A novel dimensionless approach to analysing the capability of a solar electricity supply system with seasonal hydrogen storage to supply a constant load throughout the year is presented. The only input required specific to the location is its solar ratio, defined as the minimum daily solar energy input during the year divided by the maximum. As well as yielding an estimate of the saving in installed primary solar electricity generating capacity, the approach gives an indicative evaluation of the economic viability of adding the hydrogen storage to a photovoltaic-based solar supply, either for a large-scale grid or small scale autonomous application. The model has been validated using the results obtained from the more comprehensive RSHAP simulation model (RMIT Solar-Hydrogen Analysis Program). The dimensionless model is applied to a selection of 78 cities with varying latitudes across all five continents. For a round-trip storage efficiency of around 45% and the base-case unit costs of components assumed, solar-hydrogen systems would be economic in 55% of these cities. At 50% storage efficiency and/or lowered unit costs, solar-hydrogen systems would become viable in the vast majority of the cities, excepting those near the equator where the net benefits of adding storage are lower because of the more constant solar radiation over the year. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.