Lowest OCV An MPPT Is "Worth It"?
There has to be some experience here on this forum to share. When I look at the MPPT manufacturer's data specs, the incredo-hyperbole gives me diarrhea.
Forum Discussion
Hi,
I used to have a PWM 15 amp controller, and to that I connected a 3 way switch. With it I can turn off the solar, or switch from PWM to directly to the battery. I could watch the amp meter both ways, and got a minimal increase in amperage with it "On", VS going through the PWM controller. The controller triac does get warm, so there is some voltage loss there.
With my SolarBoost 50 controller (MPPT) they report that I should get 20% more power under certain conditions. They measure the amperage going into the controller and the amperage going to the battery, and claim that their controller magically increased the amperage. And it does! So I might have 22 amps going into the controller and 25 amps going out. This is because the controller it letting the solar panels put out nearly 16 or 17 volts, while the controller is converting it's 22 amps X 17 volts to 25 amps X 13 volts to recharge the depleted battery.
The math works too, as there is more wattage going into the controller than coming out. 374W input and 325 W output.
What they do not tell you is that the solar panel will also put out more amperage when it is not restricted in producing higher voltage. So if a bypass switch is installed, the 21 volt open circuit panel can put out 13 or 14 volts at a much higher amperage than while putting out the 17 volts that the MPPT controller restricts them to.
So back to the original question. I probably will not be buying another MPPT controller (well the SP50 will handle my needs for now) because the cost of solar panels has dropped significantly! Even tilting and tracking panel racks have become a much longer time to pay for themselves with the extra wattage they allow you to collect. Why? The cost of solar panels themselves has dropped by 1/3 to 1/2, so installing more panels and not tilting them has become cost effective. So is the lower cost PWM controllers. At $13 for a 10 amp controller, you can afford several of them for the system, and not spend $300 or more for the MPPT controller.
If you are working with high voltage panels and 12 volt batteries, then the MPPT controller is sort of a requirement. Yet you can also order 12 volt nominal panels and connect them with the lower cost PWM controllers, and install the whole system fairly low cost.
So to have 1,000 watts input to the battery each hour, you can install a 2 axis 1,100 watts worth of panels, and a MPPT controller, and hope for the best. This would be the most expensive system. $1,000 in panels, $600 for the two controllers, and $600 -$800 depending on the cost of the panel mounts and the base they need to sit in.
You can install 1,200 watts worth of panels and fixed mounts, still collect about 1,000 watts with a MPPT controller. $1,200 in panels and $600 for two controller rated at about 50 amps each.
You can install about 1,400 worth of solar panels, 4 each PWM controllers, and fixed mounts, and have the lowest cost system. It will still put more than 1,000 watts into the system, using only about $1,400 in panel cost, $80 in controller cost, and wiring.
Fred.
I used to have a PWM 15 amp controller, and to that I connected a 3 way switch. With it I can turn off the solar, or switch from PWM to directly to the battery. I could watch the amp meter both ways, and got a minimal increase in amperage with it "On", VS going through the PWM controller. The controller triac does get warm, so there is some voltage loss there.
With my SolarBoost 50 controller (MPPT) they report that I should get 20% more power under certain conditions. They measure the amperage going into the controller and the amperage going to the battery, and claim that their controller magically increased the amperage. And it does! So I might have 22 amps going into the controller and 25 amps going out. This is because the controller it letting the solar panels put out nearly 16 or 17 volts, while the controller is converting it's 22 amps X 17 volts to 25 amps X 13 volts to recharge the depleted battery.
The math works too, as there is more wattage going into the controller than coming out. 374W input and 325 W output.
What they do not tell you is that the solar panel will also put out more amperage when it is not restricted in producing higher voltage. So if a bypass switch is installed, the 21 volt open circuit panel can put out 13 or 14 volts at a much higher amperage than while putting out the 17 volts that the MPPT controller restricts them to.
So back to the original question. I probably will not be buying another MPPT controller (well the SP50 will handle my needs for now) because the cost of solar panels has dropped significantly! Even tilting and tracking panel racks have become a much longer time to pay for themselves with the extra wattage they allow you to collect. Why? The cost of solar panels themselves has dropped by 1/3 to 1/2, so installing more panels and not tilting them has become cost effective. So is the lower cost PWM controllers. At $13 for a 10 amp controller, you can afford several of them for the system, and not spend $300 or more for the MPPT controller.
If you are working with high voltage panels and 12 volt batteries, then the MPPT controller is sort of a requirement. Yet you can also order 12 volt nominal panels and connect them with the lower cost PWM controllers, and install the whole system fairly low cost.
So to have 1,000 watts input to the battery each hour, you can install a 2 axis 1,100 watts worth of panels, and a MPPT controller, and hope for the best. This would be the most expensive system. $1,000 in panels, $600 for the two controllers, and $600 -$800 depending on the cost of the panel mounts and the base they need to sit in.
You can install 1,200 watts worth of panels and fixed mounts, still collect about 1,000 watts with a MPPT controller. $1,200 in panels and $600 for two controller rated at about 50 amps each.
You can install about 1,400 worth of solar panels, 4 each PWM controllers, and fixed mounts, and have the lowest cost system. It will still put more than 1,000 watts into the system, using only about $1,400 in panel cost, $80 in controller cost, and wiring.
Fred.
