Why is my solar not working properly?

This is a question we get asked often. Once fellow travellers discover that I have an electrical background and training, I am regularly asked to examine their solar installation to determine why it is not working.

Motorhome solar roof

Here is a list of the top 5 causes for Solar that does not perform on caravans and motorhomes (in order of least common to most common…

5. Bad Connections. Incorrectly made connections cause high electrical resistance, these high resistance connections or joins result in two serious issues. The first is a reduction in the flow of current from the solar panel. A good analogy is to imagine that the high resistance connection is like a kink in a hose pipe, water can flow past the kink, but the flow is reduced. The second issue that these bad connections cause is heat. The heat generated by the connection can be calculated and expressed in watts. W=I2XR  where W is watts (of heat), I is current in amps and R is resistance of the connection in ohms.  Unintended heat in any electrical system is never good and in the worst case scenario could cause a fire.

4. Dead Batteries.  Most people use flooded deep cycle lead-acid batteries in their motorhomes and caravans. These (like all batteries) have a limited life span. The speed at which lead-acid batteries lose their ability to store energy is affected by many factors. The most common reason that these batteries die prematurely is abuse. Failure to properly charge and maintain lead-acid batteries is the second easiest way to bring death to your expensive acid filled friends. The easiest way to kill your batteries is to regularly discharge them to the point where the lights go dim – you will find yourself waving goodbye to them at the recycle yard in no time. No matter how many solar panels you have attached to the roof, if the storage system is faulty, you are going to have a failing fridge and warm beer.  The best way to test your flooded batteries is with a good quality hydrometer.

3. Incorrect metering. Almost all solar regulators are capable of reporting many important system health related pieces of information. If the system is not setup correctly or the regulator is not programmed correctly, the information it reports will be very misleading. I have looked at a number of systems that provide “State of Charge” (SOC)  information (normally a percentage) – but only track the charge flowing into the batteries from the solar panels – NOT the current flowing out of the batteries. These systems happily report a State Of Charge of 100% even as the lights are dimming and the fridge has long since stopped cooling.  Remember that battery voltage is not a reliable indicator of systems status. The only reliable (electronic) way to know how charged your batteries are right now, is to have measured how much current has flowed into them (from the panels) and how much has flowed out since the last time they were fully charged. A correctly setup solar regulator (or battery monitor) does exactly that.  If you have an inverter onboard and you do not have a shunt attached to your regulator, then it is unlikely to be reporting correctly.

2. Incorrect Wiring Size. Much has been written on this subject and you would expect that this issue would now be uncommon – it is not. In the last year we have encountered at least 6 travellers who report issues with their electrical system that when investigated turned out to be caused by insufficient wiring size. The worst case was an 11 meter motorhome with ten 80w solar panels mounted on the roof. These panels were connected to the regulator by a 14 meter length of speaker wire (0.5mm of copper). At $10/watt that is about $8000 of solar panels that failed to operate for the lack of about $90 worth of adequately sized cable.  Once we replaced this speaker wire, the entire system began functioning very well. It is (sadly) vey common for professional installers to use undersized cable to “keep the price down” – clearly this is false economy. I have also seen a number of installations where additional panels have been added and simply looped onto the existing wiring.  Before allowing the lazy installer to do this – ask yourself “was the original cable over specified enough to allow for these additional panels”. If the answer is not affirmative, insist that they run additional cable.

1. Unrealistic Expectations.  Yes, the number one reason why people report “My solar system is not working properly” is that they have unrealistic expectations. Nobody has bothered to explain to them that you must put back MORE than you take out! Put your electric toaster and electric kettle away and look closely at how much power you can collect from the sun each day …. if you use more than that each day sooner or later you are going to be in trouble. In this sense, solar electrics are no different than bank accounts, if you take out more than you put in, pretty soon you are going to find yourself in the red. Of course it is perfectly reasonable to supplement the solar production by running a generator or wind turbine, but this too needs to be monitored. Be like the accountant … count every amp-hour that you bank into the batteries and deduct every amp-hour that you use, and always make sure you bank more than you consume.

If you have any questions about solar or have any comments about this article, please use the reply box below to share these with others.

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8 Responses to “Why is my solar not working properly?”

  1. Bri Says:

    Hi there,

    You definatly sound like you know what you are talking about! I have a quick question in regards to our solar set up. We have 2x80W panels connected to a regulator then connected the the battery via a 12v plug and socket with a 15A fuse. we have amde a battery box up with 4 outlets on the other side for fridge and lights etc(this is 4 when we go camping) I ahve a question about the regulator. we have been getting funning readings of it and cant understand what is going on…we are starting to put it down to a faulty regualtor…but as we just purchased it we find it hard to believe. from the input side from the panels to the regualtor we are getting a solid 18V and on the output side, to the battery we can not get a solid reading as the meter is jumping around from 18v to 6v and everywhere inbetween. we had it running for 2 days with little load. we disconnected the cable from the regulator to the battery and tested at the terminals and still get the same strange reading. we are baffeled and not sure what is going on?

    your wisdom will be muchly appreciated!! 🙂

    many thanks


  2. Hobo Says:

    Hi Brianna,

    Thanks for the question – it is a very good one and had me thinking.

    I have had a look at the diagram of your solar setup that you emailed – and it looks like it is correctly wired.

    Your two 80w panels are connected in parallel – this is correct for a 12v system.

    A solid 18 odd volts is what I would expect on the panel side of the controller (when the battery is not connected OR the controller is disconnecting the panels from the battery (as it would if the battery were fully charged)).

    Thus I think it is reasonable to say that the panels are working fine.

    The behavior you mention from the regulator seems odd – but is not without a possible explanation….

    Measuring the voltage at the output of the controller seems like a reasonable thing to do – but with the battery disconnected there may be an issue…

    I note that the controller is a 12/24v model – it is very possible that the controller is disconnecting the panels momentarily from the battery side to check the voltage at the battery terminals (without solar applied) to decide if it should be in 12v or 24v mode. Because it reads no voltage (as there is no battery there to read) – it just cycles and repeats.

    Here is how I suggest you test the system…

    1. Disconnect the battery from the controller and discharge it for an hour or two (use the fridge or something like that). This is to make sure that the battery not fully charged and is able to accept charge.
    2. If you have a multi-meter that is able to measure current – set it to do so (take care – current meters go in series NOT across the battery terminals).
    3. Now connect the solar panels (that are in the sun) DIRECTY to the battery (not via the regulator) via the ammeter and note the current that is flowing into the batteries – you should see around 8amps (at midday with full sun). This confirms that the battery system AND solar panels are working fine and correctly setup.
    4. Now wire things back the way you have them in the diagram – but put the ammeter in series with the positive lead that comes from the controller to the battery to read how much charge current is flowing from the regulator.
    5. If this does not read more or less the same current as the reading you took with no regulator ( and assuming the controller is correctly setup) – the controller is faulty.

    If you don’t have a meter that can read current – measure the battery terminal voltage with the solar disconnected – then again an hour after the solar has been connected (via the regulator). If you see a reasonable rise in voltage– it is a good guess that the system is working ok (this is only a very rough guide – ammeter measurements are far better)

    It is very unlikely that a solar regulator could damage a battery (unless it is wildly under or over charging it).

    I hope this helps

    Note to others reading this – this testing procedure will NOT work if your regulator is an MPPT type (currently very few regulators are MPPT – this is likely to change).

  3. Leif Caswell Says:

    My partner and I absolutely love your blog and find most of your post’s to be what precisely I’m looking for. Do you offer guest writers to write content in your case? I wouldn’t mind composing a post or elaborating on some of the subjects you write concerning here. Again, awesome website!

  4. Hobo Says:

    I am working on a new section for the site that will allow other caravanners and motorhomers to contribute (in relation to their own caravans and motorhomes). It should be ready to launch in about a month. You are very welcome to place any comments with existing articles.

  5. Rod Says:

    my panel was working just fine then quit charging I diconnected from the battery and voltage controller and it showed no voltage

  6. Rod Says:

    I have a solar panel hooked to a 12v battery and it has stopped charging I have disconnected it from the reg and it shows no voltage. can you suggest anything to help me

  7. Hobo Says:

    Hi Rod,
    Firstly test the panel in good sun by checking the voltage at the terminals on the panel (not on any connecting wiring). If you show zero volts then the panel is open circuit and effectively dead. This is often caused by hotspots on the panel and if you look closely at each of the soldered joints on the individual cells, you may see the dis-coloration that is typical with this issue.

  8. Hobo Says:

    Hi Rod,
    Firstly test the panel in good sun by checking the voltage at the terminals on the panel (not on any connecting wiring). If you show zero volts then the panel is open circuit and effectively dead. This is often caused by hotspots on the panel and if you look closely at each of the soldered joints on the individual cells, you may see the dis-coloration that is typical with this issue.


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