Combining solar panels

[Al Slitter]

I am now planning a complete redo of my small solar system, at present I have 2- 55W Sun Power Mono Crystaline panels connected in Parallel running to a PWM controller then to a 12 volt battery.
My thinking is if possible for me to add a 110 Watt Mono Crystalline panel to the existing 2-55 Watt Poly Crystalline panels in a series connection to get to a 24 volt system? Is this possible or would it be best to tie the panels together in a Parallel connection? Is that possible.
There is so much to think about when it comes to an upgrade to Lithium Ion Phosphate. I not only want it to work now but also some form of future proofing.

Thank you in advance for you views.

 

[MisterSandals]

panels in a series connection to get to a 24 volt system

Your battery arrangement (2x 12v in series) determines your system voltage.

You need to arrange your panels to satisfy the SCC. In your case, PWM SCCs usually have specific input voltage ranges, and even smaller optimum voltage ranges.

In general for SCCs, the input voltage must be 5 or more volts (headroom) above battery voltage.

To answer your question properly, your panel voltages (listed on back of panel, Voc) and SCC input voltage requirements are needed.

 

[Al Slitter]

Thank you for replying.
Here is the specifications that are on the back of each of the two panels.

Maximum Power 55 Watts
Operating Voltage 21.5 Volts
Short Circuit 3.28 Amps
Max Power Current 3.06 Amps
Maximum Voltage 18.0 Volts
Maximum System Volts 600Volts DC

 

[Bud Martin]

Thank you for replying.
Here is the specifications that are on the back of each of the two panels.

Maximum Power 55 Watts
Operating Voltage 21.5 Volts
Short Circuit 3.28 Amps
Max Power Current 3.06 Amps
Maximum Voltage 18.0 Volts
Maximum System Volts 600Volts DC

So the two 55W panels you have has teh following spec.
Voc of 21.5V
Vmp of 18V
Is of 3.28A
Imp of 3.06A

How about the spec of the 110W panel?

 

[Al Slitter]

Model 110 Watt 12v Mono-Crystalline
– Maximum Power (Pmax) : 110W
– Power Tolerance : 0 to +- 5%
– Open Circuit Voltage(VOC): 21.5V
– Short Circuit Current (Isc): 6.56A
– Maximum Power Current : 6.12A
– Weights(KG) : 7.21 KG
– Dimensions : 1006x664x35mm

 

[Bud Martin]

OK, you should read this:

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

If you put that 110W panel in series with the two 55W you have, the current will be limit to the 55W panel current rating.

 

[Al Slitter]

I started to read the information on the link provided and while I was able to follow it somewhat until I found myself drifting off.
Basically it is best to stay with the exact same panels when doing either a parallel or series connection.
My situation is not as bad as one might think (Me) as the panels are from the same manufacturer and a new panel (110Watt) has the
same basic specifications times two of what I currently have.
Thank you for the link more reading is needed.

 

[Bud Martin]

So base on the spec of the 55W and 110W panels, the total power when all connected in series = 18Vmp * 3 * 3.06Imp = 165W.

 

[Al Slitter]

Thank you Mr. Martin for you excellent assistance.

 

[MisterSandals]

So base on the spec of the 55W and 110W panels, the total power when all connected in series = 18Vmp * 3 * 3.06Imp = 165W.

Why not connect the 2x 55w panels in series and then connect that in parallel with the 110w panel.

It should be exactly like 2x the 110w panel in parallel.

 

[Bud Martin]

Why not connect the 2x 55w panels in series and then connect that in parallel with the 110w panel.

It should be exactly like 2x the 110w panel in parallel.

Because the 55W panels and the 110W panel has the same Vmp of 18V, so the series connected 55W panels will have Vmp of 36V, then you connect that in parallel with the 110W panel that has Vmp of 18V which means the Vmp of the whole panel setup will be 18V, OP want to get higher Voltage than 18V to feed the SCC.
OP needs to get another panel with Vmp of 36V to be able to parallel with the series connected 55W panels.

 

[Al Slitter]

Mr. Martin your math is correct, unfortunately my supplier does not have a panel with a Vmp of 36 Volts.
So basically this will not work. I will have to replace the panels or add 2-more 55 Watt panels to try and get it to work in the serial/parallel connection method?
Am I missing something here????

 

[KaFun]

My two cents:
If you keep your two 55W modules in parallel, you'll end up at maximum power point with Vmpp of 18V and Impp of 2x 3.06A = 6.12A
If you then put your 110W module in series, at least Impp (AKA current at maximum power point) is also 6.12A according to the specs you've given above. As you have not given voltage at maximum power point for the 110W module but VoC is similar to the 55W modules, this also won't be too far off.
So I'd say, give it a try: 2x 55W in parallel plus 110W in series! You should be able to get almost full power out of the three panels with the overall system values of:
Vmpp_total = 36V
Impp_total = 6.12A

 

[Al Slitter]

The potential loss of Amperage in adding a new 110 Amp panel is a concern. The price given by the supplier that I have used in the past is now
nearly equal to a new 345Watt panel. With this in mind I will be better off buying a new 345 watt panel and pulling the 2- 55Watt panels out of the array!
There is always something to be charged going forward and the 55watt panels will not be sitting around for long.

 

[Bud Martin]

The potential loss of Amperage in adding a new 110 Amp panel is a concern. The price given by the supplier that I have used in the past is now
nearly equal to a new 345Watt panel. With this in mind I will be better off buying a new 345 watt panel and pulling the 2- 55Watt panels out of the array!
There is always something to be charged going forward and the 55watt panels will not be sitting around for long.

Yep, the price of the panel is quite low compared to what it used to be.

 

[KaFun]

The potential loss of Amperage in adding a new 110 Amp panel is a concern. The price given by the supplier that I have used in the past is now
nearly equal to a new 345Watt panel. With this in mind I will be better off buying a new 345 watt panel and pulling the 2- 55Watt panels out of the array!
There is always something to be charged going forward and the 55watt panels will not be sitting around for long.

Absolutely agree! On top of that, by using one panel instead of three you reduce many plugs and wires and every connection is not only a potential failure source but also a point of power loss as there is always an ohmic resistance of the connector.
This resistance is mostly in the milli Ohms but at 10 Amps and an assumed connector resistance of 10 milli Ohms gives you already 1W power loss. Now 10 milli Ohms is quite a lot and not realistic for new connectors, but give them time and humidity (let them lay on the ground!) and they might end up there ...