A PV modules that, in addition to producing electricity, is also integrated into a building is called Building Integrated (BIPV); it is also a building material. A product that is applied outside of an envelope is called Building Applied (BAPV). Below are more facts about solar energy and what the various technical terms mean, how much our solar photovoltaics produces in unshaded position and in different directions, as well as technical descriptions.
What is U-, G- and Lt-value?
A measure of how much heat escapes through the glass.
The lower the U-value, the better the insulation. The U-value can be improved in that the glass is coated with a metal-based surface which reflects long-wave radiation back into the room. U-value of 1.0 means a heat flux of 1 watt / square meter area for every degree that is different between the outdoor temperature and the indoor temperature.
A measure of how much of the sun’s heat (infrared radiation) coming in through the glass.
A low G-value indicates that a window transmits a low percentage of solar heat. G value can be improved by the outer glass is coated with an IR-reflecting surface that reflects a part of the heat radiation. In homes with large glass surfaces, especially in the south and west, it can be an advantage with low solar transmittances.
A measure of the amount of daylight entering through the glass.
Windows with low U and G values will usually also lower LT values which affects daylight in negative. BBR Section 6’s demands on natural light for rooms where people are present more than temporarily. As general advice indicated a window glass area corresponding to at least 10% of the floor area when the windows are 2 or 3 clear glass with an LT value of about 70%.
How much electricity does the PV modules produce?