Belgian researchers have designed a solar-powered electrolyzer that uses standard-sized, wide-area shingled silicon PV to split water. The system is said to be able to achieve 10% solar-hydrogen efficiency with electrolyzer current densities of about 60 mA cm-2.
“The novelty of our approach consists in utilizing a standard-sized large-area shingled silicon PV to produce a voltage above 1.23 V for water splitting, combined with low-cost anion-exchange water electrolysis, which combines the higher operating current densities of polymer electrolyte membrane (PEM) with low-cost alkaline electrolysis materials,” said researcher Nina Plankensteiner pv magazine.
The scientists presented their findings “Photovoltaic electrolyzer system Operates >50 mA cm−2 combining a large-area shingled silicon PV module with large-area nickel electrodes for low-cost Green H2 Generation”, which was published recently RRL sun. They explained that PV-ECs offer the highest level of technological readiness and the highest solar-to-hydrogen efficiency of any electrolysis technology.
“The photovoltaic technology of choice in PV-EC systems, which produce commercially affordable electricity with a stable 20-25 percent efficiency at 30-40 mA/cm2, are series-connected silicon solar cells that provide more than 1.23 V for water splitting,” said researcher Joachim John. “Over the next decade, silicon tandem assemblies with perovskite-capped cells may play an additional role as conversion efficiencies approach 30 percent.”
They described the proposed system as a “commercially relevant configuration”. They said the AEM electrolyzer has nanomesh electrodes with a huge surface area of 26 m2/cm3 made of soil-rich nickel, as researchers previously. reported.
“Serial rotation of silicon solar cells is a particularly attractive approach to solar water splitting because a sufficiently high voltage per normal cell area can be achieved,” they said, referring to shingle panels.
The modules are railless structures, and only a small part of the cells are not exposed to sunlight. The cells are densely connected to form a shingle, and the resulting strips are connected with conductive glue. A smaller number of busbars reduces shading losses.
The lab-scale single-cell electrolyzer developed by the academics has two 4-micrometer-thin high-surface-area nickel nanogrid electrodes. It also has six silicon heterojunction cells with 38.5 cm2 shingles cut from standard 15.6 cm2 x 15.6 cm2 cells.
“The cells were connected in series and cover a variable open-circuit voltage in the range of 0.7 V to 4.3 V, depending on the number of cells connected,” the researchers explained, noting that the average efficiency of the cells was about 20%. fill factor about 80%. “The current-voltage characteristics of the electrolyzer showed that 1.8 V to 2.2 V is required to match the electrolyzer current density between 20 and 100 mA/cm2. This minimum voltage requirement can be achieved by connecting three or four silicon cells in series.”
The PV-EC system tested under normal lighting conditions was able to produce hydrogen for about 20 hours and achieved 10% solar-hydrogen efficiency at electrolyzer current densities of about 60 mA cm.−2which the group described as the highest current density reported for PV-EC systems in the literature.
The efficiency between solar and hydrogen was determined by on-site monitoring of the most important system parameters, such as operating current, voltage and hydrogen gas flow. Determining this figure of merit accurately is important when comparing PV-EC systems with each other, the researchers said. They noted that longer stability measurements should be tested at high enough current densities to stress the system.
The researchers also performed a series of performance dynamic load tests with gradual and sudden power changes during half a year of solar radiation. They claim that the tests showed that changes in cell voltage are negligible and have very little effect on PV-EC operation and hydrogen production.
“The next steps towards commercialization of the presented PV-EC system are long-term outdoor stability testing together with a longer dynamic load measurement protocol,” they concluded.