Solar power | Key observations from the Solargis maps include:
● India: The Solargis irradiance maps indicate up to seven percent below average solar irradiation for the sub-continent over the last four years – reflecting the concerns of local asset managers about a decline in irradiance levels. This is particularly notable around highly developed areas where aerosols and cloud cover can impact resource availability. If this data isn’t considered by developers, it could result in solar farms underperforming, with wider implications for investor confidence in one of the world’s fastest growing solar markets.
● North America: The Solargis maps indicate below-par irradiation in the north and southeast when comparing the last ten years of averages vs long term trends. The above average levels in the northwest, particularly last
year, reflect anomalies such as the recent heat dome, which saw temperatures reach record highs of 49.6°C.
By harnessing a long term, data-driven approach to solar power generation that can flag anomalies with high accuracy, developers and asset owners in North America can better prepare their projects for variable weather conditions. This will be critical as the Investment Tax Credit (ITC) phases out, impacting long-term revenue security.
● Australia: As a country with great potential for solar power, the last five years of maps indicate significant irradiance variability across the continent when compared to long- term averages, reflecting extreme weather conditions such as those that contributed to notable events like the “Black Summer” bushfire season of 2019-2020.
With the Solargis team seeking to understand phenomena such as El Niño and La Niña through their long-term data analysis, the future of solar integration on the continent depends on expert, reliable understanding of how investors and asset managers can prepare for and manage extreme weather events while integrating these future technologies into the grid as the nation transitions from fossil fuels.
Suri concludes: “Controlling the weather is outside of our capabilities, but what solar developers, owners and operators can control is their knowledge. Vital, trusted intelligence on the solar resource, albedo, and specific geographical conditions at project sites can be the difference between an asset which retains its value throughout its lifecycle, and one which fails to live up to its potential.”
ZSW shifts focus to PV tandems
ZSW (Zentrum für Sonnenenergie-und Wasserstoff-Forschung Baden-Württemberg) says it is going to fast track ‘tandem’ solar technologies – which combine cells of different materials – with the aim of reducing their time to market. To this end, it has put two new high performance coating lines into operation. “Companies in the solar sector can take advantage of these capabilities to optimise their developments in the area of tandem solar cells”, says ZSW.
The efficiency of silicon-only cells, which currently dominate the market, is gradually approaching the practical limit of around 27%, ZSW notes, but tandem solar cells, which consist of different solar cell materials layered on top of one another, present a way round this limitation. “Together, the layers make better use of the width of the solar spectrum than each single solar cell”, says Dr Jan-Philipp Becker, the new head of the ZSW’s PV materials research. The top solar cell converts light in the visible region of the solar spectrum into electricity, the bottom cell converts light in the near-infrared part of the spectrum. This combination enables tandem solar cells to have a higher efficiency, which is expected to rise to well over the 30% mark in the years ahead. Several variants of tandem cells are now available. A particularly interesting variant of tandem solar cells, says ZSW, uses layers
of perovskite as the light-absorbing material, with some compounds in this class of materials exhibiting “excellent optical and electronic properties” and “on top of that, they are cheap and earth-abundant.” For the second absorbing layer, ZSW researchers are looking at: CIGS (copper, indium, gallium and selenium); silicon; or another perovskite with a modified spectral sensitivity range.
Combinations of different cell types – that is, perovskite and CIGS, perovskite and silicon, or perovskite and perovskite – hold great promise as a means of significantly boosting efficiency. Tandem solar cells that pair perovskite with perovskite or perovskite with CIGS have benefits beyond high efficiency, says ZSW. As a thin-film technology, they can also be deposited on plastic or steel films to make light, flexible modules, perfect for integrating into building façades or roofs.
One of ZSW’s new coating lines makes perovskite thin-film solar cells and the other CIGS thin-film solar cells. Tandem solar cells employing silicon will be produced on various types of silicon cells sourced from external partners. “Excellent conditions are now in place in the institute to develop tandem solar cells, particularly in terms of the process technology for manufacturing solar cells in a vacuum under ultra-clean lab conditions. We want to use these
assets to explore the technology’s physical boundaries,” says Becker.
An extensive set of material analysis tools helps with that. The in-house Solab test laboratory and field-testing facilities are able to rigorously analyse and assess the manufactured solar cells and modules for long-term stability. The new coating lines will serve to develop innovative processes for the solar industry, says ZSW, which will then be able to bring to market more efficient and cost-effective solar modules. ZSW says it draws on a “deep well of more than 30 years’ experience with CIGS technology.” ZSW developed, optimised and ramped up thin- film PV systems for mass manufacturing. Now it wants to build on that achievement with tandem solar cells.
Arrayed around a central robot, the new perovskite line (or ‘cluster’) has four coating chambers that can produce a wide variety of cell types with sputtered transparent layers and with evaporated metallic or organic layers. A vacuum chamber provides an optimised means of vacuum-coating perovskites. The system will be able to create very homogenous and highly reproducible multi-component perovskite layers. Even at this early stage, ZSW says it “has already made great strides in optimising the cell structure with vapour-deposited organic electron conductor layers.”
The German Federal Ministry of Economic Affairs and Climate Action (BMWK) funded the two new coating lines as part of the CAPITANO and CIGS-Cluster projects.
UK start up Oxford PV is developing tandem solar cells employing a silicon/perovskite combination. See Modern Power Systems, June 2021, pp 30-32.
Above: Left, the new perovskite cluster (photo Alexander Fischer / Leybold) and, right, CIGS cluster (photo ZSW) at ZSW
32 | May 2022|
www.modernpowersystems.com
Perovskites are also attracting interest in Japan, where NGK has invested in perovskite solar cell developer, EneCoat Technologies, a Kyoto University spin-off, noting that perovskite solar cells are “thinner and more light weight than
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