bob day wrote:So you're saying if I hook up in parallel, two panels of different voltage without a controller, and read the open circuit voltage, I won't get some voltage in between the high and low values of the panels?
S Bengi wrote:In parallel, the system voltage will always be the lowest voltage.
So if they all have around the same amperage, in series is actually better.
Do have an idea of ho many panels and amperage.
S Bengi wrote:Solar Panels have two set of voltage; open voltage (no load), and regular closed voltage (with a load e.g battery)
So a 20V panel will actual have a open voltage closer to 26V
And a 36V panel will actually have a open voltage closer to 42V
So when you combine them in parallel you will see a voltage of 26V for the open voltage which might look like the 'mid-way point' between 20V and 36V, but that 26V is just the open voltage and once an actual load is added it will go to the regular/loaded voltage of 20V
Also we are looking at overall power from the panels not just voltage or current.
So if you can, connect them in parallel with a load get the total power (V x I), then connect them in series, that would give better comparisons.
The load has to request more power than what the panels are rated for, because unlike wind/hydro solar panel only give as much as is requested including zero, which is why no dump load is needed.
Also it is best to think of a controller as a dynamic 'transformer', it will always try to change the actual panel voltage to what it thinks the battery needs.
So if the string of panels is 60V it will step it down to '26V' to charge a 24v battery.
Likewise if the string of panels is giving it 20V it will step it up to '26V' to charge the battery.
The voltage and current profile actually depends on if the battery is floating, charging, etc,
Thus measuring the voltage after the controller will not give the actual panel/string voltage, just the 'transformer' voltage.
Another more ideal (but super expensive) way to mix solar panels is after the multiple controller.