Use of sunlight in road tunnels: An approach to the improvement of light-pipes’ efficacy through heliostats

•A coupled system heliostat-light-pipes for energy savings in tunnels is studied.•The heliostat is fixed above the road before the portal gate of the tunnel.•It continuously seeks the orientation to inject parallel rays in the pipes.•The rays are guided through the light-pipes and distributed on the threshold zone.•The improvement of the efficacy of light-pipes and savings is remarkable. A coupled system consisting on a heliostat and a matrix of light-pipes inside one road tunnel where the heliostat injects sunlight, is proposed. Its reliability and efficiency from theoretical calculations and a mock-up, is analyzed as a function of tunnel orientation. The heliostat is fixed above the road some meters before the portal gate of the road tunnels. It continuously seeks the correct orientation so that the angle between sun, heliostat and light-pipes in the portal gate, injects of parallel sunrays every moment. Then, these rays are guided through the light-pipes and distributed on the road in the threshold zone with a remarkable improvement of the efficacy of light-pipes and the relevant savings in electrical consumption and number of luminaries. The results of calculations and measurements on mock-up, that show energy savings above 20% in the most favorable tunnel orientations and 14% in arbitrary orientations, as well as a discussion about the most accurate tunnel orientations are analyzed and presented.