This tool estimates the required rating and physical size of grid-connected photovoltaic (PV) and battery storage to provide power for extended periods during a large scale grid power outage. SolarResilient is designed for buildings that form part of a cities resilience strategy – it allows building owners and city departments to develop equipment sizing before embarking on more detailed studies. When used on a portfolio of buildings, optimum performing scenarios can be selected to provide a holistic energy security strategy for a city or county.