There is provided a solar collector comprising an evacuated transparent envelope having an absorber arranged therewithin. A duct containing a heat-transport medium is arranged at least partially within such envelope and is so associated with the absorber that heat derived from incident solar radiation is transferred to the heat-transport medium in the duct during operation. A reversible heatable hydrogen getter consisting of a partial metal hydride is positioned in the envelope, together with a fully hydrogenized metal hydride thermally more stable and having a higher affinity for oxygen than the partial hydride.