question

There's a more detailed explanation on it way, but given the way panels work, most of the time not.

Hi @cporath,

Thanks for your post. Sorry for the delay in replying, it has triggered a few changes behind the scenes, and I wanted to make sure they were all complete first.

The oversizing ratio used in the recommended design is now shown when you click to reveal the calculations:

I have also updated the blog post that is linked when you click the (i) that explains a little bit about why we allow an oversizing ratio in the design; it's under the heading "Oversizing a PV array"

https://www.victronenergy.com/blog/2014/03/28/matching-victron-energy-solar-modules-to-the-new-mppt-charge-regulators/

While that covers the essential gist of the situation - there is some more colour I can add here.

There is a good article that models some of the effect of this oversizing clipping - https://www.solarchoice.net.au/blog/should-you-oversize-your-solar-array-undersize-your-inverter/

Enphase has published an even more in-depth and scientific approach here - https://www4.enphase.com/sites/default/files/Enphase_White_Paper_Module_Rightsizing.pdf

From their data - in a perfect solar day - with a 120% sizing, you capture the orange section, but lose the grey section:

Over 12 months - you lose a total of much less than 1% of production from a 130% panel oversize.

And that is performance when brand new - the difference is reduced even further as time goes on and the panel output drops from its rating.

So while at first glance it looks like you might be losing 30% of the potential from the spec sheets, when taken in the real world as an energy harvest over time, the results make that a very efficient and cost effective design.