Potential energy cost and footprint reduction in Mediterranean greenhouses by means of renewable energy use

Greenhouses are intensive agricultural systems and require optimum combination of solar lighting, heating, cooling and ventilation. Various methods are suggested for the control of internal space factors of greenhouses but require significant amount of energy. Photovoltaics integrated in the greenhouse roof could be used to supply a part of this energy with no significant effect on greenhouse crop yield. Accordingly, aim of this work is to present the potential reduction of the cost of energy needed for greenhouse heating and cooling in southern European and Mediterranean regions, by implementing renewable energy sources. Furthermore, the potential carbon footprint reduction resulting when using renewables compared to conventional energy sources is also studied. Thus, the integration of a PV system on the greenhouse roof for electricity production was studied and the effects on energy needs and greenhouse environmental impact were considered. Two case studies were considered for a 1 ha tomato greenhouse in central Greece: (a) covering a small percentage of the greenhouse roof (0.65%) by a PV system of about 10 kWp and (b) covering about 6.5% of the greenhouse roof by a PV system of 100 kWp. It was found that a PV system covering only 6.5% of the roof surface could be enough to completely cover the electricity needs for the auxiliary processes of a greenhouse. The estimated PV electricity production could reduce the life cycle impact of a greenhouse by 5-10%

Passive and Low Energy Cooling 977 for the Built Environment

ABSTRACT The fresnel lens concept is suggested for solar control of the building in order to keep the illumination and the interior temperature at the comfort level. The collection of 60%-80% of the transmitted solar radiation through the fresnel lens on linear absorbers leaves the rest amount to be distributed in the interior space for the illumination and thermal building needs. The fresnel lenses can be combined with Thermal, Photovoltaic, or hybrid type Photovoltaic/Thermal small width absorbers to extract the concentrated solar radiation in the form of heat, electricity or both. Laboratory scale experimental results are presented in the paper, giving an idea about the application of this new optical system for lighting and cooling control of buildings

Development of a Seawater-proof Hybrid Photovoltaic/thermal (PV/T) Solar Collector

AbstractHybrid photovoltaic/thermal (PV/T) systems provide both electrical and thermal energy. The development of seawater-proof PV/T systems can enlarge the, by now, very limited PV/T application fields to a new one: sustainable reverse osmosis (RO) desalination. There, the PV/T systems’ disadvantage of heat at low temperature level can redound to its advantage: the RO freshwater output is increased at elevated seawater temperatures while the PV efficiency is improved due to cooling with seawater. In this paper, the development of a novel seawater-proof PV/T system with the aim of low cost and high electrical and thermal performance is presented. Low-cost is achieved by using standard components combining a polypropylene thermal absorber with a commercial PV system. Experimental investigations on a PV/T prototype include thermal and electrical efficiency characterization at different fluid temperature levels, mass flow rates and ambient conditions. The results are compared the state-of-the-art PV/T systems

Building implementation of photovoltaics with active control of temperature

Paper explores the building implementation of photovoltaics with active control of temperature

CPC Solar collectors with flat bifacial absorbers

Summarization: The design, construction and test results of non-evacuated stationary CPC solar collectors with flat absorbers are presented and discussed. The proposed collector design is based on a truncated asymmetric CPC reflector, consisting of a parabolic and a circular part. A flat bifacial absorber is installed at the upper part of the collector, parallel to the glazing to form a thermal trap space between the reverse absorber surface and the circular part of the mirror. Two prototypes based on the same collector geometry were constructed and tested. The first model consists of one mirror–absorber unit and the second of three smaller units integrated in one collector device. The truncated CPC mirror and the installation of the absorber parallel to the glazing keep the optical efficiency at a satisfactory level. The reduction of radiative thermal losses by using selective absorbers and the suppression of convection thermal losses from the reverse absorber surface to the collector cover result to a significant decrease of the total collector thermal losses. The experimental results showed that the proposed CPC collector could achieve a maximum efficiency of 0.71 and a stagnation temperature of about 180°C, with the multiunit collector device being more efficient and practical.Παρουσιάστηκε στο: Solar Energ

Cost effective asymmetric CPC solar collectors

Summarization: Low cost CPC solar collectors were designed, constructed and tested. The collectors consist of two separate absorbers, which are horizontally incorporated in a stationary asymmetric CPC mirror. The efficient operation of the proposed collectors is due to the direct absorption of a large part of the incoming solar radiation and to the thermal losses suppression by the inverted surface of both absorbers. Two collector types with the same basic design are presented. The first type has tubular absorbers which are used for direct water heating and the second has flat fin type absorbers with pipe. Test results showed that the proposed collectors operate efficiently and are suitable for hot water applications.Παρουσιάστηκε στο: Renewable Energ

Temperature fields for double glazings under partial shading

Μη διαθέσιμη περίληψηNot available summarizationΠαρουσιάστηκε στο: 1st TMR Users Workshop, TMR Programm