Buoyancy-induced air flow in photovoltaic facades: Effect of geometry of the air gap and location of solar cell modules

The aim of the paper is to derive analytically expressions for the mass flow rate, velocity, temperature rise and location of neutral height (location where the pressure in the air gap is equal to the ambient pressure) in air gaps behind solar cells located on vertical facades. The flow is assumed to be turbulent or laminar and behave as bulk flow, i.e. the velocity and temperature is assumed to be uniform across the air gap and only a function of the height channel. Both the geometry of the air gap and the location of the solar cell module are varied. Aerodynamic end losses are taken into account but only buoyancy-induced flows are considered. The location of the solar cell panel is considered by introducing a configuration factor which is a factor varying between 0 and 1. Redistribution of heat by radiation within the air gap is dealt with. When the aspect ratio is larger than 60 the effect of the location of the solar cell panel is considered by introducing a geometrical configuration factor. The derived expressions for the mass flow rate, velocity and temperature rise are verified against measurements made, using a mock up in the laboratory, where the heat input to the air gap is controlled and the location of the input heat (“solar cell module”) can be varied.