Implementation of an off-grid photovoltaic system in a greenhouse for hydroponic production

Resumen

Hydroponics has emerged as a well-established cultivation technique in recent years, particularly due to its smaller installation area requirements and reduced water consumption compared to traditional soil-based cultivation. Among hydroponic methods, the NFT (Nutrient Film Technique) is the most widely adopted in commercial production. However, its operation relies heavily on electricity to pump nutrient solutions to the cultivation benches. In this context, solar power has been used as a sustainable energy solution to address this dependency. Thus, this study aims to implement a photovoltaic system for powering a hydroponic production greenhouse located in the experimental area of the Postgraduate Program in Agricultural Engineering (PPGEA) at the Federal University of Recôncavo da Bahia (UFRB), Cruz das Almas, Bahia, Brazil. The photovoltaic system was designed to meet the simultaneous energy demand of six submersible aquarium pumps (15 W each), distributed across six independent production units. This off-grid solar system (with battery storage) operates at a 12 V DC nominal voltage. To evaluate the energy self-sufficiency of the solar-powered hydroponic production, four complete lettuce cultivation cycles (46 days of continuous operation) were conducted using two distinct hydroponic systems: a roof sheet-based cultivation and conventional hydroponic channels. The total implementation cost for the photovoltaic system was of R$1,799.09, including the following components: 150 W solar panel, 1000 W power inverter (12 V DC to 110 V AC), 20 A charge controller, two deep-cycle batteries (30 Ah and 70 Ah), electrical wiring, and a circuit breaker. The photovoltaic system demonstrated full energy autonomy throughout the 46-day experimental period, continuously meeting all power demands for hydroponic lettuce cultivation. Total pump runtime reached 141 h 50 min, maintaining a consistent daily operational cycle of 3 h and 5 min. The roof sheet-based cultivation system demonstrated significantly greater fresh shoot biomass production across four successive harvest cycles, with yields of 381.41, 233.76, 272.96, and 240.93 g plant^-1 for the four sequential harvests, respectively. These values represent yield increases of 32, 15, 29, and 23% compared to traditional hydroponic channels. Therefore, this study demonstrates that integration of roof sheet-based NFT cultivation with solar energy constitutes an effective solution for small-scale hydroponic farmers, particularly in are where electrical energy is not available or presents frequent failures in supply.