Best electrolyser/photovoltaics combinations demonstrated in test fields
Integrated PV-EC device during performance tests in the outdoor test bed for realistic operating condition. © Sonya Calnan/HZB
One of the most promising ways to increase the availability of solar energy is to convert excess production into hydrogen. The PECSYS project has investigated the best possible material and technology combinations to facilitate such an operation.
It all comes down to electrolysis. By combining photovoltaic (PV) modules with electrolyser systems, you can convert excess electricity into hydrogen and use it later, as demand starts exceeding supply. No more need for backup batteries or DC-DC converters. The hydrogen can be used in multiple industry processes, and users are provided with a zero-net carbon energy cycle, from generation to storage and use.
The PECSYS (Technology demonstration of large-scale photo-electrochemical system for solar hydrogen production) project aimed to advance this technology by exploring various combinations of electrolysers and PV cells.
“Initially the plan was to test different materials and then select the best for final implementation in a demonstrator. However, we soon learned that different approaches provide different benefits. Instead of deselecting several options and keeping only one, we therefore decided to investigate a number of technologies,” says Sonya Calnan, group lead, photovoltaics to fuels technology at the Helmholtz Zentrum Berlin (HZB) and project coordinator.
Coupled or integrated?
On the electrolyser front, the consortium focused on both direct coupling and PV-integrated electrolysers. The direct coupling of PV and electrolysers is not new, but the team found there was still scope to optimise their engineering. As Calnan explains: “Our colleagues at Forschungszentrum Jülich developed unique polymer electrolyte membrane PEM stacks with reduced platinum group catalyst loading and systems. These receive water input only on the cathode side. In so doing, we reduce the complexity and lower the cost of our solution compared to conventional electrolysers.” PV-integrated electrolysers, on the other hand, were chosen to fill an existing research gap. No study had ever demonstrated their long-term outdoor operation in sizes exceeding laboratory scale. Both HZB and Uppsala University filled this gap, while avoiding the use of platinum group metals for catalysts and using proven PV technologies for capturing solar energy. On the PV front, the consortium opted respectively for silicon heterojunction PV cells and CuInGaSe PV cells. They chose the former because of their high solar to electricity conversion efficiency, low temperature coefficient, high open circuit voltage and their intrinsic bifacial ability. Finally, the move was justified by existing plans to build one or more big manufacturing facilities in Europe. “CuInGaSe PV cells, on the other hand, were chosen because the bandgap is easily tuned. We can optimise the matching of the voltage of the PV and electrolysis cells based on local climatic conditions at the operation site,” Calnan adds.
Test fields in Germany and Italy
The project’s two most notable outcomes are undoubtedly its test field demonstrations. In Jülich, Germany, project partners set up a solar collection area of 8.2 m². It consists of full-sized silicon heterojunction modules and CuInGaSe modules connected to detached PEM electrolysers. The installation generated an average of 42.9 g/h of hydrogen with an average solar to hydrogen efficiency of 10 % over 1 month of continuous outdoor operation. A second demonstration by the Italian Research Council in Catania, Italy involved a 730 cm² collection area using silicon heterojunction PV modules in bifacial operation. “Bifaciality represents an innovative solution to increase the hydrogen production yield without increasing cost. We could demonstrate a solar to hydrogen efficiency of 13.5 % and a hydrogen production rate of 307 mg/h at a solar irradiation level of 1 000 W/m2 and an ambient temperature of 25 °C. This is an increase of 14 % compared to a monofacial operation,” Calnan and her colleagues explain. The project is set for completion in December 2020. In the meantime, the team will be completing the final assembly of the integrated demonstrators as well as quantifying the benefits of their solutions. In the long run, they hope the project will contribute to new ideas for the deployment of low-cost, autonomous renewable energy systems.
The project leading to this application has received funding from the Fuel Cells and Hydrogen 2 Joint Undertaking under grant agreement No 735218. This Joint Undertaking receives support from the European Union’s Horizon 2020 research and innovation programme and Hydrogen Europe and N.ERGHY” .
This article is published in the print edition of the Research*EU Magazine and is also available in a web version in German, Spanish French, Italian and Polish.
- New instrument at BESSY II: The OÆSE endstation in EMILA new instrument is now available at BESSY II for investigating catalyst materials, battery electrodes and other energy devices under operating conditions: the Operando Absorption and Emission Spectroscopy on EMIL (OÆSE) endstation in the Energy Materials In-situ Laboratory Berlin (EMIL). A team led by Raul Garcia-Diez and Marcus Bär showcases the instrument’s capabilities via a proof-of-concept study on electrodeposited copper.
- Green hydrogen: A cage structured material transforms into a performant catalystClathrates are characterised by a complex cage structure that provides space for guest ions too. Now, for the first time, a team has investigated the suitability of clathrates as catalysts for electrolytic hydrogen production with impressive results: the clathrate sample was even more efficient and robust than currently used nickel-based catalysts. They also found a reason for this enhanced performance. Measurements at BESSY II showed that the clathrates undergo structural changes during the catalytic reaction: the three-dimensional cage structure decays into ultra-thin nanosheets that allow maximum contact with active catalytic centres. The study has been published in the journal ‘Angewandte Chemie’.
- An elegant method for the detection of single spins using photovoltageDiamonds with certain optically active defects can be used as highly sensitive sensors or qubits for quantum computers, where the quantum information is stored in the electron spin state of these colour centres. However, the spin states have to be read out optically, which is often experimentally complex. Now, a team at HZB has developed an elegant method using a photo voltage to detect the individual and local spin states of these defects. This could lead to a much more compact design of quantum sensors.