Charge controllers are sized based on the solar system voltage and current or amps. The controller must be large enough to deal with the power generated by the solar panel. If your solar panel is less than 150 watt. Charge controller amp ratings range from 1 to 60. The most widely used are 10A, 20A, 30A, 40A, 50A and 60A. Voltage ratings for charge controllers are 12V, 24V and 48V. Solar panel watt. Solar panel output does not always match its rating. Because of how solar power works,the output on average will be lower than its rating. A 150W solar panel in theory generates 750 w. MPPT charge controllers cost more than PWM because they are more efficient. But for a 10A charge controller, a PWM is sufficient.The following will illustrate the difference betwe. The other thing you need to consider though is the reserve power. If you add a 10% to 25% to the calculations, a 10A solar controller will be insufficient for most systems. So this.