<p>The collector has an outer glass cover (2) and an inner glass sheet (2') with a thermally insulating gap (a) between them. The energy absorber (6) is below the inner glass sheet with a second thermally insulating gap (b) between them. The two glass sheets and the absorber are linked round their edges by side spacer pieces (7) which seal the air gaps and hold the glass sheets and absorber together in a rigid assembly. This assembly is placed inside a light sheet casing (3) which is not rigid. The sides and base of the outer casing (3) are lined with insulating material (8). Because the inner assembly is rigid the outer case need not be and can therefore be made lighter and cheaper.</p>
