Series or Parallel?

[ZoNiE]

OK, so my solyndra panels will not fit on the RV in any configuration I want to live with, so they will go on the patio and run some other loads at the house.

I have been looking at panels, and three Kyrocera 140W KD140SX-UFBS panels seem to be a good fit in the rooftop envelopes I have. So the question is:

                  Series @ 6.33 Isc and 66.3 Voc
                                            or
                  Parallel @ 18.99 Isc and 22.1 Voc?

End output is basically the same at 29.2A to the battery bank, but the Series setup allows me to run smaller (read cheaper) wire. Voltage is higher, current is lower. To me, a series arrangement is a no brainer, but is it?

66VDC does not bother me...


This will be a 12V system with 2 GC2's possibly adding two more GC2's when these crap out.

[Halfcrazy]

Well thats tough. Parallel is to close in voltage for my comfort. I guess as long as shading is not an issue I would go Series

[vtmaps]

Putting them in series also means that you will not need a combiner and circuit breakers.

Part of the decision should be based on the distance between the array and the controller.

The best arguments for putting them in parallel is that there is a small increase in efficiency, and that you could use lower voltage DC breakers, fuses, switches, etc.

Generally, I am not too concerned about a fraction of a percent of efficiency... the exception being when you are using the controller at its limits.  If you spend a lot of time drawing 30 amps from the Kid, then you should lean towards lower input voltage.  But as halfcrazy points out, there's not much headroom.

What I would really like to see is 4 of those 12 volt panels (100-110 watts each) connected in series/parallel. 

--vtMaps

[ZoNiE]

Since I posted this, I have been looking at other panel sizes. Larger wattage panels give better bang for the buck and lower weight due to less frame material overall, but I run into "things" on the roof. This is one instance where my Carrier Low Profile 15K heat pump is a problem as it is longer and wider than the usual RV AC units. My roof is also curved...

4X100W is also a good fit for me as I can put three of them on the right side and the fourth on the left side and not have it shaded by the other three if I tilt them. It also helps balance the weight somewhat as the Left side of my coach is a bit heavier due to the genset location.  (I have a Honda EV4010 for the heat pump when camping in the desert in the summer) Cost and weight go up a bit with four, and there are more roof penetrations for the mounting rails. I really want to get as close to 500W as possible, however.

The controller will probably be mounted high on the wall near the front of the trailer so it is as close to the battery bank on the tongue as possible, but still be able to use it without sticking my head in a compartment hatch. Wiring will come through it's own penetration sealed under a sealed electrical box instead of the usual through the refer vent to prevent dripping. No matter how much you work to put drip loops in wiring, 70MPH and road vibrations will probably work against me.

Just where do people mount the Kid controllers on RV's anyway? Sure would be better to have a controller and a separate control panel  that could be remote mounted anywhere.  I guess it doesn't really matter as I will have less than 30A and can upsize the charge wires a few gauges, although I have about 200' of 10-3 find strand cable made in Japan, that really holds up in weather. I have an extension cord made out of the stuff and it has stood in the sun for years with a gate sliding over it almost daily...

[Westbranch]

2 x2  was my first  thought  too.  No combiner CBs needed just one disconnect, less wire than 3 and less loss also. Closer to final V  of b. bank so less heat losses in downconversion.  can you find some 140 or 150W pv's??

[ZoNiE]

Yeah, looking at the Grape 135 mono's as they are longer and narrower so I can actually fit 4.

I could squeeze 5 Grape 100's or three Kyocera 140's/Grape 160's.

Starting to look like I have a lot of options.

Any thoughts on the Grape's? Not much out there, Homeowner Depot carries them.

[vtmaps]

Any thoughts on the Grape's? Not much out there, Homeowner Depot carries them.

Some Grapes are or were positive ground. They didn't work too well with a conventional negative ground.

--vtMaps

[Westbranch]

The minute you go over 2 wires going to the CC you will need a combiner box with CBs to protect your investment...  so 2 x 2s or 2 x 3s ( s = series) etc...

[ZoNiE]

OK, I am now looking at some other options.

A local dealer/contractor here has some leftovers from larger jobs. I presume they buy them by the pallet, and end up with extras, but not enough to do a full job.

I can fit two 240W Sunpower panels, (three will fit, but 480W is about my target for Watts and Weight) but are these positive ground?  They are 19-series, 19% efficient.  I really want to use these, and at $160 each for new, and no shipping, a really good price.

Then there are some Kyrocera 140's, and some used Alps 123's. I can fit four of each of these, but it is not ideal.

Is the positive ground an issue with the Kid?

The roof is rubber over Wood, with nothing metal except the radio and TV antennas. The TV antenna is nowhere near where these will go, and the radio Antenna will be replaced with a rubber one anyway.

any advice on the SunPowers?

[ZoNiE]

Pulled the Trigger on three KC130GT black panels today. It's a little less than I can fit, but the price was right, they were local, and 390W was pretty close to my 400W goal. I could have had a fourth panel, but then I'd be over on total Wattage on the Kid and I'd have to remove the TV antenna from the roof of my trailer to squeeze the fourth panel in, as my Rooftop AC unit is wider than normal being a Carrier Low Profile.

[ZoNiE]

Ok here is what I have:

Two panels will be mounted on one side, end to end, and the other across from them.

I can wire in series or parallel just as easily, so wire runs do not matter.

Since I have an odd number of panels @ 20V / 8A each, it is also not an issue wire size-wise. I will be running #10 regardless, as I have 100's of feet of good cable already.
(note, volts/amps are rounded)
So, 60VDC into the Kid @ 8A for 12V output @ 24A
Or, 20VDC into the Kid @ 24A for 12V output @ 24A

Sure, I will need three breakers for Parallel, instead of one for series, but they are cheap. It's also more wire weight, but that's negligible.

Efficiency wise, is 60VDC to 12V charge really a problem?

[Free Energy Freak]

Negative ground?

[tecnodave]

Zonie,

In your case parallel would better for two reasons ......the charge controller will be more efficient at a 1.4 to 1 conversion ratio than it will be at 5 to 1 conversion........more work to do....more heat..less efficient and with your RV  you will be much more likely to have  of shading issues. Parallel configurations will be less affected as only the shaded panel will have a power loss where if you are all in series all panels in the string will be down to the same power as the shaded panel.

td

[ZoNiE]

Negatve Ground, Yes.

Zonie,

In your case parallel would better for two reasons ......the charge controller will be more efficient at a 1.4 to 1 conversion ratio than it will be at 5 to 1 conversion........more work to do....more heat..less efficient and with your RV  you will be much more likely to have  of shading issues. Parallel configurations will be less affected as only the shaded panel will have a power loss where if you are all in series all panels in the string will be down to the same power as the shaded panel.

td

Good point, and that is what I was looking for. I had considered the conversion ratio, but NOT the shading issue, which will probably be an issue.

Parallel it is!

[tecnodave]

Zonie,

I have tried the setup I have suggested , it is a bit close in voltage , but the kid does pretty good at low voltage input and getting every available watt. I am using L-16 and GC-2 battery format and I do equalization at 15.6 to 16.0 volts for my 12 volt systems but with a p.v. Output V@pmax rating of 18.7, sometimes I cannot finish an EQ due to low light levels. My preferred system would have a 34 volt string voltage for 12 volt system ( two 36 cell or one 72 cell panel ) and 68 volt. ( two 72 cell panels in series ) for my 24 volt systems, because I live in the coastal pea soup fog belt and need to scramble for every watt. I have done 105 volt and 140 volt strings but all controllers will run hotter doing this, the kid is no exception, heat produced is power lost, and heat is one of the killers of electronic gear.

If you can possibly squeeze one more panel in there and run two strings it would be worth doing but real estate on a motorhome is difficult. Modern 6 inch cell panels are just too big. Most of my good panels are 5 inch cells at about 32 X 64 inches for the panels. The Eoplly panels work well for an RV.

td