NOVELTY - The collector has a transparent thermal insulation unit including a set of superimposed layers made of a transparent thermal insulating material between an absorbent surface (4) and an exterior transparent cover (1) e.g. transparent quartz cover, where a transparent silica aerogel layer or material (7) is provided. The transparent thermal insulating unit comprises a transparent honeycomb structure insulation material layer (2) made of glass or transparent polymer, and/or an air chamber, and/or a vacuum chamber. The cover is made from a group of glass, quartz and transparent polymer.    USE - Solar thermal collector e.g. low-medium temperature collector such as flat-type solar collector and concentration-type solar collector (all claimed), for transforming captured solar energy into heat energy in a heating installation or sanitary hot water installation. Can also be used for a high temperature collector for industrial or electrical power generation installation.    ADVANTAGE - The transparent thermal insulation unit increases performance of the collectors by reducing heat losses by using the superimposed layers. The collector absorbs or captures the solar energy and converts the solar energy into heat energy at low temperature and medium temperature, thus improving efficiency, and minimizing production costs and weight of the collector.    DETAILED DESCRIPTION - The absorbent surface is convex or concave surface. The silica aerogel layer or material is made of a silica aerogel material or a silica xerogel material.    DESCRIPTION OF DRAWING(S) - The drawing shows a side view of a flat-type solar collector with a transparent silica aerogel layer or material and a transparent honeycomb structure insulation material layer arranged on an exterior transparent cover.    Exterior transparent cover (1)    Transparent honeycomb structure insulation material layer (2)    Absorbent surface (4)    Transparent polymer separator (6)    Transparent silica aerogel layer or material (7)