Measuring solar yield approaching winter solstice

[HiTech]

I need to get a temporary setup on the RV roof to measure solar yield around the winter solstice.

How deeply discharged will I need to get my 85 Ah battery so that it allows pretty full production from one 68w panel without clipping it and skewing the amp hour charging numbers? I am ok living with the battery only being charged up to 90 percent daily for a week or 10 days.

I was thinking daily yield on a sunny day might be 10 Ah max in Houston for a flat 68w 16.5 v panel? 15 Ah? I am not sure how much penalty there is for a flat orientation for a full sunny day. I get only short periods mod full sun in the backyard.

I am planning to leave some small load on to try to balance charging to usage.

It's not trivial to mount a thin film panel temporarily. I am thinking a big battery on a board on one end and a big but flat board on the other end unless I can find a hunk of metal maybe 1/2" thick. Cannot have any shadow cast on the south end.

Jim

[HiTech]

You are in time for the summer solstice. The more solar for us thread has amazing amounts of info to read.

Jim

[Old___Slow]

HiTech wrote:
Who is set up for a good measurement for the upcoming summer solstice?

O&S will you have anything to measure? Has your panel arrived?

Also where is the really really long running thread Mr. Wizard had going on solar? Having some challenges getting search to locate it for me.

Jim

Hi 'tech'-Jim,

Yes, Yes, need a place to land, for long term info'... MrWizard thread if he would like the pile-on. I've noticed the short running threads are not as helpful as one that is long running.

My questionable Mppt is to arrive today. It's 24v, so I will have the 24v to 24v, the panel is due tomorrow, 24v/120w. Yes, I would like to kill the two birds with one stone. Hobby and mini lab. I will be dependent on all the techs to interpet what I find. 🙂

O&S
Floyd

[MrWizard]

this one ?

http://forums.woodalls.com/Index.cfm/fuseaction/thread/tid/24418302.cfm

if the weather cooperates, i will post summer solstice readings

[HiTech]

Who is set up for a good measurement for the upcoming summer solstice?

O&S will you have anything to measure? Has your panel arrived?

Also where is the really really long running thread Mr. Wizard had going on solar? Having some challenges getting search to locate it for me.

Jim

[HiTech]

Learned something new - again. Thanks!

I averaged 18.6 Ah or so just after solstice on less than perfectly sunny days. Finding the most beneficial use for all these bonus watts is high on the agenda as a hobby endeavor. Lots more power than I expected is being produced, and just wasting it after the batteries are charged seems, well, just wasteful.

Jim

[mena661]

Edge of cloud effect probably.

[HiTech]

Well I did not check the Unisolar output yesterday at the end of the day or reset the amp hour meter. Today we had clouds until early afternoon but good sun after. I Had a little surprise when I read the meter at the camper this evening.

I turned off the extra loads in the TT two days ago but left it hooked up so the parasitics could draw it down. I thought they might take the old group 27 battery down to 10.5 v but when I read the meter the minimum voltage had dropped to 10.24 v pre dawn on day 1. When i took a reading a few minutes ago the system was up to 12.4 v after 2 days of charging and then resting for a few hours after sunset this evening.

My peak amps on the flat Unisolar were an all time high due to the strip driving into a more discharged battery - 3.68 A within a day or two of the solstice solar minimum, with a theoretical Isc or 4.0 A.How does that even happen?

Watts peaked out at 51.1 W against a theoretical peak of 68, and 68 watt output on this unit is way up at a voltage of 16.5. V. I do not have the charts right in front of me on what the theoretical peak watts should be at 12.4 (I am sure it was higher in the sun, but under 14 v for sure), but 51.1 is a very high percentage of max output at 14 v and an even higher percentage if it was achieved at a lower voltage.

Total watt hours produced over the two days were 471.1, W and total amp hours were 37.327. These seem like very high numbers to me, especially for two days, neither of which were full sun, though the cloud cover was only light to medium.

Jim

[HiTech]

Wow. Still learning but they seem really robust at making watts in less than ideal conditions. We clouded up late in the day so I did not go out to take a reading. I will see how many days it takes to recharge my poor test battery. I took it way down before I shut off the optional loads. It is now just one Unisolar vs a discharged and beat up SLI battery and some parasitic charges.

[pianotuna]

Hi Hitech,

This year I got about 12 amp-hours on Dec 22 from ice encrusted panels--mostly sending power from the panels to the engine as I drove. It was overcast later in the day--but Unisolar's don't mind that as much as other technologies.

[HiTech]

The hour by hour forecast makes is look like a clear, crisp day here. Might have a shot at a solid solstice production number for amp hours.

Jim

[MrWizard]

934.5 watt hr

71.05 amp hrs

slightly less out put today
but this much difference is NOT due to minutes of lost sunlight.
more likely the air was less clear, not as cold and windy as yesterday

[HiTech]

Had some clouds early and late but almost completely clear for most of the day. 16.438 Ah and 204.1 WH.

Jim

[HiTech]

Nice - today should be a good proxy for the solstice yield for you.

Jim

[MrWizard]

anothet sunny day here,two in a row...
wea ther forecast is expecting cloudy weather tomorrow the 21st