TECHNOLOGY FOCUS - ELECTRICAL POWER AND ENERGY - Preferred Mirror: The substrate comprises a planar glass sheet mirror element, preferably 2 mm thick. The mirror element is retained using a sleeve member, preferably of trough construction made from a single sheet of metal suitably worked and folded, having a substantially parabolic groove for receiving each lengthwise edge of the planar glass sheet mirror element. The mechanical support comprises one or more sheets folded or pivoted on a hinge about at least one curved fold line or curved hinge line. The reflective substrate is not brittle and is integral with the sheets. The mirror is made from a single sheet having folded sides and correspondingly curved lengthwise sides, preferably a thermoplastic sheet made less stiff along the fold line by local heating. The reflective surface is supported by the mechanical support along an entire length of the reflective surface. The mirror is a parabolic cylinder. The substantially continuous mechanical support is adapted to adjust a shape of the reflective substrate for adjusting a focal distance and/or a focal spot shape of the mirror. The mirror further comprises a mounting base for mounting the mirror to a frame. The mirrors are mounted to a frame with their directions of curvatures rotated slightly relative to one another so that their foci substantially maximally overlap. Preferred Solar Concentrator: The frame comprises substantially identical curved rails for supporting the mirrors; substantially identical ribs for supporting the rails; and a truss extending across the concentrator substantially orthogonal to the ribs and adapted to support the ribs in a substantially curved arrangement in a direction of the truss, the truss being supported by the two-axis mounting. The concentrator further comprises a receiver mounting, the receiver mounting comprising three legs attached to the frame to provide a tripod support for the receiver, where two of the three legs are pivotally mounted to the frame to rotate about an axis, and another of the legs being detachable from the frame and/or the receiver to allow the two legs to pivot with the receiver toward the frame to facilitate access to the receiver for servicing. The concentration is at least 1000 suns, preferably at least 2000 suns, the mirrors having substantially a paraboloid of translation shape with a width of at least 500 mm, and an aperture of the frame being at most 7.2m on a side. Preferred Solar Photovoltaic Receiver: The groups each have a single tube, and a number of the cells are arrange electrically in parallel on each of the tubes. The cells connected in series overlap with the first electrical contact of one cell touching the second electrical contact of another cell, preferably with the cells extending across the tubes in a substantially saw tooth manner. The cells are characterized by a light conversion enhancement structure comprising one or more of: a raised, substantially triangularly shaped raised profile on cell contacts provided on the front surface to increase light reaching a photoreceptive body of the cell that is otherwise lost to the cell contacts: and an off-axis silicon layer sliced from a silicon ingot at an angle such that the lattice constant of the silicon ingot divided by the cosine of the angle is substantially equal to the lattice constant of a material of a non-silicon junction of the cell to allow junction materials that are lattice matched to each other but not to silicon to be used in a multi-junction cell able to convert more light than a single junction cell. Preferred Photovoltaic Cell: The structure comprises the substantially triangularly shaped raised profile on the cell contacts, and a conductive footer supports a tall core of a higher melting-point material that is surrounded by a reflective material of a lower melting point, and where the amount of the lower melting material is such that when liquid its surface tension will pull it into a substantially triangular cross-section bounded by the footer and the core. Preferred System: In the solar tower system, an improved mean-to-peak solar concentration ratio at the receiver tower is achieved. At least one of the receiver towers comprises two receivers, a first one for converting light to heat, and a second one for converting light to photoelectric power, with a mechanism to switch the first and the second receivers during operation. In the system of (7), the mirror structures are supported by an axle that runs through or near the mutual center of gravity of the mirror structures. In the system of (8), the receiver is rotatable in the second dimension and comprises a secondary concentrator that concentrates the solar energy in the second dimension. The system comprises multiple secondary concentrators that rotate to track the angle of the sun in the second dimension. The primary concentrator is a parabolic trough reflector, the receiver comprising a number of receivers spaced out along the trough reflector.