Combining Different Solar Panel Sizes : (2) 30w + (2) 100w

[KenSmithMT]

Hello all. I'm new to solar and learning a lot. Thanks for your help. I'm working on the layout for my van and would like to maximize solar panel size in the minimum space around the fan. I know it is not ideal, but is it ok to combine (2) 100w and (2)30w solar panels in parallel to an MPPT controller. They are all 12v Newpowa panels from the same manufacturer and same product line. Thanks

 

[KBWaldron]

As long as they have the same Voc and Vmpp I don't believe there will be any issue combing them in parallel. Don't combine differing panels in series though.

 

[KenSmithMT]

At maximum 100w panel produces 17.2v / mpp5.8A VOC 21.6v. The 30w panel produces 17.0v / mpp1.7A VOC 20.23v. The VOC is very close. Wouldn't the amps just add together in parallel?

Thanks!

 

[gnubie]

Check the specs on the label on the back of the panel, or from the manufacturer/seller's web site.

Ideally you want the VoC and Vmp of each string to be the same but you can get away with up to 10% difference without many problems. The main one being the array will produce less power than the paper ratings would have you believe. Usually an arrangement like this will result in the higher voltage panels being pulled down to where the lower ones are. The datasheet, if you can find one!, for the panels will give you graphs that show the power output at a given voltage so you will be able to get a rough idea of the sort of loss in production by running a panel off its Vmp.

If you go over 10% you, IMO, should fit a blocking diode in line with the lower voltage string to prevent it from drawing power from the higher voltage string should the charge controller not be drawing enough current to pull the higher string down to the lower string.

Panels in parallel should have closely matched voltages, but current can vary as much as you wish.

Panels in series should have closely matched current ratings, but the voltage can vary as much as you wish, within the maximum rating for the panel which is typically 600 or 1000 volts.

The overall current of an array of panels in parallel is the sum of the production of each panel.

*edit to include more information*

 

[KenSmithMT]

Check the specs on the label on the back of the panel, or from the manufacturer/seller's web site.

Ideally you want the VoC and Vmp of each string to be the same but you can get away with up to 10% difference without many problems. The main one being the array will produce less power than the paper ratings would have you believe. Usually an arrangement like this will result in the higher voltage panels being pulled down to where the lower ones are. The datasheet, if you can find one!, for the panels will give you graphs that show the power output at a given voltage so you will be able to get a rough idea of the sort of loss in production by running a panel off its Vmp.

If you go over 10% you, IMO, should fit a blocking diode in line with the lower voltage string to prevent it from drawing power from the higher voltage string should the charge controller not be drawing enough current to pull the higher string down to the lower string.

Panels in parallel should have closely matched voltages, but current can vary as much as you wish.

Panels in series should have closely matched current ratings, but the voltage can vary as much as you wish, within the maximum rating for the panel which is typically 600 or 1000 volts.

The overall current of an array of panels in parallel is the sum of the production of each panel.

*edit to include more information*

The 100w panel has Vmp17.2v / Impp 5.8A / VOC 21.6v, The 30w panel has Vmp 17.0v / Impp 1.7A / VOC 20.23v. The Vmp and VOC are both within 10% so should be good to go.

Thanks! I appreciate your time and help.

 

[Rbertalotto]

When I asked about this to my SCC manufacturer, they suggested that I simply use another SCC to feed the smaller panels into the system.

 

[KenSmithMT]

When I asked about this to my SCC manufacturer, they suggested that I simply use another SCC to feed the smaller panels into the system.

It’s not worth that to me for 60w. I will have two small rectangles of space available on my roof rack where 30w panels fit nicely. For $100 I would do it. If I need to start adding controllers and more cost I’ll just skip them. Thanks though.

 

[nibs]

Perhaps ignorance is bliss but have been combining panels for years without even thinking about it, have even combined a small wind turbine with panels on my sailboat many years ago.
electrons is electrons.

 

[Geriakt]

Here you can read up on combining different solar PV and calculate your loss of efficiency by doing so. You may want to consider different options.

Mixing solar panels – Dos and Don’ts • SOLAR POWER SECRETS

Mixing Solar Panels: Discover Now Dos and Dont's of Mixing the Same Types or Different Types of Solar Panels. Act Now to Save Your Money!

solarpanelsvenue.com

 

[nibs]

I think the above article misses a few things.
Efficiency (insolation converted to electricity) is a minor consideration, cost effectiveness is much more important. PV panels are not really efficient, they have been at 20% +/- for years, But they are daily becoming more cost effective.
Cannot speak for LI batteries, but when you connect panels of different outputs in parallel to lead acid batteries, the battery internal resistance dictates the voltage, a 30 volt panel connected to a 12v LA batt will output just enough volts to break over the batteries internal resistance then the variable becomes the amps the panel will put out. Throw in a controller, and once the voltage the battery needs to be fully charged is reached, the panel's output is shut down.
Does the article give actual test results, or is it just one, well meaning, persons opinion?
As always if I am mistaken, please show me test results that show my errors.
Came to this site to learn because it is difficult to keep current on such a rapidly developing science for this geezer's two remaining brain cells.

 

[Geriakt]

Clearly you have to combine similar PVs in both parallel and specifically in series to a charge controller or your are always see a loss in output across the system. By separating different panels with separate charge controllers you will get 100% possible output, but extra controllers come as a cost and may not be worth just buying more matched PV panels.
Yes electrons are electrons but they all travel the path of least resistance. So if you are blocking flow on one side you limit your total output. Math is finite not magic.

 

[Rbertalotto]

In many cases, simply buying a Chinese $15 PWM charge controller for the additional panels will give you the best performance.

 

[nibs]

My point is simply that one needs to calculate the max power delivered for the bucks, available.
A brief story:
About 10 years ago, at the Quartzsite AZ RV show, a gentleman was demonstrating a solar tracking device for a PV panel, it was a beautiful piece of equipment, elegantly engineered and beautifully crafted, a joy to behold. I watched and listened his price was $2,000 and very reasonably priced.
At that time $200 watts panel were selling for around $500. I really wanted to buy his machine, until I realized you could get the same power increase by adding a 200 watt panel on the flat for a quarter of his price.
Cost benefit calculations are most important criteria in my opinion.