Solar Radiation

Intensity of the sun varies by the clarity of the atmosphere and the angle the sun strikes the surface, called the “incident angle”

More perpendicular the suns rays are to the surface, the more heat and light energy

Given in units of energy per area (w/m2 or BTU/hr/ft2)

Sometimes quoted in energy accumulated per day or year (kWh/m2/day)

Direct/Diffuse radiation

Direct radiation, measured perpendicular to the sun’s rays

Diffuse radiation, measured horizontal to the surface

Cloudy sky reduces direct radiation and increases diffuse radiation

From the total energy of the sun, up to 1/3 can be lost (reflected into space), about 20% reaches as diffuse radiation and the rest is direct radiation

Incident solar radiation values are calculated and visualized within Revit

Hourly direct and diffuse radiation data, building geometry and time period of the analysis are taken into account

Absorbed, transmitted, and reflected

Incident is the amount of energy striking a surface not how much is absorbed, transmitted or reflected back

Material properties affect the aboveSolar radiaton for a specific time is

valuable when finding an initial number for available energy on your site

Average incident solar radiation across the entire earth is 240 W/m2

  Location and Time Incident Solar Radiation (BTU/ft2/day)

  City Month Horizontal South Face North Face

Far from equator

Anchorage, AK

January 70-110 310 38

July 1160-1700 990 550

Near equator Miami, FLJanuary 990-1270 1320 300

July 1500-2100 550 610

- See more at: http://sustainabilityworkshop.autodesk.com/buildings/solar-radiation-metrics#sthash.S7brDUuU.dpuf