Technical and economic study of solar energy concentration technologies (linear Fresnel and parabolic trough collectors) to generate process heat at medium temperature for the dairy industry of Spain

•PTC technology is slightly more efficient than LFC technology up to THTF = 140 °C. The opposite is true above 150 °C.•The efficiency of the installation (Ecf/energy demanded) depends on both the installed collector surface and the installation layout (series–parallel).•The CTEU depends mainly on the economy of scale factor and the %U (necessary to match the demand profile with the generation profile).•For medium sizes (10 GWh), the CTEU for LFC technology is lower than for PTC. For large sizes (60 GWh) there is hardly any difference.•The difference in performance of the installation between the most favourable and unfavourable location is approximately 35.7 %. Real energy consumption data were taken from the 17 most important companies of the dairy industry distributed across different Spanish geographical locations, studying the technical and economic feasibility of integrating solar concentration technologies suitable for the required thermal level of medium temperature in that industrial sector. The results show that the percentage of use of available thermal energy (%U) and the size of the solar plant, in addition to many other variables such as location, are decisive parameters for determining the cost of generating thermal energy and comparing it with the cost of conventional energies (natural gas, diesel and fuel oil). A 20-year time horizon is considered and three different scenarios are taken into account as regards the price evolution. Likewise, it is observed that, as the temperature of the heat transfer fluid rises, the generation of thermal energy decreases. The prices of solar thermal energy would improve the conditions offered by any conventional fuel (natural gas, diesel and fuel oil), unlike what happened just 2 years ago with natural gas. The lowest thermal power generation costs would be 3.41c€/kWht for LFC technology, and 3.69c€/kWht for PTC technology, both in Granada; being much lower than current prices (21 November 2022) for conventional fuels: 10.53c€/kWht for diesel (5.48c€/kWht, in 2021); 6.08c€/kWht for fuel oil (3.70c€/kWht, in 2021); and 7.29c€/kWht (Band I3) and 7.71c€/kWht (Band I4) for natural gas (2.35c€/kWht for Band I3 and 1.99c€/kWht for Band I4 in 2021).