Optimizarea modului de estimare a eficienţei panourilor solare
Finding the optimal way to estimate the solar panels efficiency

Author(s): Horaţiu Gabriel DRAGNE
Subject(s): Architecture
Published by: INCD URBAN-INCERC
Keywords: solar panels; efficiency; optimisation
Summary/Abstract: The use of solar thermal panels can make a significant contribution to meeting the demand for heat in residential buildings as a renewable energy source at affordable prices and is therefore an appropriate source of energy for low-energy houses and passive houses. The purpose of this study is to determine if there are defects and deficiencies in design, installation and to analyze the consequences for the energy performance of the solar panels. The experiences of this campaign will then form a basis to determine as accurately as possible the actual performance of the system using thermal solar panels. In 2015 a solar panel was installed in the Thermo-technology Laboratory of the Faculty of Engineering of Installations in Bucharest, which provides thermal heating and domestic hot water. The experimental campaign that has been running since May 2016 shows a considerably lower performance of solar collector performance than intended. In addition, a gravity-driven circulation is suspected due to temperature differences in the collector circuit even if the pump does not work, which leads to energy loss. The project allows the production of domestic hot water and thermal space heating by means of a closed-loop solar system consisting of solar panels, storage tanks, solar pumping groups, anti-freeze heating elements, containing the following: flat plate solar panel with a gross surface area of 2.5 m, optical yield of 75%, coef. thermal transfer with the environment k = 4.15 W / m2K, the panel inclination is 30 °; slide holders for solar panels; 120 l storage tank and 24 kW thermal input; solar pump group (3 speed pump, one way valve, deaerator, flow and return thermometers, flowmeter, pressure gauge, safety valve, expansion vessel connection, manual pump filling system connection); expansion tank of 10 liters; drain valve; automatic air vents; impurities filter; the solar circuit is made of externally insulated copper pipes with a 4 cm insulation; the secondary discharge circuit consists of externally insulated copper pipes with a 4 cm insulation, a circulation pump and a convector valve; working fluid (glycol) to gel at temperatures below -25 ° C (outdoor coverage temperature). From the start of its operation in 2015, the preliminary measurements suggest that the solar panel has a slightly lower performance than that given by the manufacturer. The objective of this paper was to determine possible faults and weaknesses both in the design and operation of the system and in determining the closest possible reality to the solar collector. To this end, the functioning and performance of the investigated system was studied. this was made by collecting and processing the measured data available in connection with an ongoing study. Determinations have been made to obtain the efficiency of the solar collector in a linear form, and the precision of this method has been improved by the quadratic method. The results show that collector efficiency has diminished during operation, which was expected, the system operating at lower yields than in the design, the most important factor being the diminishing efficiency of the solar panel. It can be concluded that although the potential for increasing solar utilization is considerable, whatever changes the system brings, it has to be evaluated according to the additional costs. Furthermore, the results demonstrate the importance of researching the potential factors for performance reduction already during the design phase. Once the system is installed, it is just as important to ensure proper monitoring of system operation control. The square shape determined to appreciate the performance of the solar panel has a high degree of confidence and shows its operation very close to its reality. If all the factors of the system (including climatic ones) are taken into account, it is possible to determine the energy balance of the system that should correspond to the reality as much as possible. The assessment of the solar collector performance becomes more accurate as a result of the measurements in this paper.

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