Solar Azimuth & Altitude - Incorrect Values

solaranalysis
dynamo

#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


#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




#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.