Small solar set up for TT.

mike-s wrote:

pianotuna wrote:
One difference is that if you have no more roof space MPPT may allow you to harvest about 8% more.

How much more roof space? Show your math, because I suspect for the difference in cost between PWM and MPPT, you can get more return from adding another panel.

The difference in price between a Morningstar PS-30M (PWM) and a TS-MPPT-30 (MPPT) is about $200. That will easily pay for a 100W panel. So, you'd have to have over 1000 W in panels for an 8% savings to pay off.

Well, he's pretty clear by stating "no more roof space". No need to show math. But I do get your valid point.

I have been taking part in a solar panel forum lately and just sticking the RV camping/off grid subforum. It is a very different place than RV.net with respect to solar ideas and the majority vibe there is very "MPPT ALL THE TIME, NO EXCEPTIONS, PWM IS FOR FOOLS". I have made a similar point as you with respect to realistic return on investment, but soon learned that there is no changing the minds of their frequent posters. But the truth is they are not leading folks into designing bad systems, just often massively overbuilt. But it has made me rethink some things.

My thought process regarding MPPT is that it will save you money if you're building a system with several panels because you can and should use high voltage panels. These panels cost less on a $/watt basis than 12V nominal panels. So the more expensive controller is more than offset by the money you save in panels. But if you're only installing a panel or two, PWM is probably a less expensive route. When I built my system, I read a rule of thumb that the tipping point for going MPPT is in the 500 watt range. On the solar forum I'm referring to, one poster says this is more like 200 watts. Actual solar harvest is not part of this dilemma.