Integrating photovoltaics into windows provides the possibility of including an additional function of energy production to a conventional building fenestration component. There is no doubt that electrical power can be generated on-site. However, the effect of PV windows on the indoor luminous environment of the space served by them has not been comprehensively researched. This paper investigated the daylight performance of integrating four types of photovoltaics (semi-transparent thin film Cadmium telluride (CdTe) solar cells with 10% and 50% transparency, crystalline silicon solar cells with and without crossed compound parabolic concentrators (CCPC)) to a window of a typical south-facing office under different Window-to-Wall Ratios (WWRs). Annual useful daylight illuminance (UDI), daylight uniformity ratio (UR) and daylight glare probability (DGP) have been analysed based on dynamic simulation using RADIANCE. The simulation results show that windows integrated with crystalline silicon cells and CCPC optics have the potential to provide best daylight availability when compared with standard double glazed windows and other tested PV window prototypes, if it is applied to rooms with large WWRs (e.g. 60% or 75% WWR) at high latitudes (e.g. city of Harbin). Its application also improves the uniformity of daylight spatial distribution and eliminates the risk of glare. Semi-transparent CdTe PV window with 10% transparency can also improve the percentage of working hours that fall into UDI. range, however, it will result in the most sharp illuminance contrasts within the room. Applying all of these tested PV windows can effectively reduce the possibility of glare. 500–2000lux

Concentrator photovoltaics have several advantages over flat plate systems. However, the increase in solar concentration usually leads to an increase in the solar cell temperature, which decreases the performance of the system. Therefore, in this paper, we investigate the performance and temperature limits of a high concentration photovoltaic Thermal system (HCPVT) based on a 1 cm2 multi-junction solar cell subjected to a concentration ratio from 500× to 2000× by using three different types of cooling fluids (water, ethylene glycol and water mixture (60:40), and syltherm oil 800). The results show that, for this configuration, the maximum volumetric temperature of the solar cell did not exceed the manufacturer’s recommended limit for the tested fluids. At 2000× the lowest solar cell temperature obtained by using water was 93.5 °C, while it reached as high as 109 °C by using syltherm oil 800, which is almost equal to the maximum operating limit provided by the manufacturer (110 °C). Overall, the best performance in terms of temperature distribution, thermal, and electrical efficiency was achieved by using water, while the highest outlet temperature was obtained by using syltherm oil 800.

A low concentrator photovoltaic is presented and the optical losses within a double glazed window assembly are described. The use of plastic instead of glass is analyzed for its reduced weight and hence greater power to weight ratios. Although the transmittance of glass is higher, the power to weight ratio of the plastic devices was almost double that of the glass counterparts and even higher than the original non concentrating silicon cell. The plastic Topas material was found to be the best performing material overall. Crystal Clear, a plastic resin, had a higher average transmittance but had a lower optical efficiency due to the cold cast manufacturing process in comparison to injection moulding of the other materials. This proves the importance of considering both the materials and their associated manufacturing quality. External quantum efficiencies, optical properties, silicon cell temperatures and performance is analyzed for concentrating photovoltaic devices made of varying optical materials. The measurement methods for optical analysis are given in an attempt to separate the optical losses experimentally. The Silicon cells were found to gain higher temperatures due to the insulating plastic optics in comparison to glass but these effects are eliminated during vertical window orientation where instead the encapsulate dominates the insulation of the cell. The results presented here prove plastic optics to be a worthwhile alternative to glass for use in low concentration photovoltaic systems and have the significant effect of reversing the weight disadvantage concentrator photovoltaic technology has compared to standard flat plate solar panels.

In concentrating photovoltaic (CPV), increasing the incoming sunlight to the solar cell influences the performance of the solar cells. The optical efficiency of the CPV components is a key factor to improve the electrical efficiency. Two types of homogeniser materials (K9 glass and crystal resin) were investigated in the CPV application. The results show a higher power generation of the CPV module when using K9 glass homogeniser compared to the crystal resin homogeniser by 27% due to the high transmittance value of the K9 glass material. In addition, the K9 glass material shows an excellent resistance to the heat produced by the concentrated sunlight compared to the crystal resin material.

The lenses in compound eyes of butterflies and moths contain an array of nipple-shaped protuberances, or corneal nipples. Previous work has suggested that these nipples increase light transmittance and reduce the eye glare of moths that are inactive during the day. This work builds on but goes further than earlier analyses suggesting a functional role for these structures including, for the first time, an explanation of why moths are attracted to UV light. Using a phylogenetic approach and 3D optical modelling, we show empirically that these arrays have been independently lost from different groups of moths and butterflies and vary within families. We find differences in the shape of nipples between nocturnal and diurnal species, and that anti-glow reflectance levels are different at different wave-lengths, a result thereby contradicting the currently accepted theory of eye glow for predator avoidance. We find that there is reduced reflectance, and hence greater photon absorption, at UV light, which is probably a reason why moths are attracted to UV. We note that the effective refractive index at the end of the nipples is very close to the refractive index of water, allowing almost all the species with nipples to see without distortion when the eye is partially or completely wet and providing the potential to keep eyes dry. These observations provide a functional explanation for these arrays. of special interest is the finding that their repeated and independent loss across lepidopteran phylogeny is inconsistent with the explanation that they are being lost in the 'higher', more active butterflies.

A high concentrator photovoltaic design is proposed of 5800x geometrical concentration ratio based on multiple primary Fresnel lenses focusing to one central solar cell. The final stage optic is of a novel design, made of a high refractive index (n = ∼1.76), to accept light from four different directions but very easily manufactured. The high geometrical concentration of 5800x was chosen in anticipation of the losses accompanied due to alignment difficulties. Two scenarios are however simulated, one with state of the art optics (achromatic Fresnel lenses and 98% reflective mirrors) and one of standard, relatively cheap optics. An optical efficiency of ∼75% is achieved in simulations if high quality optics are utilised, which gives an optical concentration ratio of just over 4300x. Simulating standard optical constraints with less accurate optics results in an optical efficiency of ∼55% which translates to an optical concentration ratio of ∼3000x. In this way the quality of the optics can be chosen depending on the trade of between cost and efficiency with room for future advanced optics to be incorporated at a later date. The optical efficiency of each component is simulated as well as experimentally measured to ensure the accuracy of the simulations. A theoretical acceptance angle of 0.4° was achieved in ray trace simulations for this design which is considered good for such a high concentration level. The need for achromatic Fresnel lenses is apparent from this study to reach optimum performance and concentration but even 55% optical efficiency results in a >3000x concentration not yet experimentally tested. The solar cells irradiance distribution of the design is also presented along with performance and rough cost comparisons to other systems in the literature. The cost of the optics compared to more complex shaped optics is also given.

When integrating photovoltaics into building windows, the photovoltaic glazing modules inhibit the function that glass performs, with the additional function of energy production. Semi-transparent Photovoltaic (STPV) glazing will absorb part of the solar radiation incident on the window surface to generate electrical power. In turn, this affects the overall solar energy and natural daylight penetrating into the indoor space. Various factors determine the building energy performance and indoor comfort level as a result of adopting STPV glazing. The factors regarding window design alone (window size, PV glazing coverage ratio and PV glazing placing position) require rigorous study. In this paper, an innovate model (combined optical, electrical and energy model) was developed to comprehensively evaluate the performance of an office equipped with STPV window and firstly analyse the effect of window design on overall energy efficiency. A double-glazing unit integrated with thin film CdTe solar cells with 10% transparency was electrically characterised by Sandia Array Performance Model (SAPM). The annual energy performance of a typical office served by window integrated STPV glazing was investigated through EnergyPlus simulation for various window designs under five typical climatic conditions in China (using weather files of Harbin, Beijing, Shanghai, Guangzhou and Kunming for representation). The optical performance (defined by a Bidirectional Scattering Distribution Function) of this STPV glazing was also obtained using a ray-tracing technique. Then, the annual daylight performance of the porotype office was assessed using RADIANCE. We found that when compared to a conventional double-glazed system, the application of PV window can result in considerable energy saving if the office has a relatively large window-to-wall ratio (i.e. ≥ 45%), while the position of placing STPV glazing has significant influence on the lighting energy consumption. In the specific climates under test, the optimal design scenario of applying window integrated PV can result in a reduction in energy consumption of up to 73%. The simulation results also show that this PV window offers better daylight performance than conventional double glazing and effectively reduces the possibility of glare.

The conjugate refractive reflective homogeniser (CRRH) is experimentally tested within a cassegrain concentrator of geometrical concentration ratio 500× and its power output compared to the theoretical predictions of a 7.76% increase. I–V traces are taken at various angles of incidence and experimental results showed a maximum of 4.5% increase in power output using the CRRH instead of its purely refractive counterpart. The CRRH utilises both total internal reflection (TIR) within its core refractive medium (sylguard) and an outer reflective film (with an air gap between) to direct more rays towards the receiver. The reflective film captures scattered refracted light which is caused by non-ideal surface finishes of the refractive medium. The CRRH prototype utilises a 3D printed support which is thermally tested, withstanding temperatures of up to 60 °C but deforming at >100 °C. A maximum temperature of 226.3 °C was reached within the closed system at the focal spot of the concentrated light. The material properties are presented, in particular the transmittance of sylguard 184 is shown to be dependent on thickness but not significantly on temperature. Utilising both TIR and standard reflection can be applied to other geometries other than the homogeniser presented here. This could be a simple but effective method to increase the power of many concentrator photovoltaics.

A compact high concentrating photovoltaic module based on cassegrain optics is presented; consisting of a primary parabolic reflector, secondary inverse parabolic reflector and a third stage homogeniser. The effect of parabolic curvatures, reflector separation distance and the homogeniser’s height and width on the acceptance angle has been investigated for optimization. Simulated optical efficiencies of 84.82 – 81.89 % over a range of ±1 degree tracking error and 55.49% at a tracking error of ±1.5 degrees were obtained. The final singular module measures 169mm in height and 230mm in width (not including structural components such as cover glass).The primary reflector dish has a focal length of 200mm and is afocal with the secondary inverse reflector which has a focal length of 70mm. The transparent homogenising optic has a height of 70mm, an entry aperture of 30 x 30mm and an output aperture of 10 x 10mm to match the solar cell. This study includes an analysis of the optical efficiency, acceptance angle, irradiance distribution and component errors for this type of concentrator. In particular material stability and the surface error of the homogeniser proved to be detrimental in theoretical and experimental testing – reducing the optical efficiency to ~40%. This study proves the importance of material choice and simulating optical surface quality, not simply assuming ideal conditions. In the experimental testing, the acceptance angle followed simulation results as did the optical efficiency of the primary and secondary reflectors. The optical efficiency of the system against increasing solar misalignment angles is given for the theoretical and experimental work carried out.

The concept of a high-concentration optical system is introduced detailing the various design types and focusing only on those aimed at photovoltaic (PV) applications. This will include point focus, line focus, imaging, nonimaging, and the classical cassegrain set-up. The theory of high-concentration optics is explained in terms of idealised concepts and maximum limits for each concentrator type and combination. The optical system is broken down into the different stages and materials possible in a high-concentration configuration. The physics of reflective and refractive optics are described, and their associated errors, advantages and a brief overview of past milestones, and recent research trends in the area of high-concentration PVs are presented. Current primary and secondary optics are geometrically explained covering Fresnel, parabolic, heliostat, compound parabolic, hyperboloid, v-trough, and dome-shaped optics. This chapter also covers examples of new secondary optics, such as the three-dimensional crossed-compound parabolic concentrator and the square elliptical hyperboloid concentrator. The aim of this chapter is to provide the basic optical behaviour of high-concentration designs aimed at PV applications considering their geometry, materials, and reliability.