Techno-economic evaluation of voltage dependent active and reactive power control to reduce voltage violations in distribution grids

High penetration of PV plants or numerous electric vehicle (EV) charging station stations connected to the low voltage distribution grids (LVDG) may cause a voltage rise or voltage decrease respectively. There are several measures of maintaining the voltage stability such as grid reinforcement, battery energy storage, line voltage regulator, etc., although they vary in effectiveness and economic viability. This paper focuses on using decentralised voltagedependent active and reactive power (PQ(V)) control of PV inverters to stabilise the voltage in the grid. Using two grid models in Southern Germany and Switzerland the best PQ(V) control strategy is evaluated using load flow calculations. The weakest node in the first grid exhibits a maximum voltage of 1.072 pu on a sunny day. Due to the implementation of the PQ(V) control the maximum voltage is reduced to 1.024 pu at the same node. Costs considered for PQ(V) control are the PV yield loss and the additional reactive power compensation, which amount to roughly CHF 2’600.- per year. The future installation of EV charging stations may positively interact with PV feed-in. The voltage decrease can further be limited using PQ(V) control. Further grids and means for voltage stabilisation will be analysed in the future

Performance analysis of PV modules installed in the alpine region

Several mono- and bifacial mc-Si PV modules were installed at a location 2500 m above sea level in the Alps and grouped in six segments with different inclinations 30°, 70° and 90°. The PV modules and the meteorological conditions are monitored minutely and compared to a 30° tilted PV module installed in the urban region of Zurich. During the analysis period between October 2018 and September 2020, the yield loss due to snow coverage was mini-mal. The highest loss was 2.3 % (2018/19) and 3.6 % (2019/20) for the 30° inclined PV modules evaluated by the introduced snow coverage model based on electrical and weather data. The two segments with a 30° inclination showed a 20.9 % to 27.2 % higher yield than the PV module installed in the urban region, mostly produced in the winter season. The bifacial alpine energy yield is about twice as high as that of the urban PV module from November to May. The highest yields of 1800 Wh/Wp in 2018/19 and 1696 Wh/Wp in 2019/20 was measured at the 70° tilted bifacial PV module without losses due to row shading as it is expected in PV plants

New PV system concept : inductive power transfer for PV modules

The proposed new PV system concept is based on several AC modules that are connected in series using inductive power transfer. These modules include a cell matrix that is connected to a module integrated DC/AC inverter. The high frequency AC current flows through the primary side planar coil generating a magnetic flux. Outside of the PV module, there is a clamp including ferromagnetic material for the magnetic circuit that caries the magnetic flux to the secondary winding. The magnetic flux induces an AC current in the secondary winding, which is formed by the common cable. An AC/AC converter is placed at the end of the PV module strings to generate the 50 Hz and to connect the PV power plant to the electricity grid. This new PV system concept is a fundamentally new approach of the electricity transmission in the field of PV system technology. It is not restricted to the replacement or optimisation of an individual system component, but it requires the continuing development of the PV module construction and the contactless connection technology to the common cable. The proposed inductive power transfer per each PV module opens up a complete new field for the PV system technology

Investigation of local voltage control solutions for the integration of renewable power sources into the low-voltage networks

​© 2020 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.This paper is devoted to the problem of voltage limits violations in low-voltage networks with high share of photovoltaic power plants and provides a vision and comparison of different technologies based on their advantages and disadvantages and classification of technical methods for performing cost effective control in the various distribution grids categories. It was carried out based on the proposed methodology, which covers a wide range of technical solutions, to have a clear comparative analysis between different solutions. Technical and economical comparison between the results gained from the load flow calculations in Matpower and the additional functionalities provided from the OpenDSS were used to classify smart grid solutions for various low voltage distribution grids categories and to generate the ranking matrix

Long-term power degradation analysis of crystalline silicon PV modules using indoor and outdoor measurement techniques

Annual degradation rates of PV modules are important in the yield prediction. For a high-quality PV module, these rates are lower than the measurement uncertainty of a nominal power measurement performed in todays most advanced certified photovoltaic reference laboratory. Therefore, the analysis requires a well thought out methodology that can compare the data relative to each other or relative to an unused module stored in the dark on an annual base. Over the past 10 years, several multi c-Si and HIT modules have been accurately monitored in a string and single module setup by an outdoor performance measurement system. Additionally, all modules have been dismantled and measured using an indoor flasher measurement system once every year. With this unique measurement setup, the annual degradation rates of multi c-Si modules and HIT modules are quantified based on three different analysis methodologies. The multi c-Si modules showed an average annual degradation rate of 0.18% ± 0.06% and 0.29% ± 0.06% measured by the outdoor and indoor system, respectively. The indoor analysis of the HIT modules yielded an average annual degradation of 0.26% ± 0.05%. That corresponds to half of the degradation observed by the outdoor analysis method. Further evaluations of the performance ratio PR confirmed the results gained by the indoor methodology. The comparison of the standard PR with a temperaturecorrected PR’STC for both technologies showed that the benefit of the lower temperature coefficient of the HIT technology is eliminated by its worse low light behaviour

Performance analysis of shaded PV module power electronic systems

Video of the talk is available at: https://youtu.be/NlLg1MOyvWgIn the last decade decentralized Modul Level Power Electronics (MLPE) equipment has gained tremendous market share due to the potential to operate each Photovoltaic (PV) module in their optimum power point even in partial shading condition. The total losses of the group of decentralised DC/DC converter combined with the coupled centralised DC/AC inverter not always offer an advantage to the standard String Inverter System (SINV), like in the unshaded moments of high-power operation of a PV system at noon. The customer expects a clear answer about the quantified gain in annual power of a roof top system either operated by MLPE or SINV. Today, even the experienced planner is not able to elaborate these numbers in an economic efficient way. This is the case due to a lack of complex geometrical data of the shading obstacles and absence of software tools which are able to simulate the MLPE and SINV by calculating the shade of each solar cell in all PV modules together with an appropriate loss model of all used power electronic components. Up to know no standards exist to measure the set of MLPEs in the lab and the manufactures have not proposed detailed loss models up to now, whereas only max efficiency number of the MLPE are stated in their data sheets. This paper shows that detailed loss measurements performed in the lab, provided up to three percent higher losses of the MLPEs in the relevant operation area commonly used through a year of operation. It is recommended to use a very narrow range of numbers of MLPE in the string for high efficiency power conversion, due to the fact, that losses increase by 1.5% if the input/out voltage ratio of MLPE differ 5% from unity. A concept is presented to estimate the final so-called shading adaption efficiency which is based on the efficiency measurement of the MLPE in the indoor lab at a few operation points and by using weighting factors. Thus, the comparison of the shading adaption efficiency is given, either for different MLPEs or SINVs power electronic systems for a typical PV system with shading, relative to the same aggregated sum of maximum decentralised DC power at the PV Modules. Finally, one example of a tilt PV roof top system with partial shading of a chimney is given, were the standard SINV shows 1.2% percent higher losses estimated for a whole year of operation compared to a MLPE system. This value will change if the number of MLPE in the string is modified

PV installations based on vertically mounted bifacial modules evaluation of energy yield and shading effects

Bifacial solar modules promise an increased energy yield, compared to systems with standard, monofacial panels, and also offer new opportunities with regard to the installation. One particular approach is the vertical mounting of PV modules, which is reported to be an effective measure to avoid soiling or dust deposition and is an option to obtain a broadened energy generation profile. In spite of the general interest in this type of installation, the amount of published data is very limited, especially with regard to arrays, for which pronounced shading effects can be expected. In this work we present an analysis of the energy yield and the respective losses for arrays of vertically mounted bifacial solar modules with varied installation conditions

Performance analysis of vertically mounted bifacial PV modules on green roof system

A combination of PV and green roof is an ideal fusion in terms of ecology. The green roof improves the water retention in the city, whereas the PV system produces electric power at the place where it is consumed. Flat tilted modules in south or east west direction on green roofs generally require intensive maintenance to prevent them from being shaded by plants and often cover the roof area to a large extent. Because of the space requirement conflict between PV on the roof and green roofs, it is essential to combine these two systems in a smart way. Vertically mounted bifacial modules can be an option to combine PV and green roof and to also allow a cost-effective maintenance. In this paper we report about the layout and the performance of a corresponding system, subdivided into two groups with differing albedo. Custom made bifacial modules with 20 cells were produced to reduce the wind load and to improve the general appearance. This 9.09 kWp bifacial plant achieved a specific yield of 942 kWh/kWp in one year (11.08.2017 to 10.08.2018). High quality DC power measurement systems are installed to monitor two modules in each bifacial test field and a reference south-facing module. This allows an energy yield comparison between the vertical bifacial test system with east-west orientation and the monofacial south-facing reference over four months of outdoor measurements. The use of plants with good reflective properties, which are also well suited two the ambient conditions on flat roofs, resulted in a yield increase of 17 % compared to a standard green roof planting. The vertically installed bifacial modules obtained an almost identical specific yield (-1.4 %) compared to a stand-alone monofacial southfacing reference module. Due to the increased yield in the mornings and afternoons, the vertical bifacial modules can achieve higher self-consumption depending on the load profile

New PV system concept : wireless PV module prototype

A first wireless PV module prototype is presented. The energy transfer from the solar cells to the string cable is done using the inductive power transfer technology. A half-bridge LLC resonant converter is designed for the DC/AC conversion. The wireless module consists of 60 half-cells and an integrated planar coil. The resonant converter is not yet integrated into the module, but it can be connected externally to the planar coil. The energy is transferred from the primary coil to the secondary planar coil placed outside of the PV module on top of the primary coil. An active rectifier is connected to the secondary coil and it feeds the DC system cable. The first measurements yielded in an efficiency of 88.2 % including the resonant converter, the inductive power transmission and the active rectifier efficiencies. The corresponding output was 207 W