How big should my battery be?

Solar photovoltaic systems have been planned using rules of thumb and theoretical models, often in Excel spreadsheets, to size and explore the system required. These programs implement models based upon first principles and consider seasonal changes, location and orientation. Several are beginning to model battery storage. These methods depend on average data and ignore possible extreme behaviour. In this paper, we report on using grid energy data from a smart meter and harvested solar energy data collected from an existing domestic solar PV system. We use this data to explore the effects of varying solar system size and of adding a battery of various sizes. We examine the relationship between available solar energy, solar PV system size, grid data, house load and battery size using this data.