The use of renewable energy sources for electricity is one of the most promising techniques in order to face environmental problems and high CO2 emissions. However, the power production from photovoltaics and wind energy is not stable and this fact creates issues between the production profile and the demand profile. Therefore, an effective storage technique is needed, except for the idea of batteries. The objective of the present investigation is the investigation of a novel pumped thermal energy storage system. This system uses the volatile electricity from renewables in order to feed a heat pump that produces heating at a medium temperatures level (e.g. 150oC) and stores it in a latent storage unit. The stored thermal energy can be used later in an organic Rankine cycle for power production when there is the proper demand. The novelty of this work is the incorporation of flat plate collectors for assisting the heat pump in order to increase the overall performance of the examined storage system. According to the results, the ambient source system leads to maximum power to power ratio of 38.5% and this value is lower than the respective values of the solar-assisted system. The maximum system efficiency was found for storage tank temperature at 220oC and evaporator temperature at 30oC, and in this case, the system energy efficiency is 19.1%, while the system exergy efficiency is 19.7%. For the typical case of (Tst=150oC and Tevap=70oC) the solar-assisted system presents a 61.1% power to power ratio which is 58.7% higher than the ambient source case.