Theoretical part of this masters thesis presents the molten salt reactor, storage of thermal energy and electricity market. The rest of the thesis discusses basic economic systems for storing thermal energy with molten salt in combination with a molten salt reactor. Sample calculations for Slovenia, Denmark, Norway, Spain and Germany are performed with the purpose of analyzing the effect of energy mix on the market’s electric energy prize for the next day. The calculated net present value of thermal energy storage systems for the 2019 market value was negative for 30 years of operation for all examples, except Slovenia. For Norway, the calculated net present value was negative also for the conditions as in years 2021/2022, but for all other countries the net present value was positive after four to sixteen years of operation.