RFB is, by its very nature, a modular and highly flexible technology with very rapid response, little environmental impact and considerable potential for cutting costs. This is the reason why Redox Flow Batteries are emerging as a very promising option for stationary storage in general and for renewable applications in particular. Renewable energies There is no doubt that the development of renewable energies will be a key milestone in the way towards a new environmentally-friendly energy model., However, their variability and limited predictability are posing a problem for the operation of the system and, as a result, a barrier to their massive penetration. A clear example of these difficulties is the need to maintain backup systems that generate energy during low wind or low solar irradiance periods. On the other side, high renewable generation can lead to energy waste during low demand periods. Redox Flow Batteries are considered as a highly adequate technology to mitigate the variability of renewable energies and to improve their dispatchability, that is, to provide the capability to regulate the output in a similar way to conventional power stations. The energy stored during periods of high renewable production can be used to compensate for the lack of generation when the weather conditions are less favourable. BBC World has burst into Tecnalia’s facilities to find out about these Redox Flow Batteries.