UNCERTAINTY IN SOLAR THERMAL SYSTEMS SIMULATIONS

Soteris A. Kalogirou

Department of Mechanical Engineering and Materials Science and Engineering, Cyprus University of
Technology, P. O. Box 50329, Limassol 3603, Cyprus

Tel. +357-2500 2621, Fax. +357-2500 2769, Email: soteris. kalogirou@cut. ac. cy

Abstract

Usually solar systems are modeled with programs, like TRNSYS, using a typical meteorological year data and a constant consumption profile. This is the most practical method as all systems modeled are simulated with the same weather conditions and the same load demand profile, thus it is easier to compare systems of different configurations. In this paper the effect of introducing uncertainty or noise in the weather data and load pattern is examined. As it is proved the annual performance of the system is not very much different compared to the normal non-noisy model whereas the daily and hourly performance shows some considerable variations. It is believed that the present method gives more reliable results to the long-term performance evaluation of the systems and should be followed once the optimum system is obtained as it produces more reliable results. This is more important in case where guaranteed solar results schemes are followed where possible mistakes could result in significant financial penalties.

Keywords: Modeling of solar systems, simulation, uncertainty, long-term performance.

1. INTRODUCTION

As part of the design process of a solar system, simulation tools are often employed both to investigate the implication of a design change on the system and its long-term performance. The simulation is usually performed by using typical meteorological year (TMY) data and a constant hot water demand profile. Such applications can be seen in [1,2].

The proper sizing of the components of a solar system is a complex problem, which includes both predictable (collector and other performance characteristics) and unpredictable (weather data) components. For the modeling and simulation of the systems presented in this paper, the well — known TRNSYS program is employed [3]. This program is considered as the most accurate for modeling of solar systems.