In this study, we investigate the performance ratio (PR) of about 100 German photovoltaic system installations. Monitored PR is found to be systematically lower by~2-4% when calculated with irradiation data obtained by pyranometers (henceforth denoted as PR Pyr ) as compared with irradiation amounts measured by reference cells (denoted as PR Si ). Annual PR Si for the~100 systems is found to be between~70% and~90% for the year 2010, with a median PR of~84%. Next, simulations were performed to determine loss mechanisms of the top 10 performing systems, revealing a number of these loss mechanisms may still allow for some optimization. Despite the fact that we do not see such values from our monitoring data base up to now, we believe PR Si values above 90% are realistic even today, using today's commercially available components, and should be expected more frequently in the future. This contribution may help in deepening our knowledge on both energy loss mechanisms and efficiency limits on the system level and standardization processes of system-related aspects.

Measured and modelled JV characteristics of crystalline silicon cells below one sun intensity have been investigated. First, the JV characteristics were measured between 3 and 1000 W/m 2 at 6 light levels for 41 industrially produced mono-and multi-crystalline cells from 8 manufacturers, and at 29 intensity levels for a single multi-crystalline silicon between 0.01 and 1000 W/m 2. Based on this experimental data, the accuracy of the following four modelling approaches was evaluated: (1) empirical fill factor expressions, (2) a purely empirical function, (3) the one-diode model and (4) the two-diode model. Results show that the fill factor expressions and the empirical function fail at low light intensities, but a new empirical equation that gives accurate fits could be derived. The accuracy of both diode models are very high. However, the accuracy depends considerably on the used diode model parameter sets. While comparing different methods to determine diode model parameter sets, the two-diode model is found to be preferred in principle: particularly its capability in accurately modelling V OC and efficiency with one and the same parameter set makes the two-diode model superior. The simulated energy yields of the 41 commercial cells as a function of irradiance intensity suggest unbiased shunt resistances larger than about 10 kO cm 2 may help to avoid low energy yields of cells used under predominantly low light intensities. Such cells with diode currents not larger than about 10 À9 A/cm 2 are excellent candidates for Product Integrated PV (PIPV) appliances.

Solar cell performance parameters (open circuit voltage, short circuit current, fill factor and efficiency) are derived for different solar cell types for the irradiance range 0.1e1000 W/m 2. Also it is demonstrated how spectral mismatch factors for indoor lighting conditions are calculated. The presented methods and particular results may aid product designers in selecting appropriate solar cells for Product Integrated PV (PIPV) operated indoors and allow for more certainty in energy balance estimations of PIPV design concepts.

The direct and indirect emissions associated with photovoltaic (PV) electricity generation are evaluated, focussing on greenhouse gas (GHG) emissions related to crystalline silicon (c-Si) solar module production. Electricity supply technologies used in the entire PV production chain are found to be most influential. Emissions associated with only the electricity-input in the production of PV vary as much as 0-200 g CO 2 -eq per kWh electricity generated by PV. This wide range results because of specific supply technologies one may assume to provide the electricity-input in PV production, i.e., whether coal-, gas-, wind-, or PV-power facilities in the ''background'' provide the electricity supply for powering the entire PV production chain. The heat input in the entire PV production chain, for which mainly the combustion of natural gas is assumed, adds another $16 CO 2 -eq/kWh. The GHG emissions directly attributed to c-Si PV technology alone constitute only $1-2 g CO 2 -eq/kWh. The difference in scale indicates the relevance of reporting ''indirect'' emissions due to energy input in PV production separately from ''direct'' emissions particular to PV technology. In this article, we also demonstrate the utilization of ''direct'' and ''indirect'' shares of emissions for the calculation of GHG emissions in simplified world electricity-and PV-market development scenarios. Results underscore very large GHG mitigation realized by solar PV toward increasingly significant PV market shares.

In this paper, we show that photovoltaic (PV) energy yields can be simulated using standard rendering and ray-tracing features of Computer Aided Design (CAD) software. To this end, three-dimensional (3-D) sceneries are ray-traced in CAD. The PV power output is then modeled by translating irradiance intensity data of rendered images back into numerical data. To ensure accurate results, the solar irradiation data used as input is compared to numerical data obtained from rendered images, showing excellent agreement. As expected, also ray-tracing precision in the CAD software proves to be very high. To demonstrate PV energy yield simulations using this innovative concept, solar radiation time course data of a few days was modeled in 3-D to simulate distributions of irradiance incident on flat, singleand double-bend shapes and a PV powered computer mouse located on a window sill. Comparisons of measured to simulated PV output of the mouse show that also in practice, simulation accuracies can be very high. Theoretically, this concept has great potential, as it can be adapted to suit a wide range of solar energy applications, such as sun-tracking and concentrator systems, Building Integrated PV (BIPV) or Product Integrated PV (PIPV). However, graphical user interfaces of 'CAD-PV' software tools are not yet available.

A solar powered wireless computer mouse (SPM) was chosen to serve as a case study for the evaluation and optimization of industrial design processes of photovoltaic (PV) powered consumer systems. As the design process requires expert knowledge in various technical fields, we assessed and compared the following: appropriate selection of integrated PV type, battery capacity and type, possible electronic circuitries for PV-battery coupling, and material properties concerning mechanical incorporation of PV into the encasing. Besides technical requirements, ergonomic aspects and design aesthetics with respect to good ''sun-harvesting" properties influenced the design process. This is particularly important as simulations show users can positively influence energy balances by ''sun-bathing" the PV mouse. A total of 15 SPM prototypes were manufactured and tested by actual users. Although user satisfaction proved the SPM concept to be feasible, future research still needs to address user acceptance related to product dimensions and user willingness to pro-actively ''sun-bath" PV powered products in greater detail.

The main purpose of PV system performance monitoring is to determine whether the system is operating as expected. This requires measuring the actual output of the system as well as the conditions under which it is operating. Solar radiation intensity in the plane of the array (POA) is by far the most important operating condition and is the basis for calculating performance ratios (PR). However, differences in spectral and directional response between pyranometers and PV modules lead to intraday as well as seasonal fluctuations in the performance ratio, even though the system may be operating without faults or degradation. For c-Si PV systems, a reference cell can be used instead of (or in addition to) a pyranometer to measure POA irradiance. Since reference cells have spectral and directional responses that are similar to PV modules, their output signals correlate better with system output. As a result, it is becomes easier to identify abnormal system operation. In this paper, we present a practical alternative to using a spectrally matched reference cell for measuring POA irradiance. The method uses dual sensors with different spectral responses whose outputs are combined to produce a composite signal. That composite signal can effectively match the spectral response of any PV module type over a wide range of irradiance conditions. As a result, this method makes possible the rapid and accurate detection of abnormal system operation for thin-film systems

An overview on quality assurance measures for large-scale PV power plants is given. Areas discussed include yield assessment, module testing and power rating, on-site system testing and yield monitoring. In addition, we present a procedure for the analysis of module and system long-term stability using performance monitoring data of systems. For PV systems with standard c-Si modules, calculated rates of change in the initial 5-7 years are statistically insignificant. Although this gives confidence about the fairly good long-term stability of c-Si modules, longer monitoring durations may be needed in order to address degradation rates by monitoring data analysis. Concerning PV performances more generally, today's high Performance Ratio is proof that solar PV has matured into both a highly reliable and well-performing technology