The paper presents the results of the research on effectiveness of conversion of solar radiation into heat with the use of plate and vacuum solar collectors. Studies on effectiveness were carried out on a measurement stand, where the obtained results were monitored and archived with a computer measurement system. Based on the obtained results, thermal and economic effects of use of the investigated collectors on production demands of cultivated greenhouse tomatoes were analysed. After determination of the model surface area of a greenhouse and a type of cultivated plants, an annual amount of heat was calculated. With the assumed data, in the year's scale, as a result of the used collectors for the needs of plant cultivation, it was calculated that the suggested system of collectors provides almost 45 GJ of heat. As a result of the economic analysis that was carried out, it was concluded that in the present condition of prices the most advantageous solution is to use flat collectors for which, in relation to the fuel type, the payback period of the installation is within 13.5 to 16.7 years.