Dragsted, Janne

Energi fra solen er en ren og naturlig energikilde. Solstrålingen på jordens overflade – inklusive i det Arktiske klima – er så stor, at det er muligt at udnytte solens energi i stor skala. Ved at udnytte solens energi nedsættes brugen af fossile brændstoffer. Anvendelsen af solenergi varierer fra land til land, lige som udformningen af et solvarmeanlæg.Formålet med dette forskningsprojekt er at undersøge solstråling i Grønland og undersøge, hvordan et solvarmeanlæg bør udformes til brug i Grønland.I det Arktiske klima er der flere faktorer som gør sig gældende i forhold til solstrålingen ved disse breddegrader. Solen står lavere på himlen, hvilket bevirker at den optimale hældning på en flade er større. Størstedelen af solstrålingen forekommer om sommeren, hvor der ved breddegrader over denArktiske Cirkel er solstråling 24 timer i døgnet og stråling fra alle retninger. Reflektion fra sneen øger endvidere solstrålingen på en hældende flade.Potentialet for anvendelsen af solenergi bliver undersøgt på basis af målinger fra flere forskellig målestationer i Grønland. Derudover undersøges solstrålingsmodeller i relation til deres egnethed på Grønland. Den diffuse korrelation udviklet af ’Erbs et al.’ og ‘Orgill and Hollands’ bliver undersøgt.Resultatet viser, at begge korrelationer overvurdere den diffuse stråling og overvurderer den direkte solstråling. ’Orgill and Hollands’ er dog den mest præcise. Derudover bliver fire forskellige strålingsmodeller undersøgt, og resultatet viser, at de ikke er anvendelige på forholdene i Grønland. Afde fire modeller er ’Liu and Jorden’s model – den simple isotropiske model – dog den mest præcise.Siden 2003 er der i Sisimiut udført målinger af den totale solstråling og den reflekterede solstråling. Disse målinger danner baggrund for undersøgelsen af reflektionskoefficienten både med og uden snedække. Målingerne viser, at sne reflekterer solstrålingen som et spejl. Den effektive albedo bliver givet som enfunktion af forskellen mellem solens azimut og fladens azimut. Funktionerne for den effektive albedo bliver bestemt på månedsbasis på baggrund af målingerne og kan anvendes som input i simuleringsmodeller.Solvarmeanlæggene i henholdsvis Lavenergihuset og på Knud Rasmussen Højskolen i Sisimiut har tilvejebragt praktisk erfaring med drift og ydelse af solvarmeanlæg i et Arktisk klima. Erfaringen fra installation og reparation af anlæggene har vist, at det er yderst vigtig at have uddannede installatører forat sikre en god ydelse fra anlæggene. Driften af solvarmeanlægget i Lavenergihuset viser, at selvcirkulation er et problem i de kolde vintermåneder. Dette er nu forhindret ved at installere en magnetisk ventil, der styres af pumpen i solfangerkredsen. Solvarmeanlægget i Lavenergihuset hargennemgået flere ændringer for at forbedre ydelsen. På nuværende tidspunkt er der fortsat mulighed for at forbedre anlægget ved at koble solvarmeanlægget på rumopvarmningen. Anlægget på Knud Rasmussen Højskolen yder ikke optimalt, hvilket til dels skyldes en elektrisk fejl. Målinger viser, at anlægget kan dække størstedelen af varmtvandsbehovet i fire måneder om sommeren samt forsynerumopvarmningskredsen med energi fra solvarmeanlægget. Begge anlæg er installeret med ekspansionsbeholder og solfangerkredse under tryk, hvilket har vist sig at fungere i det Arktisk klima, hvor der oftere forekommer strømsvigt.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

Online Research Database In Technology

Solar heating in Greenland:Resource assessment and potential

http://orbit.dtu.dk/ws/files/6320162/Janne%20Dragsted%20-%20Solar%20heating%20in%20Greenland.pdf

Solar heating in Greenland:Resource assessment and potential

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Online Research Database In Technology