How much do my panels really produce?

[Photowhit]

careful photowhit as it's starting to look like you are agreeing with me.

Darn... Maybe it's setting up my 'next' system with too much array... I'll work on it.

[ggunn]

Sorry, but I live in the bush where power is precious and how can it be so hard to understand what I mean? "What I could potentially produce"! At any given day. Sort of what pvwatts calculates. I would just love to know how many kwh I could produce max on a cloudy and on a sunny day. Just so I can plan my usage a little better!

I don't see how you will ever be able to directly measure what you are looking for on an off grid system. Using a weather station with a pyranometer you could collect data on solar irradiance normal to your array surface and then use it to calculate what your array would produce if it were fully loaded, like with a grid tied system. That's going to a lot of trouble and expense, though.

[vtmaps]

Problem solved!!
This thread caused me to think about how to get every last electron from my panels. So I decided to read the manual for my Outback Flexmax controller. There is a function called "AUX diversion SSR". It allows the Flexmax to control a SSR to utilize power in excess of what the batteries need. There is quite a bit of info on the Outback site.
Start here: http://outbackpower.com/forum/viewto...tart=25#p17441

--vtMaps

[Vic]

VT,

Yep, Crewser Jim who used to Moderate here, did a lotta work on this when he was at OB.

The Midnite Classic lslo has this function built-in. And, if one is willinfg to discharge their battery bank to a point what is below the capability of the PV to recharge the bank, the Kh/AH display on the CC will tell, at the end of the day, the amount of power that the array was able to deliver on that day.

Here in Northern CA almost every Summer day is very much like the preceding, and successive days -- essentially no measureable rain for about 6 months, and very days with any clouds. So knowing the max available on one day, is easily within 10% of the power produce on the following day. IMHO, m, YMMV and so on, Vic

[EagleOne]

aleman -
In response to the original post...

I also wondered this same thing when I set up my panels back in May of this year. What I did, just to satisfy my curiousity, was to get my batteries fully charged to start with. Keep in mind that I do not 'need' to use my batteries/panels as a power source for daily use (kind of an RV setup). After fully charging the batteries, I checked the weather predictions waiting for an expected good sunny day.

The night before an expected sunny day, I put a load on my batteries to draw them down during the overnight period. This would allow the system to use all the available sun to charge the bank(s) during the bulk stage. I kept a load on them so they would not get to absorb and just stay in bulk mode all day. Like I said, I don't 'need' the batteries for daily use, so try this method as you see fit. I had a reasonable expectation that I would have a second day of good sun to get them back to floating as needed.

FWIW, I was able to use my 630W of panels to produce over 4,000 WH of power during the day in question. This was back in June when we had a long, warm (not hot) sunny day in the Seattle area.

The folks on this forum have much more knowledge and experience than I, and I am impressed by the lengths they are willing to go to in order to get an accurate answer to questions. The way I read your question, it seems to me that you just want to know what to expect in a hypothetical 'great day' situation.

Are you in a position to experiment with your system? Meaning, can you put enough of a load to keep your batteries in bulk all day and also have the ability to turn off the load at night without draining your batteries too deeply? The long days of summer are dwindling down - at least for me - so time might not be on your side. I have the TriStar MPPT60 and it logs a lot of the info mentioned earlier, with an ethernet connection to a PC, but I cannot speak to the Midnite Solar.

Good luck,

- Chris J.