Olivier Guisan

Ground-reflected radiation and albedo

The diffuse radiation incident on an inclined plane is composed of both the ground-reflected radiation and the sky diffuse radiation. The evaluation of the sky diffuse radiation has already been described in many references. In this paper we focus on the ground-reflected radiation, its relation to insolation conditions and its evaluation by means of models. We used six data banks from the following four countries: Switzerland, France, The Netherlands, and the U.S.A. We investigated how the albedo depends on the amount and the composition of the incident radiation, on geometrical parameters such as the height and/or the azimuth of the sun and on meteorological parameters such as the humidity. We did not find any notable dependence. We also tested different models evaluating the ground-reflected radiation on tilted planes with corresponding measurements on an inverse horizontal plane (facing the ground) and on inclined planes. We came to the conservative conclusion that the best results are obtained when using a constant averaged measured albedo, for transposition to tilted surfaces, when assuming the ground-reflected radiation to be isotropic.

Thermal analysis of five outdoor swimming pools heated by unglazed solar collectors

Abstract We have analysed measurements from five outdoor swimming pools located in Switzerland and heated by unglazed solar collectors. The main contributions to the daily energy balance of the swimming pools are evaluated. They include the active and passive solar gains, as well as the heat losses related to radiation, evaporation, convection, and water renewal (in order of importance). Coherent results are obtained using multilinear regressions in order to determine the best fitting values of the empirical parameters involved in the thermal equations.

Infrared sky radiation in Geneva

Abstract Continuous measurements of sky radiation have been performed in Geneva for more than two years. We present here some results, and we show that the radiative earth-sky deficit is correlated to the clearness of the day as evaluated from the amount of solar radiation reaching the ground. The corresponding model allows to determine the sky temperature within 2–3°C, with respect to ambient temperature, diffuse and global solar radiation. These results can be of help when computing energy balances involving sky radiation, especially in buildings and solar energy fields.

Thermal analysis of five unglazed solar collector systems for the heating of outdoor swimming pools

The performance and behavior of five unglazed solar collector installations, devoted to the heating of five outdoor swimming pools located in Switzerland, is studied on the basis of experimental data collected in 1988. Due to the low temperatures involved, hourly efficiencies often exceed 80%. The mean daily collector efficiency is of the order of 60% in optimal conditions and is in good agreement with the G3 simulation program.

Solar radiation transposition models applied to a plane tracking the sun

Many solar radiation transposition models, from a horizontal plane to any fixed inclined surface, have been compared with measurements from different sites. The tests here were carried out for four top-ranked models and with measurements taken on a plane tracking the sun. The best precision obtained in this study is ±7% on the global solar radiation and ±20% on the diffuse solar radiation with a zero bias.

SOLAR RADIATION IN GENEVA, SWITZERLAND : VALIDATED MODELS AND CORRELATIONS

ABSTRACT We extracted many results from solar radiation measurements performed in Geneva during 4 years; we present here some properties about diffuse radiation, infrared sky radiation, usual correlations (Angstrom-Black, clearness index, etc…), monthly average days and models allowing to transpose the solar radiation from horizontal to any plane.