Sometimes, your solar power build can be budget limited. The solution, in this case, is adding up to a base system as money comes by. One of the easiest ways to do this is by buying a beefy charge controller and skimping on the battery bank and the solar panels.
You can then modify your energy consumption and keep on expanding as you add new panels and batteries to your system.
The problem with this approach is you will easily end up with different spec equipment.
You will end up with different wattage (or voltage) panels and the big question of whether it is safe to hook them up to a single battery bank.
Is Mixing Different Wattage Solar Panels a Good Idea?
Well, it depends. To answer the question, we will have to look at the consequences of mixing different wattage panels in your array.
One formula will come in handy (you might have encountered it if you went through our article on how to properly size a solar array)
Power = Current x Voltage
What Happens if You Mix Different Wattage Solar Panels
Let’s imagine you started off with a single 200 Watts solar panel and later added a 100 Watts panel to your collection.
If we assume that they are all designed for a 12V system and have a working voltage of 18V.
- The 200W panel will produce its ideal max power at 18V and will push around 11.11Amps
- The 100W panel will also produce its ideal maximum power at 18V with a current of 5.55 Amps
The total output after combining these panels depends on how you wire them together.
Wiring in Series
Wiring your panels in series increases the voltage while keeping the current constant.
The overall voltage is the sum of individual panel voltages. In our case, this will be
18V + 18V = 36V
The overall current will be equal to the least current the smallest panel in the array can produce. For our case, this will be 5.55Amps
To get the theoretical maximum power, (Power = Voltage x Current)
Power= 36V x 5.55Amps
Power = 199.8 Watts
This is just 66.6 percent of the total panel capacity (300W) meaning you will be losing 33.4% of your installed capacity.
Mixing different wattage panels in series will lead to considerable installed capacity loses. Even though your system might produce more than what a single panel can in gloomy conditions, you still won’t get maximum power when the sun shines and there’s no shade.
Wiring in Parallel
Using the same panels in the same use case above will yield the following results.
- The overal current will be a sum of individual panel output currents. This will be 5.55Amps + 11.11Amps = 16.66Amps
- The voltage will be equal to the lowest voltage rated panel in the array. In our case, they all produce 18V
The ideal produce power will be
Power = 18 x 16.66
Power = 299.88 Watts
In our example its seems as if mixing different wattage panels will still give you around the same wattage.
This is only so because our example has same voltage panels.
If one of the panels had a lower voltage, say 16V, the perceived power would be (16 x 16.66 = 266.56Watts)
You might get away with mixing different wattage panels in parallel if their voltages are the same (or almost the same.) The only catch is you will have to invest in thicker wires to carry the increased amps. This could sometimes be as much as what you saved when buying the smaller panel.
Should You Mix Different Wattage Solar Panels
No. You shouldn’t. There are some reasons that make it a bad idea
- You will lose a considerable chunk of installed power depending on if you wire them in series or parallel
- Different wattage panel are of different sizes. They won’t look cool and neat once installed. It might even be hard to mount them onto a single rack
Read this too: Can You Mix Different AH Batteries
What to Do If You Must Mix Different Wattage Panels
What if someone donates a different wattage panel from what I already have. Should I turn down the kind gesture?
If you have no option but to mix different wattage panels, you could still end up losing less if you make the right choices when buying and wiring.
- Look for a panel that matches the voltage of what you already have so that you can wire them in parallel and get as much power as possible from the system (if you ignore cable losses)
- If you can, get a cheap programmable charge controller to control dissimilar panels in your array. This is the best solution especially if you have multiple mismatched panels. The different charge controllers will ensure you get the maximum power possible from each array.
Always do some math before adding a panel to your array – especially if you are buying it with your own money. Sometimes, some patience and investing in matched units might be all you need to build the perfect off grid system for your home, RV, or boat.