The purpose of this thesis was to produce summary key figures and evaluate the accuracy of the calculation tool based on existing solar plant data. Data from six solar thermal plants was obtained and formatted to be used in the calculation tool. Due to problems with two plants, only four plants were analysed. The data form the plants gave global solar radiation values but diffuse and beam values were needed for the calculation tool. Different models were considered but, in the end, a two-variable regression was made based on Meteonorm water data to calculate the diffuse and beam components for each plant.

The results from the calculation tool have some variation when compared to the measured data. That could be partially due to the irradiation splitting method and each data set having missing values. The annual heat production values vary from 2-18%, but when excluding the overly high values, the average comes to 4,75%, which is an accurate enough result. However, since there are some bigger differences in the monthly production values, further analysis should be conducted to understand what causes these differences and if the accuracy could be enhanced.