FiT for purpose?

By Liam Stoker, Solar Media

The UK’s small-scale feed-in tariff closed to new applicants earlier this year, forcing policy makers and installers alike to run the rule over new models and legislation. Liam Stoker takes a look at the government’s Smart Export Guarantee and what it might mean for UK solar.

China’s bid to fill policy vacuum

By Carrie Xiao, Solar Media

Slowly but surely, China’s solar policy void is being filled with a 30GW auction at the heart of it. Carrie Xiao digs into the details as the draft proposals take the first steps towards official status.

Regulatory roadblocks ahead for EU subsidy-free solar

By José Rojo, Solar Media

Despite its coming of age from the days of state support, European PV remains at the mercy of regulatory whims. José Rojo examines how bureaucracy, grid bottlenecks and other pitfalls of government action can cripple solar as it becomes the driving force of a clean EU energy system.

Embracing the future

By Representatives from Enel Green Power, Aquila Capital and Pöyry

As outlined on the previous pages, although still relatively embryonic in the solar industry, big data-based analytics innovations are already being deployed. Representatives from Enel Green Power, Aquila Capital and Pöyry discuss where their digitalisation efforts have so far been focused.

Big data and predictive maintenance in PV – the state of the art

By Alessandro Betti; Fabrizio Ruffini; Lorenzo Gigoni; Antonio Piazzi

Big data-based predictive analytics techniques using artificial intelligence technologies offer exciting new possibilities in the field of solar operations and maintenance. Alessandro Betti, Fabrizio Ruffini, Lorenzo Gigoni and Antonio Piazzi examine how the power of data can be harnessed to safeguard the technical and economic performance of the PV fleet.

Codes, standards and certification for safety and performance of distributed energy resources and systems

By Scott Picco, UL; Laurie Florence, UL; Tim Zgonena, UL

The advent of distributed generation and renewable energy sources is requiring a swathe of new regulatory standards to ensure safety and grid stability. Scott Picco, Laurie Florence and Tim Zgonena of UL look at some of the latest and upcoming codes designed to addressing the proliferation of battery storage systems and distributed energy resources.

Half-cell solar modules: The new standard in PV production?

By Jens Schneider; Hamed Hani€; David Dassler; Matthias Pander; Felix Kaule; Marko Turek

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.

Taking the temperature of bifacial modules: Are they warmer or cooler than monofacial modules?

By Bas Van Aken; Gaby Janssen

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.

Efficiency and cost effectiveness of large-area perovskite-based tandem solar cells

By Manoj Jaysankar; Tom Aernouts

Tandem solar cells combine several solar cells with different photoabsorbers, stacked in a descending order of bandgap energies. They come in many flavours, but one promising combination is a bottom cell of c-Si or copper indium gallium selenide (CIGS) and a top cell of perovskite. Perovskite solar cells are thin-film solar cells with many advantages, such as a low-cost, high-throughput sheet-to-sheet and rollto- roll production, and a tuneable bandgap. Their long-term instability, however, is a challenge that needs to be overcome in order to make these cells a success. In this paper it is demonstrated that, by combining comprehensive loss-reduction strategies with effective large-area fabrication, perovskite-based tandem solar modules have the potential to yield power conversion efficiencies (PCEs) that are significantly higher (PCE of up to 45%) than those of established PV technologies, and can be manufactured on an industrial scale.

LED solar simulators and new test approaches for high-efficiency solar cells

By Marko Turek; Kai Sporleder; Christian Hagendorf

Solar simulators are among the most important and fundamental measurement tools in photovoltaic production facilities as well as in R&D labs. Two major solar simulator technologies can be distinguished: xenon light sources and, more recently, light sources using light-emitting diodes (LEDs). While xenon solar simulators are a well-established technology, LED-based systems appear to be promising candidates for future applications, as they provide a higher flexibility with regard to the flash times, spectral light composition and intensity. Measurement recipes for power quantification under standard test conditions (STC) can be adapted to high-efficiency cells, which require longer flash times. Furthermore, fast inline spectral testing, such as a rapid external quantum efficiency (EQE) test or a rapid reflectivity test, becomes feasible. However, the development of LED-based systems requires well-designed optical and electronic components to ensure high-precision measurements on the basis of a laterally uniform and temporally stable light field.

Beyond boron–oxygen deactivation: Industrially feasible LID-free p-type Czochralski silicon

By Bianca Lim; Agnes Merkle; Robby Peibst; Thorsten Dullweber; Yichun Wang; Rui Zhou

Today’s industry-standard B-doped monocrystalline silicon still suffers from light-induced degradation (LID) of the carrier lifetime. Illumination at elevated temperatures leads to a so-called regeneration, i.e. a recovery of both the carrier lifetime and the solar cell efficiency. However, even though the carrier lifetime on test wafers increases from about 1ms after processing to 3ms after regeneration, the corresponding PERC+ cell efficiencies in both states are identical; possible reasons for this discrepancy are discussed in this paper.

Solving all bottlenecks for silicon heterojunction technology

By Christophe Ballif; Mathieu Boccard; Antoine Descoeudres; Christophe Allebé; Antonin Faes; Olivier Dupré; Jan Haschke; Pierre-Jean Ribeyron; Matthieu Despeisse

Silicon heterojunction (SHJ) solar cells are the archetypes of ‘fullsurface passivating contact’ solar cells; such contacts are required in order to achieve typical open-circuit voltages of up to 730–750mV. Although SHJ technology has fewer manufacturing steps and enables higher efficiencies than standard passivated emitter and rear cell (PERC) technology, the market has been slow in taking it up. This paper discusses some of the obstacles that have been overcome in the last 10 years, and shows why the technology is now readier than ever for a competitive mass-market launch.

Low-cost standard nPERT solar cells towards 23% efficiency and 700mV voltage using Al paste technology

By Radovan Kopecek; Zih-Wei Peng; Thomas Buck; Corrado Comparotto; Valentin D. Mihailetchi; Lejo J. Koduvelikulathu; Joris Libal; Jan Lossen; Masahiro Nakahara; Kosuke Tsuji; Marwan Dhamrin; Wolfgang Jooss

Stable high voltages in solar cells and modules are becoming increasingly important as large PV systems are being set up in desert regions and are therefore exposed to high temperatures. High-voltage solar cells have lower temperature coefficients and thus produce a higher energy yield for such PV systems. Standard passivated emitter rear cell (PERC) devices have moderate voltages below 680mV, and also have the risk of degrading in such regions, because of light and elevated-temperature induced degradation (LeTID) effects and, in more recent observations, passivation degradation. This paper presents a solution for PERC producers to easily make the switch to n-type passivated emitter, rear totally diffused (nPERT) solar cells, which are capable of stable efficiencies above 22% and voltages close to 700mV, at almost no additional cost.

Pioneering the industrialization of PERC technology: A review of the development of mono- and bifacial PERC solar cells at SolarWorld

By Phedon Palinginis; Christian Kusterer; Stefan Steckemetz; René Köhler; René Härtwig; Torsten Weber; Matthias Müller; Gerd Fischer; Holger Neuhaus

SolarWorld has played a pioneering role in triggering and implementing the shift from p-type multicrystalline aluminium backsurface field (Al-BSF) to p-type monocrystalline passivated emitter and rear cell (PERC) as the next mainstream solar cell technology, and recognized PERC to be the door opener to an extremely simple and cost-effective implementation of a bifacial solar cell. This paper reviews PERC technology development at SolarWorld, featuring an industrial baseline process for monocrystalline five-busbar (5BB) p-type PERC solar cells exceeding 22.0% median (22.5% maximum) cell efficiency by May 2018, before operations at SolarWorld came to a final halt.

Effects of texture additive in large-area diamond wire cut multicrystalline silicon solar cells

By S. Saravanan, RenewSys India Pvt Ltd, Hyderabad, India; Ch.S.R. Suresh, RenewSys India Pvt Ltd, Hyderabad, India; V.V. Subraveti, RenewSys India Pvt Ltd, Hyderabad, India; K.C. Kumar, RenewSys India Pvt Ltd, Hyderabad, India; U.K. Jayaram, RenewSys India Pvt Ltd, Hyderabad, India

The silicon PV industry has predominantly used silicon wafers sliced by a steel wire, with silicon carbide particles (slurry wire – SW) as an abrasive and polyethylene glycol as a coolant. Low yield, high total thickness variation (TTV), significant material waste and short wire lifetime (and thus high downtime) of SW cutting technology have prompted the wafer slicing industry to develop an alternative technology. Researchers have developed diamond wire (DW) cutting technology for slicing the silicon and demonstrated that it overcomes the drawbacks of SW cutting technology. Although the DW cutting technology has been demonstrated for slicing wafers, the wafer surface is different after the conventional acidic texturing in a silicon solar cell process. It is therefore important to improve the existing process or to develop a new process, in order to produce a homogeneous texturization on DW-cut wafers. In this work, a systematic approach has been pursued to improve the existing process by using an additional etchant (a texture additive) in the acidic mixture. Different etch depths and the corresponding mean reflectance were studied. Optical and morphological studies on DW-cut wafers processed with and without a texture additive have been carried out and interpreted in terms of electrical performance.