At the Innovation and Demonstration Centre CO2 from Outdoor Air in Bleiswijk, Netherlands, tests are being carried out on the use of CO2, directly from the air, in cultivation. Dennis Medema shares an update on Kas als Energiebron.
The availability of sufficient CO2 from external sources is crucial for making greenhouse horticulture sustainable. Direct Air Capture (DAC) technology offers a solution by capturing and concentrating CO2 directly from the air. This innovation is now being explored.
Pilot site, summer 2024. Photo by EnergiekEvent
Testing DAC technology on cucumbers
Capturing and concentrating CO2 directly from the air is an alternative to CO2 from fossil fuels. To explore this innovation, the Innovation and Demonstration Centre CO2 from Outdoor Air was launched in January 2024, funded by the Greenhouse as Energy Source program, at Wageningen University & Research's Glasshouse and Flower Bulbs business unit in Bleiswijk.
In the coming years, various DAC technologies will be tested and compared, collecting data on CO2 quality, CO2 production capacity, and concentration, energy consumption per kilogram of CO2 produced, quantification of additional production inputs needed (e.g. sorbents), and the quantity and quality of other outputs (e.g. water).
CO2 quality is an important issue and thus much attention is given to determining whether known phytotoxic gases are present that can negatively affect plant health. To do this, there are two identical greenhouse compartments: one with DAC source CO2 and the other with OCAP CO2 as reference. The compartments have a high-wire system, assimilation lighting (all-LED), and a cooling system.
Besides a comprehensive measurement system for CO2 concentration and flux of CO2 dosed in both compartments, a comprehensive measurement protocol is carried out. Cucumber is grown year-round maintaining a CO2 concentration of about 750 ppm. Greenhouse ventilation only needs to be used sporadically due to the cooling system. Chances of any damage to the crop due to the accumulation of gases other than CO2 that can mix in the greenhouse air during CO2 dosing are therefore maximized. This summer, the vents could remain closed more than 95% of the time.
No differences
The first DAC machine to be tested is the Skytree Cumulus (beta), which has been in operation for 10 months. Two cucumber trials have been conducted: the first ran from January to June, while the second has been ongoing since July. Results from the first trial, already completed, indicate a yield of 71 kg/m2 (177 pieces/m2) for about 166 days of cultivation, with no differences between the DAC (test) and OCAP (reference) compartments. Weekly measurements, including stem length, leaf and flowering, leaf area, fruit growth period, and fruit abortion, were similar between the two greenhouse compartments. No signs of phytotoxicity were observed, based on flower and leaf color data, both for DAC-CO2 from the Skytree Cumulus (beta) and the OCAP CO2.
It is important to note that although this machine is not specifically designed for greenhouse cultivation, its capacity - up to about 10 kg CO2 per 24 hours - fits well within the scope and scale of this project using compartments of 144 m2. The same absorbents and core process are used in Skytree's new, larger unit designed for greenhouses (Stratus). Therefore, the absence of phytotoxicity in tests with the Cumulus system can also be considered indicative of the performance of the Stratus system in greenhouses.
So far, the results of the second trial are consistent with those of the first. As yet, no differences have been observed between the two compartments.
Harmful gases
As part of the risk analysis for phytotoxic gases, gas analyses of the CO2 concentrate were carried out to detect known harmful gases to plants. Some NOx was found, but so far the source is unclear. As outdoor NOx levels can sometimes be higher than expected (e.g. near a busy road), additional measuring equipment has been installed to measure NOx concentrations, both outside and inside the compartments. In addition, technical interviews are held in collaboration with chemical analysts specializing in DAC technology to assess the machine's processes and identify in advance, whether other phytotoxic gases are to be expected based on the design and technology.
The process also releases some condensate. From a circularity perspective, this can be useful input for irrigation water if the water stream is 'pure'. It has been seen in many projects that suppliers of equipment for the greenhouse industry often underestimate or overlook the importance of 'clean' water, usually due to a lack of awareness. Therefore, information on the quality and quantity of water condensate produced is also collected.
All results will be collated after the completion of the 2nd cultivation so that they can draw the first conclusions after one year of the project.
In January 2024, the Innovation and Demonstration Centre CO2 from Outdoor Air was launched, funded by the Kas als Energiebron program, an innovation program of LVVN and Glastuinbouw Nederland. The IDC CO2 from Outdoor Air is located at Wageningen University & Research's Glasshouse Horticulture and Flower Bulbs Business Unit in Bleiswijk.
Source: Greenhouse as Energy Source