Solar Panel Strange Output (2x 40W panels)

Oct 30, 2008
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Hi, I have a couple of solar panels fitted to my van roof and thinking they are not giving out max output I did some checks on what was going off.

My setup is 2x 40W panels connected in series to a simple 10A regulating controller and a 110Ahr battery.

The other day when the sun was out & bright I was getting 1.6A charge to the battery. When I covered one panel I still got 1.6A but when I moved the cover (my rolled up ground sheet so nice thick & dark) from the 1st panel to the next again I was still getting 1.6A charge (both panels covered and charge obviously dropped to zero)

Strange?? Would it not be expected that the charge rate would drop by half (give or take a little) when one panel is covered.

Your thoughts please: Poor installation - faulty panel /regulator /battery - ........ ??????
 
May 24, 2014
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If its of any help for reference, I have an 80w panel on the roof and that puts 3.2 amps into the battery. Sounds like the regulator to me, but Im no expert.
 
Aug 30, 2018
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Looks like you are seeing something of an anomaly. Firstly did you mean that your your panels are wired in series not parallel? If this is the case then you should be seeing an output from the panels of approximately 34V.
The output from the regulator is dependant on 2 factors. Firstly and most obviously the output from the SP’s doh! But also the state of charge of the battery if the battery is fully charged then even in the brightest of sunlight then it shouldn’t be putting anything into the battery. Also in reality even small amounts of shading has a devastating effect on the output of a solar panel you don’t need to cover half the panel to halve the output. It is difficult to say what your exact problem is I would suspect the controller, but I would invest in a cheap multimeter to check what’s going on in terms of inputs and outputs. For reference I have a 150w panel and the most I have seen recorded as charging output is 9amps
 
Mar 14, 2005
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The results you report are what I would expect from series connection of solar panels. But I'm wondering if series or parallel connection would be better for you? That will depend on the competence of your charge controller, and whether it contains full boost and buck power converter. or whether it's just a voltage limiter.

You would need to check the controllers instructions for how to wire for best performance
 
Mar 8, 2017
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Surely the two panels should be connected in parallel rather than in series. In serries I would expect the output voltage to double and for that to be reduced to a nominal 12v by the controller so effectivly only providing 40w. If they were connected in parallel then the current should double whilst the voltage is still reduced to a nominal 12v but now providing 80w.

Or am I missing something?
 
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As I understand it a MPPT controller can handle higher input voltages and has some thoeretical advantages. Of course if you double the voltage you halve the current.
 
Oct 30, 2008
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The series / parallel comments are the most interesting.

When I first had the solar panel system I put them out manually each time at site and had them wired in parallel (didn't have amp or multi meter on the output but the controller light flashed as battery full fairly early each morning).

To make life easier we had the panels professionally fitted to roof and it was only of recent I have seen the guy has wired them in series (now I often run out of power on a weekend).

The controller I have is a Photonic Universe PU1024.

Should I be thinking of changing the wiring of the 2 panels back to parallel?
Do you think it is worth upgrading the controller (what is a MPPT)?
 
Aug 30, 2018
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I am not an expert but: if your panels are connected in series, then they will have pushed too high a voltage into your battery. I think your battery will be toast sorry! Beg buy borrow or steal a multimeter and measure what is going on. If in bright light and the voltage going into your controller is more than 18v then it will work in 24v mode according to the manual.
Manual

Apologies. I got this wrong the controller selects it’s mode based upon the battery voltage it detects not the output from the solar panels

From the manual
“The controller will determine the system voltage at start up. If the battery voltage is lower than 18V, it will work in 12V mode. If the battery voltage is higher than 18V, it will work in 24V mode.”

A higher voltage / lower current is more will result in a lower power loss than a lower voltage / higher current. Which is why electricity is transmitted had high voltage.
So maybe your battery isn’t toast. Doesn’t explain what’s going on in your system and why it is displaying 1.6amp. Another factor to consider is that panels mounted on the roof are very inefficient compared to a freestanding panel that you can angle and aim at the sun.
 

Parksy

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Nov 12, 2009
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I'm not an electrician but I'd have thought that wiring your solar panels in series would increase the voltage but not the amperage. I could be wrong but you may have inadvertently changed your 12 volt system into a 24 volt system but this wouldn't provide necessarily more charging capacity.
If you're lucky your solar panels and controller will have over-voltage protection and your battery will not be damaged because the fuse that you fitted to protect the system (you fitted a fuse didn't you?) would have popped.
If you decided to re-wire in parallel you might have to increase the gauge of the wiring for your system to the controller.
There are basically two types of controllers a PWM (pulse width modulator) or 'shunt' controller or the slightly more expensive but more efficient MPPT (multiple power point tracking) controller. The MPPT controller is more efficient because as the available sunlight and ambient temperature changes the controller 'tracks ' the data and also the state of your battery (the amount of charge needed) and the optimum charge is delivered using that data. A PWM (often known as a shunt) controller simply switches on and off.
 
Mar 14, 2005
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Parksy is correct series connection of panels will double the voltage produced, but keep the current the same, (subject to both panels being the same design and exposed to the same amount of lights,)

Parallel connection would double the current capacity, but keep the voltage the same.

Power (W) is calculated by multiplying the Voltage (V) by the Current (A) , so doubling up a panel in either parallel or series has the potential to double the power of the array.

You have to look at the instructions for your charge controller for advice on the best method for your system.
 
Aug 30, 2018
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ProfJohnL said:
Parksy is correct series connection of panels will double the voltage produced, but keep the current the same, (subject to both panels being the same design and exposed to the same amount of lights,)

Parallel connection would double the current capacity, but keep the voltage the same.

Power (W) is calculated by multiplying the Voltage (V) by the Current (A) , so doubling up a panel in either parallel or series has the potential to double the power of the array.

You have to look at the instructions for your charge controller for advice on the best method for your system.

Sorry this is not correct in an array if you double the voltage then current (amps) will halve and the Watts will remain the same. Otherwise you are effectively making power for nothing. The advantage of higher voltage is that ,if I remember my o-level physics correctly powerloss is a function (A^2 )xResistance. Which is why electricity is transmitted at very high voltages and very low current. Rather than at 240V and high current.
 
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Thank you for the replys so far but before we wonder off track, I now understand having the panels in parallel (the original temporary hook-up method I used) is the better way, rather than using the series layout (as the professional fitter perminatly installed them as).

Now I have 2 options:
1) re-wire changing to parallel, but for this I will need a junction box adding on the roof due to the way the installation has been completed.
2) Change to a MPPT controller, a more expensive method but I believe these controllers can drop the voltage in a more efficient way so that the additional potential current is recovered and I get back the higher charge rate.

More comments about the benefits of the MPPT controllers would be appreciated, along with confirmation I am correct (hopefully) on my belief that a MPPT controller will solve the problem.
 

Parksy

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Gra1 said:
Thank you for the replys so far but before we wonder off track, I now understand having the panels in parallel (the original temporary hook-up method I used) is the better way, rather than using the series layout (as the professional fitter perminatly installed them as).

Now I have 2 options:
1) re-wire changing to parallel, but for this I will need a junction box adding on the roof due to the way the installation has been completed.
2) Change to a MPPT controller, a more expensive method but I believe these controllers can drop the voltage in a more efficient way so that the additional potential current is recovered and I get back the higher charge rate.

More comments about the benefits of the MPPT controllers would be appreciated, along with confirmation I am correct (hopefully) on my belief that a MPPT controller will solve the problem.
This explanation about the differences between PWM and MPPT controllers is a bit long winded but it gets there eventually.
To cut a long story short, a MPPT controller provides more amps for the same voltage, but for small caravan systems the cost difference might outweigh the advantages.
It might be less expensive and better in terms of weight to sell the 2x 40 watt panels and to invest in a single panel of say, 100 watts with greater capacity to charge your leisure battery but it depends really on how often you go off grid.
 
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I would wire them in Parallel. From what you said earlier when the same panel was freestanding and with the same regulator? You said it was working. An mppt controller is going to be expensive you won’t see much change out of £100. It could be that your controller is was seeing 30v input x 1.6 amp and outputting 14 volts at 1.6amp and effectively dumping the rest of power.
 

Parksy

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The costs of solar power has reduced in recent years, a top of the range MorningStar MPPT controller is a bit overkill for 12v leisure battery charging.
MPPT controllers can be bought for under £50, there's one. Here on Fleabay
It would be best to check the output of each panel individually first before spending any money just in case one of the panels or it's connectors are duff.
 
Mar 14, 2005
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Boff said:
ProfJohnL said:
Parksy is correct series connection of panels will double the voltage produced, but keep the current the same, (subject to both panels being the same design and exposed to the same amount of lights,)

Parallel connection would double the current capacity, but keep the voltage the same.

Power (W) is calculated by multiplying the Voltage (V) by the Current (A) , so doubling up a panel in either parallel or series has the potential to double the power of the array.

You have to look at the instructions for your charge controller for advice on the best method for your system.

Sorry this is not correct in an array if you double the voltage then current (amps) will halve and the Watts will remain the same. Otherwise you are effectively making power for nothing. The advantage of higher voltage is that ,if I remember my o-level physics correctly powerloss is a function (A^2 )xResistance. Which is why electricity is transmitted at very high voltages and very low current. Rather than at 240V and high current.

Hello Boff,
I don't think you have fully understood my comment. I carefully chose the phrase "Has the potential to double" indicating there are other variables that are likely to limit the increase in the power gain, and in particular the charge controller is definitely one of them. It is vitally important to follow the instructions for the charge controller, and as we don't know the details we can only speculate as to the best method of miltiple panel connection for the OP.

My description of the increase in power capacity (Watts) of the panels I can assure you is correct. Whether the systems they are connected to can take full advantage of that capacity is a different point, and can only be resolved by reference to charge controller's instructions.

Your statement that by doubling the voltage the current halves is in the wrong context. That would be correct if you were maintaining a constant power, but in the context of my comment we are doubling the power, by doubling the voltage, and maintaing the same series current. It's basic electrical theory...and practice.

Transmission powerloss is a real problem for the national grid which as you correctly point out is one reason they use very high voltages to get power distributed around the country. Exactly the same processes of current passing through a resistance in 12V systems does cause voltage drops and losses, and where necessary appropriate precautions should be taken, but in the context of a caravan the scale of the losses are small and often seen as acceptable. The standard for UK nominal mains is 230V not 240V

You point about fake controller's is important.
 
Sep 2, 2018
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Only just seen your entry.
I have always dealt with:
Photonic Universe
12V solar panels charging kits for caravans, motorhomes, boats, yachts, marine
Tel.:+44 (0) 203 150 11 11
Email:info@photonicuniverse.com
They are very knowledgeable and helpful.
Good luck
 
Aug 30, 2018
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I think that this below gives a rationale for what you saw a ie 1.6amp charge with either 1 or 2 panels exposed. It is copied from Northern Arizona Wind and Sun.

What happens when you use a standard controller

Standard (that is, all but the MPPT types), will often work with high voltage panels if the maximum input voltage of the charge controller is not exceeded. However, you will lose a lot of power - from 20 to 60% of what your panel is rated at. Charge controls take the output of the panels and feed current to the battery until the battery is fully charged, usually around 13.6 to 14.4 volts. A panel can only put out so many amps, so while the voltage is reduced from say, 33 volts to 13.6 volts, the amps from the panel cannot go higher than the rated amps - so with a 175 watt panel rated at 23 volts/7.6 amps, you will only get 7.6 amps @ 12 volts or so into the battery. Ohms Law tells us that watts are volts x amps, so your 175-watt panel will only put about 90 watts into the battery.

This what I think is happening. Each of your panels was producing arround 17v at 1.6 amps. That is 27.2W which isn’t too bad. Wired in parallel, as they were presumably when the panels were free standing the controler was receiving 3.2amp @ 17volts. Which it can convert to 14.4volt @3.2amp When the panels wired in series the panels combined produce 34v @ 1.6amps. The controller sees this and converts it down to 14.4v @1.6amps. You have lost half your power. Cover one of the panels the voltage seen by the controller is reduced to 17volts at 1.6 amps which it converts to the charging voltage 14.4v at 1.6amps. So much more efficient interms of using the available power.

Conclusion Buy a MPPT controller as it can handle the higher voltages and convert them to lower voltages and higher currents or rewire the panels in parallel. Personally I would chose the second option as it’s cheaper and I’m tight.
 
Mar 14, 2005
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I agree with Boff's last comments, and definitely think the sofistication of MPPT type of controller can make good sense where system efficiency is required.

If you only have the basic controller, then as light levels fall such as on a cloudy day, or at the ends of the day, with single panel or parallel connection the panels terminal voltage may not be enough to charge your battery. By series connection, you will get better charging in low light conditions, because the array has a terminal voltage that will exceede the battery voltage for longer.
 
Mar 8, 2017
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ProfJohnL said:
I agree with Boff's last comments, and definitely think the sofistication of MPPT type of controller can make good sense where system efficiency is required.

If you only have the basic controller, then as light levels fall such as on a cloudy day, or at the ends of the day, with single panel or parallel connection the panels terminal voltage may not be enough to charge your battery. By series connection, you will get better charging in low light conditions, because the array has a terminal voltage that will exceede the battery voltage for longer.

That is certainly a theoretical advantage, however since the loaded output voltage of a panel is about 19 volts I doubt that it is a factor.
 
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If you look on the web you can currently buy solar panels for arround £1 per Watt, so personally I would be inclined to add Watts rather than an Mppt controller. This of course doesn’t take into account the additional weight of more SPs or fitting them. Like Dodger524 I have my doubts what real advantages have with a single panel system.

A couple of observation. The first panel I bought was 40W freestanding and it seemed to keep up with demand March to October. This was replaced with a 135W panel on the same van so the same demand, this kept up with demand March -October basically the same. This of course is subjective but I think illustrates how inefficient a roof mounted panel is.

Second observation. We go away non ehu over new year. I have a plug in voltage display and this tells me that it takes until about 9 30am before the sun is high enough in the sky to start to raise the voltage and by 2 30 pm it has dropped so low to stop charging the battery. Compare this to the situation when in high summer, by 9 30am very little is going into the battery simply because it is already fully charged.

For us because the van is in storage a roof mounted panel makes the most sense because it is always deployed. But I am seriously thinking of getting a folding panel to supplement it during the depths of winter.
 
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Latest update, I have now taken the plunge and invested in a mppt controller.

Talking with Photonic Universe* they explained in exactly the same way as you did Boff in your post when you mentioned the quote from Arizona Wind & Sun.
* - Yes Smokey53, they were very knowledgeable and more than happy to help.

Rewiring the panels was an option which would of been far cheaper but swapping the controller was far easier.

I did try moving the van round to use some of the battery capacity to see if the controller would kick in and give an increased charge rate but that didn't show up enough so will have just wait until next time we go off grid.

Just for your interest I will post up another update once the new setup has been put into action.
 

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