Solar Water Heating Modeling with Backup

We have solar thermal system to provide heated water for a swimming pool, sinks and showers. The system has an electric water heater backup system. 1. Should the base system be modeled based on electric water heating? 2. Would the design model have the same electrical energy use as the base case less the solar thermal contribution? 3. Can we claim credit for additional savings for a electric backup system that is more effecient (say better insulated tank and/or water lines), and/or more efficient pumps than teh base case system?