Solar panel output

Hey West, understanding PV output would make all solar threads unnecessary :)

Almot wrote:

westend wrote:
In the original post the OP states two 250W modules will be installed.

And then later on stated that he already has some MPPT running 390 AH battery bank. With... what?

He is using a 40 amp MPPT controller, as stated.

I am guessing that he is in the process of installing this gear so that he is using different tenses when referring to his equipment, that might be confusing.

I'm assuming that the intent of this thread is to ascertain if an additional 190W module would be necessary and worth the time/expense of installation.

A careful energy audit of use and understanding of PV output would make this thread unnecessary, IME.

westend wrote:
In the original post the OP states two 250W modules will be installed.

And then later on stated that he already has some MPPT running 390 AH battery bank. With... what?

In the original post the OP states two 250W modules will be installed. There is very little possibility that the 190W module will be alike the larger modules.

The OP's choice of a separate controller for the additional panel may have some merit. It would eliminate either getting a larger MPPT controller if he was already close to maximum throughput and would keep any controller confusion at bay from connecting all three together.

Need more data.

1) He didn't tell what panels he already has with MPPT, i.e. if there is a mismatch issue with added 190W.
2) He didn't tell the voltage of that planned 190W - they are (usually) 24V nominal, so his idea of getting a cheap PWM to run this added panel sounds odd.

Mixing panels with different electrical characteristics may confuse your controller. MPPT (at least the better ones) is always searching for the optimal charging "knee" of voltage, amperage, and battery acceptance. I've watched mine in real time and it is changing every few seconds, even with a single module.

MW will put a dent in your daily energy balance. "Few" minutes won't get you anything, my MW at home runs 3.5-4.0 minutes to reheat a plate of meal from 40F, multiply this by 2 or 3 times daily, plus other uses. The biggest issue is high current of MW, it overloads the battery and makes it losing charge faster than normal.

If that 190W panel is more-less same voltage as others, and MPPT has enough margins in volts or amps, just add it to the chorus and be done with it.

Thanks everyone. This is the info I needed. I'm a newb to solar, but learning. I do have a 40 amp MPPT charge controller running a 390 AH battery bank. 180 AH is more than I need, though I might be stretching it winter. The reason for my post is I have ab opportunity to purchase a 190 watt Canadian solar panel for $130 negotiable. I'd have to get another charge controller. I was thinking of getting an inexpensive PWM and putting it on an independent circuit, but wasn't sure I'd need the extra panel or not. My loads are minimal,though I use my laptop a lot. I might be interested in running an Xbox now and again, though, and maybe the microwave a few minutes a day.

First, boring stuff. Flat panels are not really flat, they conform to the roof curve. Making it perfectly horizontal you'll have water pooling there, leaves etc. So... as long as you realize that they aren't flat...

On an average December day in AL, flat 500W system would harvest about 80 AH.

Compared to tilted panel you will lose less in summer and more in winter. Solar output calculator: Clicky. Enter your location, power 0.5KW, tilt=0. Ex, for Montgomery AL in June it gives 69,000 WH, divide this by 30 days and by 13 volt. Average 180 AH a day. This is average, so you could get 200 on one day and 160 on another.

Do you need more than 180 AH in summer or more than 80 AH in winter? If not, then you're fine with flat panel. On a dark and cloudy winter day it would harvest at least 25-30 AH except for when it really rains non-stop all day long - then you'll get almost nothing, rain is a byatch.

12A current? My 30A MPPT controller rarely has a chance to output more than 7A with 2*250W array because I'm a light user and don't dip below 80-85% SOC in the morning. It "can" do 12A but the battery doesn't want it. No high loads like microwave either. No furnace, catalytic heater instead. On those days when I'm not charging laptop, my daily needs are less than 40 AH.

You will need 30-40A MPPT controller. They tend to be pricey. For worry-free living you do want MPPT, and a good one, that will do all the wizardry, boosting amps and adjusting volts without you checking on it few times a day. With MPPT you'll also get the benefits of an easy #10 AWG series wiring without junction box.

Edit-PS:
Somebody said this already - 250W panels are 24V nominal. MPPT will convert extra volts into amps, ex. 8A @24V input to controller becomes 16A @12V after the controller. Like I said, with 2*250W I rarely see more than 7A AFTER the controller - my batteries don't want it, they are near full most of the time.

depending on the sun angle you will get 50% in southwest during winter to 100% in the southwest during summer. And yes I know what I am talking about as I keep records while I work with my solar system