Two system concepts were considered in the project.
In the first, representing, the next generation of solar hydrogen generation systems, photovoltaic (PV) modules were both directly electrically coupled to and thermally integrated with alkaline electrolysers using earth abundant electrocatalysts. A CuInGaSe photovoltaic mini-module with a total collection area of 100 sq. cm was integrated to an alkaline electrolyser at Uppsala University, Sweden. This prototype achieved a maximum ηStH 13.5 % under 1000 W/sq. m illumination with an H2 generation rate of 3.7 g/h/sq.m on an active area 82.2 sq. cm basis). Also, a scalable 64 sq.cm aperture area device consisting of triple-junction thin-film silicon solar cells coupled with a bifunctional NiFeMo catalyst was developed at Forschungszentrum Jülich (FZJ, Germany). This device achieved an ηStH of 4.5% with an area specific H2 production rate of 1.56 g/h/sq.m.
Additionally, a silicon heterojunction (SHJ) photovoltaic module was thermally integrated with an alkaline electrolyser and scaled-up from 294 cm² to 2600 cm² solar collection area at Helmholtz Zentrum Berlin (Germany). Thanks to insights from the analysis of the outdoor performance of the smaller device, the heat transfer between the PV module and the electrolyser in the larger prototype, increased leading to a 34% relative improvement in ηStH to 5.1 % at 1000 W/m². Under these conditions, the scaled-up prototype achieved an H2 generating capacity of 85 mL/min at an area specific rate of 1.56 g/h/sq.m.
In the second concept, PV modules were directly coupled to proton exchange membrane (PEM) electrolysers to form a modular generation unit. This layout is unique because the balance of plant was minimised by feeding water to the electrolyser from the cathode side only using hydraulics and not pumps as well as by eliminating both power management electronics and active heating/cooling of the electrolyser. At Consiglio Nazionale delle Ricerche (Catania, Italy), the effects of bifaciality were studied on a 730 sq.cm SHJ bifacial PV module that was directly electrically coupled to a single PEM electrolyser cell. The albedo effect of ~ 30% combined with a bifacial factor of 90 %, increased the ηStH, by 17% relative, to 13.5% compared to a mono-facial SHJ PV mini-module with an average production rate of 4.2 g/h/sq.m.
The final Project outdoor demonstrator installed at FZJ, consisted of a 10 m² array of several units using either CuInGaSe (from Solibro Research AB) or SHJ (Enel Green Power, S.p.A) PV modules. The demonstrator was operated continuously for 9 months (2680 h) before the project ended. In this time a total of 22 kg of hydrogen were collected with an average ηStH of 10% with less than 10% relative degradation, exceeding the respective project targets. The costs and green house impact of this technology can be reduced to levels below 5 €/kg-H2 and below the green hydrogen threshold of 36.4 g CO2. Eq./kg- H2, by improving the energy conversion efficiency, operating the system in sunny regions such as in Southern Europe and /or extending the system lifetime beyond 20 years.
The results of the project are available in open access peer reviewed publications, in public deliverables and on the project website. The consortium plan to scale the directly coupled SHJ PV-PEM electrolysis concept, with a reduced balance of plant, to the 250-kW range. Other results are now used by the partners as background in newer research projects and as additions to course materials in universities.
