Economic and environmental life cycle assessments of solar water heaters applied to aquaculture in the US

Abstract

Global aquaculture production has increased rapidly over recent decades, playing an important role in serving an essential protein source for world population. Understanding and mitigating its resource use and environmental impacts are important for the sector to grow in a sustainable manner. As a renewable resource, solar energy has been considered to reduce energy burdens as well as environmental impacts of fish farming practices. This study aims to investigate the applicability of solar water heating systems under different geographical conditions (cold, moderate, and hot climates) with consideration of both environmental and economic impacts. In addition, different operational strategies and design factors were considered including water sources (groundwater and streamwater), heating amounts (0 to 100% heating), and solar system designs (horizontally or optimally oriented solar panels). Energy requirement was estimated based on a recirculating aquaculture system for Nile tilapia production under indoor and outdoor conditions. Instead of energy savings, the potential economic improvements due to the temperature effect on fish yields were considered as an economic benefit of using solar water heating systems for aquaculture. It was found that environmental impacts of solar water heaters under the cold climate decreased as heating increased from 20% to 80% due to the large improvement in fish production, while the impacts increased with increased heating in the hot and moderate climates. In life cycle costing, the use of solar water heater for aquaculture was economically favorable at any heating strategy as well as under any setting and climate, except for a 20% heating in the cold climate. When compared to electric water heaters, solar water heaters generally showed lower environmental impacts across all cases. However, economic benefits of solar water heaters over electric heaters were dependent upon heating strategy, setting and climate condition. Due to the variations of heating demand and efficiency of solar system, considerations of water source and solar system design could further mitigate environmental and economic impacts. The sensitivity analysis showed that life cycle environmental impact assessment results in this study were most sensitive to the choice of species, while life cycle costing results were most sensitive to the inputs associated with the annual incomes and the cultured fish. This study can provide insights to the optimal operational strategies of the solar water heating systems for aquaculture to seek environmentally and economically sustainable energy systems.