One or more sheets of glass or other diathermic material (radiation transmitter). Tubes, fins or passages. To conduct or direct heat transfer fluid from inlet to outlet. Absorbent plates. Flat, corrugated or grooved plates, to which tubes, fins or passages are attached. The plate can be integral with the pipes. Headings or varieties. To admit and discharge fluid. Insulation. To minimize heat loss from the back and sides of the collector. Container or casing. Surround the above components and keep them free from dust and moisture,