#160702  by gerard
 Mon Apr 06, 2020 3:31 pm
I hope you are all coping well under the lockdown. Frustrating for many, but a good time to do some work on the camper.
Recently we had a Cvana awning added to our Ducato buscamper. Inevitably, this has meant that we would introduce a shading issue for the solar panels next to it. We have two 150 watt panels, one across and one along the new awning structure. Both will be affected when the awning starts shading the panels (it is about 15 cm higher than the panels and only a few cm away from them), one row of cells at the short side and one of the long side of the panels.

I did some experiments today by artificially creating the shading by putting pieces of wood over the areas of the panels that would be most affected by this shading (sunny conditions this morning).
Shading one row of cells on both panels reduced the panels output by 77% using this method (I put a load on the batteries and measured with and without shading. Watt produced as well as Voltage and Amps were recorded).

There are some options to remedy this.
1 Shift the panels away from the awning. This is an option for one panel only (and I can’t shift it much anyway), the other panel will run into shading by the satellite dish
2 Lift the height of the panels (not practical).
3 Replace with other panels and or relocate. Replacing the 1510 mm panels across the roof by a much shorter panel will be easy and effective. I can also replace the longitudinal panel with a shorter panel going across as with the first panel.

I intend to go for the replacement option. There are panels which are almost 20 cm shorter (170W) which can be used.
I am also aware of the experiments that Neddy did with the 180W PERC panels. They are a little bit shorter than the current panels, and could be used if also shifted a bit more away from the awning. There would still be some shading at lower sun angles as I can shift them only a few cm.

I have some questions however. Currently we have unknown brand panels, all I know is they are rated 36 Volts and 4.16A (?). I found out they are wired parallel, and there is a 6mm2 cable to connect them with the regulator (6 m for the furthest panel).

The solar regulator is a Tracer 2210AN (Rated panel 260W, 390W max). It will only take 6mm2 cable max.
I’m thinking of replacing the panels with either
• Sinosolar 175 W (open Circuit V 23.5V, Max power V 18.7V, Max power Amps 9.36A). These panels are only 1324 mm long, which would solve most of the shading problem and increase Wp
• Or the PERC panels Neddy was talking about (180W, Open Circuit 22.9 V, Max power V 19.3V, Max power Amp 9.32 A) . The panels are longer than the Sinosolar but at 1480mm only 30 mm shorter than the ones we have now, they are also cheaper and increase Wp even slightly more.

Would it be better to stick with high Voltage panels? The installer at the time dais that the 36 V panels would start producing earlier in low light, but I now think that is debatable.
If I go from high voltage panels (36V) to low voltage panels (around 20V?) it basically doubles the Amps. Is this a problem for the wiring (6mm2 over 6 m)?
Would I be pushing the regulator too hard? I would think that the Wp is seldom reached, and even so, it is still below the Max W for the regulator (but above the rated W).

And what panel choice would you think is best? I like the PERC panels (we have them on our house roof, as well as some non PERC that were installed earlier, and they perform well). But the physical panel length issue would make me go the other way to reduce the shading impact.
Any comments/advice is really appreciated.

Gerard
 #160704  by Allanz44
 Mon Apr 06, 2020 4:57 pm
Fit the 2 new panels in series this fixes any problem with voltage drop . Just confirm that your solar controller can handle the voltage of the combined panels. Fit 2 equal panels , don’t mix different sizes etc , the type of panel will make bugger all difference , they are mounted flat so are not in optimal position , the specs between panes are all at peak conditions on the perfect day, you will never achieve this .. Mount as high as you can to reduce shading , tghis will also improve the cooling of the panels.. Quality connections , go for it
 #160705  by Neddy
 Mon Apr 06, 2020 5:04 pm
Hi Gerard, some good questions there.

"Would it be better to stick with high Voltage panels?"
Definitely not!. The higher the solar input voltage, the lower the controller efficiency. To maximise efficiency you need low voltage panels connected in Parallel.

"The installer at the time said that the 36 V panels would start producing earlier in low light"
He is wrong - in fact, the reverse applies! At low light levels MPPT controllers are in "direct connection" mode, and the Panel current IS the Charge current. An 18v 150W panel supplies double the current of a 36v 150W panel. This means that it will start charging earlier than an equivalent 36v panel. When MPPT function kicks in, the 18v panel will continue to outperform the 36v panel, but this huge advantage shrinks to a small advantage.

"If I go from high voltage panels (36V) to low voltage panels (around 20V?) it basically doubles the Amps. Is this a problem for the wiring (6mm2 over 6 m)?"
Two of your proposed panels connected in parallel would give a maximum current of around 18.6 amps. This would not be a problem for the existing wiring, but there would be a transmission loss of about 3.5%. This is not an unacceptable level and heavier cable would reduce this, but here is a suggestion you might like to consider. You could run another 6mm² cable and parallel the two panels at the controller.

"Would I be pushing the regulator too hard? It is still below the Max W for the regulator."
That is the most important figure, so what you propose would be just fine.

. "I like the PERC panels but the physical panel length issue would make me go the other way to reduce the shading impact."
Good decision. I really like PERC panels too, but in your situation, you stand to lose more from shading than you would gain from using PERC panels.

Gerard, please feel free to ask for evidence supporting any of the above assertions. I am happy to provide it but didn't want my response to your questions to turn into a long, boring epistle.

Neville.
 #160708  by gerard
 Mon Apr 06, 2020 6:03 pm
Thanks guys for the quick and helpful responses.

*Allanz44, I am not too worried about the voltage drop. At 3.5% drop as mentioned by Neddy will be more than compensated (in terms of output) by the increased efficiency of the new panels, in effect going from 300W to 350W installed. The voltage drop won't be much more than it is now I suspect, and the system, has worked pretty well (although you never have enough when toy charge ebike batteries and make coffee on a Nespresso). I just wanted to make sure the increased Amps were not a problem.

*Paul, I thought of that too. We tend to park North/south to catch the morning sun on the awning side where we have the large slider. Worst possible position for early morning solar shading. When parked that way the bottom of the panles would still need lifting. I feel the shorter panels (further away form the shading zone) would be an easier solution for us.

*Neddy, as always, thanks for you comments. I might go for the non PERC but shorter panels as suggested. One of the problems with the controller is that the maximum wire size it accepts is 6mm2. I know you can double up and join them just before they reach the controller, but if the current wire size is good enough I think I will stick with that (easy, just plug in the new panels I hope), An extra connection also has disadvantages I suspect. The 3.5% voltage drop is a bit more than I expected, but with the current setup I would have losses too)or are they much less in terms of output in Watts when you run higher voltage?

Gerard
 #160711  by Neddy
 Mon Apr 06, 2020 8:27 pm
Gerard, don't forget that a 3.5% loss is a theoretical maximum that would only occur when the panels are operating at their absolute peak power - and they never will be. Most all of the time losses will be much lower than that and on sunny days they don't matter much at all because you will have a surplus of power. At very low light levels, however, you might only be getting, say, 3 Amps and your cabling losses under these conditions would be a miniscule 0.5%.
Power transmission losses pale into insignificance when compared with what can be lost by wiring the wrong panels the wrong way - especially in low light conditions. Here is a comparison of 170 watt 12v vs 24v panels when connected in Series vs Parallel, giving their current output in poor light (Taken here as 1/6 that of full sunlight).

2x 24volt panels 30.6v, 5.6A connected in Series. 0.9 Amp
2x 12volt panels 18.4v, 9.24A connected in Series 1.5 Amps
2x 24volt panels 30.6v, 5.6A connected in Parallel 1.9 Amps
2x 12volt panels 18.4v, 9.24A connected in Parallel 3.1 Amps
 #160717  by vansvilla
 Tue Apr 07, 2020 7:06 am
How much effect is the shading going to have in practise?
Will the shading only occur when the vehicle is facing one direction?
Do you run out power that you need 100% efficiency?
Are you using a sledge to crack a walnut?
 #160721  by gerard
 Tue Apr 07, 2020 9:37 am
Vansvilla, thanks for your input. We have limited roof space, and panel space is competing with staelite dish and two hatches. We love our nespresso coffees, and need to recharge the Ebike batteries when doing one of our rail trails in tis beautiful country. We love cycling rail trials and often park up for two nights, cycling in both directions over two days. And more often than not we are not on power. In other words, we need to make the most of our solar panels.
Yes, the shading will only happen if the sun is on one side of the van. This time of the year the shading would "kick in at around 1 PM" if parked up North South (se earlier comments also). Moving the van is not a real option (nuisance , impractical and often not possible). Even with half the cells od the row closest to the awning being shaded (about 6 cm of shade), production drops 40%, quickly going up to 77% shortly after (just before the whole cells of that row are covered). Especially this time of the year or under cloudy conditions it is an issue. It is not a matter of life and death, we could go somewhere we have power to hook up to, but that is not the point. We could also forgo our coffees (5-6 a day), or make coffee a different way. We could also stay home.
I suspect for many motorhome homers, tinkering with technical aspects of the camper/motorhome is part of our addiction. Well, it it for me anyway. Part of the human condition I think. I know our Nespresso are not cheap (by the time you add all the hardware including inverter), but this is what we choose. By the way, we still enjoy coffee from coffeeshops we find on the way.

Neddy, thanks for the additional information. Convinced me which way to go.

Gerard
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