saltydawg wrote:The biggest reason to go mppt is two reasons. One you spend a lot of time with the panels partially shaded, or limited room for more panels when you need more power.
Not being in direct sun, is the reason I will go mppt when I do solar.
Socal Tom wrote:The conventional wisdom I've seen on the web is that PWM controllers aren't worth using, and if you don't have MPPT you have a 2nd rate system. The truth is that PWM can be just fine for many of us. The truth is that for a weekend camper like myself, I can probably go the whole weekend without charging and still be above 50% power, so I probably don't need solar at all. This system should keep my batteries in the 20 to 25% discharge range, so I can see some value there.
Tom
saltydawg wrote:Yeah the big reason is not in full sun. A pwm cant do any charge if the panel is putting out less voltage due to shade than the batteries voltage. Where as a mppt can take 2volts of the panel and get it up to the voltage the battery needs to charge at that moment even thou it would only be like 1 amp of charge.
Tom&Shelly wrote:
So if your panel is in full Sun, but not pointed optimally, is it the voltage output that drops? I'm designing a solar power system for our non-electrified garage to charge and maintain the teardrop battery, just did some calculations of the solar angle throughout the year, and now I'm wondering if I made a mistake ordering a PWM controller.
Tom
tony.latham wrote:I've got a 100-watt panel on the roof and a 30-watt panel on the tongue box. The panels are controlled with a PWM controller.
I went with a PWM because MPPTs are big and more expensive.
We use 8-10 amps per night. (Mostly from my CPAP).
Even in the camp above with a canopy and a broken cloud cover the battery was charged by noon. If we're in the open, it's charged up by 11:00 at the latest ––depending on how high the ridges are to the east.
Sure, I could change the controller out with an MPPT .... but why do I need a more efficient system?
Tony
Tom&Shelly wrote:
Since both of your panels are basically horizontal, if the voltage out of the panels were strictly proportional to the (cosine of the--but never mind that detail) angle of the Sun to the panel, a PWM controller would almost never work--the voltage would never reach 12 volts. Since Tony's system works (well), that's obviously not how the panels work! Most of the power drop due to imperfect pointing must be the result of current (amperage) out of the panels.
Tom
saltydawg wrote:I dont know your install so I cant say what charger you need. But hopefully the above info can help answer that for you.
saltydawg wrote:Tom&Shelly wrote:
Since both of your panels are basically horizontal, if the voltage out of the panels were strictly proportional to the (cosine of the--but never mind that detail) angle of the Sun to the panel, a PWM controller would almost never work--the voltage would never reach 12 volts. Since Tony's system works (well), that's obviously not how the panels work! Most of the power drop due to imperfect pointing must be the result of current (amperage) out of the panels.
Tom
another reason why panels put out more, if you look at the chart I posted, you are right it does not look like a direct proportional math problem. Each cell on the panel is going to put out x number of volts, at y amps, until it does not put out anything usable. I used the 50 % number just as an example.I would bet the amperage drops faster, but the volt are going to drop too. Vs a battery where as the volts drop, the amerage used goes higher.
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