Smart meters are currently replacing conventional electricity meters. This enables the calculation of the profitability of a solar system with electricity storage according to a customer's individual behavior and his climatic circumstances. This book shows how to implement a thorough time series based savings calculation in Excel. On the one hand physical and technical factors are taken into account (i.e. component efficiency), on the other hand a thorough non-standard statistical model is developed. This model corrects the effects of 15 min interval based smart meter resolution. The validity of the model is proven by applying existing time-series of load and solar power and comparing the results to a reference model.