Objective
Many demonstration projects have shown, that PV systems deliver considerably less energy (up to 30 % in the German '1000-Dächer-Programm') in outdoor conditions than is expected by an estimation from the installed peak power. A reliable and precise estimation of the energy delivered by the power generating module is the most fundamental input information for the design of any PV system. Generally, the use of an energy rating concept under realistic reporting conditions will promote PV by reducing costs and attaining a higher reliability. To facilitate this, a European map of realistic PV efficiencies will be set up on the basis of European Test Reference Years. This European map of realistic efficiencies will give information on the site- and climate-dependent performance of PV-modules at European sites. On the basis of theses data generator sizes for PV systems can be easily designed. For the first time, a European energy rating scheme for PV modules will be established.
Many PV demonstration projects exhibit a poorer performance at the test site as is to be expected by a calculation of the installed peak power, only. A considerable contribution (30 %...50 % of the 'total losses' in the German '1000 Dächer Programm') is due to the performance deviations of PV modules dependent on the meteorological conditions as in comparison with the peak power rating at STC. For example, many PV modules work less efficient for irradiances below the Standard Reporting Conditions point (1000 W/m2 global irradiation). This bright irradiance is only seldomly encountered in Europe and never occurs, when annual or monthly averages are considered. Similar losses are present, when temperature effects are taken into account. Again, the 25° C STC temperature is an unrealistic operational temperature for outdoor conditions. PV system designers need a realistic estimation of the obtainable power as a basic input information. That is: the realistic modul efficiencies have to be known. The Fraunhofer ISE RRC concept (module performance ratio at Realistic Reporting Conditions, RRC) provides this valuable information, it is a site-dependent energy rating concept. The deviations between the realistic performance and the idealised STC efficiencies of solar cells can be classified as caused by 4 single effects: G-effect, that is: the different irradiance G encountered during the time period under investigation (a month or a year) cause a different physical performance of the solar cell as compared to STC. T-effect, that is: working cell temperatures differ often from the STC specification of 25°C and may have a strong influence on cell behaviour. E-effect, as caused by differences between the spectral distribution of the irradiation light and the AM1.5 spectrum of the SRC peak rating. R-effect, i.e. the influence of the light incidence angle for tilted systems.
The following tasks are part of the project: Attempt to set up a classification scheme for existing modules due to material, temperature coefficient, NOCT, etc. Investigation of a possible reduction of input parameters for RRC calculations (FhG-ISE). Compilation of the European map of effective RRC efficiencies and development of a computer program (FhG-ISE). Proliferation of a large data base from module measurements (GENEC). Preparation of the applicabalibility of the European Solar Radiation map as meteorological input data set for the RRC map (PRE).
Due to our experience with the behaviour of smaller solar elements the following parametrisation is expected: Meteorological characterisation on the basis of the European Test Reference Years TRY. Module characterisation (at each location): classification scheme according to material (amorphous, crystalline, polycristalline silicon), temperature coefficient, NOCT (i.e.: the thermic behaviour) and irradiance-dependent performance of the module. Modifying factors, that may account for different manners of installation (tilt angle, thermal properties, specific properties of reflection relying on installation etc.). These information will be compiled in tables indicating yearly and monthly effects for every location.
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79100 Freiburg
Germany