3x100w or 2x150w solar panels, waddayafink? (1 Viewer)

[hilldweller]

I never can get my head round this,.

I'm a little bit closer now..............
http://www.mpptsolar.com/en/solar-panels-in-parallel.html

This implies that the output of a solar array is current based, so both a shaded panel and full brightness panel will ( within reason ) both output 18V but the current will vary from each which is just what is needed.

 

[andy63]

If you connect your panels in parallel then even if one panel is well shaded you will still get the output from the unshaded panel... they don't need separate controllers... if both panels are shaded then the output is reduced (often drastically) even if they are on separate controllers.. so I don't see the need generally for separate controllers in the average installation..
In series you would need bypass diodes to bypass the shaded panel ... which is different from a bypass diode built into a panel solar cell connections to help it's output if it's part shaded... I've never been able to find out if most panels in fact have them fitted... the diodes I've seen on panels are I think blocking diodes...
Andy..

 

[DBK]

As far as I know very few panels have the diodes which reduce the effect of shading.
My suggestion about having two controllers was made slightly tongue in cheek. It does give a higher output if one panel is shaded but most folk wouldn't consider it cost effective.

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[Richard n Ann]

I asked the question to Photonic Universe "do your panels have built in bypass diodes across the individual cells?" The prompt reply I got was "each of our panels have a bypass diode in the junction box". So in other words he either didn't know, or didn't understand the question. I take it they haven't.

 

[andy63]

As far as I know very few panels have the diodes which reduce the effect of shading.

That's what I was thinking John. .. it would be hard to wire a panel cell configuration to take into account the shade pattern on a panel...
I've mucked about with a portable 80w panel consisting of two 40 w in parallel. .
Even with one totally shaded there is still output from the other... slightly shade that one and the output drops drastically..
Shouldn't be a concern to the op as it's a new installation and whatever he does the panels will be similar...
But just as a reminder and to refresh my mind cause I often get confused lol....
In series the panels should have the same current capability ...if not then the max current that you will get from the system is that of the lowest rated panel in the array..
In parallel the voltage of the panels has to be similar or the array will only be capable of the max voltage of the lowest rated panel...
Andy.

 

[funflair]

Unfortunately, we are swamped with marketing bollocks regarding solar power. Salesmen are motivated to sell rather than inform and I have found no measurement to demonstrate how much one solution is better than another. I approached the Centre for Alternative Energy (in Powys) for information about efficiency under different conditions and even they could not answer my questions.

Solar works, but it’s difficult to determine how well. If you have the money and payload, there can be little harm in fitting as much as you are able. The roofspace available may define the number and sizes of panel that you could fit.

I’d get one panel at a time until I had the solution I needed. Putting additional panels through a independent controllers would avoid problems due to incompatibility or shading but I’d start by linking them together, first, and seeing how effective that was.

I think there is no doubt that "Solar" works but the question how much is right is so difficult to answer as we all use our systems differently, there will be plenty of time when you have more than enough and again times when you don't have enough, I'm in the "if you have the space and payload camp use it" so stick up as many as is sensible along with a MPPT controller as that means that if you fit 4 panels you essentially get one free without taking up the roof space.

Martin

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[andy63]

I asked the question to Photonic Universe "do your panels have built in bypass diodes across the individual cells?" The prompt reply I got was "each of our panels have a bypass diode in the junction box". So in other words he either didn't know, or didn't understand the question. I take it they haven't.

That's where I've sourced my panels from and the response I got when asking that question...
All I know is that it doesn't take a lot of shade on a panel to reduce its output massively... so I came to the same conclusion.
Andy

 

[DBK]

I asked the question to Photonic Universe "do your panels have built in bypass diodes across the individual cells?" The prompt reply I got was "each of our panels have a bypass diode in the junction box". So in other words he either didn't know, or didn't understand the question. I take it they haven't.

That would be a blocking diode, to prevent current flowing backwards through the panel at night. Not strictly speaking required if a controller is used but as you say, they either don't know the answer or don't understand their product.

 

[Richard n Ann]

Wouldn't be a very good controller would it if it let the batteries discharge at night
No, all big panels need controllers, so the panels have bypass diodes in parallel with them in case they are configured in a series array and one of them is shaded.

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[Minxy]

Purely on the solar panel issue, I would go for 3 x 100Watt. Simply because if one fails, or is covered in bird poo, or is shaded by trees you will still get the benefit of the other two.

Yes a tiny bit more wiring and a few more screws (or sikaflex) but the benefit in usage terms would push me towards the 3x rather than 2x all else being equal.

My thoughts too, but initially only a couple of panels and see if there is actually a need for a third, if so it can be added at a later time, if not then quids in!

 

[Tony50]

I want to fit 2 solar panels either 2x 100watt or preferably 2 x150watt but I am concerned about the weight of 2 x 150watt each weighing up to 12to 15kgs will the roof of a 718XLB Chausson take the weight although the vehicle is a 4.4 tonne I have already a 12 kg sat.dome fitted .
Second question as I am confused about what I need when ordering solar panels although I have read all the above posts I just do not understand , I would like to see how much the panels are charging as well as controlling the panels output, or has this been laid out some where in another post , help would be very much appreciated.

 

[funflair]

I want to fit 2 solar panels either 2x 100watt or preferably 2 x150watt but I am concerned about the weight of 2 x 150watt each weighing up to 12to 15kgs will the roof of a 718XLB Chausson take the weight although the vehicle is a 4.4 tonne I have already a 12 kg sat.dome fitted .
Second question as I am confused about what I need when ordering solar panels although I have read all the above posts I just do not understand , I would like to see how much the panels are charging as well as controlling the panels output, or has this been laid out some where in another post , help would be very much appreciated.

You should be OK with the weight on your roof as it is spread over a fairly large area. A simple way to see what the panels are putting into your batteries would be to go for the Votronic MPPT regulator and one of their solar computers which simply plugs into the regulator, But if you done understand what you need are you planning to do it yourself or get somebody to fit it for you.

Martin

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[Tony50]

Hi martin Thanks for reply I am planning to get a m/home electrician to do it , as he is not available at the moment I thought I would do some research.

Tony A