A wind energy conversion system for a building comprises one or more wind powered turbines, a pitched roof structure having a first pitch on which the turbines are mounted, and a cover supported on the pitched roof structure above the turbines. The cover has a second pitch that is less than the first pitch. The cover and roof structure together create a wind tunnel that directs wind to flow through the turbines. Cowlings are also provided for each of the turbines. Each cowling surrounds an upper portion of a corresponding turbine. The cowlings are aerodynamically shaped and configured to concentrate air flow across or through a wind rotor of its respective turbine. The cowlings extend in a vertical direction between the cover and the roof structure.