Issue with Insolation data curve?


#1

Recently, the Insolation data for Live data plots are showing power levels much lower than actual (by about a factor of two). Previously, the isolation data tracked actual power fairly closely (like within 10-20%). I hadn’t checked insolation data for a couple of weeks, so I cannot say when the issue first appeared.


#3

Welcom the the PVOuput community.
You can check the insolation for any past data you have accumulated. Just select the date and click on the “insolation” option in the menu just below the graph.
I see that you just recently joined this community and probably don’t have a great deal of past data but you will find a lot of useful functions available on the website. When unsure there is an excellent help facility available at the top menu bar of the main page. You may search the community page for past posts on your subject as well. In a lot of cases the question you have may have already been answered.


#4

Yes, I just joined the Community, but I’ve got PVOutput data going back to Oct. 2013 and have been donating to PVOutput.org annually since 2014. I only joined the Community to ask the question posed.
The algorithm for computing insolation data seems to have changed in the past few weeks. The insolation curve and power/energy estimates are very low compared to the live data.


#5

The data they use depends on your location and the orientation of your panels. You should check you settings in those areas to see if they have changed or have been altered. The values you need are your longitude and latitude, the clockwise degrees of your array from North in the Northern Hemisphere, and the angle of tilt from horizontal (probably the pitch angle of your roof,) You can input data from two arrays with different orientations if your panels are split like mine between NE and SW.


#6

I checked Edit System. All inputs (panels, orientation, tilt and zip code) are correct and unchanged from initial setup. The insolation data appearsl ow by a factor of 2, independent of date selected. Something has changed with the calculation in the past few weeks.


#7

Try refreshing the page again. Temperature in F was used instead of C which resulted in a higher than usual temperature derating estimate.


#8

Bingo! A solar array at 125deg C (rather than 125F) would lose almost 50% efficiency. Thanks!!