Incident solar radiation results for Greece-Athens - Wrong Results

[Fokaides]

I have created a cubicle of 1m³ and attempted to calculate the incident solar radiation on each side of this cubicle, using the command “solar access analysis”, using the meteorological file if Athens - Greece. Running Ecotect to calculate the incident solar radiation cumulatively throughout the year on all surfaces of the cubicles, for all hours of the day ( from 0:00 till 23:59 ) and having performed detailed shading calculations, the results do not seem to make much sense. Particularly the incident solar radiation on the eastern side of the cubicle is 713 kWh/m² and on the western 342 kWh/m² or approximately half of that on the eastern side radiation - these two numbers should not deviate more than 10%. Trying to find out why Ecotect gives these results, I looked at the weather files as they appear in the command “solar exposure”, to discover that in most days of the year, the maximum intensity of solar radiation in Greece appears to be at 10am, something that is not valid, but which might explain why the eastern side of the cubicle is found to receive double the radiation of the western. Also the direct solar radiation seems to have values in the summer at 4am, something illogical for Greece and have its latest values at 6pm, which is also wrong (in Greece we still measure direct radiation in summer until 8pm and the sun rises at 6am) . Is there an issue with the meteorological data in Ecotect and the time at which they are connected? Should the data in Greece be converted to GMT +2 time, so as to calculate a similar incident radiation on east and west, as well as to have the maximum solar intensity at 12 noon and not at 10am?

[mstein7484]

We recommend you use the EPW file or the Green Building Studio (GBS) file (both import as EPW or Separated Value from the Weather Tool or Weather Manager).

- the WEA file uses generic solar radiation with cloud pattern adjustments

- the GBS data is modeled data from specific year 2006

- the PVWatts data (below) is IWEC standardized data assembled from a bunch of years

It's better to use Vasari for it, as it will have direct access to GBS files, and to keep an eye on the Revit space for solar radiation updates.

Lastly, you can do a sanity check on any data you use by looking at PVWatts for international sites and doing annual calcs on different orientations and tilts to get relative performance and compare with Vasari, Ecotect, EnergyPlus EPW files, etc.

http://rredc.nrel.gov/solar/calculators/pvwatts/version1/