The Solar Energy Research Institute of Singapore (SERIS) at NUS is embarking on a series of research projects over the next 10 years to strengthen and deepen its solar capabilities.
The efficiency of single-junction silicon solar cells is limited to about 29% under natural sunlight, whereby the world record is 26.7% at present. To lift the efficiency of silicon solar cells above the 30% threshold, they need to be combined with a second solar cell on top, to achieve a better harvest of the solar spectrum. The most promising technology path to cost-effective 30% efficient solar cells is to combine a thin-film top cell with a crystalline silicon bottom cell.
In this flagship project, SERIS collaborates with the Nanyang Technological University (NTU) and the Singapore-MIT Alliance for Research and Technology (SMART). Both III-V materials and perovskite materials are being investigated for the top cells. SERIS develops customised silicon bottom cells while NTU (perovskites) and SMART (III-V) are developing the thin-film top cells. The tandem cell integration is conducted at SERIS.
III-V top cells:
III-V solar cells have an excellent track record for both efficiency and long-term stability. The world record efficiencies for III-V on Si tandem solar cells are presently 32.8% for GaAs/Si 4-terminal tandems and 32.5% for InGaP/Si 4-terminal tandems. The main challenges are the high cost and the low throughput of the fabrication process of III-V solar cells. For III-V solar cells to be suitable for tandem applications, it is important to remove (or thin down) the original substrates to allow sufficient infrared light to reach the silicon bottom cells.
Perovskite top cells:
Perovskite thin-film materials have reached high PV efficiency (> 20%) in the laboratory using low-cost processing methods. Although further research is required before these solar cells can be mass produced, for example the long-term stability must be improved, this is presently a fast-moving field with many technology breakthroughs. The world record efficiencies for perovskite/Si tandem solar cells are presently 27.3% for 2-terminal devices and 27.1% for 4-terminal devices. Highquality perovskite top cells with a bandgap in the 1.6 - 1.8 eV range and a high infrared transparency of at least 85% are required to enable 30% perovskite/silicon tandem cell efficiency
Customised silicon bottom cells:
The thin-film top cells presently available for this project are rather small (~1 cm2 for III-V and significantly less for perovskites). Given these size limitations of the available top cells, SERIS has established processes for fabricating customised smallarea silicon bottom cells (1 - 4 cm2) on 6 inch wide substrates, using SERIS’ R&D pilot line for industrial silicon solar cells. With careful optimisations - including customised antireflective coatings, laser ablation patterns and metal patterns, as well as a specifically engineered locally diffused emitter - smallarea cells customised for tandem cell applications have been realised in 2018 using an industrial high-efficiency silicon solar cell architecture (p-type PERC solar cells). Research is under way at SERIS to develop other cell architectures with higher open-circuit voltage potential, such as monoPolyTM and biPoly passivated-contact solar cells, for bottom cell applications.
Present status of thin-film on silicon tandem cells:
As shown in the table, a perovskite/silicon 4-terminal tandem cell efficiency of 23.4% has been realised in 2018 using a perovskite top cell from NTU and a PERC silicon bottom cell from SERIS.
For further information, please contact:
Dr Serena LIN Fen
Development of low-cost, high-efficiency BIPV modules and systems to replace conventional materials of the building envelope with PV products, including the facades, is critical for Singapore to increase the available spaces for the accelerated deployment of solar energy in a densely built-up urban environment. With an existing stock of more than 100,000 buildings and little land for utility-scale ground-mounted PV systems, the vast majority of Singapore’s PV capacity will be installed on, or attached to buildings. While rooftop PV systems are standard commercial practice, adding PV to the facade of existing or new buildings poses more challenges due to aesthetics and factors such as building regulations.
SERIS takes a holistic approach to BIPV, which not only includes the development of innovative, light-weight and highly efficient solar technologies, but also test-bedding of new deployment options and building a BIPV community by bringing together relevant stakeholders from both the PV and building sectors, in order to remove actual and perceived barriers for a widespread adoption of BIPV in Singapore and beyond.
A team of scientists at SERIS is developing new and innovative BIPV products. Working closely with relevant industry players (PV scientists, PV manufacturers, architects, engineers, building contractors, developers), the aim is to develop cost-effective BIPV modules with high power density, which will be designed to seamlessly integrated with innovative construction process technologies such as Prefabricated Prefurnished Volumetric Construction (PPVC).
The main objectives of this project are:
BIPV Centre of Excellence
The Centre of Excellence (COE) for BIPV was established at SERIS in 2017 to testbed innovative BIPV applications in a tropical environment and provide a collaborative platform with relevant stakeholders from the private and public sectors.
The main objectives of the BIPV COE are: i) Test-bedding of innovative BIPV technologies; ii) Acting as an information platform and providing best practices for industry, academia and government bodies; and iii) Develop tools and business models around financing of BIPV (see graphical overview).
The BIPV COE aims to work closely with architects, engineers, building developers, façade consultants, and BIPV industry to bring innovation to the Singapore market and conduct thorough indoor and outdoor testing in the tropics. This effort has been realised in two BIPV testbed projects, in collaboration with the School of Design and Environment (SDE) at NUS, a leading PV/ BIPV manufacturer from Singapore (REC Solar, “all black” highefficiency TwinPeak modules) and companies from abroad (AGC from Japan, semi-transparent modules; Kromatix from Dubai, coloured modules; Solaxess from Switzerland, pure white modules). This collaborative effort enables relevant stakeholders to see “with hands” the state of the art in BIPV technologies, which can be used for the integration into the building facades be it in form of windows, claddings or spandrel areas.
In addition, the BIPV COE is also actively engaged with relevant government agencies such as SCDF, BCA, NEA, HDB, NCCS and EDB to discuss regulations for innovative BIPV products and to ensure a smooth future deployment of BIPV solutions in Singapore and the region.
Floating Solar is taking the solar industry by storm! It is already considered as the third pillar of the solar industry along with ground-mounted and rooftop PV, with the cumulative installed capacity having surpassed 1GWp in 2018, up from just 150 MWp in 2016. Furthermore, it has the potential to unlock 400,000 km2 – and thereby a new TW-scale opportunity for PV − on freshwater reservoirs alone . Floating PV (FPV) offers great opportunities, particularly for countries with land constraints but lots of water bodies, like Singapore or Japan.
From a technical perspective, FPV installations generally enjoy higher annual energy yields (due to the cooling effect from the water), while they also reduce the evaporation losses of the water, which is beneficial for drinking water reservoirs or irrigation ponds. One striking application is the combination of Floating Solar with existing hydropower stations, whereby the reservoir can be utilised as a large storage facility for short-term variability management, but also for the diurnal and possibly even seasonal cycles. In addition, interconnecting the FPV system to the electric grid connection of the hydropower station lowers the initial capex. There is great potential for such FPVhydropower hybrid systems in South-East Asia.
SERIS, in close collaboration with Singapore’s national water agency PUB and the Singapore Economic Development Board (EDB), has designed, built and is operating the world’s largest testbed for Floating PV at Tengeh Reservoir, officially launched in October 2016.The key features of the testbed are:
The project and its key findings have been widely covered in local and international media reports and scientific journals.
In addition, SERIS is disseminating the knowledge to the international Floating PV community by publishing a first-of-itskind report series in collaboration with the World Bank Group (see Figure 1) . These reports will help policymakers, developers, and practitioners around the world to understand the market potential, cost and challenges to overcome. Furthermore, SERIS is building a Floating Solar community by organising the annual International Floating Solar Symposium (IFSS) and participating in IEC standards for Floating PV.
As part of this flagship project, SERIS will further expand its leadership role in the following two areas:
The work will involve spearheading multi-agency collaboration to demonstrate off-shore test-bedding and solving the technical challenges associated with the harsher environment faced by PV systems in the sea, such as high salinity or biofouling. For that, we will reach out to the well-established marine industry in Singapore to take key learnings and adapt them to Floating Solar. Moving from drinking water reservoirs (which are often restricted due to possible contamination) to sea spaces also offers more degrees of freedom and hence the opportunity to add more functionalities to the floating structures. Combinations of floating solar with fish farming and/or vegetable growing are perceivable. Likewise, the energy generated could be used for hydrogen generation (for a future hydrogen economy) or seawater desalination. Off-shore floating solar allows to solve more than one problem at once, i.e. beyond the mere generation of renewable energy. If cooling via seawater is taken into account, even floating data centres powered by floating PV could be a future option for high-tech hubs like Singapore.
 Source for 400,000 km2 of man-made reservoirs: Shiklomanov, Igor A., 1993, “Chapter 2: World Fresh Water Resources”, in: “Water in Crisis”, ed. Gleick, Peter H., Oxford University Press  First report available at: http://documents.worldbank.org/curated/en/579941540407455831/Where-Sun-Meets-Water-Floating-SolarMarket-Report-Executive-Summary
For further information, please contact:
Dr Abhishek KUMAR