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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. So let us look in depth on what PWM controllers have to offer.

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 out-gassing 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 set point, 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. These include:

  • -Ability to recover lost battery capacity and

desulfate a battery;

  • -Dramatically increase the charge acceptance

of the battery;

-Maintain high average battery capacities (90%

to 95%) compared to on-off regulated state-ofcharge levels that are typically 55% to 60%;

– Equalize drifting battery cells;

-Reduce battery heating and gassing;

-Automatically adjust for battery aging;

-Self-regulate for voltage drops and temperature

effects in solar systems.

The benefits noted above are technology driven.

The more important question is how the PWM

technology benefits the solar system user.

Jumping from a 1970’s technology into the new

millennium offers:

• Longer battery life:

– reducing the costs of the solar system

– reducing battery disposal problems

• More battery reserve capacity:

– increasing the reliability of the solar system

– reducing load disconnects

– opportunity to reduce battery size to lower

the system cost

• Greater use of the solar array energy:

– get 20% to 30% more energy from your

solar panels for charging

– stop wasting the solar energy when the

battery is only 50% charged

– opportunity to reduce the size of the solar

array to save costs

• Greater user satisfaction:

– get more power when you need it for less


The final function of modern solar charge controllers is preventing reverse-current flow. At night, when solar panels are not generating electricity, electricity can actually flow backwards from the batteries through the solar panels, draining the batteries. You’ve worked hard all day using solar power to charge the batteries; you don’t want to waste all that power! The charge controller can detect when no energy is coming from the solar panels and open the circuit, disconnecting the solar panels from the batteries and stopping reverse current flow.

When assessing which type of solar charge controller to purchase, you need to know about their functionality and features but it’s also helpful to see a straightforward comparison of your options.