Abstract: A solar panel (FIG. 7) comprises an extruded plastics matrix (20) comprising a plurality of side-by-side compartments each of which provides an actual fluid-flow channel without the need for providing separate metal pipework. Each compartment may include a filler (62) to define a fluid-flow channel between the upper surface of the filler and the lower surface of a membrane (28) of the matrix. The provision of the filler (62) is optional and the cross section of each compartment may be optimized to the fluid-flow channel size requirements. At least part of a surface of each fluid-flow channel has a covering comprising a solar radiation absorber; for example, the absorber may comprise a channel-shaped foil (72) which exhibits high absorbence of solar energy together with low emittance of infra-red radiation.

Abstract: A method and apparatus for monitoring the fineness of solids in a first suspension of solids in a liquid medium is described. The apparatus comprises a cyclone for separating the first suspension under the influence of a force field into two second suspensions containing respectively solids generally coarser than and generally finer than a predetermined separation size. A constant head device is provided to cause the first and second suspensions to flow through the apparatus. Density measurement means comprising radiation sources, presentation columns, and detectors measure the density of the first suspension and the second suspensions respectively. A computer determines from the measured densities the fineness of solids in the first suspension.