The important criterion for the location a thermal solar plant is gaining the optimal amount of sunlight energy available at that site over the year. Molten salt is used to store this thermal energy produced on the days when there is abundant sunshine, this enables the production of electricity even on days with little or no direct sunlight via a heat exchange process. This molten salt is usually stored in two large vessels. One vessel contains salt at a lower temperature (approx. 300° C), the other contains salt at a higher temperature (approx. 400° C). Accurate level measurement is essential to monitor the system capacity.