Susie Maestre

user Electronics Engineer

city Innovuze Solutions Inc.

  • Solar Street Light with MPPT Charger

  • Created: Mar 14, 2017

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Most solar charge controllers are inefficient in a way since it can only harvest 50% to 70% of the maximum solar energy over 10 hours of daily charging. Selecting a properly designed charge controller is very important to the longevity and efficiency of the battery-based photovoltaic system. To address the inefficiency among solar charge controllers, Maximum Power Point Tracking (MPPT) solar charge controllers are used. Maximum Power Point Tracking is usually digital. The charge controller looks at the output of the panels, and compares it to the battery voltage. It then figures out what is the best power that the panel can put out to charge the battery. It takes this and converts it to best voltage to get maximum current into the battery. Most modern MPPTs are around 93-97% efficient in the conversion.

In this design, the MPPT has a typical electrical efficiency of 97% at full load. This efficiency figure includes the losses in battery reverse protection and panel reverse flow protection MOSFETs. The design has built-in battery charge profile for 12V Lead acid batteries. The design uses ‘perturb and observe’ algorithm for MPP tracking. This gives fast acquisition of MPP operation. This design is developed using the MSP430F5132 microcontroller. Also, the design can drive up to 15 LEDs in series with 700mA of current. The LED driver section is a boost converter. The electrical efficiency of boost section is about 93% while driving 12 LEDs at 700mA, and is around 91% while driving 6 LEDs at 350mA. The section is protected with load and converter cut-off during overload; short circuit and load open fault situations. There is also provision to dim the output after specified time intervals.

The circuit is designed for low power solar charger and LED driver solution in solar streetlights. It is capable of charging 12V batteries with up to 10A output current from 12V solar panels. However, it can be easily adapted to 24V systems by just changing the MOSFETs to 60V rated parts.



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