wiggy
Well-Known Member
I’ve come by 3 10w solar panels that I thought would be handy to keep the batteries fully charged Instead of leaving my 100w portable panel. Do I Join them in series or parallel?
Parallel, series or paraseriel
- Thread starter wiggy
- Start date
VicS
Well-Known Member
I would wire them in parallel but provided you use a MPPT controller that will accept the OC voltage of all three in series ( probably nigh on 70 volts) there may be some benefits in a series connection.
pvb
Well-Known Member
If you wire them in series, shading on one panel, or a fault on one panel, will cause problems. Wiring in parallel makes them less susceptible to problems.
MikeBz
Well-Known Member
If you wire them in series, and they are 'cheap' panels which don't have bypass diodes, then if any of the panels is shaded you will lose output from all of them. If they are in parallel then you only lose output from the shaded panel(s). If the panels don't have blocking diodes then wiring them in parallel won't be very good either.
wiggy
Well-Known Member
Well that’s confused me even more! To add all the panels have blocking diodes. Does that alter any opinion? Att eh moment I’m eyeing towards parallel.
pvb
Well-Known Member
Good plan!
Stewproud
New Member
If you wire in parallel you increase the current, in series you increase the voltage. I have 2 x 100W panels. In series 36 volts and 5,6 amps, in parallel 18 volts and 11 amps. So checkout the loss in your cable and remember to double the distance for the return.... Example 2.5mm cable with 5 meters from controller to panel. Resistance per meter is 0.0782 ohms. For a parallel connection at 11 amps the volts drop is 0.86volts with a loss of 9watts.
MikeBz
Well-Known Member
Blocking diodes prevent the battery discharging through the panel when there is insufficient sunlight to get the panel voltage up to the battery voltage (unlikely to be required if using a controller). They are not the same as bypass diodes which are to mitigate against shading.
Blocking and By-Pass Diodes Used in Solar Panels
RichardS
N/A
I agree. There will be reduced cable losses if you go for max voltage rather than max current. However, make sure that none of the panels will be in shade because, in series, one in shade is like all in shade.
Richard
VicS
Well-Known Member
Does that apply if they have bypass diodes ?
RichardS
N/A
The bypass diodes do prevent panels overheating if the distribution of light is not uniform but they are not very effective at optimising output and it is rather exceptional where one panel is fully shaded and the others are generating full power. Ultimately, it all depends upon the degree and pattern of shading but it many cases with a more general pattern of shading the output would actually be greater without the diodes.
Richard
rszemeti
Well-Known Member
Theoretically correct, but we are talking about 3 x 10W panels here ... if your cable losses even in parallel mode come to more than 0.1W, I will be VERY surprised! In high power systems with long cable runs, it is a cosnideration .. but on 3 x 10W panels, even on thin cable the I2R losses will be negligible. The losses due to shading will be significantly more, even with bypass diodes.
Note that discharge protection diodes are not the same as shading bypass diodes ... discharge protection diodes are in seroes with the cell, shading protection diodes are in parallel
Paulg25
Well-Known Member
Think that may be wrong. Approx 7.5 ohms per kilometer... 0.0075 ohms per meter.
MikeBz
Well-Known Member
That may or may not be true of a single panel, but if you have multiple panels in series and some are shaded/partially shaded whilst others are not then surely the overall output will be significantly better if the shaded panels have bypass diodes?
Graham_Wright
Well-Known Member
Wire in a switch then you can choose between the two. Quite interesting.
RichardS
N/A
That is very true. I was speaking in general terms but, as you say, we are only talking about 10W panels here, so none of these considerations are very important.
Richard
Stewproud
New Member
You are correct, I mis-quoted using a 10 meter example..
wiggy
Well-Known Member
So what is the answer to my original question, series or parallel? 3x10w panels make it simple for me please.
Stemar
Well-Known Member
I've had 2 X 20w panels, wired in parallel though a standard, cheap controller for the last 7 tears. I asked a supplier at the boat show about this and, because the only place I could put them was under the boom he recommended two panels in parallel to reduce the losses caused by shading. So far, they just do what it says on the tin. You may get a theoretical, maybe even a real advantage from wiring in series, but it'll be small.
To my mind, though I may be a bit behind the times, parallel is simpler, more robust and more forgiving. It also means you could use a controller like this EP Solar Duo-Battery Solar Charge Controller 12/24v 10A. £33.30, which will maintain two banks of batteries.
To my mind, though I may be a bit behind the times, parallel is simpler, more robust and more forgiving. It also means you could use a controller like this EP Solar Duo-Battery Solar Charge Controller 12/24v 10A. £33.30, which will maintain two banks of batteries.
