Page 115 - New Trends in Green Construction

PUMP-AS-TURBINES FOR ENERGY RECOVERY: AN ATTRACTIVE SOLUTION FOR AUTO CONSUMPTION IN AGRICULTURAL FARMS
Miguel Crespo Chacón, Aonghus McNabola, Juan Antonio Rodríguez Díaz, Jorge García Morillo
Keywords: Pump as turbine; Energy recovery; Irrigation networks; GHG emission savings; Auto consumption
1. Introduction
Agriculture is one of the largest energy consumers in the European Union (EU), accounting for around 2.2% of the total energy consumed in 2016 (European Commission, 2019). In some regions where agriculture is an intensive activity, this consumption is even more significant. In the case of Spain, agriculture was reported to consume 3% of the total energy in 2016, which constitutes an increase of 43% since 1990 (IDAE, 2019), being responsible for important greenhouse gases (GHG) emissions and climate change contributions.
This research aims to study the potential benefits of pump as turbine (PAT) installations for energy recovery and auto consumption of this energy at farm level in pressurised irrigation networks, recovering energy from the existing excess pressure that is currently dissipated. The design and potential savings of a micro hydropower plant, which aimed to replace a diesel generator for a PAT in a farm located in Southern Spain, is discussed in this research.
2. Materials and methods
The research has been carried out in a farm located at the left bank of the Genil river irrigation district (GMI), in Southern Spain. The irrigated farm has a surface of 163 ha, with walnut as the sole crop. The hydraulic infrastructure feeding the farm is part of an on-demand irrigation network, where water is available 24 hours per day. Different devices on the farm require electrical energy during irrigation activity, with a maximum power of 3.6 kW. The pressure at the hydrant of the farm varies along the irrigation season, always having at least an excess pressure of 20m that is dissipated using a pressure reducing valve (PRV). The water demand also varies between zero, where no power is required, and 190 l s-1 along the irrigation season from April 1 to September 30, depending on the crop water requirements.
The plant proposed in this research consists on the installation of a 4 kW PAT installed in a by- pass, which will recover energy from the existing excess pressure. However, large flow fluctuations make the anticipation of its performance and design complex (Lydon, 2017). To select the PAT, analyze its performance during the irrigation season and assess its economic viability, the methodology proposed by Crespo Chacon et al. (2019) was applied. The selected PAT was tested in a hydraulic model, to ensure no impacts on network performance along the season were produced. The environmental impact of the installation was also assessed.
3. Results and conclusions
-1 The minimum flow to be turbined to have a constant production of 4 kW was 37 l s . Its
cumulative occurrence probability was 84% along the irrigation season. However, the minimum
115
New Trends in Green Construction