How does a tower system produce steam more efficiently?

Parabolic trough systems lose a relatively large proportion of heat, with about two-thirds of the losses occurring at the heat-collecting pipes in the troughs themselves and the remainder in the long pipes distributing the oil throughout the solar field. More energy is lost when reflected sunlight must pass through an evacuated glass tube in order to reach the heat-collecting pipe. Tower systems have much lower heat losses because their heat-collecting pipes are concentrated in the receiver and not dispersed around the solar field. Other factors are related to the geometry of the mirrors and their targets. For example, the mirrors in a tower system receive sunlight at a more advantageous angle than parabolic trough mirrors because they track the sun on two axes (i.e., in three dimensions) rather than on only one axis. The tracking advantage is particularly important when the sun is relatively low in the sky, such as in winter, or even in the early and late daylight hours at other ...  more