Pinball (or others with years of PV production data),

Since you have over five years with your array, you can perhaps answer/comment on my summer/winter PV array kWhr production question.

I (like most of us) use PVWatts to give me the effective number of sun hours per day for my lat/long., array pitch and direction. Knowing the total max kW of the system, this allows me to calculate a predicted number of kWhrs for the month.

But PVWatts does not account for varying outside daytime temperatures (by month) and all panels have a negative correlation coefficient for output voltage. The STC is based on a 20 degree C base and temps above that decrease power and energy output and colder temps increase it. The PTC value (generally about 90% of STC) kinda sorta includes temperature.

PVWatts simply assumes more sun in summer and less in winter with no inputs for summer/winter temperature changes.

For my predictive spreadsheet, I have used a -12% decrease for monthly July kWhr output and a +10% increase for January with intermediate coefficients in between for other months.

Without this temperature modification, my predicted monthly kWhr output was lower in summer months and higher in winter months compared to what PVWatts predicts.

I just finished designing another client's home (all Enphase installs) and adding my + and - temperature coefficients really closes in on a better monthly kWhr prediction.

Are you aware of a better predictive algorithm (one that includes historic monthly daily average temperature) than PVwatts?

Thoughts?


Steve

Hi PB,
Here's my intertie, figure about half for my other system or about 1.2Mwh for July.

Hi Steve,

Here's my intertie system over the last 5 years if this helps at all. (SolarEdge microinverters)
Rob

Lat = ~42

I think PVWatts is close enough for what it does. I am performing a little better than the estimate 105% for the lifetime of the system.
That is close enough for me in looking at what you want to install. But others want in to be more accurate. Year to year it is different so you are looking for a great guess based over many years of data.

Here is actual posted data for my system
Flynns Arcade 12.560kW
This data gets posted directly from Enphase.

I find this graph interesting.
http://ecorenovator.org/forum/attach...1&d=1470158545

For calender July, our 6.81kW system made 953kWh.

I want to chime in on PV Watts, even though I only have 3.63 years of production. PV Watts has me calculated at 31700kWh total for 3.63 years {8733 kWh annual} and I have an actual value of 35516 kWh. That works out to 12% more than the estimate.

I credit the extra production to manually adjustable arrays. Both my little array and big array can be adjusted from summer to winter and back. I faithfully change the tilts on the day closest to each equinox where it isn't raining. Obviously, if I were not to tilt them those two times each year, my production would be less and more closely resemble the predicted value.

Catching up with the 4.4kW array...
May 2016: 589kWh
June 2016: 541kWh
July 2016: 607kWh

August 1, 2016 was my 3rd year anniversary of my system going online. It has generated 18.2MWh in total, in 3 years.

Congratulations on three years!! :thumbup:

If you are like many of us, going live with your solar array was the start of a journey that is better than you ever expected.

Great Were2!

Next month I'll be online for 5 years with 28.4 MWh of power produced from my intertie and about half that from my intertie/off grid system for a total of about 43 MWh. That's not counting the 5 years I ran my off grid system before the intertie got integrated here.
Rob

“Where2” Good to see you back. Nice numbers.
At what point will your system be paid off with the savings?

Seeing all this solar power being produced makes me smile.:thumbup:

At present electric rates ($0.105/kWh), it honestly takes "seemingly forever" (15 yrs) to recover the initial expense of the PV system, permitting, structural engineering, parts, racking and miscellaneous costs. FL offers no incentives to DIY systems, and no guarantees net metering will continue beyond the next election cycle.

I stopped looking at "years to pay off" the PV system, and now simply look at it as an investment that pays to air condition my house for free. Several of my coworkers were recently complaining about how large their electric bills were this summer. My last electric bill was $63 for an all electric house in South Florida.