A solar energy collection system comprising: a solar energy collector comprising: a first member having a cavity and a longitudinal axis, the first member having a longitudinal window extending the entire length of the first member and forming a part of the first member, and a body forming the rest of the first member, said longitudinal window being made of a material adapted to pass solar energy, said body having an exterior absorptive surface and an interior reflective surface; a second member located within the cavity of the first member and generally parallel to said longitudinal axis, said second member being adapted to carry an energy absorbing fluid; and an insulative material filling the cavity between the first member and the second member; wherein: said first member is a tube and has a circular cross-sectional shape; said second member is a tube and has a circular cross-sectional shape; said second member is surrounded by the interior reflective surface of the first member; said insulative material is a fluid or a vacuum; and said window is configured to allow solar energy radiation from outside said first member to inside said first member through said window and prevent solar energy radiation from inside said first member to outside said first member through said window; said solar energy collection system being characterized in further comprising a solar energy director adapted to direct solar energy through said window and in that: said window has a circumferential cross section perpendicular to said longitudinal axis; said body has a circumferential cross section perpendicular to said longitudinal axis; and an angle of said circumferential cross section of said window is smaller than an angle of said circumferential cross section of said body. a solar energy collector comprising: a first member having a cavity and a longitudinal axis, the first member having a longitudinal window extending the entire length of the first member and forming a part of the first member, and a body forming the rest of the first member, said longitudinal window being made of a material adapted to pass solar energy, said body having an exterior absorptive surface and an interior reflective surface; a second member located within the cavity of the first member and generally parallel to said longitudinal axis, said second member being adapted to carry an energy absorbing fluid; and an insulative material filling the cavity between the first member and the second member; wherein: said first member is a tube and has a circular cross-sectional shape; said second member is a tube and has a circular cross-sectional shape; said second member is surrounded by the interior reflective surface of the first member; said insulative material is a fluid or a vacuum; and said window is configured to allow solar energy radiation from outside said first member to inside said first member through said window and prevent solar energy radiation from inside said first member to outside said first member through said window; said first member is a tube and has a circular cross-sectional shape; said second member is a tube and has a circular cross-sectional shape; said second member is surrounded by the interior reflective surface of the first member; said insulative material is a fluid or a vacuum; and said window is configured to allow solar energy radiation from outside said first member to inside said first member through said window and prevent solar energy radiation from inside said first member to outside said first member through said window; said solar energy collection system being characterized in further comprising a solar energy director adapted to direct solar energy through said window and in that: said window has a circumferential cross section perpendicular to said longitudinal axis; said body has a circumferential cross section perpendicular to said longitudinal axis; and an angle of said circumferential cross section of said window is smaller than an angle of said circumferential cross section of said body. said window has a circumferential cross section perpendicular to said longitudinal axis; said body has a circumferential cross section perpendicular to said longitudinal axis; and an angle of said circumferential cross section of said window is smaller than an angle of said circumferential cross section of said body.