Solar The Solar Panel Thread

Clewsy

Member
Apr 17, 2017
60
46
18
Cairns
Looking good.

See what you mean about average junction box and no cable gland, they spared no expense.

Sounds like you already know that you only have to shade a single cell in a panel (if it has 36 cells) and the panel output pretty much goes to 0W. Bugger of a thing.
 
  • Like
Reactions: Crusty181

mikerezny

Well-Known Member
Sep 11, 2016
1,630
2,728
113
Mount Waverley, VIC
Sounds like you already know that you only have to shade a single cell in a panel (if it has 36 cells) and the panel output pretty much goes to 0W. Bugger of a thing.
Not quite, each of these particlar panels is actually two sub-panels wired in series. Each sub-panel has a bypass diode across it. If a single cell is in shade, the output will be down to 50% for that panel. If the other two panels are still in sunlight, then 5 out of 6 sub-panels will be working, so output will be down by only 17%. for the system.

@Crusty181: The sub-panels will probably be made with the sub-panels split along the short edge or the long edge. In either case, it is likely from your photo that the A/C will only shade one of the sub-panels. So you should be down by only 17% if the A/C shades one of the panels.

cheers
Mike
 

mikerezny

Well-Known Member
Sep 11, 2016
1,630
2,728
113
Mount Waverley, VIC
Hey Mike, a couple of pics. Original panel has been removed, and was across the rear of the van where the new is positioned. New mounts for the new panels done. Conduit ready, as are additional wiring and MC4s. Jayco had glued the underside old panel to the top of the roof junction box, that was interesting. The junction box was in pretty average condition to, hidden under the panel, so that will need some love

Im a bit anal about the panels staying put, so found the aircon alum mounting frame on the drivers side, and a rafter on the passenger side for the front mounts, the rear ones I don't care so much about they can just sit on the glass roof sheet. The driver side panel will be partially shaded by the aircon unit if we're not careful, but not too much other option. We always try to park the van that side to the sun where possible anyway, so we cast shade on the awning side so it should only be an issue on the rare occasion, and I can top up with one of the blankets if need be


View attachment 63743
Hi,

It is hard to seal the figure 8 cable coming out of the junction box. I don't know of a gland that would do this. If it was me I would be sourcing a couple of normal glands and splitting the figure 8 cable running each wire through a gland.

cheers
Mike
 

Crusty181

Well-Known Member
Feb 7, 2010
6,854
13,971
113
Mentone, VIC
Hi,

It is hard to seal the figure 8 cable coming out of the junction box. I don't know of a gland that would do this. If it was me I would be sourcing a couple of normal glands and splitting the figure 8 cable running each wire through a gland.

cheers
Mike
The shading is manageable, we free camp a lot and I can't recall too many times where we've enjoyed fun sun and I've not been able to orientate the van in our favour; conveniently with this problem panel location is we prefer the sun from over that side of the van anyway because it casts the shade on the preferable awning side.

The look of the distorted roof junction box with its misaligned lid may be disturbing, but inside it's polar white, clean as a whistle and with no evidence of ever having moisture in it. I presume that's the result of the panel physically sitting on it and having the full height of the 40mm panel frame protecting it. The roof junction doesn't box leak that's evident, so I'm in two minds whether to leave it and use to dual-core or replace the dual-core with solar cable. A downside to both, removing the dual-core means I break the effective seal but using the dual-core I suspect the MC4s won't seal effectively. I'll have a better look today, and roll the dice on that one then.
 

Boots in Action

Well-Known Member
Mar 13, 2017
2,054
1,804
113
Ferny Grove, Queensland
Looking good.

See what you mean about average junction box and no cable gland, they spared no expense.

Sounds like you already know that you only have to shade a single cell in a panel (if it has 36 cells) and the panel output pretty much goes to 0W. Bugger of a thing.

Hi @Clewsy , @mikerezny is right on the ball there. That is why the bypass diodes are in parallel with EVERY sub-panel. Hence the extra value of Schottky diodes in reducing voltage and current losses.
 

Boots in Action

Well-Known Member
Mar 13, 2017
2,054
1,804
113
Ferny Grove, Queensland
Hey Mike, a couple of pics. Original panel has been removed, and was across the rear of the van where the new is positioned. New mounts for the new panels done. Conduit ready, as are additional wiring and MC4s. Jayco had glued the underside old panel to the top of the roof junction box, that was interesting. The junction box was in pretty average condition to, hidden under the panel, so that will need some love

Im a bit anal about the panels staying put, so found the aircon alum mounting frame on the drivers side, and a rafter on the passenger side for the front mounts, the rear ones I don't care so much about they can just sit on the glass roof sheet. The driver side panel will be partially shaded by the aircon unit if we're not careful, but not too much other option. We always try to park the van that side to the sun where possible anyway, so we cast shade on the awning side so it should only be an issue on the rare occasion, and I can top up with one of the blankets if need be

View attachment 63745
View attachment 63743
View attachment 63744

Hello again @Crusty181 , just having a bit of a look at your roof junction box. If the back of the panel was just resting on the top of that box, the heat from the back of the panel would stick things together pretty good. Try to avoid contact with back of panel to allow heat to be dispersed with good air flow.
 

Crusty181

Well-Known Member
Feb 7, 2010
6,854
13,971
113
Mentone, VIC
Hello again @Crusty181 , just having a bit of a look at your roof junction box. If the back of the panel was just resting on the top of that box, the heat from the back of the panel would stick things together pretty good. Try to avoid contact with back of panel to allow heat to be dispersed with good air flow.
Easier said than done I'm afraid. The rear panels location over the box is predetermined by the panels existing factory mounts, and short of moving the panel to the front of the van there's nowhere else for it to go. I can possibly lift the new panel a bit which may clear the box otherwise it would mean removing and replacing or relocating the box which I'm reluctant to do because it will create a potential leak point
 

mikerezny

Well-Known Member
Sep 11, 2016
1,630
2,728
113
Mount Waverley, VIC
Easier said than done I'm afraid. The rear panels location over the box is predetermined by the panels existing factory mounts, and short of moving the panel to the front of the van there's nowhere else for it to go. I can possibly lift the new panel a bit which may clear the box otherwise it would mean removing and replacing or relocating the box which I'm reluctant to do because it will create a potential leak point
Is it possible to source a suitable lower profile junction box?
cheers
Mike
 

Clewsy

Member
Apr 17, 2017
60
46
18
Cairns
Thanks @mikerezny makes sense. Although i thought the sub-panels were wired in parallel? Could be wrong.

@Crusty181 could you use a slightly higher aluminum bracket where the existing panel was, i custom one that bolts to existing one, ally strip. Bit more work with 2 lots of bolts but might give you the clearance over jbox.
 

Drover

Well-Known Member
Nov 7, 2013
12,723
19,450
113
QLD
Sitting on the side ,here ......................................................my LRPS is so much easier...........................
 

mikerezny

Well-Known Member
Sep 11, 2016
1,630
2,728
113
Mount Waverley, VIC
What the heck is that site, you need to get away from your computer and get outside a bit more ...................... a proper LRPS (note capital letters) is need for those typical 5 days of cloud Victorian days....... Possibly a Jeep Thing
Hi,
If I can't find it with Google, it doesn't exist.
cheers
Mike
 
  • Like
Reactions: Drover

Crusty181

Well-Known Member
Feb 7, 2010
6,854
13,971
113
Mentone, VIC
Thanks @mikerezny makes sense. Although i thought the sub-panels were wired in parallel? Could be wrong.

@Crusty181 could you use a slightly higher aluminum bracket where the existing panel was, i custom one that bolts to existing one, ally strip. Bit more work with 2 lots of bolts but might give you the clearance over jbox.
I looked at that, i can wrangle a slither of clearance doing nothing; maybe your idea to get another few mm. I have the cabling running thru suspended conduit between the panels to also take into account
 

Boots in Action

Well-Known Member
Mar 13, 2017
2,054
1,804
113
Ferny Grove, Queensland
Looking good.

See what you mean about average junction box and no cable gland, they spared no expense.

Sounds like you already know that you only have to shade a single cell in a panel (if it has 36 cells) and the panel output pretty much goes to 0W. Bugger of a thing.

Hi @Clewsy , further to your query regarding the shading of cells in a solar panel, I did comprehensive tests at home here in sunny Brisbane today. I have 3 different folding panels bought at different times. The first one is a 180 W folding panel with 72 groups of solar cells - 6 horizontal and 12 vertical in EACH portion. It has only two wires coming out of back of panel to connection box. OCV was 20.8 volts with both halves connected in parallel.. The next panel 200 W folding has 16 groups of solar cells - 4 horizontal and 4 vertical. It has 3 wires coming out the back and I have 2 Schottky diodes across both outputs. The output voltage of each sub panel was 9.0 volts, and connected in series provides 18 volts (OCV) at the terminals . The other half of this folding panel is the same and connected in parallel , so still only 18.0 volts OCV.
The last panel is 200 W with 32 groups of solar cells (4 horizontal and 8 vertical) with the same diodes and connections. OCV for each sub panel was 9.4 volts and when connected in series produced 18.8 volts OCV. The other half of the folding panel is connected in parallel with this sub panel giving me 18.8 volts OCV.
Just giving you some feed back on how heat affects panel voltage as you mentioned, the first panel was dropping very slowly as it heated up after about 15 minutes in the sun. The second panel was poor, dropping quickly from just over 18.0 volts to 17.8 volts in a few minutes. The last and more recent panel started at 18.8 volts and was fairly steady at this voltage even after 15 minutes in the warm sun. So yes, some panels do not do so well when they get hot - poor coefficient of heat resistance in solar cells.
As far as shading is concerned, the first panel would shut down if even partly shaded as only one panel in operation - no sub panels. The Schottky diode would however provide a path around the shaded panel for current generated by other panel/s in a series string. The last two folding panels each contain two sub panels with bypass diodes connected across output terminals. When I covered one half( vertically), the voltage in the unshaded sub panel remained at 9.0 or 9.4 volts, but the shaded panel voltage dropped to less than 6.0 volts in each case. However, the total of both sub panels was still around the 15.0 volt mark as they are connected in series. Even when I had shaded one complete panel (of the two folding panels) and half of the remaining one (which was connected in series) , a voltage of around 15.0 volts was still showing. I was not able to measure current as I had no connection to a controller or any load. However, I would think that the current output would then be only a quarter of total possible panel rating, but it would still be generating some power even at a lower voltage if bypass diodes are functioning properly.
I hope this helps one come to grips with these issues. It all depends on how the panel is set up (with or without sub panels) and the number of output leads coming out from the back of the panel/s.And the importance of bypass diodes cannot be underestimated!!
 
Last edited:

Clewsy

Member
Apr 17, 2017
60
46
18
Cairns
Thanks @Boots in Action that's some great testing you've done there with different panels, well done.

I agree well worth testing to know the type of panel you have and how it's wired and if you have diodes or not can make a big difference if you can run your coffee machine in the morning or not.