Beginners Help Tips - Mixing Different Solar Panels Correctly

[Crowz]

Did some panel swapping today and I figured this would be a nice cautionary tale for beginners to watch out for. This is worded and aimed at newbies so be kind



I had a bunch of random panels I had put together on a string which was a mixture of 255 watt, 290 watt and 450 watt panels.

This worked out to being :
One 450 watt renogy panel + two 255 watt panels + five 290 watt trina panels

Now on paper this should be 2410 watts.

Then I put an identical string together as above and then paralleled the two strings.

On paper this should be 4820 watts.

Right? Wrong. What most people don't take into account is you can't just go by the watts the panels are rated at. I knew I wasn't going to get full power out of these and I didn't but it did decent for what I needed it for. On average is made 3.2 kw to 3.4 kw. Sometimes with the right clouds it made 4.8kw but this was VERY rare. Once a month if lucky type rare.

So to help out folks that run across this lets see why I didn't get 4820 watts.

Lets look at the panels themselves.

Lets start with those big suckers. The 450 watt panels.

All panels come with stickers on them somewhere on the back that tells the stats of the panels.
How much info is on the sticker varies but they all have the basics you need to figure up what the panel can do.
If the sticker is missing which can happen you need to find the stats from other sources with a panel tester being ideal I would imagine.

This is what the sticker on the back of the 450 watt panels shows :

--------

Maximum Power: 450 W

Open-Circuit Voltage (Voc): 41.25V

Optimum Operating Voltage (Vmp): 34.67 V

Optimum Operating Current (Imp): 12.98 A

Short-Circuit Current (Isc): 13.89 A

Maximum Series Fuse Rating: 25 A

Maximum System Voltage: 1500V DC (UL)

Operating Temperature: -40°F to 185°F

Item Dimensions LxWxH 75.2 x 44.6 x 1.4 inches

---------

All useful information but for calculating purposes we can ditch most of it.

We need the following:

Optimum Operating Voltage (Vmp): 34.67 V

Optimum Operating Current (Imp): 12.98 A

Now we need to get this same information off one of each of the other panels.

255 watt panels are :
Optimum Operating Voltage (Vmp): 30.0V
Optimum Operating Current (Imp): 8.5A

290 watt panels are :
Max power voltage (VMP): 36.4 V
Max power current: 7.97 A

Now when placing panels in a string you add voltage but the amps stay at the lowest panel in the string.

So out of our 3 different panel types the 290 watt panels are 7.97 amps which is the lowest. Thus when put in a string all the panels become 7.97 amp panels.

Big deal right? Actually YES a very big deal.

Lets see what happens when we wave the magic electricity wand over the other panels that aren't normally 7.97 amps..

Lets start with the 255 watt ones (I know you want to see the 450 watt ones which is why I picked the 255's next )

Normally by themselves they come out to :

• Max power output: 255W
• Max power voltage (Vmp): 30V
• Max power current (Imp): 8.5A

Now lets wave the wand and turn that 8.5A into 7.97A.

• Max power output: 239.1W
• Max power voltage (Vmp): 30V
• Max power current (Imp): 7.97A

Hmm it seems by lowering the amps our 255 watts panels just changed into 239 watt panels. Each string above had 2 of these in them. So we lost 32 watts in each string. When put parallel we lost 64 watts. Not good.

Now lets try the wand on those big 450 watt panels.

• Max power output: 450.02W
• Max power voltage (Vmp): 34.67V
• Max power current (Imp): 12.98A

Now lets nail them with wand changing the amps to 7.97A.

• Max power output: 276.32W
• Max power voltage (Vmp): 34.67V
• Max power current (Imp): 7.97A

WOW. We just wiped out 173.7 watts per 450 watt panel. THATS noticeable and painful.
But wait we have two these with one in each string so were loosing 347.4 watts in the whole setup.

I just got done using two 200 watt bifacial panels to replace the two 450 watt renogy panels in this setup I've covered here and the system made the same power.
Wild huh? Here is why.

The 200 watt bifacials are rated at :

• Max power output: 200.07W
• Max power voltage (Vmp): 23.4V
• Max power current (Imp): 8.55A

Notice the 8.55A part. Since they operate almost at the 7.97A rating of the lowest they are not hurt as much as the 450 watts panels.

Thus when they are changed to 7.97A you get :

• Max power output: 186.5W
• Max power voltage (Vmp): 23.4V
• Max power current (Imp): 7.97A

With the weird boost you get with the bifacial effects it seems to makeup for it completely as far as my after swap tests show.

So the moral of the story is you can mix any panels you want in a string as long as you don't go over the max voltage of the charge controller.

But one cheap panel can wipe out all the benefits of the good panels in the string.

Remember to use a panel calculator to see what will happen when you string those panels together.

Here is a link to a very good calculator I use :

Solar Panel Series & Parallel Calculator - Footprint Hero

Use our solar panel series and parallel calculator to easily find the wiring configuration that maximizes the power output of your solar panels.

footprinthero.com

Good luck, have fun and let us know how it works out for you.

 

[Crowz]

Another tip for moving large panels when you are short, old and completely beyond the term out of shape.





Using this method you can use one hand to balance the panel and the other to drive the mower. Works great at lowering slip discs risk and heart attacks from what I can tell so far

Also remember to spin around and back into the final spot if you are like me and can't see over the panels when moving forward.

 

[Crowz]

This is the pv tester I mentioned in the first post that I use when I need to find out the stats on a panel such as when the label is missing off the back of it.

Amazon.com

Its showing $89.99 on amazon right now.