Solar Azimuth & Altitude - Incorrect Values

dynamo
solaranalysis
#1

Hi.

I am trying to create a solar position routines using Dynamo 1.3.1. I am successfully getting results from Dynamo but have sense checked them to ensure that they are accurate. Unfortunately, when comparing these values to the US National Oceanic & Atmospheric Administration (NOAA) and US National Renewal Energy Laboratory (NREL) solar positioning figures, there are large discrepancies. Both NOAA & NREL agree closely with each other. Attached are screenshots of the necessary information that highlights the differences between Dynamo & NOAA’s values.

The NOAA solar positioning website here: NOAA Solar Positioning:
The NREL documentation and code is available here: NREL Solar Positioning Documentation and Code

Dynamo Solar & Location Data
Dynamo Solar & Location Data.png607x661 27.7 KB

#2

@TomJ Your site location is the screen shot is in the UK, while your link points to a location in the US.
Check if your site location is correct in the Revit project.

#3

Pretty confident that the Revit and dynamo project locations match (see attached image).

Lat & Long Conversion Values

NASA Solar Position Data (Exc DST)
NASA Solar Position Data (Exc DST).png751x829 20.2 KB

NASA Solar Position Data (Inc DST)
NASA Solar Position Data (Inc DST).png729x828 20 KB

Revit - Project Site & Weather Location
Revit - Project Site & Weather Location.png1209x752 777 KB

#4

The above images show that:

Source Azimuth Altitude
Dynamo 130.21… 52.42…
NOAA (exc DST) 140.71… 38.87…
NOAA (inc DST) 124.44… 32.02…

I feel that Dynamo should match one of the NOAA outputs.

#5

Your time zone should probably not be 0. On my side, I get identical results if DST is unchecked, which could reveal a limitation of the Revit analysis tool.

#6

Cheers for the input Yna.

I am confused as to why this the time zone would be anything other than 0, given the UK is based in Greenwich Mean Time (GMT), which is 0 too.

#7

Sorry, no idea about that, could be related to summer and winter time. Try with 1 to see if it matches, someone else could have an explanation…

#8

I should clarify that technically the UK is UTC/GMT between November and March (Timezone = 0) and UTC + 1 between April and October (Timezone = 1).

This is automatically incorporated within a “Daylight Savings Time” (DST) option. If a DST or similar option be available, then this should take precedent over the above paragraph or manual timezone adjustments.

#9

OK, it does not look like a Dynamo issue. Just for information, which number returns the correct result for you?

#10

NOAA (inc DST) 124.44… 32.02…given the reading was taken in British Summer Time.

As a side point, there appears to no link between the “Sun Settings” and “Site Location”. Is this correct?

#11

I have read this from here:
“When you create a project it is possible to specify the geographic location using the street address or the latitude and longitude. This is useful for generating location-specific shadows for views that use them, such as daylight studies. The location provides a basis for weather information, which is used during daylight analysis.”

But for a more accurate information, the best would probably be to ask real specialists such as Honeybee developers:

#12

I’m not sure how can I help with this topic but just in case Ladybug has a node which you can use to create a location from your inputs and can be useful if one is interested to study the effect of each parameter.

PS: There is slight difference between Ladybug’s sunpath algorithm and NOAA’s algorithm in the current release (0.1.9) which has been addressed and will be fixed in the next release.

#13

It seams that Revit doesn´t manage DST the way we expected:

https://forums.autodesk.com/t5/revit-ideas/wrong-simulations-daylight-saving-time-dst-summer-time-properly/idi-p/7937388