Howdy,

My system has been installed and working for a couple of weeks. The early opinion is that the system will create on average between 45 to 50kW-hours a day. The maximum has been 61kW-hours.

My questions:

• Does ambient air temperature have an effect on the panels?
  I don't think it does.
• In winter, how much production will I lose because of the Earth's angle change?
• Any recommendations on how often to clean the panels?
  Is once a year enough under "normal" conditions? I'm in a pretty "clean" area.

Thanks!

Regarding power output vs seasons...

Here is a nice site with government data from, roughly, the past 20+ years... I recommend downloading the PDF format and reviewing the graph at the top for the location nearest your place... It shows seasonal and long term fluctuations in the average.

http://rredc.nrel.gov/solar/pubs/redbook/

And, you can go to this link and enter your system's information (where it points, what angle, fixed or tracking, etc., and it will give you a pretty accurate estimate of the output of your system by month.

You can change the tilt and compare the yearly and monthly differences.

Also, you can download detailed data for a spread sheet--gives 365 days hour by hour information.

http://rredc.nrel.gov/solar/pubs/redbook/

Regarding cleaning--my system is on a second story roof--so it does not get cleaned often... And when I have cleaned it--I cannot really measure any difference--but there should be a 5% to possibly 10% improvement in output. If you cleaned them every 4-6 weeks, you probably will be just fine.

And yes, your solar panels are affected by temperature... The major effect is a reduction in panel voltage as they warm and an MPPT controller reduces it power output because of it.

If you have panels mounted flat against a roof, it will cost you some 5% or more percent extra in output on hot days. My roof mounted system can see upwards of 10% drop in total kWhr per day output between a very hot day and a cool windy day.

Regarding panel tilt--if you are in an area with lots of snow--tilting panels closer to vertical will help them shed snow and can also pickup on snow reflected sun to increase your panels' winter output.

-Bill

1Does ambient air temperature have an effect on the panels?
I don't think it does.

2 In winter, how much production will I lose because of the Earth's angle change?

3 Any recommendations on how often to clean the panels?
Is once a year enough under "normal" conditions? I'm in a pretty "clean" area.

1 yes it does to a point. you will lose a small bit of power during high ambient heat, and don't forget that the sun heats up the pvs too. i do hope the pvs are mounted above any surface (like a roof) by at least 6 inches and preferably more to allow airflow under the pvs for cooling. large arrays and those pvs that are not inclined very far should be mounted higher above the surface by at least 8 inches or more. one's location and weather are also a factor in this as one in the arid areas of the world may want more space between than one in a colder climatic area.

2 i can't say the exact % you will lose as this depends on many factors. follow up the links bb provided and you can roughly figure that for yourself.

3 you will have to be the judge on that one. you don't want to do this every week as that means a possible mineral buildup from the water, but as you said it's not that bad where you are. you may wish to minimumly do it once a year, but monitor the pvs with say monthly visual inspections and then you may make a good determination in time as what to expect for you. some haven't noticed much difference after a cleaning, but in theory the dust and dirt is shading the pvs to a degree and shading is obviously detrimental.
this may be too difficult for you to do often depending on where and how the pvs are mounted so this is a definite factor in how often a wash will be done too. those of us in northern latitudes that can change the pv angles to better match the winter sun angles have the benefit of the dirt washing off easier due to the steeper angles.

What size and orientation is your system ? (just wondering, 60KWH/day seems like 5 - 7 WH installed)

1) air temp does have effect (described earlier)

2) if air is cold, and you have snow reflections, expect MORE power, at worse angle.

3) I'm in Los Angeles, downwind from a freeway. Filthy dust everywhere, likely rubber, lead, asbestos, hydrocarbons....
I clean 1x a year, about mid August, that's the wide gap between our winter rain in Jan, and last rain in June.
On a cool morning, before the panels heat up. I use a "sidewalk sweeper" nozzle, and just blast. I'd thought of the DI water rinse, but for 1x a year, likely not needed. If I actually saw any good output effect, I'd do it more often, but for as much mud as i wash off, output is unchanged.

I'm not sure what happened to my reply.

I have 57 panels in 3 arrays
- 14 east
- 16 west
- 27 south

The long axis of my house sits almost due north/south. If memory serves me correctly, I'm 2 degrees off.

If y'all want to see my production, let me know as I can post the URL.

Cheers!

re Sun angle - Winter vs Summer.
With the 2 combined with the shorter days, I see about a 50% reduction in daily output, from Summer Solstice, to Winter Solstice. (high & low points, and longest / shortest days) Simmer about 24KWH, winter 12KWH on a clear day (no clouds)

i'd like to see it out of curiousity.

> If y'all want to see my production, let me know as I can post the URL.

Yes please. post it.

The forum supports attachments, you can upload pictures of your system.installation as well

The URL is http://www.frontrangegroup.com/solar.

I'll take some pictures and get 'em posted.

Typically what I find is that the east and west arrays output equals the south's output.

Cheers!