What kind of output are you getting in Seattle/Northwest?

[crashintoty]

I have my sun hours, calculations and all that jazz, but I'm curious as to what folks in Seattle/Northwest are actually getting from their solar panels. For those who have their numbers ready - how many panels do you have, their wattage rating, yearly average wattage output and best & worst monthly wattage output?

[solarix]

And compare that with what PVWatts predicts...

[Ampster]

And compare that with what PVWatts predicts...

I don't know what kind of geographic granularity PVWatts uses but PV Watts is a good start. From my frequent visits to that area I know there are lots of micro climates. The San Juans are not referred to as Banana Belt weather because they grow bananas there. I often stay on Bainbridge Island and from my friend's house I can occasionally see Seattle when the weather is clear.

[J.P.M.]

Cashintoty:

Further to what Solarix writes, check out a website : PVOutput.org

I believe you will find most all and more of what you are looking for.

[J.P.M.]

I don't know what kind of geographic granularity PVWatts uses but PV Watts is a good start.

PVWatts, SAM and most other models mostly use the NSRDB data base for irradiance data. It's a 10 X 10 km grid. The old and still useful TMY data doesn't have a specific grid size. The NSRDB uses some satellite derived data for irradiance and mostly synthetic data at a site for weather variables.

Like all models, the output is an approximation. Usually however, that approx. produces a pretty good match, modeled to actual measured device performance.

[oregon_phil]

Oregon Willamette Valley
28 x 365 watt solar panels, 7.7kW SMA string inverter

PVWatts annual estimate: 12,200 kWh

Actual average: 11,700 kWh

Worst month: january, 260kWh
Best month: June 1820 kWh

I would say the PVWatts estimate is pretty good. The actual average takes into account a 12 day winter power outage (no grid, but minimal sun anyway) and a 7 day wildfire power outage (No grid, sun available, but obscured by lots of smoke).

[J.P.M.]

Oregon Willamette Valley
28 x 365 watt solar panels, 7.7kW SMA string inverter

PVWatts annual estimate: 12,200 kWh

Actual average: 11,700 kWh

Worst month: january, 260kWh
Best month: June 1820 kWh

I would say the PVWatts estimate is pretty good. The actual average takes into account a 12 day winter power outage (no grid, but minimal sun anyway) and a 7 day wildfire power outage (No grid, sun available, but obscured by lots of smoke).

Phil: How many years is the actual average comprised of ?

[oregon_phil]

only 3 full years and two partial years. I averaged the three full years.

[SunEagle]

only 3 full years and two partial years. I averaged the three full years.

Great info. Hopefully the weather doesn't change much and the PVwatts estimates get closer to the actual

[oregon_phil]

We get a lot of farm dust during planting and harvesting season. And we get a lot of rain too. I stopped washing my panels. things even out.

[J.P.M.]

only 3 full years and two partial years. I averaged the three full years.

Thank you. Not a knock, but a 3 year average is a bit short of a time period. The model help/info screens suggest planning on the variation of any 365 day period from the long term (probably ~ 30 yr.) average of +/- 10 %. My 365 day running average over ~ 8 1/2 yrs is about +5/-4 % or so for PVWatts and a little less using SAM and a model I wrote some years ago. I wouldn't be surprised if some of that variation you see is due to the small sample size.

[oregon_phil]

I don't disagree with you. I hope to have many more sample years in the future. I am taking data daily because I am wired that way.

We have NG for winter heating with solar providing 90 to 98% of our annual electric needs. In addition to the power outages for ice and wildfires, I forgot to mention that I was also down 1 month in the winter waiting for an inverter RMA. Winter was a perfect time for a month of downtime, but if it was in the summer, I would have been more upset. That's why I have spares for everything ready to go.

[J.P.M.]

I am taking data daily because I am wired that way.

Understood. I do the same for energy use, irradiance, array performance and weather variables.

[crashintoty]

Oregon Willamette Valley
28 x 365 watt solar panels, 7.7kW SMA string inverter

PVWatts annual estimate: 12,200 kWh

Actual average: 11,700 kWh

Worst month: january, 260kWh
Best month: June 1820 kWh

I would say the PVWatts estimate is pretty good. The actual average takes into account a 12 day winter power outage (no grid, but minimal sun anyway) and a 7 day wildfire power outage (No grid, sun available, but obscured by lots of smoke).

A couple of questions...

1) 28 x 365 is 10.2 kW, but you have a 7.7 kW inverter - is that the limitation of the inverter or the real world output from your 10.2 kW panel array?
2) Why is June your best month and not July or August?

[Ampster]

A couple of questions...

1) 28 x 365 is 10.2 kW, but you have a 7.7 kW inverter - is that the limitation of the inverter or the real world output from your 10.2 kW panel array?
2) Why is June your best month and not July or August?

1) The output is limited by the inverter. That relationship is often called the DC to AC ratio. Your example is 1.32 to 1 which could see a little clipping depending on orientation and/or tilt. 1.25 to 1 is common, I once had one that was 1.5 to 1. Saw a lot of clipping in Spring and Fall but the winter was not as bad as a lower ratio.
2) June 21st is the soltice ie. the longest day of the year in Northern Hemisphere.