Direct gas heating in linear concentrating solar collectors for power and industrial process heat production: Applications and challenges

Parabolic trough collectors and linear Fresnel collectors are mature technologies for power production, and they are being recently applied to provide solar heat for industrial needs. Conventionally, they use a liquid as heat transfer fluid, either thermal oil or water, to carry heat from the receivers up to the point of conversion or delivery. Although liquids offer excellent thermal properties, they show technical limitations, besides environmental concerns, which have encouraged the research on alternative solutions. This work reviews the main research works on the use of gases as heat transfer fluid in linear concentrating collectors, including solar power and heat production, highlighting the potential applications and technical challenges. The review indicates: first, gases offer potential to replace liquids, and second, there is a need for more research and development to define the best technical compromises to reach practical application in every sector.