There are few things more annoying than when you get up in the morning, but your solar panel monitor shows low power even though the sun is shining. Even worse, your batteries are low. What's going on and how do you locate the problem? This is especially important if you are out in your mountain shack or on the farm and the extra power from your solar system is really needed.
Normally solar cells and arrays are extremely reliable and stand up to weather extremes and even hail if properly constructed. Fortunately, solar panel systems suffer from few problems, but faults can happen, so you need to be able to locate the possible failure. With some faults, they need to be corrected quickly as they can damage other parts of your system by placing them under undue power loads.
Wood Ladder Shelf
We will assume that your arrays have been operating properly for some time. Also, this power drop has gotten worse quite suddenly or is unexpected. Similarly, there has been no run of cloudy days, and nobody has been secretly hogging the power. Unfortunately, we don't have the space in this article to cover troubleshooting the Controller or Inverter problems.
If your solar array is a commercial "off the shelf" system, it may be best to pull out the manual and read up on their diagnostic section. Otherwise, pick up the phone, they should have all the answers to your questions. However, if your array is a DIY Solar Panel project then lets make start. Let us assume that you have checked the obvious, like someone hasn't snagged and pulled one of the panel output leads out with a ladder, there are no bullet holes through your array and no pile of leaves on the solar panel face, especially in autumn. While the autumn is beautiful it can be a hassle making sure that the panels remain free of those pretty leaves, especially if you are out in the woods.
Before you you go poking around your system, remember that your array produces electricity so take proper care of your safety. If you're not confident, get a professional to assist. Please take care, throw the power isolation switch, and even better, remove the battery terminals. Remember, your batteries can pack quite a punch, and shorting your battery terminals is extremely dangerous.
So, here is a simple checklist for your solar panels:
Check the panel is free from leaves and dust Check there is no new appliance that draws more power than expected Check any machine has not faulted and so is draining power by not operating properly Check there is no physical damage to the solar panel surface or their structure Check the battery terminals are free from corrosion Ensure your controller and inverter are working properly and connections are good Walk back along the power leads and check that an animal has not chewed the cabling Check that all your cables are all intact, no breaks, no worn insulation, or tree branches wearing the cables. Have a quick look in the ceiling and check there are no electrocuted animals that have chewed your in-house wiring, shorting something out. The panel output leads are connected and free from corrosion Lastly, disconnect the panel and check that in full sun they are producing close to full power
Once we have checked the basic system, we need to go through the panels performance. Disconnect the array and simply check that at the output lead, current is flowing. If it's operating properly and power is good, go back and check your controller, inverter system, house wiring and appliances.
Over-Heating Problems If you are in a hot location, you may simply be experiencing overheating of the panels. In very hot locations and during the hottest part of the day, the voltage coming out of the system can drop due to the cells operating outside their optimum temperature range. This is normal and they recover once cooled. A typical 18V PV cell is designed to work at about 17 - 18V at 25C. So, you should still get about 12V even when their efficiency falls at higher temperatures. If your "drop off" is worse, then its very likely there is a weak PV cell or faulty electrical connections somewhere in the array. Corrosion and heat expansion of connections can increase resistance causing output drops. Try cooling the array, either shade it for a while or pour water over the array(with the cover on). Once cool, your voltage should return to normal, but if not, look for a faulty cell using a shading test.
Checking the Array with a Selective Shading Test Before you start pulling a panel apart, we can locate a faulty cell or wiring section by simply shading parts of the panel in turn. By shading about 3 or 4 cells at a time, you should drop an arrays output to less than half. With the panel disconnected, monitor the output with a multimeter or test load such as a small fan. If when you shade an area of the panel, power does not drop, then the cells in that area of the panel is not working properly. Have a close look at the tabs and wiring junctions of all the nearby series of cells. Any sign of corrosion may be the source of your power problem. This needs to be quickly corrected before you damage a cell from overheating. The extra resistance of faulty solder increases the load and resistance at that point, overheating the cell until it fails.
Problem Soldering or Faulty Connections Apart from a visual check of all connections, you can use the shading test to locate the affected cells that may have a problem with their soldering. If moisture gets into your panel, you have a real problem. Moisture will start corrosion, affecting all your electrical connections. If you happen to live near the sea, salty moist air can soon corrode electrical connections, and aluminum frames. Moisture can also cause wood to warp, and the twisting of a wooden panel container can break tab connections or even crack a cell. Where possible, go the extra expense and use an aluminum or perspex sealed panel. You will need to replace all corroded or oxidized metal parts and connections you find.
Damaged Blocking Diode While not common, a blocking diode can start to fail. Most PV arrays use a blocking diode to prevent your array from discharging your batteries at night. In this case,you may find simply no power output at the leads. Once you have checked all other possibilities, do a Diode Test. If the diode is faulty, replace the diode, or if in a remote location, remove the diode from the circuit until you can get a replacement. BUT, remember to disconnect the panels at night until you can get a replacement or you will drain your batteries.
On another note, I have come across people cutting costs by "ganging" several smaller diodes to match the "blocking amperage". This is a problem waiting to happen and you should not do this. A single properly rated diode must be used. Otherwise, current will flow through the point of lowest resistance, i.e. the smallest diode until it overheats and fails, current then flows to the next diode until it fails and so on. Eventually the whole thing shorts and blows with a serious risk to your system, and is a fire hazard. If you need a diagnostic on how to test blocking diodes, feel free to visit our website for instructions.
As we mentioned, solar panels are typically very reliable, even in cloudy or snowy conditions, if they are properly cared for and kept clean. Moisture is your greatest threat, so keep them sealed. Good luck, and may your panels keep powering you.