The dark side of lighting: A critical analysis of vertical farms' environmental impact

Vertical farming (VF) is a type of farming system where crops are cultivated in enclosed and sunless environments, offering a high level of precision and control of the crop environment. Several recent reviews have highlighted VF as a potential solution to global challenges like population growth, urbanization and climate change, thanks to land conservation, sustainability, reduced water usage, enhanced food safety, and shorter supply chains. This review critically analyses claims regarding the sustainability and other proposed benefits of VF, by focusing on what is known about crop energy budgets and productivity. It makes evident that staple crops, vital for calorie intake, cannot be economically grown in VF. Nonetheless, leafy vegetables can and are grown in VF. Based on existing literature, VF's annual production potential and its associated electricity consumption are quantified here. Figures about electricity production demonstrate that it is doubtful that urban VF production is more climate-smart than transport from far away. Even in a future world of green (but not unlimited) electricity, there will be a need for balancing grid usage, which does not fit well with the electricity craving of VFs. A review of pros and cons of growing systems of increasing technology content, shows that reduction of water use and of chemical emissions can be attained as well in greenhouses, without the environmental impact of the electricity consumption associated to VF. It is indeed wishful thinking that there is no environmental cost to getting rid of (free and non-polluting) sunlight, even for the very best lighting fixtures. VF may have potential for niche crop production, or be employed for other practical reasons. However, this review challenges the claim that VF production is inherently more environmentally friendly than conventional agriculture. •Quantify productivity and electricity requirements of vertical farm cultivation.•VF's energy use is double that of greenhouses, and 100 times that of open field.•Open field farming and transport usually causes less emissions than local VF.•Water savings and reduction of chemical use are also achievable in greenhouses.•Benchmark for evaluating VF should be high-tech greenhouses, not open field.