Abstract: Ressspi is an open-source simulation code for solar process heat applications. Although it is based on SHIPcal engine, Ressspi has solved SHIPcal’s main limitations in terms of flexibility (adding 12 integration schemes) and managing issues (adding a git control system to allow open-source development). The main line of work at this moment is reducing the computing time needed in order to perform a complete annual simulation. And, although simulation times closed to 3 min have already been achieved using greedy algorithms, new alternatives are also being tested. At this moment, more than 267 simulations has been performed in Spain and several countries in South America