On the astronomy page it is showing 9:38 hours of daylight. Today the sunrise is at 6:56 and sets at 4:34 = 9.38. But my solar reading is showing 4:56 hours of daylight. It was a clear day with not a cloud in the sky. Why are the hours of daylight not even close to where they are supposed to be? Is there a setting that I need to adjust?
What percentage of theoretical maximum solar radiation have you set as the minimum for ‘sunny’ in the solar sensor setup? WD will only count sunshine hours when the measured solar is above that value.
Note that your humidity of 50% to 80% will cause the actual solar received/measured to be significantly less than the calculated theoretical maximum, even though the sky appears to be ‘clear’.
I have the “Sunny” set at 90%, but there was not a cloud in the sky all day. So on a clear day I would have expected the measured solar of 4.56 hours to be far closer to the available 9.38 hours. It does get lower readings just after dawn and before dusk when it is clear and sunny, these readings do not count toward the sunshine hours? If it is only counting time over the 90%, what is the use of this information? Now what value is the % of? I see a “Maximum radiation for lat/date” figure -where does this figure come from? Currently today it is noon/overcast and it has a “0” value. If it is from data collected from my station, will it improve as more data is gathered over time? Also, what does humidity readings have to do with it?
The more I look into this, the more questions I have. :?
- How to use the “shadow offset”? does this need adjusting all the time? the sun/shadows do not stay in the same place/time year round.
- What is the “Attenuation finetune”?
- What does the “Set time to set icon” do?
3.1. “Minutes after sunrise”? - What does the “Minutes after/before sunrise/set before able to start increasing sunshine hours” do?
Sorry for all the questions. 
True sunshine hour measurement requires a sensor that follows/focuses the sun rather than the Davis type which measures radiation received on a horizontal surface. Due to the demand for sunshine hours Brian implemented the sunshine hour ESTIMATE in WD using the solar radiation data from the Davis VP and other types of consumer solar sensors.
The theoretical max is calculated from your latitude, longitude, date and time. It assumes a maximally clear/clean atmosphere, that’s not something we see too often in the N hemisphere except at high altitude or in the desert when humidity is very low. The actual reading is calculated as a percentage of the theoretical max and thresholds set for “sunny” and other conditions.
For Kentucky I would suggest somewhere around 60% might be more suitable for a sunny threshold, see this thread, one of a series of discussions with Burgus.
The humidity reading is not part of the calculation, just something that will affect your results.
- How to use the “shadow offset”? does this need adjusting all the time? the sun/shadows do not stay in the same place/time year round.
It’s an attempt to make the ESTIMATE work better when the sensor does not have a clear horizon to horizon view. My personal opinion: it might work in some circumstances but basically it’s trying to do something that is scientifically impossible, measure sun that isn’t falling on the sensor. Some errors just can’t be fixed, YMMV.
- What is the “Attenuation finetune”?
The attenuation (=reduction) is a factor that’s used in the calculation of the theoretical maximum, changing it will affect the maximum value but for most purposes just changing the sunny percentage is a simpler option.
- What does the “Set time to set icon” do?
Sets how long the solar has to be above a threshold before the icon will change.
3.1. “Minutes after sunrise”?
- What does the “Minutes after/before sunrise/set before able to start increasing sunshine hours” do?
When the sun angle is very low, i.e. around sun rise/set, the theoretical maximum and the measured solar radiation values are very small so any error in the measured value can result in a large error in the percentage of maximum.
Also the sensor is the least accurate at the same times (low sun angle), especially sensors other than the Davis which do not have such good optical design. (Remember the comment above, sunshine hours normally needs a different type of sensor.)
Also very few sites have perfect horizon to horizon view for the sensor.
That minutes setting was added to allow the user to block the sunshine hours from being calculated during a time when it may be inaccurate.
Thanks for the reply. You answers will help get this lined out for my location.