# SolTrace Background

Since the late 1980s, a number of different optical design codes have been developed at NREL for designing and modeling solar concentrating systems. Each of these codes was written to model a very specific optical geometry, and each one built upon the others in an evolutionary way. Examples of such codes include: OPTDSH, a code written to model circular aperture parabolic dish concentrators; ODMF, a code based on OPTDSH that modeled multifaceted parabolic dish concentrators; and SOLFUR, a code written to model a very specific solar furnace geometry, which, in turn, was based on ODMF.

As more complex solar concentrator designs began to be realized, it was determined that a more general tool was needed. The Monte-Carlo ray trace methodology on which these prior codes were based was considered to be appropriate for accurate representation of these varied and complex systems. Other modeling codes existing at the time were limited in both geometry definition and optical surface representation. Commercial optical modeling codes were (and are) available, but the time and effort needed to learn these complex packages and apply them to solar concentrating systems is significant. They also do not easily allow the sun to be modeled as a source and are not "solar engineering friendly." As a result, SolTrace was developed. Based on its predecessors, SolTrace uses a Monte-Carlo ray trace methodology. It provides the user the benefits of a general purpose optical design tool, but from a solar engineering design point of view.