Analysis of on-site use and sellback in residential photovoltaic systems

One promising early use of photovoltaics is grid connected residential systems without batteries. In these systems, photovoltaic power is used onsite as much as possible, and the remainder is sold back to the utility. The amount of direct on-site use versus sellback of photovoltaic power depends on the instantaneous load patterns. A method is developed for characterizing the instantaneous load based on the on/off probabilities of individual appliances. A monthly step simulation method based on the instantaneous load characterization is presented and verified. Simulations are performed for several residential load mixes, including the use of energy efficient appliances and passive solar design. Results show that on-site use of photovoltaic power is much less, and sellback much more, than previous results indicated for single family residences. Even small systems are found to sell back 50% or more of generated power to the utility.