Andrea Padovan

Measurement of Solar Radiation for Renewable Energy Systems

In this paper the authors present a new set of solar radiation data taken at the latitude of 45.4°, in Padova, Italy. These measurements are performed within a new laboratory for the study of solar energy conversion systems. The global and the diffuse irradiance is measured on the horizontal plane and the global irradiance is also measured on sloped planes. The experimental uncertainty of the measurement of solar radiation is fully analyzed. In the design of a solar system, it is crucial to know the solar radiation on the inclined surface, but generally only data on the horizontal is available and solar radiation on the tilted plane is predicted using the information collected on the horizontal. There is need for assessment of prediction methods for estimating the solar radiation on inclined surfaces. In this paper, new data of global and diffuse radiation is compared to some most used correlations. Besides, the values calculated for the tilted plane are compared against those directly measured by a pyranometer installed on the sloped plane.Copyright

Solar Thermal Collectors with Low and High Concentration

This chapter describes the performance analysis of different concentrating technologies through experimental and numerical modeling activities. Two solar thermal systems with different designs and, accordingly, different concentration ratios have been studied. The first solar device is a stationary compound parabolic concentrator (CPC) collector: it is provided with truncated or full CPC reflectors and evacuated tubes. Each evacuated tube is composed of an outer glass envelope and a glass absorber with selective coating in thermal contact, via absorber fin, with a U-shaped channel for the liquid flow. The second system is a parabolic trough concentrator (PTC) with two-axis solar tracking: the primary optics consists of a segment of parabolic cylinder which concentrates the direct normal irradiance (DNI) on a linear receiver. In this system, two types of flat receivers have been tested. One receiver has been designed for thermal energy extraction, and it consists of a canalized roll-bond plate provided with a semi-selective coating. The other receiver has been designed for cogeneration of electricity and heat (CPVT), and it is equipped with triple-junction photovoltaic cells, which are actively cooled by an aluminum roll-bond heat exchanger. The performance of the described collectors has been experimentally characterized at the Solar Energy Conversion Laboratory of the University of Padova (45.4°N, 11.9°E), Italy. The collectors have also been mathematically modeled, and the numerical data have been validated against the experimental measurements.

Experimental Daily Energy Performance of Flat Plate and Evacuated Tube Solar Collectors

New comparative tests on different types of solar collectors are presented in this paper. Tests have been performed at the solar energy conversion laboratory of the University of Padova. Two standard glazed flat plate collectors and one evacuated tube collector are installed in parallel; the evacuated collector is a direct flow through type with external CPC (compound parabolic concentrator) reflectors. The present test rig allows to make measurements on the flat plate, on the evacuated collector or on both simultaneously, by simply acting on the valves to modify the circuit. In this paper measurements of the performance of the evacuated tube collector and flat plate collectors working at the same conditions are reported. Efficiency in stationary conditions is measured following the standard EN 12975-2 [1] and it is compared with the input/output curves measured for an entire day. The main purpose of the present work is to characterize and to compare the daily energy performance of the two types of collectors. An effective mean for describing and analyzing the daily performance is the so called input/output diagram, in which the collected solar energy is plotted against the daily incident solar radiation. Test runs have been performed in several conditions to reproduce different conventional uses (hot water, space heating, solar cooling).Copyright