Solar Costs - MPPT vs PWM
The continued lower price of the larger panels has now dropped the MPPT costs just below PWM for a larger RV solar setup. SolarBlvd Cynergy 3x$200 250W panels 750W $600 SolarHome Morningstar MPPT ...
Forum Discussion
I am not so sure that the MPPT controller will be worth it. This is because solar panels can put out more amperage at a lower voltage than when at a higher voltage.
So a 120 watt solar panel putting out 13.5 volts directly to a battery with a switch the only thing in between should be putting out more amperage than when the same solar panel is connected to a MPPT controller and putting out say 18 volts to the controller, then that controller is putting amps into the 13.5 volt battery.
It would take a bypass switch to find out, and accurate amperage readings though a shunt, with accurate voltage drop across the shunt readings. Then switch the power leaving the panel to the MPPT controller or directly to the battery, and see what one puts out the most apperage into the panel.
I found that if I changed my PWM controller (1994 - that is all they had back then) to a switch, I could get an additional 0.5 amps into the battery. Then when close to dark, I could switch it back to automatic (through the controller). This would give me an additional 3 - 4 amp hours per day from my original 90 watt solar system.
My MPPT controller (SP50) is not putting out nearly as much amperage as I expected, based on what I could get from the pair of 45 watt panels on a cold day in NOvember at 4,500' elevation in CA.
For my money, I will be buying more panels and PWM controllers. Not spending $300 on a MPPT controller anymore.
Fred.
So a 120 watt solar panel putting out 13.5 volts directly to a battery with a switch the only thing in between should be putting out more amperage than when the same solar panel is connected to a MPPT controller and putting out say 18 volts to the controller, then that controller is putting amps into the 13.5 volt battery.
It would take a bypass switch to find out, and accurate amperage readings though a shunt, with accurate voltage drop across the shunt readings. Then switch the power leaving the panel to the MPPT controller or directly to the battery, and see what one puts out the most apperage into the panel.
I found that if I changed my PWM controller (1994 - that is all they had back then) to a switch, I could get an additional 0.5 amps into the battery. Then when close to dark, I could switch it back to automatic (through the controller). This would give me an additional 3 - 4 amp hours per day from my original 90 watt solar system.
My MPPT controller (SP50) is not putting out nearly as much amperage as I expected, based on what I could get from the pair of 45 watt panels on a cold day in NOvember at 4,500' elevation in CA.
For my money, I will be buying more panels and PWM controllers. Not spending $300 on a MPPT controller anymore.
Fred.
