Sun hours

[DanS26]

I keep detailed records of my solar production both predicted by PVWatts and actual production. As I mentioned earlier I use 0.7% degradation factor for my Kyocera panels. In the 13.5 years, actual production of my plant was 309.9 mWh compared to PVWatts pridiction of 310.5 mWh. So my plant produced 99.8% of prediction so I think that was pretty good. I got the 0.7% degradation factor directly from the Kyocera engineers way back in 2011.

Now I was also interested in how much my shoulder array would decrease my plant efficiency. Efficiency being defined as Average Daily Production divided by DC plant size in kW. My plant size before erecting the shoulder array was 17.28 kW and after it was 23.16 kW. Efficiency was 3.64 before and 3.106 after. So it is very apparent that the shoulder array reduced production from having a standard south facing array. These are long term numbers so I'm confident in my statement.

[J.P.M.]

I keep detailed records of my solar production both predicted by PVWatts and actual production. As I mentioned earlier I use 0.7% degradation factor for my Kyocera panels. In the 13.5 years, actual production of my plant was 309.9 mWh compared to PVWatts pridiction of 310.5 mWh. So my plant produced 99.8% of prediction so I think that was pretty good. I got the 0.7% degradation factor directly from the Kyocera engineers way back in 2011.

Now I was also interested in how much my shoulder array would decrease my plant efficiency. Efficiency being defined as Average Daily Production divided by DC plant size in kW. My plant size before erecting the shoulder array was 17.28 kW and after it was 23.16 kW. Efficiency was 3.64 before and 3.106 after. So it is very apparent that the shoulder array reduced production from having a standard south facing array. These are long term numbers so I'm confident in my statement.

Dan:
Thank You.

From what you write, it sounds like you and I kept similar types of information and records.

I kept daily and more often records of array and inverter (at 5 minute intervals ) performance and weather records (at 1 minute intervals) continuously between system startup (10/13/2013 at solar noon) and about 3 years ago when Sunpower when belly up and when I passed the 3/4 century mark, and decided to spend less time on my roof including less time in the 12"-14" or so clearance between the bottom of my array and the roof deck measuring panel temps. with an IR thermometer which, on a hot day seemed like being stuck in tight toaster inclined at 19.75 degrees to the horizontal.
I've written epistles on those efforts in these archives over the years with all the gory and probably boring details, but I, like you probably, had a lot of fun and learned a lot doing it all.

One item I looked into was my array's average annual performance degradation. The Sunpower spec sheet for my panels said to expect up to a 5 % burn in loss the 1st year and 0.4%/yr. performance loss of STC performance thereafter. By my measurements and calculations, my array lost 2.9% of STC power the 1st year (burn in) and, as best as I can measure and calc, about 0.4%/yr. thereafter, +/- about 0.02% or so
FWIW, if it doesn't rain my array's performance seems to roll off at a rate of very approximately 1% of clean performance/week somewhat linearly and, if not hosed down with tap water about every 4 weeks, seems to stop experiencing further performance loss at somewhere between 12 and 14 weeks or so incurring about a 12% performance loss stop fouling. I'm still trying to figure that one out. Interesting subject but not very amenable to analysis.

One thing you wrote above confused me - the 3.64 and 3.106 numbers. if you produced 309.9 mWh over 13.5 years, not accounting for the output of the shoulder array, that averages out to 309.9mWh/13.5 yrs = 22.96 mWh/yr., or (22.96mWh/yr.)/(17.28 STC kW) = (1,329 kWh/yr.)/(installed STC kW), again, not accounting for the shoulder array, which seems to make rough sense.
But, I don't understand what the 3.64 and 3.106 numbers represent.
Can you enlighten my ignorance ?

[bcroe]

I see no mention above of how an array might be optimized for frequent
clouds, not to mention smoke in wildfire seasons. Certainly building
twice as large a system could double energy collected under any
situation. Fine for a clean sheet build, not an option here. I would need
twice as many inverters. The hundreds of feet of 8 gauge wire carrying
inverter output to the house and meter ran 75% of capacity, would have
to be replaced for a larger system. Then the 200A house box might be
at capacity (some belt and suspenders people think I am way over) so
convert to 400A box plus more hundreds of feet of wire to the pole trans,
which would also need to be changed. Besides, the net metering
contract limits the AC output to 15kW.

Instead of all that, I just increased the cheapest part of the system, the
panels. Orienting them E-W kept them from over driving the inverters,
added many hours to high level output per day, and at least doubled
output under clouds. Even the expensive panel ground mounts are
greatly reduced, since panels are on both sides. I think in this situation
this is the cheapest way to get to the desired energy collection level.

I do not understand adjusting to maximize winter production. Here we
have gone up to 29 December days in a row without seeing the sun.
In spite of that, and shorter days, this system manages about 1/3 the
summer month production. With Net Metering what matters, is the
yearly total. I just take whatever little the winter will give me.

Let's mention, the sun is weaker at the fringe hours than at noon. The
Idea here it to get into clipping at soon as there is no shading. The E-W
panels to do that leave a bit of a drop near noon, but that is compensated
for by enough S facing panels.

A tracker was mentioned, but besides all that complication, it does not
compensate for intensity variation over the day. But it is totally unable
to deal with the clouds, as mine does.

As it is, my annual production exceeds a straight S facing system in
the SW desert. Unless, it had even more over paneling than mine, with
even more panel mounts, which might blow the inverter at noon.

There is a lot more than the solar array going on at these 5 acres. Solar
has fallen into a mostly minimum maintenance mode. The spinning disc
in the basement notes which way power is flowing, roughly how much, and
the scale keeps track of my annual net metering reserve. I could fine tune
some things better, but with all the energy I need, why bother? Meanwhile
there are other science projects to play with. Bruce Roe