What they don't tell you is sure the conversion efficiency of MPP controllers is in the high 90s but to get that they have to turn off the panel, measure the Voc, calculate the Vmp then turn the panel back on.
This is true with SOME older tech MPPT controllers. Controllers such as the Genasun MPPT, Rogue etc. do not turn off to check Vmp.. The Genausn is constantly testing the power point with a modified P&O approach, about 20 times per second, and does not disconnect from the panel or batteries in order to do so. They also do not shut down in low light like some older tech MPPT controllers can. All MPPT controllers are not created equal. Even controllers that do track the Vmp by disconnecting the array vary in the speed of tracking. Some do it as quickly as .25 seconds and others can take a full 30 seconds to do so (usually Cheap Chinese eBay junk)...
That said if you have the real estate more panel wattage is often the least expensive way to gain more power. However on sailboats, where real estate is very limited, an MPPT can make a lot of sense.
I have done side by side's on boats with the Genasun and PWM and the Genasun beats the pants off the PWM even in early morning and late afternoon. I've observed 8-18% gains over PWM. Still not the claims of up to 30% but better than nothing.
Soooooo you have the panel turned off about 5% of the time. That pushes the total efficiency into the low 90s so why bother? A straight panel can get that kind of efficiency so you can use a pulse width controller at lower cost and achieve the same thing!
Your overt generalizations of all MPPT's is simply an incorrect assumption.
Also check the controller max input voltage. A 24 volt rated panel puts out around 36 volts in full sun and cool temps. i know my controller has a max input voltage of 30 volts.
When buying any panel and controller one has to be cognizant of the limitations of the controller, batteries, temp sensing, panel voltage, max array current, voltage drop in wiring etc. etc....
