Cdash wrote:
MPPT sounds great, but comes at a cost, more than double. Enough to buy almost 200 watts of panels. I read about plenty of people that share that they are fully charged by noon or 1pm, with their MPPT controller. That means that the system has quite a bit more power than is required.
To me, it seems like a WPM could still charge the batteries, but may not do it till a little later in the day.
Is my thinking flawed?
Pieces of info are missing. You won't get an answer specific to your situation without providing more details. Several people talked/asked about your energy audit and planned panel wattage - this is what you should figure out first.
About fully charged by 1 pm with MPPT - the picture is bigger than that.
People with MPPT typically have more panel wattage. Plus, MPPT would harvest more energy – about 10-20% more – but there is also more wattage, these two effects work together.
Also - no matter what controller - if battery has been through all the charging stages and is 100% full by, say, 1 pm - it doesn’t mean that system has "more power than required". There is a huge difference in harvest on a good and bad day. On a good day you may get more than enough, and on a bad day - just enough. If you can barely make it full by sunset on a good day, then with any clouds you won’t get it full on that day.
When panel wattage is too low, neither PWM nor MPPT will charge battery full "later in the day" - it will never charge it full, period. You don’t want to leave it undercharged very often. OTH, there is no penalty – other than system cost – for getting it full earlier on some days.
"Cost more than double" – yes, sort of. You should compare controllers with same features. Also, consider that with MPPT you can wire panels in series -> thinner cable and no rooftop junction box -> simpler work and slightly lower wiring costs. Most important is the ease of install and no J-box, with MPPT. With 12V bank and panel wattage under 250W there are no savings on thinner cable and no need in J-box either.
Handy Bob’s blog is inspirational but it’s difficult to sift through the rant and get enough of useful info there. A bit dated, too.
