Choosing Solar Panels

Some things we have learned after building several different types of electrical systems

In order for solar to deliver and prevent disappointment, you need to engineer the system properly and know your actual budget, not just dollar wise, but power wise.
Visit our Power Budget page for more info.

Plan for producing less than 80% of the panel rating in Watts. In our experience reaching 80% output is just not the norm.
The picture below is from a recent swap out of panels.

The original system consisted of (10) - 100W standard panels that are for 12V systems, meaning they produce up to about 20V and then convert that to nominal 12V, usually between 13-14V depending on battery chemistry which you need to input in your Solar Charge Controller (SCC).
Both systems are wired in Parallel, Panels and Batteries.

The SCC for this system is a:
Victron Energy SmartSolar MPPT Tr Solar Charge Controller (Bluetooth) - 150V, 70 amp, 12/24/36/48-Volt

First we replaced the batteries, swapped out the (4) - 100ah LifePo4 and installed (2) - 300ah LifePo4 batteries.

We hooked up the old panels to the new batteries and read the max output via the MPPT SCC, which as you can see was 604W.
Then we disconnected the panels and did not charge the batteries any further until we could connect the new panels.

Then we swapped out the panels to (3) - 405W panels with a higher voltage rating at 31.35V.

This is where we confirmed using higher voltage panels is the way to go.
Roughly the same time of day so the sun was in nearly identical position, clear with zero clouds and temps in low 80's to keep it fair.

The lower voltage panels were only supplying 60% of their rated potential and 43.3 Amps to the batteries.
(Old panels were approximately 3 years old and cleaned before testing)

The brand new higher voltage panels were putting out 78% of their rated potential and 66.1 Amps or a 52.6% increase in Amps to the battery.

Wattage went from 604W to 952W or a 57.6% increase, even though it was only a 21.5% increase in rated wattage.

Click on pictures to see full size image



For background info:
Old 100W panels were roughly 2ft x 3ft in size
New 405W panels were roughly 4ft x 6ft in size

Bottom line, if you have room for larger, higher voltage panels and you have an SCC that can handle them, you will be much happier with the outcome than trying to use the small 12V panels.