Photovoltaic (PV) inverters increase the line voltage in Distribution Grids (DG) by active power feed in. Today, modern PV inverters are also able to feed in reactive power to mitigate the above voltage rise. The favoured, cost effective implementation is the control of reactive power feed in according to the instantaneous measured line voltage. The stability of this decentralised Q(U) PV inverter closed-loop control is mandatory and analysed in this work. The DG operator must guarantee the voltage limits given in the regulatory framework. This is challenging due to fast changing solar irradiance, load flows and the interaction of an overlying automatic voltage control-loop of a connected substation. The performed tests in the AIT SmartEST laboratory resulted in very stable operation even at small Time Constants (TC) below 5 seconds of the Q(U) control parameter. As one test scenario, an abrupt rise of solar irradiance immediately followed by load drop is realized by use of the PV and load emulators. The PV inverter reduces the resulting voltage rise by increasing its reactive power, depending on the Q(U) control time constant. It was found that even at smaller Q(U) time constants than the typical applied values of 5 or 10 seconds no sign of instability arises. It is recommended to the DG operator to apply TC of 1 or 2 seconds of Q(U) control to minimise the duration of overvoltage condition during the transient voltage adjustment. Applying irradiance conditions of a typical cloudy day in the lab test yields 45% of the time the line voltage was above a given grid voltage limit, while applying Q(U) at TC of 1 second there was no occurrence of overvoltage. In detail at Q(U) TC setting of 20 seconds the overvoltage arises 3.4% of the total period and only 0.3% at TC 5 seconds. Only stable operation conditions were found including the automatic voltage control of the transformer sub-station at a typical setting of 10 seconds delay time of that sub-station control setting. Summarized, in combination with that delay time setting the smaller Q(U) time constant of the PV inverters below 5 seconds are beneficial due to the minimised overvoltage time.
In this paper we present our latest developments in bifacial 6” cells featuring polysilicon carrier-selective passivating contacts which can be seen as an upgrade to bifacial cell architectures such as PERC+ and PERT. In this study we present improvements of p+ polySi passivation on industrially relevant textured surfaces by means of advanced hydrogenation schemes, involving novel dielectric stacked layers, and modification of the B-profile leading to a record passivation level of ~8 fA/cm2 and 724 mV before firing and ~9 fA/cm2 and 722 mV after firing. The results promote industrial implementation of p+ polySi on 6” bifacial cells with excellent passivation properties and compatibility with screen-printed and fire-through metallization, especially as our latest results show Jo,contact being reduced down to 200 fA/cm2. Bifacial solar cells have been manufactured with industry compatible processing with front-and-rear passivating contacts with efficiencies above 20% in the first attempt and this development shows a potential of 23% with a bifaciality factor of 90%.
The simulation of the energy yield of Bifacial PV modules is not straightforward, since most of the light reaching the back side of the PV modules is scattered back from the ground. For tracking systems this is particularly challenging since the geometry is changing as the sun moves through the sky. In PVsyst, a simplified 2D model was introduced to describe bifacial horizontal single axis trackers with regular spacing. The approach uses view factors to model the fraction of light that is scattered back to the back side of the PV modules. The bifacial calculation includes direct and sky diffuse contributions on the back side, as well as ground scattering to the front and back side of the modules.
This work presents the use of a combined measurement system for spectrally-resolved photoluminescence (PL), time-resolved photoluminescence (TRPL) and transient photocurrent decay (TPCD) to characterise the physical properties of solar cells and their materials. A physical model is proposed to quantify the localised carrier collection efficiency of solar cells from the measured localised minority carrier lifetime from TRPL measurements and the localised minority carrier diffusion time from TPCD measurements. A single excitation laser source is used to measure TRPL and TPCD at the same spot on the solar cell. Combined PL, TRPL and TPCD measurements are conducted on a CdS/CdTe and a CIGS sample. The resulting PL spectra for both samples show that the emission spectra can yield information on the material bandgap. TRPL and TPCD yield localised carrier lifetime and diffusion times of τTRPL=3.91ns and τTPCD=40.5ns respectively for the CdS/CdTe sample, and τTRPL=2.45ns and τTPCD=196.8ns respectively for the CIGS sample. The ratio between the τTRPL and τTPCD values is shown to be proportional to the localised carrier collection efficiency, yielding collection efficiencies of 21.97% and 7.93% for the CdS/CdTe and CIGS sample, respectively. The initial results show that the localised carrier collection efficiency may be affected by the sample’s metal contact configuration. In short, this combined measurement approach can offer a novel and useful method of characterising the material quality of solar cells and the localised carrier collection efficiency of finished PV devices.
In the Solar Highways project, knowledge institutes ECN and SEAC, and the executive body of the Dutch Ministry of Infrastructure and the Environment (Rijkswaterstaat) teamed up to build a bifacial fully integrated solar noise barrier. Not only is it the largest solar noise barrier in the Netherlands to date, it will also be the largest bifacial noise barrier in the world. The solar noise barrier will be 400 m long and 5 meters high and will be facing east and west. To achieve the objectives of maximum solar energy output and minimum operation and maintenance costs, we designed and published a procurement based on the principles of ‘Most Economically Advantageous Tender’ (MEAT), enabling the weighing of monetary alongside non-monetary aspects in the same procurement. Six system designs were submitted by contractors. After assessment of all submitted offers in the MEAT framework, the assignment was granted to Heijmans Infra. By submitting a design that enables a high cell coverage ratio together with minimized construction shading, the output is maximized. Smart design features ensure minimum operation and maintenance effort. After commissioning of the installation in December 2018, we will carefully monitor it with respect to energy output and maintenance costs
Good quality images are necessary for electroluminescence (EL) image analysis and failure quantification in solar panels. In this work, a method for determining image quality in terms of more accurate failure detection in PV panels through EL imaging is proposed. The goal of the paper is to highlight the different methods for image quality improvement and to determine if the enhanced image provides more useful diagnostic information for accurate micro cracks and fracture detection. From the work carried out in this paper, it is to be noted that averaging technique helps in improving the SNR value. Additionally, subtracting the background from the obtained averaged EL image proves to be an enhancing method for cell fracture identification and more number of edges are also detected which can be useful for micro crack quantification.
The realization of Building-Integrated Photovoltaics (BIPV) facades with black and blue conventional modules has represented a first step of innovation in the process of PV transfer in sustainable buildings. Nowadays, architects are looking for additional BIPV products to design active facades with novel architectural languages. For this reason, BIPV manufacturers started to customize BIPV modules in order to meet architects and clients’ requirements. However, changing traditional front solar glass to obtain coloured PV, can influence the final module power output. Even though there are already investigations about the reduction of PV energy output due to the front glass aesthetical treatments, there are not yet clear correlations between alternative design options (glass treatments and colours) and their operative conditions as facade elements. This paper is firstly aimed at providing a systematic investigation about novel mono-chromatic BIPV products in order to identify the influence of some main design options on the electro-thermal performances of modules. Specifically, this analysis is performed by evaluating, in collaboration with a Swiss industrial partner, a range of customized mono-chromatic BIPV prototypes by means of indoor measurements and outdoor tests. Furthermore, these results have been used to preliminarily assess the electro-thermal behaviour of multi-chromatic BIPV configurations both at STC and outdoor conditions. As a result, it arises that the operative condition should be carefully considered to qualify the behaviour of multi-chromatic BIPV modules with novel aesthetical designs in order to provide reliable data about the real electro-thermal behaviour.
One major loss mechanism for the currently highly relevant passivated emitter and rear cells (PERC) is locally enhanced recombination at the interface between semiconductor and front side metallization. For investigating these losses in detail, a reliable detection technique is crucial. A method we call calibrated photoluminescence imaging (PLI) method is a promising technique to extract the local dark saturation current density in the metallized area j0,loc. To investigate the sources of error of this method, metallized test samples are processed and the influence of sample specific parameters is considered in detail. Additionally, the difference in the resulting j0,loc between the calibrated PLI method and a simulative approach using numerical PLI simulations (Quokka3) is evaluated. We find that the results from the calibrated PLI method strongly depend on the accurate knowledge of the base resistivity ρB (including the impact of thermal donors) and less strongly on the reflectivity R of the illuminated side of the sample. In addition, metastable defects in the Si bulk can falsify the results, due to changes in the PLI intensity as a function of the illumination time. The difference in the resulting j0,loc between the calibrated PLI method and the simulative approach is within the error tolerances, which implies that the calibrated PLI method delivers accurate results despite the assumption of a uniform Δn throughout the sample. Here, it is important to mention that the non-uniformity of Δn is expected to be stronger for structures without a highly doped region at the investigated side (e.g. PERC rear contacts).
The energy yield of PV systems with horizontal single-axis tracking and bifacial panels was calculated using BIGEYE. BIGEYE is a versatile code developed at ECN part of TNO to calculate the yield of bifacial PV. Comparison to recent measured data with the BIFOROT set-up at the Zurich University of Applied Sciences showed very good agreement. Our BIGEYE results show that the bifacial energy gain and the tracking gain are mostly additive, making the combination of bifacial panels and tracking a very attractive option. For two different locations, Doha and Amsterdam, increases of energy yield in the order of 25% compared to monofacial, fixed tilt systems are possible at relatively modest ground cover values.
