Sorry if this is a dumb question but this looks to be the best place to ask it. My limited understanding of what MPPT is trying to acheive is to fined the best voltage point a panel produces the max amps and converts that to a lower useable voltage at even higher amps that way increasing the max yield from the solar panel. Have i got that part right?
If i am correct in that part of the operation then it would stand to reason that the voltage measured at the panel side would be around the quoted 17v on the panel manufacturer and the output side would equal to battery voltage. Have I got that bit right?
The reason for me asking is that I have 2 Chinese solar controllers I'm testing that claim to be MPPT type but panel voltage and battery voltage are very close to the same which to me would indicate they are nothing more than PWM controllers.

T1 Terry

T1 Terry wrote:Sorry if this is a dumb question but this looks to be the best place to ask it. My limited understanding of what MPPT is trying to achieve is to fined the best voltage point a panel produces the max amps and converts that to a lower usable voltage at even higher amps that way increasing the max yield from the solar panel. Have i got that part right?

Well you sorta got it right. They find the panels best voltage at which 'voltage x amps' is at max. Remember, for a solar panel when the voltage increases the current decrease following the panels I/V curve.
Then it converts that to a lower required voltage at higher amps.

T1 Terry wrote:If i am correct in that part of the operation then it would stand to reason that the voltage measured at the panel side would be around the quoted 17v on the panel manufacturer and the output side would equal to battery voltage. Have I got that bit right?

Yep, most panels have a MPP at around 16 - 17 volts, however this MPP shifts during the day with varying light conditions and heat. So a panel with a MPP at 17 volts, when hot, could have a MPP at 15 volts. That is, when hot, it'll produce ore power at 15 volts as opposed to 17 volts.

T1 Terry wrote:The reason for me asking is that I have 2 Chinese solar controllers I'm testing that claim to be MPPT type but panel voltage and battery voltage are very close to the same which to me would indicate they are nothing more than PWM controllers.

Well if lighting conditions weren't great, or your panels were running hotter than usual, maybe hot weather, then your MPP (maximum power point) would drop a little from say 17 volts to 16 volts. Basically it depends on the conditions.
A good test is to cool the panels with water, after they heat up, and see if the panel voltage increases. It should increase by around 1.5 volts for a 12 volt panel if tracking correctly.

Thanks for that explaination Tony, interesting test method. What is the idea panel temp? I would imagine there is a point where the temp could be too low for good power production. Does the MPP voltage rise at a lower temp?

T1 Terry

Normally the manufacturer states the ratings at the NOCT (normal operating cell temperature), which is around 50-55 degrees Celsius. You may find dodgy manufacturers which state panel ratings at 25 degrees.

You will find that the MPP voltage will rise with lower temperature, and drop with higher temperature, and you will have around 10% higher power when operating at 25 degrees as opposed to 55 degrees.

On another forum(yet another) someone posted an interesting idea. Mounting Peltier effect modules under the panels with a wet back system to preheat water for the hot water service. The power generated by the Peltier modules could be used to drive a circulation pump. I wondered how much gain in panel output this approach would have, obviously powering the Peltier modules would cool the panels much more but I doubt the gains would near equal the power draw, the "no free lunch" principle.

T1 Terry

Peltier units are really low efficiency, I can't imagine you'd produce enough juice to do anything, but adding water cooling to the back should improve the efficiency of the panels by about 0.5% per degree improvement ... probably be enough to power the pump plus a little (if designed right you shouldn't need a pump), however it would likely void your panel warranty if it required any mod to the panel, you'll have to worry about freezing, leaking, and it will add to the panel weight significantly. Another bonus on the plus side though ... if it keeps your panels cool enough it could significantly increase the life of the PN Junction potentially doubling the life (assuming all other factors stay the same).