Portable Solar Power – 5 Most Common Mistakes That Cause System Failure

This article will examine my 5 most common portable solar power system mistakes that lead to system failure.  

  • PV module Shading & positioning
  • wire and connections in poor condition
  • controller or diode failure
  • weak or failed battery
  • insect infestation

I travel quite a bit around central Florida working to maintain solar powered gate systems. A very big part of my day involves remedying voltage issues caused by either inadequate or under-powered systems, poor system design, lack of proper maintenance and other many other problems.

These issues all translate to the portable solar power arena, and are worthy of examination and reflection. Much of what I see can be described as little problems with big consequences, so I thought it would be helpful to examine the 5 most common mistakes and problems I see and in doing so, may spare you some down-time and unnecessary expense.

Also, please note that these are not in any particular order and I am likely to see any or all of them during the course of my work week with equal frequency. I often see two or more of the listed items on a single repair, but any single item can be a ‘show stopper’ as far as generating sufficient solar electrical power is concerned.

With that said, here we go…

Mistake #1 : PV module is totally or partially shaded

Don’t smirk, ride with me for a week to visit paying customers and you will quickly note how many panels are covered in full or part by vines, tree limbs, are located behind ornamental shrubs, are moss-covered, mold-covered, etc.

The average solar consumer simply does not understand the internal series-wiring of the individual cells contained in the module, and how covering one cell screws up the series. It also creates hot spots in the panel as adjacent, unshaded cells are shouldering more load and resistance, and has a disproportionately large downward affect on panel output than its individual relative area.

Portable solar users have the advantage of being able to adjust the direction and angle of their array throughout the day to absorb as much solar energy as possible. This is also why I much prefer portable, non-mounted panels to rig-mounted. Its just so much more convenient to relocate panels than the rig itself.

The homeowner may simply be more likely to fall into complacency as far as the PV module array is concerned. We are, after all talking about a very low (typically) maintenance system, which quietly goes about its daily business of producing direct current out of thin air, and is soon forgotten. Unless, of course, it fails to do its intended job.

Sounds crazy-simple but it must be said that keeping your PV modules clean and unshaded is your primary concern if full potential power production is important. We in the northern hemisphere want our panels facing south, if possible, but regardless, panels located behind or under obstacles can face downward as it will not make much difference at that point – you can’t get solar power from a solar panel without light photons!

Mistake #2: Wire and connectors are in poor condition

Another big mistake is making the assumption that since your PV module will last 20 to 30 years with only a 20% drop in output, that the wire and connectors used in attaching it to your electrical circuit share that superior longevity. I’m here to tell you that this is not what I see at all.

It is true that photovoltaic interconneciton cable is designed to be UV and weather resistant. In fact, current plastics in use today even afford superior abrasion resistance and it is common to see exposed cable runs of tens or even hundreds of feet with minimal performance depreciation due to sun and weather.

This is all great, but from my perspective, someone forgot to tell the rodents how great solar cable is. Maybe they did, but used words like ‘delicious’ and ‘cotton candy’, because I see an awful lot or shorted or just broken cable with chew marks throughout the run.

The other common theme I run into are the cable ends and connectors. This has more to do with the installer than with the cable design, which is doubly unfortunate.

Basically, what happens is in applications of especially long runs, or any run without the MC4 connector, the tendency of the field technician is to over-strip the wire insulation, and also using connectors of less than top shelf quality. This often leads to a brittle and thus weak wire at the connector, and a heavily oxidized and brittle connector itself. This quite often leads to failure of the system in just a few years after installation and the homeowner usually blames the PV module itself and in fact have called me requesting a module replacement to begin with!

The worlds greatest most efficient and powerful PV module will eventually be no better than the cheapest and weakest if you never check and maintain your connections, or if sloppy connections were established to begin with. Simple but common.

Mistake #3: Controller or Diode Failure

Renogy Rover 20 charge controller
Renogy Rover 20 Amp solar charge controller

Charge controller failure is by far the more common issue compared to diode failure. The solar charge controller is a charge regulator and its job is to prevent your battery or batteries from being over charged and ‘cooked’ to death. When you connect a 12 volt panel to your system, you will notice panel voltage usually in the 14 – 20 volt range. Sending 20 volts to a battery all day will cause trouble.

Were panel ratings based always on best case scenario, your 12 volt panel typically might produce 7 or 8 volts under typical conditions. This would be insufficient volt pressure to charge a 12 volt battery, which requires roughly 14 volts to charge. So, we would be purchasing higher voltage panels and extrapolating their expected output for our needs.

This is a refreshingly good thing about the solar power industry and how PV modules are rated. The panel voltage rating is a nominal, worst case measure of power output. In the field, whenever I encounter a 12 or 24 volt module which is outputting 12 or 24 volts in sunny conditions, I start to look for problems! Either a frayed wire, broken connector, ground short etc, but something is bleeding off power.

Interestingly, you could forego the use of a controller if your solar panel is sufficiently small relative to your battery or bank. A basic rule of thumb is my 2/50 rule. (TM, Patent pending – ha!)

This rule means that I want to stay around 2 watts of solar production for every 50 amp hours of battery output. If my panel outputs more juice than this, relative to the attached storage (battery), then I need an intermediary (controller/regulator).

So, take a typical group 20 deep cycle battery, which is the size you normally see in cars, but its deep cycle cousin, rather than as cranking battery. To keep the math less esoteric, (for me, not you), assume 100 amp hour capacity, applying the 2/50 rules indicates I can attach a 4-watt panel for maintenance charging before incorporating a controller.

I suppose its possible to find a 4 watt panel, or parallel-wire a couple of 2 watt panels, however, I have personally never run into a 4 watt PV module in the field. 5 watt panels every day. 6 watt panels somewhat often as well.

I would happily connect a 5 watt panel in this case without worrying about overcharging. But keep in mind that you may be dealing with a 70 or 80 amp hour battery and all bets are off at that point. I might still try to make the connection, but I would be carefully monitoring the battery every couple of days to see where its voltage is settling, checking its electrolyte etc.

There are many 12 volt battery types in use in solar systems that power automatic gates and exterior lighting and more, that are 7 or 8 amp hour capacity. Very common for me to run into this. Clearly, connecting any PV module at all to this battery will overdo it and you really must use a charge controller or regulator.

Diode failure is much less common and that’s what makes it difficult to diagnose. A diode is basically a gate that opens only one way and locks closed the other. Very necessary in electrical circuits, cardiology, and so many other areas!

PV modules employ various diodes for current routing around shaded cells, and I very occasionally find a module with an assembly defect where the panel cell circuit is poorly wired or something internally was broken during shipping.

Really though, what I’m referring to here is the reverse current and discharge protection afforded by the Schottky diode used at the panel junction. This prevents the panel from actually drawing electrical current from the battery, typically at night, when the voltage pressure of the battery exceeds the voltage pressure of the module.

Electrons are funny creatures…… they move, water-like, around your circuit with a natural tendency to flow from high pressure (high voltage) to low pressure (lower voltage). So, the same pressure equalization tendency you took advantage of during the day, when your PV module voltage was at 18, and battery was at 13 volts, reverses itself at night. Now, the battery and panel are attempting to equalize pressure, and the electrons naturally flow towards the solar panel and its lower pressure. With no charge regulation or blocking diode in the way, you will discover a discharged battery in the morning.

PV modules typically use what’s called a Schottky diode due to it’s high efficiency and very minor electrical overhead. This is usually referred to as a blocking diode and, very occasionally and for whatever reason, they will fail. Talk about a hoot! This often creates a challenge for the system owner who notices that his or her system is basically dead in the morning, but by the afternoon, everything seems to again be working normally.

The next morning, the system is again dead so everything from the battery bank to regulator, wire to PV module is checked, rewired or replaced, but the blown blocking diode was the culprit all along. When this blessed event happens to you, you won’t likely forget to check the diode ever again.

Testing Diodes (Yes, DO try this at home!) is straightforward as long as you know what to look for. All diodes are labeled in some way to let you know the direction of current flow, which is always from the + positive, A, anode or plain side, toward the – negative, K, cathode or striped side. A silicon diode has the stripe on cathode end whereas other diodes, such as the Schottky, normally show only the A and K and the direction symbol.

silicon diodes

Using your multi-meter in diode mode, which means you are injecting a small amount of current through the diode to measure it. Hold your red test lead on the anode and black lead on the cathode and you should see 500-800mV when measuring a silicon diode and 100-200mV with a Schottky diode.

Now reverse the leads, and you want to see no current flowing and thus a ‘1’ in your meter’s display, which means the diode is working properly.

When you measure and notice a ‘1’ no matter what end your leads are touching, you have a bad diode. You may also find one where the mV reading is the same in either direction, or even 0.00 mV either way, which is a short circuit, in any case you know the diode is bad and must be replaced.

Schottky diode symbol

Like I stated earlier, this is a relatively dependable part of the system and you could even possibly get away with never checking your blocking diode or even knowing you have one or what its for. But, once in a while this little soldier is, in fact, AWOL and when that happens, confusion inevitably rears its fickle head. Naturally, Fickle’s first cousin, Profanity, is never far behind!

Mistake #4 – Weak or Failed Battery

Yes, the battery…. heart and soul of any portable solar power system as well as all off-grid residential, commercial or industrial solar electrical power facility. The battery is the electrical bank where (hopefully) excess electrons are stored during the hours of power production, so as to be available whenever called upon.

One of my (many) favorite sayings when discussing various solar applications with customers is to point out that it is not the motor, pump, solenoid or whatever that does the work, moves the gate, water, lock etc,….. it’s the battery what does it! A similar analogy regarding automobiles also fits here; it isn’t the motor that makes the car go, or the brakes that make it stop, its the tires that do that.

The point is that when troubleshooting a misbehaving system we often get caught up with over-thinking possible causes and remedies when we should always, always first check battery condition, voltage drop and overall general strength of the battery. If the voltage or amps storage part of the system is low, inadequate, or otherwise wrong, unless there are other glaringly obvious problems that must be addressed, you are wasting time and effort unless you first remedy the battery or battery bank.

With a multiple battery system, a common scenario is when the owner replaces an old, weak battery in a bank with a new one, but the new battery loses capacity as it is called upon by the other, connected aging batteries to equalize their charge levels between them. Thinking of the earlier part of this post when discussing how voltage pressure, like water, flows from higher to lower pressure, it is easy to imagine how this happens with series-wired batteries.

This is why you may have heard that when replacing batteries in a bank, you always want to select batteries of the same age, type and capacity. When you ignore this advice you are ignoring the equalization affect and you are likely permanently impairing the capacity of your new battery. When one battery in a bank has reached the end of its service life, even if its siblings appear OK, it is best to replace them all.

As a rule, when troubleshooting any system, I begin with the assumption that system voltage is inadequate and prove to myself that both incoming voltage from the PV module and battery or batteries are in the normal range before ever moving on to some other possible source of the trouble.

Taking voltage for granted or starting your troubleshooting from any area other than battery voltage is a common but big mistake.

Mistake #5 – Insects

I have saved the best for last! Bugs and outdoor electronics, I could write an entire book about this. Electronics must be Viagra to bugs – especially ants. The ants of course attract the lizards, spiders, wasps and sometimes frogs, even snakes. I see just about everything here in Florida, especially in the spring. Some weeks I would swear I’m in the exterminator business because I’m clearing so many ant nests and their big, white, soft eggs. OK, so you don’t need to pack the baloney during spring, just the bread so there is an upside! I kid because I’m constantly being creeped out by them.

The thing about ants in your electronics, especially the larger ones such as carpenter ants, is the amount of water in their bodies and the damage this does to circuits. I have replaced so many control boards and related electrical components over the last few years that insect-caused failures are almost as common as battery and voltage issues.

The mistake I see people making with insects is when they ignore them. Bugs travel established routes so when you see them following system wiring, from PV module to inverter, control board to motor etc, you must take immediate action.

I have opened many systems, especially in spring but really most any time of year, and notice ants, sometimes wasps, working to establish a nest or colony. Pure luck brought me to that system at that time for some other issue, but I was able to eliminate the insects and avoid a return visit and charge a few months later to remedy a short or burned board caused by insects. It is such a common mistake to ignore the bugs – don’t do it.

With any kind of enclosed system I have seen people drop in a few moth balls to keep insects away and that does seem to help. Be careful with that as I have seen systems with so many mothballs that the surrounding plastics were warping or melting. I don’t know what chemicals are in mothballs but the phrase, ‘less is more’ seems to fit.

Let me also add that here in Florida we have an exotic invading ant commonly referred to as the ‘Crazy Ant’. This tiny ant looks like a fire ant (I have never seen a fire ant inside a control box), but its movements and the way it travels across the ground does make it appear, well, crazy. Fast, zig-zaggy, they act like fast bugs on methamphetamine. They don’t bite, and oh, they love electronics. Crazy ants have killed more than their share of electrical components in my part of the world.

crazy ants

If you have crazy ants, you may have found that you are wasting your time with Andro and other traditional ant baits and poisons used on fire ants The University of Florida did a study on this that concluded that these remedies use fats for delivery but crazy ants avoid fats, so they avoid those poisons.

U of F identified a Bayer product called Maxforce Complete, which is a granular insect bait that does not contain fat and I have recommended this to customers fighting crazy ants, and it has worked.

Maxforce granular insect bait



If you suddenly notice small ants on speed in your yard, you may want to get some Maxforce. ….Just saying….

You will want to visually inspect your solar electrical system from stem to stern from time to time and look for any sign of nesting bugs. Bugs are a common sight around electronics and switches, but they should not be. They are responsible for a great deal of expensive damage to the systems I encounter.


There you have it, my 5 most common portable solar power mistakes that usually lead to some degree of system failure. You will notice that all 5 items, or at least their effects, can be mitigated by adopting a minimal but routine inspection and maintenance program on the system.

There really is no substitution for putting your eyes on the components, wiring, mountings, and electronics that make up you portable or fixed solar power system, and being on the lookup for early evidence of potential failure.

Everything wears out, breaks, dries up, frays or burns out. Now you know the 5 most common things I see each and every day, and you hopefully will use this information as a place to start, at the very least, when assessing your own system.

Remember to have your wasp and ant spray handy but be careful spraying that stuff near your electronics! The last thing you want is to short-circuit a critical component with wet sprays while eradicating a pest before it can short-circuit the same system. Especially wasp spray – which some people use for personal defense because of its heavy, wet, high volume spray stream. You just can’t be too careful with the stuff.

You want to really keep an eye on your systems during the spring and summer months, with perhaps bi-weekly inspections and maintenance. You can probably relax a bit for the rest of the year when storm season passes, the pests are less active and the UV and heat is a bit less intense.

Just staying on top of these ‘terrible 5’ could add years to the life of your system.  There is plenty of bad stuff that can go wrong with your system that you have little or no control over.  Pay attention to the items on this list and you will have some pretty big as well as common bases covered.

Until next time.  Enjoy the sun.





small camper trailer


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