Philip C. Eames

Linear Dielectric Non-Imaging Concentrating Covers For PV Integrated Building Facades

A three-dimensional optical analysis of two dielectric, non-imaging concentrating covers for building integrated photovoltaics shows that an asymmetric concentrator is more suitable for use at building facades. For a wide range of solar incidence angles, optical efficiencies are over 90% for both concentrators. The optimum collection tilt angle for two different latitudes and the monthly and annual collected solar energy for both concentrators are predicted and compared to flat photovoltaic covers of the same photovoltaic and aperture area. Employing high transmittance materials for dielectric concentrating covers enables such refractive systems to achieve high solar energy acceptance thus requiring less photovoltaic material thereby reducing initial capital cost.

The effect of tank geometry on thermally stratified sensible heat storage subject to low Reynolds number flows

In a theoretical and experimental investigation into the thermal performance of stratified hot water stores, a transient three-dimensional finite-volume based model was validated by comparison with measured temperatures from a series of thirty-two experiments in which the inlet velocities, temperatures and initial store stratification profiles were varied. A parametric analysis ascertained the effect of inlet and outlet port locations on store performance for a range of operating conditions. The effects of finite volume size on predicted levels of entrainment and diffusion in the inlet region are reported.

Validated, unified model for optics and heat transfer in line-axis concentrating solar energy collectors

A rigorous numerical simulation model for the prediction of the combined optical and thermofluid behaviour of line-axis concentrating solar energy collectors combines two-dimensional steady-state finite element analysis of convective heat transfer and ray-trace techniques. The optical analysis considers both direct and diffuse insolation components and is therefore useful for the analysis of compound parabolic concentrating collectors. Experiments using Mach-Zehnder interferometry indicate a parametric range for which such a two-dimensional representation is valid.

A comparative performance rating for an integrated solar collector/storage vessel with inner sleeves to increase heat retention

Abstract Integral Collector/Storage (ICS) solar water heating systems suffer substantial heat loss during periods of low insolation or at night. Methods to reduce aperture heat loss include moveable insulated lids/shutters, transparent insulating glazing materials and selective glazing/absorber coatings. All of these approaches involve trade-offs with reduction in performance and/or an increase in cost. A novel ICS vessel design to mitigate heat loss is proposed. An ICS vessel utilising an inner sleeve arrangement is shown to reduce heat loss by up to 20%. This paper examines four inner sleeve design configurations, several of which demonstrate an increase in the heat retention capability over existing vessels, and an optimised design is presented.

Quantum dot solar concentrator behaviour, predicted using a ray trace approach

SYNOPSIS Using a three-dimensional raytrace technique, a model to optimise the design of Quantum Dot Solar Concentrators for photovoltaic applications has been developed. The model includes reflection, refraction and absorption of solar radiation allowing the prediction of the optical efficiency. The optical efficiency is defined as the energy emitted from the selected edge or edges divided by the solar energy incident on the material. Using the model, a parametric analysis was performed and the optical properties of a selected system optimised. Details of the model and predictions of concentrator efficiency and ray path lengths for a range of quantum dot seeding levels are shown. The effects of path length on energy absorbed in the carrier material and that reaching the photovoltaic material are presented.

Heat retaining integrated collector/storage solar water heaters

Abstract An integrated collector/storage solar water heater (ICSSWH) that can significantly reduce heat loss to ambient during non-collection periods has been developed. Two thirds of the ICS vessel is mounted within a concentrating cusp, McIntire ‘W’ modified concentrator and incorporates an inner heat retaining vessel. The remaining upper 1/3 of the vessel is situated outside the reflector cavity and is heavily insulated. Over 60% of the thermal energy stored within the total vessel, and up to 67% of that in the upper immediate draw-off region can be retained over a 16-h non-collection period. Results of an experimental analysis of this design and a comparison with a standard ICS design are presented.

Detailed parametric analyses of heat transfer in CPC solar energy collectors

A detailed parametric analysis of heat transfer in compound parabolic concentrating solar energy collectors has been performed, using a unified model for their optical and thermophysical behaviour. The effects of angular inclination and collector acceptance angles on free convection within the cavity are presented. The circumferential variation of local Nusselt number about the absorber is determined. A convective heat transfer correlation is obtained for the average Nusselt number with respect to Grashof number that takes into account acceptance angle and angular inclination. The developed correlation is extended to truncated compound parabolic concentrators.

The effect of variation of angle of inclination on the performance of low-concentration-ratio compound parabolic concentrating solar collectors

Abstract Thermal heat transfer in line-axis, symmetric, compound parabolic concentrating solar energy collectors (CPCs) has been investigated and a theoretical numerical model has been developed. The model allows the effect of the angle of axial inclination of an east-west aligned CPC and hence the effect of the latitudinal and tracking configuration of the CPC system on performance to be determined. The internal and external convective heat transfer correlations employed are angular dependent. The variation of convective, radiative, conductive and overall heat transfer coefficients and system efficiency for a range of angular inclinations, concentration ratios, total insolations and beam to diffuse insolation factors are presented graphically. The results demonstrate that there is a 10% variation in convective heat transfer with angle of inclination for low concentration CPCs (i.e. C = 1.5).

Annual performance of heat retaining integrated collector/storage solar water heaters in a northern maritime climate

The annual performance of two full-size integrated collector/storage solar water heaters (ICSSWH) was experimentally determined. The ICSSWHs incorporated a novel heat retaining storage vessel and employed a new technique for the construction and assembly of the encompassing collector unit. Systems A and B were respectively a 1.5 m long ICSSWH unit partially enclosed within the reflector sections and a 1.0 m long ICSSWH unit fully enclosed within the reflector sections. Details of the annual measured performance of the two designs are presented in this paper.

Comparison of Predictions Made Using a New 3D Phase Change Material Thermal Control Model with Experimental Measurements and Predictions Made Using a Validated 2D Model

Phase change materials are shown to be an effective means of limiting temperature rise in photovoltaic devices. A three-dimensional (3D) numerical model was developed to simulate the use of a phase change material linked to a PV system to control the temperature rise of the PV cells. The model can be used to predict temperatures, velocity fields, and vortex formation within the system. The predicted temperatures using the 3D model have been compared with experimental measurements for which the system geometry, material characteristics, and boundary conditions have been matched as closely as possible. The 3D predictions have also been compared with those from a previously developed and experimentally validated two-dimensional (2D) finite-volume heat transfer model conjugated hydrodynamically to solve the Navier-Stokes and energy equations. It was found that for the systems simulated with appropriate boundary conditions, the 2D model predictions compare well with those of the 3D model. Using the 3D model, the temperature distributions were predicted when the heat transfer to the PCM was enhanced by high thermal conductivity pin fins. The effects of the container boundaries have been analyzed.