Wiring mismatched solar panels?

[neelie]

Background info:

I recently ordered 3 x Panasonic 235W HIT panels, one was smashed in transit. I now have 2 which I am hoping are still serviceable.

And unbelievably, there is now not a single such replacement panel available in the entire USA anymore - believe me, I have tried everywhere.

I have a Midnite Classic 150 MPPT controller.

So I am now considering the feasibility of buying a third replacement panel which will be from a different manufacturer and will most likely have a different capacity and output voltage.

Questions:

Is this feasible? If so, how do I wire it up?

I suspect that the answer will be that I should simply get a second MPPT controller for that lone odd panel. This would be the most efficient solution?

Thanks

ps... Not sure if this is relevant but I also have a KISS with a Tristar 45 controller, also not yet connected.

[CAELESTIS]

Call EcoDirect in San Diego, 760-597-0498. I just purchased two from them and a Midnite 150 as well. Ask for Albert.

Where are you located?

[noelex 77]

That is a pity.
To connect to one regulator they do need to reasonably matched for best performance.

For parallel connection the general rule is that Vmp needs to be within 0.5v (43v for the panels you have). If it outside this range it will not do any damage but the output from the third panel will less. It is better to get a slightly higher voltage for the mismatched panel. (If you want to match the extra panel better apply the temperate correction coefficient to the Vmp assuming a cell temperate of about 40c instead of the unrealistic 25c where the voltage is measured).

This still may be your best solution as it saves the cost of an extra regulator and the Midnite display will still give you the correct information on the total solar output.

The approximate loss of a mismatched panel can be estimated. For example a panel with a Vmp 50v panel would give approximately output of 43/50 so a 250w panel will perform like a 215w panel (the actual output will be slightly better than this simple formula suggests, but this will hopefully help quantify the effect and help decide if an extra controller is justified).

The Midnite is a great controller and there is little risk of poor tracking with the mismatch.

[neelie]

Originally Posted by CAELESTIS

Call EcoDirect in San Diego, 760-597-0498. I just purchased two from them and a Midnite 150 as well. Ask for Albert.

Where are you located?

Fort Lauderdale.

I will call them first thing tomorrow.. my fingers are firmly crossed. Thanks for the heads up!

[neelie]

Originally Posted by noelex 77

That is a pity.
To connect to one regulator they do need to reasonably matched for best performance.

For parallel connection the general rule is that Vmp needs to be within 0.5v (43v for the panels you have). If it outside this range it will not do any damage but the output from the third panel will less. It is better to get a slightly higher voltage for the mismatched panel. (If you want to match the extra panel better apply the temperate correction coefficient to the Vmp assuming a cell temperate of about 40c instead of the unrealistic 25c where the voltage is measured).

This still may be your best solution as it saves the cost of an extra regulator and the Midnite display will still give you the correct information on the total solar output.

The approximate loss of a mismatched panel can be estimated. For example a panel with a Vmp 50v panel would give approximately output of 43/50 so a 250w panel will perform like a 215w panel (the actual output will be slightly better than this simple formula suggests, but this will hopefully help quantify the effect and help decide if an extra controller is justified).

The Midnite is a great controller and there is little risk of poor tracking with the mismatch.

And herein lies my dilemma !.. A lack of space... The Panasonics are extremely efficient and have a tiny footprint for their output and Vmp. I will start looking but but I doubt that I will find another panel with a similar Vmp, I did a brief search and found nothing. I will spend tonight Googling.

I suspect that I will be doomed to getting a second controller unless CAELESTIS's man in San Diego has one in stock. c'est la vie.

ps.. I decided on the Midnite on one of your earlier recommendations to me

[neelie]

Originally Posted by CAELESTIS

Call EcoDirect in San Diego, 760-597-0498. I just purchased two from them and a Midnite 150 as well. Ask for Albert.

Where are you located?

You sir are a freaking legend!... Saved me with that piece of info.

I have just bought one.

Don't know who you are but I owe you several beers if we ever cross paths.

Thank You, Thank You

Niels