#154905  by NeilV
 Wed Sep 11, 2019 8:47 pm
Or just use the silver bubble windscreen protector from your dash 🤔

I’m with Will on this one though, more panels does it easier :lol:
 #154930  by Paul-Carter
 Fri Sep 13, 2019 10:24 am
:ugeek: Yes I covered my roof with flexible panels held on with double sided tape. If you put one on wrong and need to take it back off you are in for a very long day.
Let no photon pass!!
 #155813  by Neddy
 Wed Oct 16, 2019 10:08 am
I have been directly comparing the performance of a 180 watt 12/18volt PERC solar panel and a 280 watt 24/36volt Monocrystalline panel. I was primarily interested their performance under low light conditions, which for the purposes of the test, I defined as less than 20% of full, direct sunshine, such as you would get at dawn and dusk or on very cloudy days. The load was a 12 volt AGM battery, 75% charged.
I discovered that at low light levels, MPPT controllers connect solar panels directly to the battery and so lose their significant advantage over PWM controllers under these conditions, when the solar panel current is the charge current.

Results. The 180 Watt PERC panel gave a 1.5 Amp charge while the 280 Watt panel gave a 1.6 Amp charge. The smaller panel gave 38% more power per Watt! I know that PERC panels are good – but they are not that good. The explanation here is that the 180 watt panel is a “12 volt” panel, providing 9.32 Amps at 19.3 volts while the 280 Watt panel is a “24 volt” panel giving 8.86 Amps at 31.6 volts. In low-light conditions when solar panels are connected directly to the battery, it is AMPS that count – and do the charging. (The panel voltage is pulled down to that of the battery.)

Panel cf.JPG

Note the negative effects of connecting solar panels in Series and/or using 24v panels for a 12v system.
See how a 560 watt solar array can give TRIPLE the “cloudy weather” output of an array of over a kilowatt!
In dull weather, even a relatively small but efficiently configured 360 watt system can supply DOUBLE the current of a huge 1095 watt array that is inefficiently configured.

All of the above figures are based on 12 volt systems and conditions of low light.
Once the light level increases, solar controller MPPT functionality kicks in and the huge advantages of parallel panel connection and low panel voltage shrink to become small advantages.
I lack the hardware to accurately compare the efficiency of PERC solar panels vs conventional panels at varying light levels. Nevertheless it is clearly evident that they offer significant advantages and are well worth their small price premium.

Neville.
 #155819  by Paul-Carter
 Wed Oct 16, 2019 7:28 pm
Today was the first chance I have had to test the 1200 w of panels in the sun as the bus is stored under cover. I went for a run to get a new self containment check. with almost full overcast the controller was showing an array voltage of 84 volts which I was pleased with. The second part of the story is amps but as the batteries were full I have not got a read on that but so far so good.
 #155836  by Neddy
 Thu Oct 17, 2019 11:48 am
Paul, say you have six 200watt 42volt 5amp panels. There are three main ways in which they could be connected, all resulting in a 1200 Watt array.

(A) All panels connected in Series, giving 5 Amps at 250 volts.
This is the least efficient option in good light, and gives a "low light" charge rate of about 1 Amp.
(B) Three paralleled pairs, each of 2 panels connected in Series, giving 15 Amps at 84 volts (so your setup must be somewhat similar).
This would give a "low light" charge rate of about 3 Amps.
(C) All panels connected in parallel, giving 30 Amps at 42 volts.
This is the most efficient option in good light, and gives a 6 Amp charge in "low light" conditions.

You can see that the higher the voltage, the lower the current and the poorer the performance, especially in low light conditions.

It might be worth reconfiguring your system. A "re-jig" could double its performance in low light - when it really matters. As is, your 1200 watt system stands to give you a substantial power surplus in Summer, but fall short on very cloudy days, especially in Winter and/or Southern latitudes.

Neville.
 #155842  by Paul-Carter
 Thu Oct 17, 2019 5:23 pm
I have six panels yes . 4 at 250 w and 2 at 100w.
Taking the data from the labels on the panels and putting it into excel the best combination I came up with was to have the 4 x 250w all in series with the two 100w panels paralleled and then seriesd in with the 250w units this gave me a theoretical 1100 watts which I am happy with.
All the panels are 12v nominal. That's why I was happy with the 84 volts I got the other day. I think it is not a bad result for under $600 worth of panels.
 #155845  by cherokee94nz
 Thu Oct 17, 2019 9:04 pm
I am setting up a system in the next 6 weeks on a caravan. Looking at getting 4 x 240 watt 12 volt panels. And 2 40 watt controllers . What will be the best way to set up this system to achieve max all year efficiency Into 300 lithium battery. Tell me if there is a better way please.

Alan
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