mixing solar panel voltages within a single solar array

 hi john,

 out of curiosity and in an effort to be of some help i have been looking at some of the product information on your proposed setup. so far it looks like you may indeed be able to run two series strings of five for your array.

 we have to look into it some more. if that option proves wrong looks like you will be limited to an array made up of seven of those pw1000 modules (the 105's?) due to temp correction for the garden state.

 where are you seeing that 192v startup requirement? from some of the info i've gathered we need a minimum vmp of 139v?
http://www.solarsupply.com/Pages/technical_data_sb_1800u.htm

here they are calling it MPP Vpv a strange way of writing it?
 it's difficult to find information for this original sb1800u. and it looks like SMA no longer supports it with a sizing calculator.

 in any case we won't be able to run some of the modules at 12v and others at 24v due to the difference in the imp and isc of the paralleled vs series modules. that would be like trying to run completely different panels.

 looks like best case would be to pick up two more modules for two strings of six. and worst case is two strings of five with the possibility of going off line on a record high temp day. or running one string of six/seven modules.

 hopefully a few more folks chime in..

best regards, dave

oops i see james beat me to the punch.

 james,

  thanks for that technical tidbit. good info as usual!

cheers,dave

edit: p.s. still curious of there is any difference in the sb1800u and the swr1800u?

�  hi john,

 "Now what if I put 9 panels in a single string. 43V x 9 = 387Vdc. Thats really high but in tolerance. 34.6 x 9 = 315Vdc thats within the Mpp range of 139-400Vdc. I really dont like the 400 volts DC. Seems awfully lethal to me."

 we have to back up a bit here. as much as we want to get the most out of the equipment we have in hand, we just can't get away with a string of more than seven of those 100watt pw1000's

 lets go back over to that SMA sizing chart james linked us to.
http://www.sma-america.com/en_US/service/solar-design-tools.html
 when we put your data in (assuming the sb1800u & swr1800u are one and the same)not knowing your exact jersey location i went with atlantic city new jersey. record low is -23*f (1942) and average high is 85*f (july). the closest choices are..�  -22* and 86*f.

 the sizing tool gives us 1 string of 5 in series, one string of 6 in series or 1 string of 7 in series,
or 2 strings of 5, of 6 or of 7 in series.

 mr. cormican has given some valid reasons to avoid the 2 series strings of 5 and i might trust his judgement on that.

 that leaves us with the 6 or 7 string option.

 the reason we can't go with more modules in the series string is just as voltage drops in the higher temps the voltage increases in the lower temps. these higher voltages can (will) be destructive to our inverter, not just stopping production as the high temps will.

 i sure like that idea of picking up a sb700u to make use of those 4 extra modules (6 on the 1800 & 4 on the 700)

 or that other option of 2 more photowatt modules to make up a 2 string array of 6 in series.

 keep at it..good to get everything worked out first.

kind regards, dave

 hi john,

 just my opinion here..i really think it would be wise to stick within the pw1000 family of modules, you might get away with the 95w or the 105w to mix with those 100watt modules you have but i would not wander too far away from there. the reason here is that each module has a unique i/v curve that the mppt controller tracks and we can throw the controller a curveball by mixing the array with different modules. be warned that there are non-ul approved pw1000 modules lurking out there and our inspector will be looking for the ul rating with a grid tied system.

"Are strings considered to be in parallel? Could strings be run at different voltages, basic question but I dont know how this inverter is designed."

 yes, with multiple strings the strings are in parallel.
all strings in an array have to be at the same voltage but you can run separate arrays at different voltages on separate inverters.

"Anybody know where I could pick up some PW1000's. I've tried E-bay?

There has to be some distributor out there with a couple laying around:)"

 i agree, you were able to find those four. just a thought here..if you find someone running one you might offer to trade it for a new module of their choice?

 are we having fun yet?

best regards, dave