1 / 2019-07-14 00:16:19

Common Algorithms Used in Charge Controllers for Charging batteries from Solar Modules: Oversizing Problem

Charge controller, RapidSolar Charger, PXtractor, PWM, MPPT, Solar Charge Controller

The results of an analysis of state-of-the-art algorithms used in charging batteries from solar modules are presented. These common algorithms include PWM-based and MPPT-based algorithms. The analysis shows that all these algorithms employ the technique of Pulse-Width-Modulation. In this technique power is delivered to the batteries in pulses of constant voltage. Many times, switch-mode converters, such as a buck converter, are used to generate pulses of constant voltage. Consequently, power is delivered to the batteries only part of the time during a switching cycle. For the remaining part of the switching cycle, no power is delivered to the load (batteries). As a result, the average power delivered to batteries is only a small fraction of the total electrical power available in the solar modules in charging the batteries from a low charge state to a full charge state. Actual measurements with a market-leading, MPPT-based charge controller, show that the power delivered to a battery in a charging cycle is only one-fourth of the electrical power that is generated in a solar module. Thus, currently, solar modules, associated electronics, cabling and mounting hardware have to be oversized by roughly a factor of four, which greatly increase the cost, weight and size of solar power systems with storage. The results of this analysis point to the need of a new constant power algorithm that delivers all the electrical power of the solar modules to the batteries all the time. This algorithm, the associated implementation and related experimental results will be provided in a separate publication.