Human-powered hydroponic systems: An environmental and economic assessment

Hydroponic systems like vertical farming have been proposed as an alternative and potentially more sustainable option for growing vegetables than conventional soil-based production methods. However, the energy required for the functioning of hydroponic systems is a key contributor to the total environmental impact and economic cost. Human-powered hydroponic systems, which utilise human muscular exertion to power the system, have not been thoroughly investigated, despite their potential as a cost-efficient alternative and less harmful to the environment. This paper presents a prototype of a novel human-powered hydroponic system and assesses its environmental impact and economic costs using life cycle assessment (LCA) and life cycle costing (LCC), considering the cultivation of lettuce as a case study. A scenario analysis was performed to assess the environmental impact of lettuce production using a human-powered hydroponic system compared to conventional soil or greenhouse-based production methods. Using SimaPro LCA software, 18 impact categories included in the ReciPe Midpoint (H) method were evaluated. The results indicated that the battery, followed by the power system, represented the primary environmental hotspots of the human-powered hydroponic system. Improving the yield (production of 6 lettuces of 500 g vs 200 g per 40-day growing cycle) of the human-powered hydroponic system can reduce the environmental impact of lettuce production compared to conventionally soil-based produced lettuce in 11 out of the 18 evaluated impact categories, and when compared to greenhouse-produced lettuce, it generates lower impacts in 14 out of 18 categories. Regarding economic cost, considering a yield of 1.2 kg (6 lettuces of 200 g) per 40-day growing cycle with the human-powered hydroponic system, it is more expensive for the consumer than buying lettuce produced with conventional soil-based open-field agriculture and greenhouses, and break-even points are not achievable within 15 years (the lifespan of the system). However, when considering a yield of 3 kg (6 lettuces of 500 g), the break-even point with greenhouse-produced lettuce was achieved between 10 and 11 years. Therefore, although a break-even point is not achievable within the considered lifespan of the developed system, it could be reached if the yield of the system increased and/or if the system had a longer lifespan, which is mainly determined by the lifespan of the battery.