Tracked and Static Panel on MPPT charge controller

Started by nigel, June 14, 2011, 09:38:05 AM

Previous topic - Next topic

nigel

OK I have a client who has a single tracked array which is maxed out with 16 x 115 watt panels (no more space for panels on tracker) giving him a total of 1840 watts at 48v batt nominal. They are wired in 4 strings of 4 giving a VOC of approx. 80v and a VMP of around 69 volts. So there is scope to add a 60 or 80 amp  MPPT controller and add more capacity to his array.

However he hasn't the money for a second tracker and panels and MPPT unit. My thinking is I can add 4 extra panels to each string but in a fixed array but still going through the MPPT charge controller.keeping well below 145v temp corrected threshold.

Yes these static  panels would vary in Vmp through out the day more than the tracked panels but as the 4 new fixed panels were feeding one of the tracked strings ie 5 panels in 4 strings, it shouldnt cause too much confusion with the MPPT charge controller.

I appreciate this is a generic question and not a direct  Midnite Product related  question let me know if these questions are OK

Nigel

ericwahl

The fixed panels should be a separate string of 4 in my opinion.

nigel

A separate string on a separate charge controller maybe  ?  But the MPPT unit has spare capacity. Or do you mean  a completly separate string going through the same MPPT charge controller as the tracked panels making it five strings of 4,  if it is the latter then I would disagree as the tracked array would have different VMp early and late sun, as one fixed panel to 4 tracked panels  per string going through the same  MPPTcc  each fixed panel would send a similar voltage to the 4 stringed  tracked panels in series , making the 5 panels in series having a similar or very close total VMP.

Could you elaborate ?

Nigel

ericwahl

Quote from: nigel on June 14, 2011, 03:06:29 PM
A separate string on a separate charge controller maybe  ?  But the MPPT unit has spare capacity. Or do you mean  a completly separate string going through the same MPPT charge controller as the tracked panels making it five strings of 4,  if it is the latter then I would disagree as the tracked array would have different VMp early and late sun, as one fixed panel to 4 tracked panels  per string going through the same  MPPTcc  each fixed panel would send a similar voltage to the 4 stringed  tracked panels in series , making the 5 panels in series having a similar or very close total VMP.

Could you elaborate ?

Nigel
I thought you were suggesting strings of 5, with one panel in each string not on the tracker. Perhaps I misunderstood. That would obviously be bad since each string would be limited by the non tracked panel.
I think you could do the 5 strings of 4 on the same controller since Vmpp shouldn't be that different.

nigel

Eric it wouldnt be limited, lets say for example the tracked array was facing the sun all day long sitting at a regular 68v vmp then i have a static array feeding each string of the tracked array with one more panel per string and the fixed array panels varied from 15 v to 18 vs each panel on the fixed array to the constant string then the mppt cc would see a constant 83v to 86v because the fixed array is always at the varying angle of the sun as it moves across the sky.

yes its vmp varies through out the day but its contributory voltage to the existing 4 tracked strings is constant . Thus the bueaty of allowing the mppt to do its stuff without any ying or yang as i see it-

if the fixed string was separate ie 5 strings then the mppt would see 4 strings at X plus 1 string at X + or minus 3v  giving it a ying yang head ache.


Hope im not making a fool of myself here :-[

Nigel

ericwahl

Quote from: nigel on June 16, 2011, 05:20:29 PM
Eric it wouldnt be limited, lets say for example the tracked array was facing the sun all day long sitting at a regular 68v vmp then i have a static array feeding each string of the tracked array with one more panel per string and the fixed array panels varied from 15 v to 18 vs each panel on the fixed array to the constant string then the mppt cc would see a constant 83v to 86v because the fixed array is always at the varying angle of the sun as it moves across the sky.

yes its vmp varies through out the day but its contributory voltage to the existing 4 tracked strings is constant . Thus the bueaty of allowing the mppt to do its stuff without any ying or yang as i see it-

if the fixed string was separate ie 5 strings then the mppt would see 4 strings at X plus 1 string at X + or minus 3v  giving it a ying yang head ache.


Hope im not making a fool of myself here :-[

Nigel
Actually the current will vary far more than the voltage, and that's the problem. You would not want a shaded panel in series with an unshaded panel, just like you do not put a small panel in series with a large panel. The lowest current member of the series circuit will limit the current in the circuit.