Why MPPT Controllers
Solar Charge Controllers & MPPT Technology
The technology that allows a PV array to deliver the maximum amount of energy to a battery bank is known as maximum power point tracking (MPPT).
A solar charge controller (MPPT Controllers), also known as a solar regulator, is essentially a solar battery charger connected between the solar panel/s and battery. Its job is to regulate the battery charging process to ensure the battery is charged correctly, or more importantly, not over-charged.
Solar charge controllers are rated according to the maximum input voltage (V) and maximum charge current (A). These two ratings determine how many PV modules can be attached.
Current Amp (A) rating = maximum input and charging current.
Maximum Voltage (V) rating = Max voltage (Voc) of the solar panel/s.
For a typical 12-volt nominal PV module, the voltage associated with the MPP is somewhere around 19 volts. PV manufacturers realized early on that this was the voltage value required to effectively charge a 12-volt nominal battery bank in nearly all worldwide geographic locations.
Why Extra Voltage is Necessary?
Keep in mind that the PV module voltage decreases when the module temperature rises, so the extra voltage is necessary to push the electrons into the battery bank when the PV module’s temperature is elevated.
The maximum power voltage of 19 volts doesn’t always equate directly to the required voltage needed to charge a battery bank, though. Depending on the technology and the charge set-point, the voltage necessary for charging a 12-volt nominal battery bank can range anywhere from 13-volts to 15-volts. Therefore, a PV module can produce more voltage than a battery bank can fully use. Enter the MPPT charge controllers.
How MPPT Controllers Works?
MPPT controllers take the power from a PV array at the MPP, regardless of the required battery voltage, and deliver that same amount of power (minus efficiency losses of course) to the battery bank because they’re able to reduce the voltage from the array to the battery’s required level.
And because power is the product of voltage and current, if the voltage is decreased, the current is increased in order to keep the same power level. MPPT controllers boost current into the battery bank in relation to the current received from the array.
Power Gained Through The Use Of MPPT Controllers
This concept is best illustrated in the figure below, which depicts the power curve for a typical 12 V nominal PV module. The peak of the curve represents the maximum power value, which is the level that the PV module can produce.
The graph also shows the location of a typical battery charge set-point. If you move straight over to the right from that point, you’ll see the power level associated with the battery-charging voltage. The difference in the MPP and the power level associated with the battery-charging voltage represents the increased power output due to the use of MPPT technology.
The PV array’s power levels move throughout the day depending on the environmental conditions, and MPPT controllers adjust right along with them.
Advantages of MPPT Controllers
- MPPT controllers have become the most popular charge controllers for larger battery-based PV systems, thanks to their ability to fully use the power produced by a PV array.
- Another good thing MPPTs have going for them is their ability to take a PV array wired for a higher voltage and still charge a low-voltage battery bank. For example, with the help of an MPPT controller, you can take a PV array that’s wired in a series configuration up to 150VDC and still charge a battery bank all the way down at 12 V nominal. Having a higher-voltage array allows your client to locate the PV array farther from the battery bank and not have to take out a second mortgage for the length of wire connecting the two.
- Finally, MPPT manufacturers are constantly adding features and increasing efficiencies. These improvements help you, the designer and installer, by increasing the flexibility in your design.