Estimating the effect of domestic load and renewable supply variability on battery capacity requirements for decentralized microgrids

Large battery banks are a commonly considered alternative for local storage of volatile energy supply in decentralized grid management. In this paper the hypothetical case of an isolated community of 15 houses with direct access to a nearby set of wind turbines and a backup grid connection (e.g. ex-urban hamlet) is being considered. The question arises as to what size of battery, relative to household average daily consumption, should be installed in order to avoid excessively fast aging of said battery bank, i.e. to avoid the need to replace it faster than standard expected battery lifetime. The basic technology of the batteries addressed in this study is lithium ion phosphate. A dynamic modeling process of aging is implemented, along with realistic wind power data and a stochastic model of domestic load, with variable morning/evening peaks, weekend and seasonal effects. It was found that simulations using domestic load profiles and variability predict a significant reduction in expected battery state of health, for comparable average loads, than standard load cycles used for industrial testing, and that increased variability in average domestic load has a minor effect on the speed of state of health reduction. Furthermore a region of high sensitivity to overall battery bank size can be observed, which subsides over approx. 200 hours of average household consumption.