Solar Harvest

plongson

Does this sound about right??

Yesterday, darn near the shortest day of the year, my Midnite 250 said I harvested 10.2 kWh from my 2.35kW array.
My thinking is that there was 5 hours of usable sun falling on the panels.

This is REAL basic stuff for you guys, but I'm still only "ankle deep" in this lake of information...LOL

Thanks, Paul

niel

Re: Solar Harvest

that 10.2 would be in kilowatt hours or kwh. dividing that 10.2kwh by your system 2.35kw rating shows 4.34hrs of charging and is very possible.

waynefromnscanada

Re: Solar Harvest

Pushing it though, as likely only a couple of hours would be at the best angle to the sun, unless you have a tracker. And I just see you don't have a tracker. That raises doubts, but I suppose anything is possible, especially if you also has sun reflecting off snow covered ground.

peakbagger

Re: Solar Harvest

How cold was it and was there snow on the ground? Depdending on your system design both can boost your output significantly.

solarvic

Re: Solar Harvest

Sounds preety good to me. My array is double your size and id Grid tied. One day in early Dec I got 24 kwh. I also had lots of days I only got 2 kwh and a couple that didn,t even register 1 kwh. It has been cloudy with a lot of days of cloudiness, drizzly rainy days here in NW Pennsylvania. :Dsolarvic:D

daryllafferty

Re: Solar Harvest

My 8 kW array has been averaging about 32 kWh per day since it was commissioned here in Tempe on Dec 21. There was one partly cloudy day when I only got 17.
This graph shows the power during a typical late-December day. The graph rises a little steeper in the morning than it falls in the afternoon because the array faces south east and catches the morning sun as soon as it rises.
Attachment not found.

The installer says that summer days will have a lot more hours of sunlight, but our 100 degree plus heat will reduce the efficiency of the panels. Still, he said we should see about twice as much total energy per day in May and June as in December. So far his estimates have been conservative, as he was predicting only 22 kWh per day in December. He may have been averaging in the occasional cloudy day we have here, but those aren't common in central Arizona.

Cariboocoot

Re: Solar Harvest

I find my best production to be Spring/Fall for three reasons:

1). I can get "optimum" angle on the panels (they don't go flat enough for Summer).
2). The days are long enough to provide sufficient "equivalent good sun" hours (as opposed to Winter when the days shrink to 6 hours).
3). The ambient temperature is not high enough to significantly affect panel output (unlike the +30 temps that occur in Summer. Although the -30 of Winter is good for high Vmp, the light doesn't last long enough to be very efficient).

Solar installs are highly site-specific.

westbranch

Re: Solar Harvest

Paul , have you tried plotting your system on this graph to see how you are performing?
http://www.midnitesolar.com/pdfs/250vKS_power_graph.pdf

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plongson

Re: Solar Harvest

Man, I'd love to plot a graph like that, but you guys lost me on that feature.

solar_dave

Re: Solar Harvest

Like this? Green = Solar, Blue= net consumption, Red = main house consumption, Pink = Out building/Office consumption, Light Blue = Volt chargers, Yellow = Voltage single leg.

solar_dave

Re: Solar Harvest

daryllafferty wrote: »

My 8 kW array has been averaging about 32 kWh per day since it was commissioned here in Tempe on Dec 21. There was one partly cloudy day when I only got 17.
This graph shows the power during a typical late-December day. The graph rises a little steeper in the morning than it falls in the afternoon because the array faces south east and catches the morning sun as soon as it rises.

The installer says that summer days will have a lot more hours of sunlight, but our 100 degree plus heat will reduce the efficiency of the panels. Still, he said we should see about twice as much total energy per day in May and June as in December. So far his estimates have been conservative, as he was predicting only 22 kWh per day in December. He may have been averaging in the occasional cloudy day we have here, but those aren't common in central Arizona.

32kWh sounds about right for AZ 8Kw system, my 12.5 Kw system mounted @ 26.5 degrees did 55 kWh yesterday and is going higher today, maybe 56-57 kWh. I think I hit 72+ in May last spring pretty regular.

Peter_V

Re: Solar Harvest

Hey Solar_Dave,

What is causing the regular 0-5kw changes in consumption? Do you use an electric heater/furnace?

FWIW My grid-tied 3.45kw array (2.85kw AC rated output) puts out about 21kwh on clear days in December and ~30kWh on clear days from Apr - mid Jun, but it's on trackers which help a little :-)

solar_dave

Re: Solar Harvest

Peter_V wrote: »

Hey Solar_Dave,

What is causing the regular 0-5kw changes in consumption? Do you use an electric heater/furnace?

FWIW My grid-tied 3.45kw array (2.85kw AC rated output) puts out about 21kwh on clear days in December and ~30kWh on clear days from Apr - mid Jun, but it's on trackers which help a little :-)

Dual Trane 3 ton heat pumps. Each uses about 2.5 Kw. We used them this AM to take the chill off. The spikey cycle is the electric dryer. all on the Red line.

a0128958

Re: Solar Harvest

daryllafferty wrote: »

My 8 kW array has been averaging about 32 kWh per day since it was commissioned here in Tempe on Dec 21 ... This graph shows the power during a typical late-December day ...

... summer days will have ... more hours of sunlight, but our 100 degree plus heat will reduce the efficiency of the panels. Still, he said we should see about twice as much total energy per day in May and June as in December. ... central Arizona.

Cariboocoot wrote: »

I find my best production to be Spring/Fall for three reasons:

1). I can get "optimum" angle on the panels (they don't go flat enough for Summer).
2). The days are long enough to provide sufficient "equivalent good sun" hours (as opposed to Winter when the days shrink to 6 hours).
3). The ambient temperature is not high enough to significantly affect panel output (unlike the +30 temps that occur in Summer. Although the -30 of Winter is good for high Vmp, the light doesn't last long enough to be very efficient). ...

Here's the big picture for the 8 KW system that I have, in a Dallas location that's probably similar in latitude to Tempe, AZ, showing peak daily harvest (blue line), 30 day rolling avg (black line), and PVWatts' monthly estimate for my location (green line), for the past 13 months:



Here we see that indeed my lowest daily output coincided right around Dec. 21st, at a peak of around 22 kWh/day. My around-Dec. 21st-peak is about 10 kWh less than the 32 kWh daily peak that daryllafferty is seeing in Tempe. It will be interesting to see if, over time, this 45% increase holds all year round or if it's because his system is more optimized for Winter months than mine. Mine clearly is oriented such that it's optimized for Summer months.

Here we also see example of Cariboocoot's points that optimum production is in Spring/Fall. Indeed my blue line peaks at about 48 kWh for the day of April 13th as shown in the above chart. 48 kWh is about the daily maximum that my 8 kW system can ever produce.

I don't have as much of a peak in the Fall. Ambient temperature just doesn't fall fast enough to get much of a kWh 'lift' from still longer early Fall days. You can see the small Fall peak at the early days of September.

Thought this chart might help to nicely illustrate, with data, the points having already been made.

Best regards,

Bill