Scientists from the Fraunhofer Institute for Solar Energy Systems in Germany created a compacted solar plant allowing for producing hydrogen directly from sunlight skipping the stage of generating and transmitting electricity among standalone installations. In the course of experiments, the new system converted up to 31.3% of solar radiation energy into the chemical energy of hydrogen. It means that almost one third of the incident sunlight energy is immediately accumulated in the chemical bonds of hydrogen – one of the most energy-intensive and environmentally clean types of fuel. And this parameter is one of the best for such technologies.
This method is based on the combination of two processes: electricity generation and water electrolysis. In the classical arrangement, solar panels at first generate electricity, which is then supplied to the electrolysis unit for de-composing water into hydrogen and oxygen. In this new arrangement, solar elements are directly connected to the electrolysis cell allowing to avoid losses during conversion and transmission.
To implement such an approach, the researchers used concentrated optics and high-performance solar elements. The Fresnel’s lenses matrix with the total area of 64 cm² reinforced the sunlight flux approximately 226 times and directed it to small but powerful solar elements. Four-transitory elements consisting of several semi-conductors’ layers were used in the plant, and each layer absorbed a dedicated part of the solar spectrum. This allowed for receiving high voltage – over 4 V, enough for launching the water splitting reaction without any additional converters.
The system also stipulated for using the emitted heat: the solar elements and the electrolysis unit were fixed on the common copper plate simultaneously removing heat and warming up water. Eventually, the input temperature reached 60 °C reducing the losses during the electrolysis process and improving the overall efficiency of the plant.
The open-air tests were conducted in Freiburg. Over 13 thousand measurements were taken during 13 days, and system was stable during operations in real settings – with changing solar radiation and temperature fluctuations. The efficiency was swaying from 25% to record-high 31.3%. Production of hydrogen decreased pro rata to the reduction of solar radiation intensity.
According to the researchers, in the regions with high direct solar radiation such systems could assure competitive costs of “green” hydrogen – circa 3 USD per kilo, which is in line with the lower limit of the forecast by International Energy Agency. At the same time, the plant did not require complicated power electronics and could operate as standalone, which makes it especially attractive for remote territories.
