Connecting Multiple Solar Panels
Theses are the Diodes that I use, they are the same ones that are used when building the panels. Find them here.
There are 3 ways to connect solar panels; parallel, series, and a combination of parallel and series. The first way I am going to talk about is parallel because this is probably the most common way that panels will be connected. For this example I am showing you connecting panels that are for a 12 volt system. This is how the panels that I have built in my other instructables are connected, and feed my solar charge controller.
In this first image there are 3 solar panels. If you look at the arrows along the white and red lines they are showing the direction of flow. The white line is the negative connection, all 3 panel negative wires are just simply tied together and to the wire that runs back to the negative connection on the charge controller.
The red line is the positive connection to the panels. You will see a symbol that looks like a triangle pointing down at a horizontal line. That symbol is for a diode, also known as a blocking diode. What this diode is doing is only allowing the positive electrons to flow in only one direction. When looking at this symbol the triangle points in the direction of flow, when looking at the diode in your hand there should be a colored line around one end of it. This line represents the line in the symbol that the triangle is pointing to. The non-colored end would be the “in” side, and the end with the colored line around it would be the “out” side. By installing these diodes on each panel it stops the electrons from going back into other panels. Diodes also use up a small amount of voltage, so don't go crazy and put to many in or you will to low to use.
If you look below the panel to the left you can follow the red arrows from the panel down and make a right turn to the diode. Then they continue through the diode and down the line to the end where they would be connected to a solar charge controller.
In this next step you can see that the left panel is covered, let’s say that a tree was blocking the sun from this panel. If you look below this panel at the red line you will see that there are no arrows coming from the panel to the right hand bend. And if you look to the right of the diode symbol you can see that the arrows have changed direction from the previous step. This is how the diode works. The diode is stopping the electrons from pushing their way back to the panel that is not producing power. If this diode was not in place then the panel not producing could be damaged. Also you would be losing some efficiency from the other panels because they would be letting power flow through the nonproducing panel as the electrons are trying to reach the negative side of the panel.
In this step I am showing you how to connect solar panels in a series configuration. For this example we are going to say that the panels are 6 volt panels in a 24 volt system. Looking at the top image, start at the bottom right that is labeled – NEG. Following this to the left you see that out of the other side of the panel the line is red, this is the positive side. With this being a 6 volt panel, and we need 24 volts we need to increase the voltage. To do this we connect the positive side of the first panel to the negative side of the second panel. There will now be 12 volts coming out of this second panel. Continuing up to the top left panel, there will be 12 volts in and coming out with 18 volts. Continue this through the fourth panel on the top right, there will be 24 volts coming out if this one. You can also see the blocking diode here; it functions the same way as in the first example to keep from back feeding power into the panels. These 4 panels wired up in this way work as if they are one large panel that produces 24 volts. Having one blocking diode is the minimum that is needed in the circuit.
In the lower image the panels are connected in the same manner, positive to negative to reach 24 volts. In addition to blocking diode there are bypass diodes. The reason for these are to allow power to go around a panel that is shaded by something. It helps to keep that correct flow of power, not that it won’t flow in the correct way if their not there.
**Personal note** I have not seen any information on about efficiencies of panels connected in series with or without bypass diodes. I have not connected panels in this way either, all my panels are 12 volt and connected to a 12 volt system.
In this step I am showing what happens when a panel is shaded by something such as a tree. You see that the bottom left panel is shaded, so the power follows the path around the blocked panel through the bypass diode. In this configuration you should be getting 18 volts. This may not be charging a 24 volt system very well, but it will be adding some charge through amperage. Less is better than none. If you have a higher end charge controller it may be able to use this lower voltage in some form, or maybe able to boost it back to the 24 volts to keep charging. You would need to check the specs on your particular charge controller.
If you do not install bypass diodes, as in the first image on the previous step, I do not see why all panels would stop producing power. They may just produce less power than if there were blocking diodes installed. This is something that would have to be considered when building a panel system. Is the loss in power worth the cost of extra diodes?
In this step I am showing a combination parallel and series configuration. In this example we will be using 12 volt panels in a 24 volt system. The 2 panels at the top of the image are connected in series of each other, and the 2 panels at the bottom are also in series of each other. These 2 rows of series panels are connected in parallel of each other. So the top row produces 24 volts, and the bottom row also produces 24 volts. Together both rows provide 24 volts there blocking diodes, then on to the collective point that would run back to the charge controller. Because each row provides the same voltage, and they are in parallel the total voltage to the charge controller is 24. The only time the voltages add together is when they are in series, like in each row. 2 panels that produce 12 volts each in series produces a total of 24 volts. And in this example I also put in the bypass diodes.
In this final step I am showing an example of a shaded panel in a combination parallel and series wiring configuration. You can see that the top row is unaffected. In the bottom row the left panel is shaded by a tree. The top row will be producing 24 volts, the bottom row will only be producing 12 volts. Because of the blocking diodes at the end of each row the 24 volts will not push back into the row producing 12 volts. You will be losing power because one of the panels are shaded, but they’re not going to back feed. You may still be gaining in amperage even though it’s at lower voltage if the battery needs the charge, or if there is another place for the power to go such as out to lighting or a tool. Again, less power is better than no power from panels.