PV Modules

The recent trends in crystalline Si-based bifacial cell development are having a major impact on interconnection technology. This paper presents an overview of various bifacial interconnection technologies.

This paper reports on the latest advances in passivated emitter and rear cell (PERC)-based shingled solar cell activities at Fraunhofer ISE. The approach taken is to fabricate 6" host wafers from Czochralski-grown silicon and separate them after metallization and contact firing into bifacial p-type shingled passivated edge, emitter and rear (pSPEER) solar cells.

Solar modules with half-size solar cells have the potential for becoming the new standard. The cutting of cells leads to electrical recombination losses at the cell level, which are more than compensated by reduced resistive losses as well as by current gains at the module level. At the same time, the cutting process must be optimized to avoid mechanical damage that could lead to cell breakage in the module. Module design opportunities for hot-spot protection, shading resistance and energy yield optimization are presented in this paper. Module power can be increased by 5–8%, which justifies the investment in additional equipment for cell cutting, stringing, lay-up and bussing. Half-cell technology is highly attractive for new solar module production capacity.

Bifacial cells and modules collect light falling not only on the front side of the panels but also on the rear; this additional collection of light increases the total absorbed irradiance, and accordingly the generated current. One of the remaining questions is: what temperature do bifacial solar panels operate at compared with monofacial panels? The extra light absorption at the rear will heat up the modules more, but at the same time, the parasitic heating by the absorption of infrared light is reduced, because infrared light is mostly transmitted through the glass–glass panels. In this paper, different bifacial and monofacial cell and module architectures are considered for the calculation of the energy spectra for all heat loss and absorption processes and the effective heat input. The heat transfer coefficients and the heat capacities of modules with different rear panels are given. Actual module temperatures for different layouts are presented and discussed for low- and high-irradiance (diffuse/direct) conditions in the Netherlands.

In an exclusive preview of a forthcoming paper in PV Tech Power, LONGi Solar and Huawei present their analysis from a bifacial project in the Middle East.

Bifacial PV promises a significant reduction in the levelized cost of electricity (LCOE) for PV systems, which, compared with efficiency improvements at the cell level, is still achievable with comparatively moderate effort. Almost all major PV module suppliers have bifacial modules in their product portfolios or have announced production. This paper gives an overview of the currently available bifacial modules and cell technologies and the performance of these modules. Special attention is given to the cells and the layout of the modules, including light trapping and interconnection technologies, the encapsulation materials and the adapted mounting solutions. Finally, an outlook is given on the basis of the compiled information.

In the evolution towards higher cell efficiencies, new cell concepts (twosided and back contacted) have been introduced and for each of these concepts, new module materials and interconnection technologies have to be developed to fulfil all the demands of a good end product in terms of lowest costs, highest yield and power and above all superior quality (reliability and durability). There is no single module concept that fits all cell concepts or module application type so existing module concepts need to be adapted or innovative module technologies are required to fit the aforementioned requirements. This paper provides an overview summarizing the recent developments of integrated cell to module manufacturing approaches such as multi-busbar, multi-wire, half-cell and shingling technologies for two-side contacted cells and advanced soldering, woven fabric and foil based module technologies for back contacted cells aiming for the highest power outputs, lowest costs and longest lifetimes.

The extra energy gain offered by bifacial PV modules has helped make them an increasingly popular choice in the global PV industry. But the question of how to define, measure and rate the electrical output from bifacial modules is a hotly debated topic, given the extent to which the rear-side contribution is dependent on a range of variable factors relating to local environmental conditions and system configurations. Drawing on in-house modelling and simulation software developed at TÜV Rheinland, this paper explores the power rating issue for bifacial devices, examining the definitions of rear irradiance, measurement test method, power stabilization and verification for type approval. Relevant reliability and safety tests are discussed, with additional modifications and suggestions for bifacial PV modules.

Crystalline silicon heterojunction (HJT) solar cells and modules based on amorphous silicon on monocrystalline wafers offer advantages over established wafer-based technologies in terms of efficiency potential, complexity of the manufacturing process, and energy yield of the modules. The temperature sensitivity of these solar cells, however, poses considerable challenges for their integration in modules. Currently, there exist three approaches for the interconnection of HJT solar cells, each with its own strengths and weaknesses: 1) ribbon soldering with low-meltingpoint alloys; 2) gluing of ribbons by using electrically conductive adhesives (ECAs); 3) SmartWire Connection Technology (SWCT).

Leading PV inverter manufacturer Huawei discusses recent technical developments to a better understanding of bifacial solar module PV power plants, using three recent case studies. These efficient PV modules need to be used with devices such as inverters to maximize value. Recently, many inverters and solutions that match bifacial modules have appeared in the industry. Which solution is the best match for bifacial modules? Based on a large amount of experimental data, this article describes the solution needed for bifacial modules.