Panel replacement

The max. production you describe may or may not be deficient depending on several factors. about the best daily production my array managed was ~ 6.7 kWh/day per STC kW with ideal conditions (relatively cold air on a windy clear day in April) on a close to optimally oriented array.

Average daily output for the prior 8 years has been ~4.76 kWh/day per installed STC kW. STC kW.

If I had a 7 STC kW array my daily max output would have been (6.7 kWh/(day*STC kW))*(7 STC kW)) = 46.9 kWh/day and my long term daily average net array output would have been (4.76kWh/(day*STC kW))*(7 STC kW)) = 33.3 kWh/day.

Your numbers are lower, but that may perhaps be accounted for by a less than optimal orientation, more shading or the likely fact that your site or array does not get as much sun as mine.

Have you compared your annual output to what a model such as PVWatts might come up with using inputs that are in line with your array's parameters and orientation ?

thank you for the reply. still learning all the technical stuff, didn't know about PVWatts but after inputting my numbers i get 11,599kWh/year.
the location is great. no shade at all. its a very high roof so it towers over any trees and i live in a rural area so no big buildings to worry about.
i don't have a full years worth of data. i honestly wasnt too concerned before but after last year when my system was down all summer i setup monitoring and also installed a whole house energy monitoring system to confirm the numbers coming from the inverter and to see where my power is going.
i will contact my utility provider and see if i can get any numbers.

You're welcome.
(11.6 MWh/yr.)/(7 STC kW ) = 1,657 kWh/yr. per STC kW does not sound out of line but still a bit higher (not lower) than you may be producing.

Read the help info screens on the model that explain weather variation and other things for more info.

Did you use the array's azimuth and tilt angles for your PVWatts input ?

How often do you clean your panels ?

Without cleaning or a rain event, my system's output decreases about 0.6 % to 0.8 % per week and seems to become asymptotic at about 8 - 10% penalty. However, array fouling is highly variable by region, location and weather. Still, some cleaning is required, Have you been affected by N.CA fires ? If so, and like others in N. CA report, without cleaning a fouled array may be affecting your performance in a noticeable way.

Your numbers do not sound awful. If your roof and panel elevation angle is poor
for your latitude, you will take a hit there. Here in ILL I have seen a substantial
loss from the west coast fires, that smoke seems to hurt more than apparently
similar clouds. More output might start with going to a ground mount.
good luck, Bruce Roe

i went through all of the options on PVW as best i could. as far as having clean panes, the smoke was an issue last year but the rain washed it away. i live in a rural area so dirt/dust is a little bit of an issue sometimes but i hose the panels off 1-2 times a year. is hosing them off enough or do i need to get up there with a brush and actually wash them?

Depends.

At this time, if it doesn't rain, I'm on my roof hosing my panels off from the roof peak about 1X/month or so, or ~4 weeks after a decent rain, which around here is ~ 0.25" of rain or more.
I rub off any owl skrocks or large bird strikes first and then use about 3/4 gal/panel of plain tap water and don't brush. Just spray from the top of the array down. No power washing, no soap. Drip dry. Takes ~ 20 min. or so.
Then, about 1 or 2X/year depending on how dirty the air has been, I use cheap dish washing soap and a soft window brush on a pole, rinsing before and after the soap rubdown and get it all squeeky clean.

This is not a precise science.

From testing/measuring I've done I cannot measure a difference in array performance if I remove the hard water spots or not.
I've decided that the human eye is a poor indicator of array cleanliness.
I use tap water and it's just fine. The above keeps my array fouling penalty to about 3 % or so on average.
BTW, commercial cleaning is a rip off. Don't waste your money.
Also, D.I. or distilled water doesn't get things any cleaner than tap water as I've found over the last 8 years or so that I've been measuring my array's performance.

Your situation will be different than mine but I bet a lot of what I've found out applies to a lot of arrays, maybe yours too.

After 11 years, I've only hosed off the panels 2x in the summer (in the cool of the mornings), and they are still fine. With a steep angle, they stay cleaner, a flatter angle collects more dirt.

after a good hosing they look good to me but thats from about 30' down so take that for what its worth haha. every 2 years or so i rent a bucket lift to trim some tall palms and clean my gutters so while i'm at at it hose the panels off a little better since i can get within 5-10'. next year i will get a taller one and get closer and see how they look.
just doing some future planning for now and was thinking i should look into upgrading in the future as they have 350w panels now. but who knows, by the time i'm ready to upgrade maybe theyll have better battery storage technology? trying to cut the utility out as much as possible.

sorry for the dumb question but could you guys help me out with this utility bill? i'm having a tough time understanding it. first one is from june and second is july.
the monthy bill is about $23 every month and every June is one big bill.

utility bill june.jpg


utility bill july.jpg

Reading into this.. I found this https://expydoc.com/doc/3803744/here...es-of-the-bill.

I am not quite sure what to make out of all of that as to why you have that annual true-up, if you are paying your monthly bill. It seems weird.

After many years of before/after measurements, if I hose as I've described prior, I restore about 2/3 to 3/4 of the performance that was lost to fouling.
In the real world, easy hosing of the type described is a lot less hassle than worrying about perfection which will be quickly lost to more dirt/fouling in a few days or a week anyway.
As for what your eye sees, it can't see in all the wavelengths of sunlight. Before/after measurements tell a more objective tale.
As I wrote, and as many years of measurements have convinced me, the human eye is a poor indicator of cleaning efficacy.

As for not getting close enough to see, binoculars help. Back off a bit if the focal length makes things blurry.

As Mike notes, do the hosing in the A.M. before irradiance heats the panel glazing.

If one goal of the exercise is a lower electric bill, as for trying to cut the utility bill as much as possible, you can further reduce POCO bills by either using less electricity (through conservation measures and/or lifestyle changes) or generating more electricity.
The most cost effective of those two is usually the first, especially if you already have an array.
That's also why it's most cost effective to do the first before the second.

Mike: Q: How often/How many times/yr. do you get, say, => 0.25" precip. ?

Thanx in advance.

J.P.M.

I usually go to the source for answers.
What did SMUD say when you called them and inquired ?

Looks like June is true up month to me.

May - Oct = 0 rain. I usually hose them off July and Aug. Most of the fouling is dust from my gravel road, or jays on the top edge of the array..

Oct - May rainfall is 40-60" Sometimes it's a week of continuous drizzle, half inch a day, sometimes it's 6" in one day. (rare)