How to decide the alignment of the parabolic trough collector according to the local latitude

Parabolic trough is a very attractive technology for using solar energy. The optical loss of the parabolic trough is related with the local latitude, either for the east-west (E-W) or north-south (N-S) orienting mounted troughs. Based on the basic transform between solar coordinate and the earth surface coordinate, the cosine loss of for both the E-W and N-S parabolic troughs are calculated, according to the local latitude. The results indicate that, while the optical loss for E-W trough almost keeps as a constant of 16%, the optical loss for N-S system is highly dependent on the local latitude. Thus the critical latitude of 37.35° is obtained. For the place where its latitude is lower than 37.35°, the parabolic trough should be mounted along E-W orientation, otherwise it should be positioned in N-S orientation, to obtain the least cosine loss.