Mixing Solar Panels

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Old 05-15-14, 07:15 PM
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Mixing Solar Panels

I have a hunting camp that is currently using 3 arrays of those Harbor Freight solar panels:

Solar Panel Kit - Save on this 45 Watt Solar Panel Kit

Each array offers a peak output of 45 watts.

I have these connected to a Tracer 20Amp MPPT Charge Controller 100VDC Input 2210RN solar controller which says it can handle up to 260 watts.

I have recently purchased two 100 W Watt 100W mono-crystalline Solar Panels that I plan on installing instead. However, I thought maybe I can use one of those arrays in the system? Any problem wiring one of the HF arrays in parallel with the two 100 mono panels all into the charge controller together? I was basically going to twist the ends together and then slide them into controller.

Any problems with this setup? Would this mess with the MPPT controller?

Thanks, any ideas?
 
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Old 05-27-14, 04:45 PM
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Mixing solar panel types, not such a good idea...

Hello,

The short answer is YES, you can mix solar panels BUT, you must have the correct type of charge controller that accepts multiple "inputs" from solar arrays. The charge controller will not work in this application if it will only accept two "input" lines, one for a positive line from the solar panels, and one negative. As you have described the way you are connecting the solar panels to the charge controller is to simply combine all the positive leads together, and all the negative (so you would have three positive wires and three negative), then plugging these two, three-wire combinations into the positive, and negative "input from panel". Therefore, while in theory it can be done, it cannot be done with the charge controller you have.

You have a very good charge controller if it is an MPPT type as it will squeeze every possible watt out of your solar array, but it will probably only have one pair of "in from panel" input options which is not surprising. This frustrates many people trying to build a modular system where they are adding solar panels slowly to an existing array. As they try to add solar panels to get more power, they are stopped by the lack of input options into the charge controller. A very common mistake is to combine panels in this fashion, but the results are generally always going to be the same, a melted charge controller and possibly a burned down cabin.

What? Did he just say fire? Yes, it can be a fire hazard because by combining the multiple positive wires together from two or more solar panels (and combining all the negative as well), and then plugging the combined pair, trio, or quartet of wires into the charge controller creates more voltage input than the charge controller can handle. If the internal fuse does not trip, and you have not placed a fuse between the charge controller and the battery bank, the amount of heat produced is easily enough to cause combustion.

Why? Remember that when pondering the performance of solar panels working together, it is that collective benefit, more than one unit gathering energy, which makes solar technology possible. One single solar panel of say, 250 watts, is indeed a powerful solar panel, but alone, very limited as to what it can power. Pair it with a couple just like it and now the collective wattage of all the panels together represents a reasonable electricity generating capacity that can have significant power generating capabilities. It is only natural to want to add solar panels to an existing array, more panels, more production right? Yes, that is right, BUT, only if the solar panels are joined correctly so that they do actually work to support each other. There are ways to boost the production of either watts, amps, or both depending on how one wires the solar panels together. If all the positive wires are joined before the battery bank, and the same with the negative, the voltage of all the solar panels will be added together, known as wiring them in "series". As the second panel is combined with the first (positive wires connected to positive, negative to negative), the single panel of 17 volts now produces 34 volts, and that number keeps climbing as solar panels are joined.

Now that there are four solar panels combined together as described above, and based upon your example of the 100 watt solar panel, the typical panel would be around 17 volts (volts x amps=watts, and to charge a 12v battery bank, the panels must product 1.5 times the battery voltage), wired in series so the amps remain the same but volts are additive. I am taking liberty with the number of panels to illustrate my point about the cumulative effect of voltage when solar panels are wired in series (positive to positive, negative to negative as the four solar panels are joined together to create one single point for each positive and negative to connect to the charge controller).

I have a Solarix MPPT 2010 charge controller which is a fairly good unit typical of the MPPT genre of charge controllers. It has a maximum of 100 volts. One can quickly calculate that there only needs to be approximately five solar panels to overwhelm even a high quality MPPT charge controller.

SOLUTION: It can't all be just problems! There is a way to hook many solar panels together safely, without overwhelming your charge controller. It requires you to use a circuit breaker box, an A/C model #HOM612L100SCP by Homeline. Then get 6-quantity D, single 15-Amp breakers, I say six because that is how many this particular breaker box holds. You then can wire your solar panels in series (positive to positive, negative to negative), so each pair is wired in series, then the positive lead is connected to the 15-Amp breaker, the other to a ground bar inside the breaker box. Wiring in this fashion allows for 12-panels to be wired safely into one single charge controller that has only one positive "in from solar panel", and one negative "in from solar panel". This allows the voltage to be additive when wiring pairs of solar panels, but keeps it below the relatively low voltage ceiling.

Just describing the wiring method above may not provide the clarity necessary for you to go out and do this if you have never seen it before. If you are interested in this method, I will provide you with a You-Tube video on how I did mine, and you can then determine how you would like to proceed. I just don't want to invest a lot of time filming if you are not interested, but if you are, I would gladly invest the time.

You can even make your own solar panels from scratch, enough to power the entire cabin, and you can do so at your own pace, a truly modular project. I built my own array which now provides part of the electricity we use monthly. I have an "off grid" system meaning I gather the energy and store it in a battery bank which is then used via an inverter. Similar to what an off-grid cabin would require, although, the small capacity of your system would only require one deep cycle 12v battery. With a good deep cycle 12v battery, that could be enough to run lighting and perhaps a small water pump. You can very easily add capacity to expand both the collection aspect (solar panels) and the energy storing (batteries), slowly over time. A word of advice though, any time you are contemplating the use of energy from a deep cycle battery, you want to make sure that whatever lights or appliances are being run off the 12v D/C system are the most efficient units available. For example, if you were using the 12v battery to provide lighting inside the cabin, those lights need to be as efficient as possible. LED bulbs for sure, as there are LED bulbs requiring approximately 15 watts yet provide significantly greater Lumens of light than a much more energy consuming incandescent light bulb which consumes 100 watts. Just doing the math, lets say you had a 12v deep cycle battery with 100 Amp-hours of stored electricity. Not considering voltage-drop attributable to wiring resistance or inefficiencies of conversion between A/C to D/C, one can estimate how many hours a specific lightbulb can burn based upon a given battery by comparing the stored wattage inside the battery with the power consumption of the bulb. To determine the number of watts stored in a deep cycle battery, divide the volts, by the Amp-hour capacity of the battery. If a 12v battery has 100 Amp-hours, (12v x 100), doing the math shows us that there are approximately 1,200 watts available for lighting, divided by the incandescent bulb wattage (100 watts), and we see that the light could burn for approximately 12-hours. Conversely, the more efficient LED could burn for 80-hours, well over three days continuous illumination compared with half a day with a less efficient light. The example shows how limited the energy is that is available if we try to apply green technology to a traditionally constructed environment. This exceeds the scope of this reply, but I hope this has helped you. IF you have any further questions, don't hesitate to ask, and by the way, the overwhelming of a charge controller is a feat I have accomplished by tying in too many solar panels into a single charge controller. In my early days of learning the technology, I learned the hard way that voltage is cumulative when I discovered a smoldering and misshapen charge controller. Using the correct size wiring is also hugely important, but also beyond the scope here, so good luck, and keep me up to date!

Pat
 
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Old 05-27-14, 04:49 PM
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Correction:
I made a mistake in my description of how to calculate the number of "watts" stored inside a deep cycle battery. I typed instructions that state one needs to divide the voltage by the Amp-Hour capacity to arrive at watts. What I meant to say is that they must be MULTIPLIED together to arrive at the wattage capacity. Sorry about that confusion!!
 
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Old 05-27-14, 04:57 PM
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Thank you for your reply. The charge controller in question, is rated for up to 100 VDC, 260 watts, 20 amps.

I have connected 2 100 watt panels with a 45 watt panel with a maximum of about maybe 15 amps possible under perfect conditions.

I guess I don't see how that could overload said charge controller? I should be well under the 260 watt/20 amp maximums.
 
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Old 05-27-14, 05:03 PM
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PatMinns

I know nothing about solar, but unless things are very different in that world, the wiring you describe (positives tied together, negatives tied together) is parallel wiring and increase the amperage, not the voltage.

Of course higher amperage on a rated input is just as bad as higher voltage.
 
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Old 05-27-14, 05:05 PM
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That's correct. The panels are in parallel, not series. The voltage of each of the panels is rated roughly the same. The voltage will not increase. As far as I can tell, the controller should be able to handle the load being sent to it.
 
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