Can I Use Solar Panels of Different Wattage?

Solar panels are available in different sizes so there is plenty to choose from. But can you connect solar panels with different wattages, say 100 watts with 200 watts? Yes it is possible, but you should not do it and in this guide we explain why.

Solar panels of different watts should not be used together because they have different voltages and amps. The system will always choose the lowest voltage or amp, which will reduce efficiency and power output.

First we need to explain how solar panels are connected and how it affects the voltage and amperage (current). This is necessary to understand why panel watts should be matched.

Solar panel parallel connection. Wiring solar panels in parallel combines the amps but the voltage remains the same.
Solar panel series connection. Wiring solar panels in a series combines the voltages but the amps are not added up.

Solar Panel Parallel Wiring Explained

To connect solar panels in parallel, connect all the positive wires together. Repeat with the negative wires. Make sure you use the right wires for the results.

Take 3 x 100W solar panels, something like the Renogy Mono PV Modules. Suppose each one is 5 amps and rated at 20 volts.

Since parallel wiring adds the amps, we get 15A and 20V:

5+5+5 = 15

We know the efficiency is 100% because amps x volts = watts.

15A x 20V = 300W

Of course there are many factors that determine solar power output, but from a connection point of view it is 100%.

You can add as many solar panels as you want and this method will still be effective.

Solar Panel Series Wiring Explained

To configure solar panels in a series, connect the positive of a panel to the negative wire. Repeat this with the other wire.

Take the same 3 x 100W solar panels, 5 amps and 20 volts each. Since this is a series connection, the voltages are added up but the amperages are not.

We get 5A and 60V. Using the same formula we did earlier:

20+20+20=60V

The efficiency is still 100% because of the following:

60V x 5A = 300W

Just like with the parallel configuration you can add as many solar panels you want in this example.

Solar Series and Parallel Connection Explained

It is also possible to configure solar panels in both a series and parallel. First you connect solar panels in a series then join the strings in parallel.

So if you have 6 x 100W solar panels connected in a series at 5A and 20V each, you get 60V and 5A.

The 6 solar panels have 60V and 5A for the two strings. If you add the two strings in parallel, you get 10A (5 x 2 = 10).

This solar series parallel combination has 60V and 10A in total. 60 x 10 = 600 so we know that 100% can go into the charge controller.

So you can see here that whether it is series or parallel, the efficiency is still 100%. But if we connect solar panels with different sizes and specifications, the efficiency goes down.

How Using Different Solar Panel Watts Together Affects Performance

We had to go over the different wire combinations to understand how solar panel sizes affects voltage, current and power output.

• If the solar panels are not properly matched in size, the system will choose the lowest value.
• If mixed solar panels are connected in parallel, the amps are added as usual. The voltages of the panels will be adjusted down to match the lowest voltage.
• If mixed wattage solar panels are connected in a series, the voltages are added. But the panel amps will be reduced to match the lowest amp in the configuration.

Effect of Different Solar Panel Watts Wired in Parallel

Even if the solar panels are properly spaced apart, efficiency will drop. We need to do some more math here, but it is pretty straightforward.

We have 3 x 200W and 3 x 100W solar panels. The 200W panels are at 8A and 25V, while the 100W panels are 5A and 20V. Total possible output is 900 watts.

Connect all solar panels in parallel. Remember that in parallel wiring the amps are added but the voltage is not. So we have 39 amps.

8+8+8+5+5+5 = 39

The voltage is not added up. But there are two voltages, 25V and 20V. The system will choose the lowest voltage available, in this case 20V.

The solar panels can generate up to 900 watts, but now it can only produce 780 watts (39A x 20V = 780W). So even in ideal weather conditions the system can only yield up to 86% of its capacity.

Effect of Different Solar Panel Watts Wired in Series

Now let us take the same solar panels and wire them in a series. In a series, the voltages are combined but the amperages are not.

So we have 3 x 100W solar panels at 5A and 20V each, and 3 x 200W solar panels at 8A and 25V each.

First we add the voltages.

20 x 3 = 60
25 x 3 = 75
60+75 = 135

We have 135V in the system. There are two amps, 5A for the 100W panels and 8A for the 200W panels. The lowest value is chosen so that is 5A.

We now have 135V and 5A. The solar panels have a maximum possible output of 900 watts. But we can only get 675 watts maximum.

135V x 5A = 675W

The efficiency goes down to 75%. The more solar panels you connect, the more the efficiency drops.

Solar Panels Different Watts, Same Voltage

What if you have 3 x 100W and 3 x 200W solar panels but all are at 20V? In this example, the 200W panels are 10A each and the 100W panels are 5A.

If the panels are connected in a series we get 60V 5A for the 100W panels and 60V 10A for the 200W array.

If the panels are connected in parallel, we get 60V and 15A. Multiply 60V x 15A = 900W, the maximum possible output.

Bottom line, you can connect similar PV modules in a series and then connect the strings in parallel. Doing so can generate 100% efficiency in terms of what can go into your system.

Summary and Important Reminders

• Solar panels connected in parallel add the amps. The voltage does not change.
• Solar panels connected in series add the voltages. The amps do not change.
• Mismatched solar panels connected in parallel will add the amps. It will choose the lowest voltage among the panels.
• Mismatched solar panels connected in series will add the voltages. It will choose the lowest amp among the panels.
• You can connect solar panels with different watts in parallel if they have similar voltages.
• You can connect solar panels with different voltages in series if they have similar amps.

If you connect mismatched solar panels without matching the amps or voltages, performance is going to suffer. As we have shown in the examples earlier, the efficiency rating will drop and the system will not run at full capacity.

Of course we have to point out that solar panel output depends on various factors. The weather, orientation, temperature etc. But the point is if the panels at not properly matched, you are not going to get good results even in ideal weather.

In ideal conditions, matching solar panels produce close or at peak output various times throughout the day. Mismatched solar panels will never be able to do that.

Also keep in mind that solar systems are not just comprised of solar panels. You also need quality charge controllers, an inverter and if you are off grid, a battery bank.

The examples here also assume the solar panels are properly wired. By that we mean the cables for the panels are the right size. The performance will be affected if wiring is incorrect for any of the components, whether it is the panels, inverter, charge controller or batteries.

Conclusion

Is it possible to mix solar panels with different watts? Yes, but you have to expect inefficiency and decreased performance. For small systems it might not be an issue. But usually it is better to get matching solar panels so you can get maximum performance.