In Spain, solar electricity (photovoltaic and thermoelectric) has reached a stable annual capacity factor above 20% since 2009; while wind achieved 23% since more than 10 years ago. This is the demonstration of an ongoing transition towards a more sustainable energy mix, further corroborated by the reduction of the capacity factor of gas-fired technology, which has seen a decline to values lower than 10% after an initial promising rise; this is a very low value for a fossil-fuel technology. Additionally, hydro installed capacity, which has been stable for the past 20 years, have demonstrated that can be used as a back-up power source in combination with solar and wind electricity, and it is capable of producing energy peaks that may increase from a stable base of 2000 GWh/month up to 6000 GWh/month and therefore meet demand at some particular times when solar and wind are generating less electricity without the need of installing new additional capacity at national level. (C) 2014 Elsevier Ltd. All rights reserved.