inexpensive panels
Hi all, I know nothing about this firm--but the prices appear to be low: https://www.santansolar.com/?fbclid=IwAR17Xx_DhkB3h13BFmTjqejxTlf92ZO7UsVEAiNjNmcyNzrOkJx9XgYN26c
Forum Discussion
BFL13 wrote:
If you are a salesman, percentages are a lot of fun.
when we did all this about eight years ago, using a 130w panel all day, it came out that around 8am you got 2.5 amp with PWM and 3 amps with MPPT.
So, 20% better with MPPT---wow!!!!
By high noon, it was more like 8 amps with PWM and 8.4 amps with MPPT for a percentage gain of 5%
that was where the battery voltage was held fairly constant by running a load on it so it would not get charged up. Why that? Because with MPPT, amps to the battery are output watts from the controller/ battery voltage.
So during the day, the battery voltage climbs so ever reducing percentage of amps to the battery for the same output watts. But output watts are also highest at high noon and lower in the shoulder hours.
You might still have a day where the overcast clears at noon and you are starting with best solar on a low battery. Say that is the case.
130w/12.2 = 10.6 amps , but then after an hour, with the solar strength still good, battery might be at 13.2, so
130/13.2 = 9.8 amps
So everything is in motion and as a salesman ("drummer") you can pick any percentage gain you want and not be actually fibbing--leave the scenario to the "small print"
Heck, at 6:30 am you might have 1 amp on the PWM and 2 amps on the MPPT and then be able to claim a 100% gain over PWM! Wow! But it is only 1 amp more (don't mention that!).
You do usually get a little more with MPPT. If it gets your batteries full by 2 pm instead by 3 pm with PWM is that worth anything? Depends!
people dont understand at high noon with the angle optimized then ya they will be simular outputs, where a MPPT shines is low light, partial shaded and off angle conditions.... hmm starting to sound like canadian campsites ;) on the camper I went with a 24V system and from the differences I motice over the 5th wheel I am upgrading the 5th wheel next. the 5th has 55 more watts than the camper (480 watts 12V compared to 325 watts 24v ) and I get more amp hours back to the batteries on the same day same location in the same amount of time from the "smaller system"
as far as I am concerned if you can save an hour or two of charging then ya it is worth it as that hour or two can be a big deal in inclamate conditions.
Steve
