• Energy Research

Abstract A methodology to estimate PV electrical production from outdoor testing data is presented. It is based on the adjustment of a well known I – V model curve slightly modified and a new maximum power output expression. The method is developed to provide PV module performance parameters for all operating conditions encountered by typical photovoltaic systems. The method, theoretically based, is reasonably simple, yet accurately predicts operating conditions performance. The main advantage of the methodology developed is that it allows photovoltaic users to control the PV modules production based on measurements that can be performed far away from specialized photovoltaic reference laboratories even when standard testing conditions can not be achieved.

Abstract A methodology to estimate PV electrical production from outdoor testing data is presented. It is based on the adjustment of a well known I – V model curve slightly modified and a new maximum power output expression. The method is developed to provide PV module performance parameters for all operating conditions encountered by typical photovoltaic systems. The method, theoretically based, is reasonably simple, yet accurately predicts operating conditions performance. The main advantage of the methodology developed is that it allows photovoltaic users to control the PV modules production based on measurements that can be performed far away from specialized photovoltaic reference laboratories even when standard testing conditions can not be achieved.

Abstract Current technologies for the cooling of high power integrated circuits (IC) chips employ single-phase liquid flow through microchannel heat sinks. The surface temperature in these devices increases along the flow direction, leading to temperature nonuniformities in the cooled device. Mitigation of this temperature nonuniformity, while enhancing the heat exchange along the flow path, has been demonstrated through the use of variable fin density microchannels. This paper demonstrates experimentally and numerically the potential of micro-pin-fin heat sinks as an effective alternative to microchannel heat sinks for dissipating high heat fluxes from small areas. Results from this experimental and numerical investigation demonstrate the ability of variable pin-fin density with offset configurations to reach low thermal resistance coefficients and reduce the surface temperature nonuniformity while presenting low-pressure drops. For the maximum Reynolds number considered in this study (2200), we demonstrate the capacity of the cooling scheme, when submitted to a heat flux of 50 W/cm2, to reach a pumping to chip power ratio of 0.37%, a thermal resistance coefficient of 0.26 cm2 K/W and a temperature uniformity along the 5 cm long cooling device of 2 °C.

Abstract Current technologies for the cooling of high power integrated circuits (IC) chips employ single-phase liquid flow through microchannel heat sinks. The surface temperature in these devices increases along the flow direction, leading to temperature nonuniformities in the cooled device. Mitigation of this temperature nonuniformity, while enhancing the heat exchange along the flow path, has been demonstrated through the use of variable fin density microchannels. This paper demonstrates experimentally and numerically the potential of micro-pin-fin heat sinks as an effective alternative to microchannel heat sinks for dissipating high heat fluxes from small areas. Results from this experimental and numerical investigation demonstrate the ability of variable pin-fin density with offset configurations to reach low thermal resistance coefficients and reduce the surface temperature nonuniformity while presenting low-pressure drops. For the maximum Reynolds number considered in this study (2200), we demonstrate the capacity of the cooling scheme, when submitted to a heat flux of 50 W/cm2, to reach a pumping to chip power ratio of 0.37%, a thermal resistance coefficient of 0.26 cm2 K/W and a temperature uniformity along the 5 cm long cooling device of 2 °C.

To develop concentrating photovoltaic systems for building integration applications, two optical devices are proposed. The concentrators are based in stationary linear Fresnel lenses and secondary CPC. The moving focal area is ten times smaller than the Fresnel lens aperture. Concentrator characteristics are studied in detail: shadowing effect, placement of the focal area and optical concentration efficiency. The main contribution of this paper is the three-dimensional optical analysis of the non-imaging concentrating systems. In terms of solar radiation, photovoltaic moving modules placed in the focal area of stationary concentrators are compared with simply fixed photovoltaic modules. In favourable weather locations, the beam radiation incident on the concentrating modules would be a large percentage, more than 50%, of the global radiation received by the fixed photovoltaic devices.

To develop concentrating photovoltaic systems for building integration applications, two optical devices are proposed. The concentrators are based in stationary linear Fresnel lenses and secondary CPC. The moving focal area is ten times smaller than the Fresnel lens aperture. Concentrator characteristics are studied in detail: shadowing effect, placement of the focal area and optical concentration efficiency. The main contribution of this paper is the three-dimensional optical analysis of the non-imaging concentrating systems. In terms of solar radiation, photovoltaic moving modules placed in the focal area of stationary concentrators are compared with simply fixed photovoltaic modules. In favourable weather locations, the beam radiation incident on the concentrating modules would be a large percentage, more than 50%, of the global radiation received by the fixed photovoltaic devices.

Abstract The performance of dense array Concentrating PhotoVoltaics (CPV) receivers is reduced by the increase of average temperature and temperature non-uniformities which arise from illumination profiles and the characteristics of the cooling mechanism used. The magnitude of the impact of both illumination and temperature non uniformities depend on the electrical configuration of the CPV cell array. In this study, the impact of a cooling device, formed by a matrix of microfluidic cells with individually variable coolant flow rate, on the performance of a CPV receiver submitted to a non-uniform irradiance scenario is assessed and compared with microchannel cooling for three electrical configurations. The proposed cooling scheme tailors the flow rate distribution, and therefore the local heat extraction capacity, to the illumination profile, allowing the reduction of the temperature difference across the CPV receiver up to one third of the one obtained through microchannel cooling. This characteristic of the microfluidic cells cooling device, combined to its low pumping power, generates an improvement of the Net PV power of 3.83% for one of the configuration, the 6x8 matrix one.

Abstract The performance of dense array Concentrating PhotoVoltaics (CPV) receivers is reduced by the increase of average temperature and temperature non-uniformities which arise from illumination profiles and the characteristics of the cooling mechanism used. The magnitude of the impact of both illumination and temperature non uniformities depend on the electrical configuration of the CPV cell array. In this study, the impact of a cooling device, formed by a matrix of microfluidic cells with individually variable coolant flow rate, on the performance of a CPV receiver submitted to a non-uniform irradiance scenario is assessed and compared with microchannel cooling for three electrical configurations. The proposed cooling scheme tailors the flow rate distribution, and therefore the local heat extraction capacity, to the illumination profile, allowing the reduction of the temperature difference across the CPV receiver up to one third of the one obtained through microchannel cooling. This characteristic of the microfluidic cells cooling device, combined to its low pumping power, generates an improvement of the Net PV power of 3.83% for one of the configuration, the 6x8 matrix one.

Abstract The reduction of CO 2 emissions is a key component for today’s governments. Therefore, implementation of more and more systems with renewable energies is necessary. Solar systems for single family houses or residential buildings need a big water tank that many times is not easy to locate. This paper studies the modelization of a new technology where PCM modules are implemented in domestic hot water tanks to reduce their size without reducing the energy stored. A new TRNSYS component, based in the already existing TYPE 60, was developed, called TYPE 60PCM. After tuning the new component with experimental results, two more experiences were developed to validate the simulation of a water tank with two cylindrical PCM modules using type 60PCM, the cooldown and reheating experiments. Concordance between experimental and simulated data was very good. Since the new TRNSYS component was developed to simulate full solar systems, comparison of experimental results from a pilot plant solar system with simulations were performed, and they confirmed that the type 60PCM is a powerful tool to evaluate the performance of PCM modules in water tanks.