The invention relates to a system for using solar energy to ventilate a space, particularly the interior of a building, although other structures may also be ventilated such as crop stores, desalination plants, glass houses and power generation plants. The system can operate in different modes so that solar energy is used to heat or cool the space, as required. Part of the system is a solar heat collector, which absorbs available solar energy. The solar heat collector includes two separate channels able to receive air from different sources and pass them in counter flow. The channels transfer heat between them using an efficient turbulence-inducing structure that enables the system to operate in the different modes to heat or cool a space.
