The technology for solar photovoltaic battery charge controllers has advanced dramatically over the past five years. The most exciting new technology, PWM charging, has become very popular. Pulse Width Modulation (PWM) is the most effective means to achieve constant voltage battery charging by switching the solar system controller’s power devices. When in PWM regulation, the current from the solar array tapers according to the battery’s condition and recharging needs.

Charging a battery with a solar system is a unique and difficult challenge. In the “old days,” simple on-off regulators were used to limit battery outgassing when a solar panel produced excess energy. However, as solar systems matured it became clear how much these simple devices interfered with the charging process. The history for on-off regulators has been early battery failures, increasing load disconnects, and growing user dissatisfaction. PWM has recently surfaced as the first significant advance in solar battery charging. PWM solar chargers use technology similar to other modern high quality battery chargers. When a battery voltage reaches the regulation setpoint, the PWM algorithm slowly reduces the charging current to avoid heating and gassing of the battery, yet the charging continues to return the maximum amount of energy to the battery in the shortest time. The result is a higher charging efficiency, rapid recharging, and a healthy battery at full capacity. In addition, this new method of solar battery charging promises some very interesting and unique benefits from the PWM pulsing.


  • Ability to recover lost battery capacity and desulfate a battery.
  • Dramatically increase the charge acceptance of the battery.
  • Equalize drifting battery cells.
  • Reduce battery heating and gassing.
  • Automatically adjust for battery aging.


  • Longer battery life
  • More battery reserve capacity
  • Greater use of the solar array energy
  • Greater user satisfaction
  • Opportunity to reduce the battery size to lower the system cost

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