  This work evaluates the potential contribution of rooftop PV to the future
electricity mix. Several sustainable scenarios are considered, each comprising
different shares of centralized renewables, rooftop PV and storage. For each
generation scenario, the storage capacity that balances the net hourly demand
is determined, and the portfolio combination that minimizes the cost of
supplying electricity is obtained. The analysis is applied to mainland Spain,
using public information and detailed granular models, both in time (hourly
resolution) and space (municipal level). For the Spanish case, when the
flexibility of hydro and biomass generation is taken into account, the
least-cost portfolio involves rather modest storage capacities, in the order of
daily rather than seasonal values. This shows that a sustainable, almost
emissions-free electricity system for Spain is possible, at a cost that can be
even lower than current wholesale market prices.
