Solar heating in Greenland : Resource assessment and potential

Abstract

Solar energy is a clean and natural energy source. The solar radiation on earth – including at Arctic latitudes – is so large that it is possible to utilize solar energy on a large scale. Using solar energy means reducing the use of fossil fuels. The use of solar energy varies from country to country, as does the design of the solar heating systems. The purpose of this study is to investigate the solar radiation potential in Greenland, and to investigate how a solar heating system for Greenland should be designed. In the Arctic several conditions must be taken into account in terms of solar radiation at these latitudes. The sun is positioned low on the sky, which means that the optimum tilt angle of a receiving surface will increase. Also most solar radiation appears in the summertime, where there, at latitudes above the Arctic Circle, is solar radiation 24 hours a day and radiation from all directions. The reflection from the snow will increase the solar radiation on tilted surfaces. The potential of utilizing solar radiation is evaluated based on measurements from several different climate stations in Greenland. An investigation of solar radiation models and their suitability for locations in Greenland is carried out. The investigation analyses the diffuse correlation methods developed by ‘Erbs et al.’ and ‘Orgill and Hollands’. The results show that the two correlations both underestimate the diffuse radiation and overestimate the beam radiation, with ‘Orgill and Hollands’ as the most accurate. Further an investigation of four different radiation models is carried out and shows that they are not suitable for the conditions in Greenland. Of the four models the ‘Liu and Jordan’ model - the simple isotropic model - is the most accurate. In Sisimiut measurements of the total radiation and the ground reflected radiation have been carried out since 2003. This data provides the basis for an investigation of the reflection coefficient for the ground for periods with and without snow. The measurements show that snow reflects solar radiation like a mirror. The effective albedo is therefore given as a function of the difference between the solar azimuth and the surface azimuth. Equations for the effective albedo is determined for each month of the year based on the measurements, and can be used as input for simulation models. The solar heating systems respectively in the Low Energy House and at the Knud Rasmussen Folk High School in Sisimiut have both provided practical experience of operation and performance of solar heating systems in an Arctic climate. Experience from the installation and repair of the systems showed that trained installers are of vital importance to insure a good performance of the systems. The operation of the solar heating system at the Low Energy House showed that thermosyphoning was a problem during the cold winter months. This is now prevented by a magnetic valve controlled by the pump in the solar collector loop. The system in the Low Energy House has over the course of five years undergone several changes to improve the performance of the system. At present further improvements are still possible regarding utilising the energy from the solar heating system in the space heating loop. The thermal performance of the system at the Knud Rasmussen Folk High School has not reached its optimum potential which is partly due to an electrical error. Measurements from the system have shown that the system is capable of covering most of the hot water consumption for four months during the summer, while also providing energy to the space heating loop. Both systems have pressurised solar collector loops with an expansion vessel, and have proved that this design works well under Arctic conditions, where power-outage is more frequent.