For today's lesson is System Design Thinking, let me share with you an example from a DIY forum in which I have some things to explain to a field tech.
Here is the original poster's question:
"I am looking at an RV that has 220w solar panels, 30w controller and a 2000w inverter. If I want to add two more 220w panels will I need to change any of the other components? TX"
Now the thing about solar is that there are a lot if different components each with their own specifications. When you change or upgrade one thing, it may effect another, so that's why you have to think about the Whole System in its entirety to know when a change in one component may effect other parts of the overall system and which will remain unaffected and can be left alone.
There are some important things that are left out of the original posters question which are important for the overall design and some which aren't. Such as are the two existing panels connected in series or parallel, and if the two additional panels will also be connected in series or parallel or even a combined series and parallel system.
The reason why this is important is because it will affect the voltage and current in DC produced by the solar system, which has consequences for the other parts of the system.
Notice that the OP says the panels are 220w, but there are two other parameters that we have to know for the system design, mainly maximum Voltage and Current (I) ratings (ignoring for the moment the cold calculations). Now a little googling will quickly tell us: "A typical 220W solar panel often has a maximum power voltage (Vmp) around 18V-22V and a maximum power current (Imp) around 10A-13A, with an open-circuit voltage (Voc) typically between 22V-24V. "
Consequently, if all four solar panels are connected in series it will give us a Vmp of between 72V and 88v at a current of 10-13 amps. If we connect them all in parallel, it will give us 18-22V and between 40-52 amps. So here we have the ranges that we can expect.
What needs to change?
So assuming someone bought bone stock PV wire with MC4 connectors, would anything have to change to run this power to the controller/charger, the batteries, and the inverter?
Another poster said quite confidently " and the wire coming down from the roof to keep the amps down." Let us ignore for the moments the bit about the wire keeping the amps down, which makes absolutely no sense. Wire is wire and can either handle the amps is asked to carry or it will potentially overheat or have a severe voltage drop over the length of the run if it can't.
Let's consider some specifications for MC4 connectors and various gauges of PV wire. So here we go again with the googling:
"MC4 connectors, designed for solar panel systems, typically (my emphasis) have a rated current of 30 Amps and a rated voltage of 1000V (TUV) or 600V (UL). Wiring Size Range: 2.5~6.0mm² (14AWG~10AWG)"
Why is this important? Well it sparked a debate with another poster (AP) who is describes himself as a "tech" who has pulled a "lots of wire" and claims to have to fix mistakes made by engineers who spec systems. Remember the context that this is a pretty simple RV system and there isn't much wire to pull. But lets indulge the AP here and take him at his word.
At the high end we have 72-88V and 10-13 amps which is clearly less then 600V and the nominal 30 amp capacity of the MC4 connectors.
On the low end with everything in parallel, things are a bit more interesting. Now we've got 18-22V which is clearly less than the 600V rating of typical PV wire. But we also have between 40-52 amps which is ostensibly much more than the nomical 30 amps at which MC4 connectors are rated. Remember when we googled the specs for PV wire? Notice that bit at the end where it says with wiring size ranges between 2.5-6.0mm squared (14awg~10awg). Again with the Googling
14 AWG Copper Wire:
Ampacity: 15 amps.
Common Uses: Suitable for lighting circuits, low-power applications, and some general-purpose circuits.
Diameter: Approximately 0.0641 inches.
Resistance: Around 2.525 ohms per 1000 feet.
10 AWG Copper Wire:
Ampacity: 30 amps.
Common Uses: Used for larger appliances like electric dryers, water heaters, and some 240-volt circuits.
Diameter: Approximately 0.1019 inches.
Resistance: Around 0.999 ohms per 1000 feet.
So clearly there is a bit of a question if the 10 AWG wire can "handle" the extra 10-22 amps on the low end of the configuration.
Remember when I said bone stock PV wire? Well here's a listing from Home Depot for 10ft of PV wire:
And when we look at the specifications, lo and behold it is rated up to: Max Amps = 40.
Which is in the range of what we'd expect in the worst case scenario. You want to quibble about those 12 amps in the worst-worst case scenario? Well, OK. Will it ever be in that corner case? Again it depends on the specifics of the panels, how they are laid out (parallel vs. serial), but in the vast majority of cases, no the wire used to bring the DC down from the panels will NOT make a difference and is irrelevant to the OPs original question.
Hope that helps, and illustrates the importance of total system design thinking, and especially the importance of knowing how to search and doing some basic googling and knowing how to interpret specifications of all of the components of a system.