The Energy Center, which is sponsored by Pacific Gas and Electric Co., uses a fixed-sun, moving-Earth arrangement for its heliodon. A table holds the building model at various angles to a 1,000-watt theater spotlight, which mounts in the ceiling about 32 feet from the table.
The heliodon swivels in three directions for setting latitude, season, and time of day.
"We try to make the heliodon experience as realistic as possible," said Ryan Stroupe, who coordinates the Whole Building Performance program for the center.
But the existence of such programs doesn't diminish the heliodon's usefulness for architects wanting to show clients how the sun will shine on a particular structure in true, rather than virtual, three dimensions.
Over the nearly 10 years that the heliodon has operated at the Energy Center, hundreds of clients have used it, Stroupe said.
A more recent installation at the Welsh School of Architecture at Cardiff University adds to its heliodon an array of lamps to recreate the illumination level of a cloudy sky.
For the solar panel study, the designers placed the larger model under the heliodon alone.
Unlike Pacific Energy's heliodon, the university's Skydome moves both Earth and sun.
The author has developed a new kind of heliodon, called the Sun Emulator, which is especially useful for both the initial teaching of solar geometry and for the actual design of buildings and communities that are in harmony with the sun.
Heliodons are powerful tools for demonstrating the potential and logic of solar design to people of any age or education level.
Prof Lechner, who himself is an inventor of different types of heliodons
(a sun emulator tool), also explained the principles for achieving solar access and shading all year round with the help of his equipment.