Experimental investigations into low concentrating line axis solar concentrators for CPV applications

Solar photovoltaic conversion systems with integrated, low concentration ratio, non-imaging reflective concentrators, could be on south facing building roofs used to generate power at a lower cost than currently available proprietary systems. The experimental investigation presented by this research provides information on the optical and energy conversion characteristics of two geometrically equivalent non-imaging concentrators; a compound parabolic concentrator and a V-trough reflector. The aim was to investigate the assumption of uniform cell illumination when PV cells located on the receiver surface with their central axes are aligned parallel with the focal line of the line-axis concentrator. Solar radiation incident was measured at the aperture and the PV cell surface using respectively a pyranometer and photodiodes at six different collector tilt angles of 0°, 10°, 20°, 30°, 40° and 52°. The analysis of the collected experimental data presented demonstrated that the V-trough system had a more even distribution of solar radiation than the CPC and a higher optical concentration ratio (ratio of solar radiation incident on the aperture cover to that incident on the receiver) though the geometrical concentration ratio of the two collectors was equal to 2.2×. Also, the V-trough concentrator had an electrical power output up to 17.2% higher than the CPC system at a specific tilt angle of 30°. The V-trough had a consistently higher receiver plate temperature as it was reflecting larger quantities of solar radiation than the CPC. Over 17 consecutive typical summer days’ similar performance was observed over the range of tilt angles studied. The development of V-trough concentrators should be preferred due to higher power production, reduced complexity, increased uniformity of illumination and lower manufacturing costs compared to CPCs

Energy and economic analysis of Vacuum Insulation Panels (VIPs) used in non-domestic buildings

The potential savings in space heating energy from the installation of Fumed Silica (FS) and Glass Fibre (GF) Vacuum Insulation Panels (VIPs) were compared to conventional expanded polystyrene (EPS) insulation for three different non-domestic buildings situated in London (UK). A discounted payback period analysis was used to determine the time taken for the capital cost of installing the insulation to be recovered. VIP materials were ranked using cost and density indexes. The methodology of the Payback analysis carried out considered the time dependency of VIP thermal performance, fuel prices and rental income from buildings. These calculations show that VIP insulation reduced the annual space heating energy demand and carbon dioxide (CO2) emissions by approximately 10.2%, 41.3% and 26.7% for a six storey office building, a two floor retail unit building and a four storey office building respectively. FS VIPs had the shortest payback period among the insulation materials studied, ranging from 2.5 years to 17 years, depending upon the rental income of the building. For GF VIPs the calculated payback period was considerably longer and in the case of the typical 4 storey office building studied its cost could not be recovered over the life time of the building. For EPS insulation the calculated payback period was longer than its useful life time for all three buildings. FS VIPs were found to be economically viable for installation onto non-domestic buildings in high rental value locations assuming a lifespan of up to 60 years