12v verses higher panel voltage advantages

[SOMF]

I tried to search for this but got so many hits I decided to ask for my self. I have a sail boat with 3 130w panels with 17.8voc wired parallel to a mppt 20amp controller. The wireing is #10 and is definitely undersized but it is what i could find in El Salvador at the time. It goes panel 1 6' to panel 2 then 20' to panel 3, then 6' to panel 4 then 12' to the controller. The controller is a bluesky 20 amp and won't take higher voltage. Now the 2 questions. 1. I plan to add a 4th 130w panel and need a bigger controller, my though is to go with a outback 60 amp that can take higher voltage but still charge 12v. And wire the panels in series giving me roughly 72v. Will this make the wire runs ok? 2. If the wire distance is still to long for 10ga would a second pair of10ga wires ran parallel to the original wires with 10/2 combined to make a heavier gauge do the trick? I think 2 10ga insulated wires tied together give the equivalents of a 8ga wire.

[waynefromnscanada]

Hi SOMF, Welcome to the form.
4 panels in series, max amps would be roughly 7 amps. In my opinion and experience, the existing 10ga wire should be fine if the panels are in series.
You don't mention the open circuit voltage of you're panels, but the total in series open circuit voltage should be less than the max that can be handled by for example, the Morningstar TS-MPPT-45 controller, which would do an awesome job for you.

[vtmaps]

The outback controller (and most other MPPT controllers) work more efficiently and run cooler if the input voltage is not too much higher than the output voltage. I think you would be better off in a 2x2 configuration, i.e. 2 panels in series makes a string, then 2 strings in parallel.

BTW, I think that you are probably wrong about the Voc. I think the Vmp is 17.8 volts and the Voc is a few volts higher. If I am correct then the Imp is about 7.3 amps. If that is correct you will be OK with 10 gauge wires. It never hurts to go heavier wire.

Since you are on a boat and the panels are so far apart I would be concerned about shading and orientation. Shading of one panel (even from a rope) will greatly diminish the output of that string. If one string has a different orientation (or shading) than the other, the MPPT controller may get confused finding the max power point. Depending on circumstances you may be better off with 4 parallel panels with one or more controllers, or two MPPT controllers, one for each of the two strings.

--vtMaps

[waynefromnscanada]

Since you are on a boat and the panels are so far apart I would be concerned about shading and orientation. Shading of one panel (even from a rope) will greatly diminish the output of that string.

--vtMaps

Agree. That was also floating around in my mind earlier. Solar on boats can be tricky, especially so when the panels are in series.

[SOMF]

Thanks for the quick replies, it sounds like I can leave the set up as is and just add the new panel and upgrade the controller. The boat is in dry storage for now but I plan to be back down in December to install the new goodies. Just before we hauled the boat out in May we went 12 days straight without starting the generator! And we have an apartment size refrigerator on a 12 hour on 12 hour off cycle, not 12 hours at a time. Also a laptop,2 fans and lot's of led lights at night. The batteries were never below 12.2 in the morning, they are 4 years old. My hygrometer broke so voltage is the only test method I had but I'll take 1 back. I have 1095ah bank, 9kw diesel generator, 1600w gas generator and 3 Kyocera 130w panels into a bluesky mppt controller.

[westbranch]

If that is the 2000e series BlueSky CC you are maxed out for panels already... It will put you way over the 20A limit for that model.. been there, done that. Look into the Rogue, it has lots more capacity.

[BB.]

Rogue 30 amp 12/24 Volt MPPT controller (still not a very high input voltage with the current units).

-Bill

[niel]

i believe you are already in excess of the max on your present controller as 3 130w pvs is 390w max and dividing by 12v is 32.5a. adding a fourth is 520w in total and at 12v is 43.33a. now most times it won't be at max as we derate to 77% of the stc ratings and you may experience shading on some pvs while others are illuminated. if it were me i'd probably opt for 40a or more for the ability on the cc. higher voltage capability on the cc may allow you to keep the same wire gauge to be used if seriesed. if going with 4 pvs you can even go with 2 strings of 2 and the same gauge would probably still work just fine. if you have doubts then you can use a voltage drop calculator, but how best to wire your pvs will be your decision as we aren't there to see. what ever would be easier for you would most likely work just fine, but a bigger rated mppt cc is needed.

[vtmaps]

we went 12 days straight without starting the generator! And we have an apartment size refrigerator on a 12 hour on 12 hour off cycle, not 12 hours at a time. Also a laptop,2 fans and lot's of led lights at night. The batteries were never below 12.2 in the morning, they are 4 years old. My hygrometer broke so voltage is the only test method I had but I'll take 1 back. I have 1095ah bank, 9kw diesel generator, 1600w gas generator and 3 Kyocera 130w panels into a bluesky mppt controller.

A voltage of 12.2 in the morning indicates your battery is about 50% SOC (state of charge). They can't possibly get recharged with your solar panels, especially since you have other loads. Even with four panels in full sun you will only achieve 2% - 3% charge rate (i.e. you will be pushing 20-30 amps into a 1095 ah battery bank). Usually we recommend a 5% -13% charge rate from the panels, but that may be impractical on a boat, so you will need to use the generator. To get back in balance, you could remove some batteries from the bank (its not clear to me what your loads are... you may or may not need such a large bank).

Your batteries are probably somewhat sulfated and no longer have a 1095 ah capacity. You should run your generator in the morning to bulk charge your battery (generator is more efficient at bulk than absorb) and then let the panels do the tapering absorb charge. You should try to get your batteries up to 100% charge at least twice a week. Anytime you get below 70% SOC you should recharge the batteries immediately or you will be encouraging sulfation. And get a new hydrometer.

--vtMaps

[vtmaps]

It goes panel 1 6' to panel 2 then 20' to panel 3, then 6' to panel 4 then 12' to the controller.

Previously I wrote that if you added the fourth panel to make a 2x2 series/parallel configuration, your existing 10 gauge wire would be OK. Since (because of shading) you are going to wire the 4 panels in parallel, I think you should use some heavier wire.

In the 2nd leg (2 panels, 20 ft) with both panels at full power you will have a 3.34% voltage drop and 8.7 watt power loss.

In the 3nd leg (3 panels, 6 ft) with all 3 panels at full power you will have a 0.27% voltage drop and 5.8 watt power loss.

In the 4th leg (4 panels, 12 ft) with all 4 panels at full power you will have a 4.01% voltage drop and 20.8 watt power loss.

Note: the voltage drop is proportional to the power produced, and the power loss in the wires is proportional to the square of the power produced. Thus at half power the 4th leg will have a 2% voltage drop and a 5.2 watt power loss.

My advice is to use heavier wire for the 20 ft run and the 12 ft run.

--vtMaps