Thermal Evaluation of a Solarus PV-T collector

Low concentrator PV-T hybrid systems produce both electricity and thermal energy; this fact increases the overall efficiency of the system and reduces the cost of solar electricity. These systems use concentrators which are optical devices that concentrate sunlight on to solar cells and reduce expensive solar cell area. This thesis work deals with the thermal evaluation of a PV-T collector from Solarus.Firstly the thermal efficiency of the low concentrator collector was characterized for the thermal-collector without PV cells on the absorber. Only two types of paint were on the absorber, one for each trough of the collector. Both paints are black one is glossy and the other is dull,. The thermal efficiency at no temperature difference between collector and ambient for these two types of paint was 0.65 and 0.64 respectively; the U-value was 8.4 W/m2°C for the trough with the glossy type of paint and 8.6 W/m2°C for the trough with dull type of paint. The annual thermal output of these two paints was calculated for two different geographic locations, Casablanca, Morocco and Älvkarleby, Sweden.Secondly the thermal efficiency was defined for the PV-T collector with PV cells on the absorber. The PV cells cover 85% of the absorber, without any paint on the rest of the absorber area. We also tested how the electrical power output influences the thermal power output of the PV-T collector. The thermal and total performances for the PV-T collector were only characterized with reflector sides, because of the lack of time we could not characterize them with transparent sides also.

Physiological demands of competitive elite cross-country skiing

Introduction Researchers have, for decades, contributed to an increased collective understanding of the physiological demands in cross-country skiing; however, almost all of these studies have used either non-elite subjects and/or performances that emulate cross-country skiing. To establish the physiological demands of cross-country skiing, it is important to relate the investigated physiological variables to the competitive performance of elite skiers. The overall aim of this doctoral thesis was, therefore, to investigate the external validity of physiological test variables to determine the physiological demands in competitive elite cross-country skiing. Methods The subjects in Study I – IV were elite male (I – III) and female (III – IV) cross-country skiers. In all studies, the relationship between test variables (general and ski-specific) and competitive performances (i.e. the results from competitions or the overall ski-ranking points of the International Ski Federation (FIS) for sprint (FISsprint) and distance (FISdist) races) were analysed. Test variables reflecting the subject’s general strength, upper-body and whole-body oxygen uptake, oxygen uptake and work intensity at the lactate threshold, mean upper-body power, lean mass, and maximal double-poling speed were investigated. Results The ability to maintain a high work rate without accumulating lactate is an indicator of distance performance, independent of sex (I, IV). Independent of sex, high oxygen uptake in whole-body and upper-body exercise was important for both sprint (II, IV) and distance (I, IV) performance. The maximal double-poling speed and 60-s double-poling mean power output were indicators of sprint (IV) and distance performance (I), respectively. Lean mass was correlated with distance performance for women (III), whereas correlations were found between lean mass and sprint performance among both male and female skiers (III). Moreover, no correlations between distance performance and test variables were derived from tests of knee-extension peak torque, vertical jumps, or double poling on a ski-ergometer with 20-s and 360-s durations (I), whereas gross efficiency while treadmill roller skiing showed no correlation with either distance or sprint performance in cross-country skiing (IV). Conclusion The results in this thesis show that, depending on discipline and sex, maximal and peak oxygen uptake, work intensity at the lactate threshold, lean mass, double-poling mean power output, and double-poling maximal speed are all externally valid physiological test variables for evaluation of performance capability among elite cross-country skiers; however, to optimally indicate performance capability different test-variable expressions should be used; in general, the absolute expression appears to be a better indicator of competitive sprint performance whereas the influence of body mass should be considered when evaluating competitive distance performance capability of elite cross-country skiers.