A pulse-width-modulating (PWM) type of charge controller sends spikes of energy to the battery when the battery requires charging (this is done when the energy pulse is ON) and then monitors the charged status of battery (when the pulse is OFF) in order to decide whether to continue charging in next cycle or to disconnect charging. PWM charge controllers are mostly designed on complex algorithms that control the amount of charge and monitors battery status in various practical conditions. The only advantage of using PWM charge controllers in our view is the low initial cost.

The limitation of PWM is that we need to arrange the charging Solar Array voltage in the closest possible proximity of battery or battery bank voltage, because when two sources of energies are connected together – the powerful one (i.e., battery) has the potential to pull down the voltage of Solar Panel to its level (say 12V) and this way the output power from Solar Panel will be lost by a proportional magnitude of the difference in two voltages.

Maximum-Power-Point-Tracking (MPPT) is thus invented to overcome the voltage mismatching issue which was resulting in loss of solar power, this type of charge controller by design assures the battery (or battery bank) voltage and adjusts the current supply accordingly to deliver almost all harvested power by the Solar Array. This technique also brings the advantage and flexibility of deploying Solar Array of higher voltages like 150Vdc to charge even a very lower 12Vdc battery/bank efficiently.

In monetary terms, let us compare the difference of energy yield using PWM and MPPT charge controllers from a 1kWp Solar Array.

  1. Say the overall efficiency of PWM is around 70%
  2. That of MPPT is around 95%
  3. Site energy potential as 1860 kWh per year per kWp
  4. kWh Units realized by PWM charge controllers would be 1302
  5. kWh Units realized by MPPT charge controllers would be 1767
  6. If we assume Rs.16/kWh unit of electricity then Rs.7440 loss per year in using PWM