editorial blooms and spreads The in electricity markets and in research laboratories brings exciting challenges in scaling- up innovative technologies and deploying them for a variety of applications.

enewable energy is changing the Research and the University of Barcelona the module power output while keeping electricity supply in many parts of discuss the mechanisms causing the the module cost almost constant. In their Rthe world. In 2017, renewable sources Cu(In,Ga)(S,Se)2 efficiency gap and outline Comment, Radovan Kopecek and Joris Libal contributed 25% of electricity generation the solutions developed in academic and from the International Research worldwide1, taking advantage of globally industrial research laboratories over the past Center Konstanz argue that while bifacial installed capacities of more than 1,200 GW decades to try to overcome the issue. modules are already being deployed, the for hydropower2, 510 GW for wind power1 Taking a photovoltaics technology from major challenge to be overcome for a true and about 400 GW for solar photovoltaics by the laboratory to the real world also requires large-scale roll-out of bifacial photovoltaic the end of the year1. As is well documented a good understanding of how it behaves technologies is to lift the uncertainty on the in this journal and many others, each of in real operating conditions, for example exact energy yield to be expected from each these energy sources has its own advantages when subjected to weather, and how it specific bifacial installation. and drawbacks. evolves with time. Indeed, the expected Alternatively, for some applications, One of the most impressive features lifetime of a product under specific use factors other than cost and efficiency may of photovoltaics is its versatility. Because conditions will dictate whether and how dominate and need to be optimized for, photovoltaics is made up of small elementary it can be deployed. Much work has gone such as weight for portable applications or units, called solar cells and modules, it into understanding the many degradation aesthetics for integration into buildings or can be deployed at small and large scales, pathways of various photovoltaic technologies urban landscapes. In their Comment on the from portable electronics to solar farms and standardized tests to assess the reliability integration of photovoltaics in buildings, reaching gigawatt scales. At utility scale, of these technologies when deployed in Ballif and co-workers from the Ecole the priority is increasing the amount of the field are under constant development. Polytechnique Fédérale de Lausanne and generated electricity while minimizing In their Perspective, Henry Snaith from the CSEM-Swiss Center for Electronics and its cost; mainstream technologies such as the University of Oxford and Peter Hacke Microtechnology argue that photovoltaic silicon are the workhorses to achieve this from the National products are reaching a stage of development goal. However, the variety of potential Laboratory describe the methodology used and tailorability where they can now be applications for solar photovoltaics generates to develop these standardized tests, discuss considered as construction materials from a diversity of technical requirements on their current shortcomings and argue that the initial stages of the building design, devices and makes room for alternative the lessons learned from this experience rather than as mere electronic components. materials and device layouts. For example, can inform studies of operational stability The multidisciplinary team discusses how the weight requirements imposed by some in novel photovoltaic technologies at the coordinated research and development emerging applications such as portable pre-commercial stage. However, they also efforts across the photovoltaics value charging or ground transportation lead to highlight that the priority in the early stages chain, including engineers, architects and innovations in thin photovoltaic materials of development is to understand degradation construction experts, are currently changing and protective layers. In this Focus issue, we pathways in realistic operation conditions. the way we perceive and implement point the spotlight on some recent efforts to As such, they review the currently known building-integration. scale-up photovoltaic technologies from the degradation mechanisms of metal halide Indeed, scale-up and deployment of any laboratory to the real world and perovskite-based photovoltaics, which are now photovoltaic technology depends on a large explore current developments in the moving into pre-commercial development. network of actors with different skills and deployment of photovoltaics. Maximizing and maintaining the priorities, from students in research laboratories Indeed, scaling-up the fabrication of photoconversion efficiency is a primary to professionals in private companies who small-area solar cells into larger-area ones research focus in photovoltaic research. ensure that the best technological solutions and then assembling several of these cells However, the efficiency is only one of the for each local context are implemented into a solar module is far from trivial. many factors directing if and how a specific and managed in the field. While this Focus Frequently, a gap in the photoconversion photovoltaic technology may be used in issue of Nature Energy is by no means an efficiency appears between the and a specific application. Minimizing the exhaustive picture of photovoltaics research and the module scales. Thin film overall cost of photovoltaic electricity is a development, we hope it illustrates the exciting

Cu(In,Ga)(S,Se)2 photovoltaic devices offer primary driver, in particular at utility scale. variety of endeavours regarding scale-up and potential cost advantages and comparable The cost of photovoltaic electricity does deployment, and that it can help cross-pollinate solar cell efficiencies relative to silicon not only depend on the module efficiency ideas between communities. ❐ photovoltaics. However, the module and cost: it also depends on the amount of

efficiencies are still low — Cu(In,Ga)(S,Se)2 electricity that can be generated per unit area photovoltaics exhibit a large efficiency gap of the installation and on the cost of land, Published online: 8 June 2018 relative to scaled-up technologies, namely installation, electronics and so on. The cost https://doi.org/10.1038/s41560-018-0185-1 silicon or CdTe. In their Review, Veronica of photovoltaic electricity can therefore be References Bermudez from (previously at lowered using these other parameters. 1. Global Energy & CO2 Status Report 2017 (IEA, 2018). EDF R&D) and Alejandro Perez-Rodriguez For example, bifacial modules can harvest 2. Renewables 2017: Hydropower (IEA, 2017); https://www.iea.org/ from the Catalonia Institute for Energy light from both sides, which improves topics/renewables/hydropower/

Nature Energy | VOL 3 | JUNE 2018 | 437 | www.nature.com/natureenergy 437 © 2018 Macmillan Publishers Limited, part of Springer Nature. All rights reserved. © 2018 Macmillan Publishers Limited, part of Springer Nature. All rights reserved.