A heat pipe acts like a low-resistance thermal conductor. Due to its thermal-physical properties, its heat transfer rate is thousand's times greater than that of the best solid heat conductor of the same dimensions. Sunda's Seido heat pipe is a closed system comprised of two meters of copper tubing, an evaporator section, a capillary wick structure, a condenser section and a small amount of vaporizable fluid. The heat pipe employs an evaporating-condensing cycle. The evaporator section is tightly bonded to the absorber plate, where it captures the heat from the absorber and evaporates the liquid to steam, which moves up to the condenser section. The condenser protrudes out from the evacuated tube and is inserted into the heat exchanger manifold. There this steam will be condensed by water flowing through the manifold. Latent heat energy will be released to the process water through this phase change of vapor to liquid. In vacuum tube solar collectors, the condensation zone is at a higher level than the evaporation zone. The transport medium condenses and returns to the evaporation zone under the influence of gravity. This process is repeated continuously thereby heating the water in the solar loop.

To achieve the highest efficiency of heat transfer the absorber treated with an aluminium-nitride selective coating, which is applied using a magnetic sputtering technique. This special optical coating transforms more than 92% of the incoming solar radiation into heat.
Heat pipes are inserted into the aluminum absorbers forming assemblies, which in turn are inserted into the glass tubes. The tubes are made of borosilicate glass, which is strong and has a high transmittance for solar irradiation. In order to reduce the convection heat lost, glass tubes are evacuated to vacuum pressure of <10-3 Pa. Sunda uses a patented technique employing high heat and pressure to insure stable glass-to-metal vacuum seals. In order to keep the stability of vacuum for a long time, a barium "getter" is used. Through evacuating air out of the glass tube the absorber material and selective coating are protected from corrosion and other environment influences.