they weren't particularly efficient or complex. They also had the problem of rapidly damaging batteries with the on/off charging style, excessive heat or undercharging. Given the high cost of back-up batteries, this was a serious concern.

By the early 1990s, a "smarter" three-stage pulse width modulated (PWM) design controller addressed this problem with a more effective and efficient charging algorithm that "shifted" voltage modes with less difficulty from constant current to constant voltage and then to lower constant voltage. Although there were areas for improvement, these second-evolution solar charge controllers allowed solar panels to harvest more energy and batteries to run longer.

Optimizing for More Energy from Less Expensive and Smaller PV Arrays

The latest generation of charge controllers builds upon prior developments in locating the highest point of operating efficiency in a PV array and converting that power to increased current at the lower battery voltage. The PV array is then able to release the most energy possible, leading to smaller and less costly arrays with greater performance relative to previous generations.

The maximum power point tracking (MPPT) controllers in the market today are sophisticated DC-to-DC converters able to continuously track and adjust to changing environments. MPPT charge controllers can dynamically adapt through active software algorithms, regardless of variations in sunlight intensity (irradiance) and output voltage based upon energy load or temperatures. This also ensures PV modules are fully optimized by the controllers, even if there are extreme changes in atmosphere or radiation.

MPPT Technology Cuts Costs and Solves Problems of Earlier Controllers

In addition to addressing the limitations of the early class of charge controllers, MPPT technology also cuts costs. Previous controllers were only designed with PV voltages in mind that would correspond to the battery bank. For example, a 36-cell "12-volt nominal" PV module was required for a 12-volt battery bank and a 144-cell array was necessary for a 48-volt battery. As module manufacturers have revamped their lines to elevate cell utilization for increased manufacturing efficiencies and reduced costs, 60-cell modules have become the industry norm whereas 36- and 72-cell modules have become increasingly rare and more costly 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. With higher voltage and fewer parallel connections, an installer has the advantage of saving costs on wiring and other expenses related to balance-of-system components.

Additionally, the latest charge controllers can add value with its ability to assess system performance and provide integrated communications capabilities for remote troubleshooting. Today's solar charge controllers have made a great deal of progress in efficiency and technology since the early 1980s and now capture greatest amount of solar power for every size of applications.