Fish, light and aquavoltaics
Global environmental concerns and increasing energy demand, combined with steady progress in renewable energy technologies, are opening up new opportunities for the use of renewable energy sources. Solar energy is the most abundant, inexhaustible, and cleanest of all renewable energy sources (Parida et al., 2011). Photovoltaic conversion is the direct conversion of sunlight into electricity without the interposition of a heat engine. All solar cells require a light-absorbing material present in the cell structure to absorb photons and produce free electrons through the photovoltaic effect.
‘Floatovoltaic’ represent an emerging power-generation technology utilizing idle water and solar energy systems—comprising floating photovoltaic (FPV) panels over water. They are an attractive source of low-carbon energy because they free up land for other uses and produce greater electricity yields compared to land-based systems. FPV designs for freshwater are evolving as the technology matures and primarily include PV panels mounted on individual floats, on racks attached to floating pontoons, or on poles fixed to the water’s bottom (Fig. 1 ) (Liu et al 2018).
However, to date little is understood of the impacts of FPV on the hosting water body. Anticipating changes to water body processes, properties and services owing to FPV deployment represents a critical knowledge gap that may result in poor societal choices and water body governance (Armstrong et al., 2020). As the world’s population increases and competition for land rises, dual-use approaches are becoming essential solutions in the agriculture and aquaculture sectors. With the constantly growing aquaculture industry and the increasing demand for eco-friendly production processes, the necessity for employing optimized aquaculture systems, supplied by renewable energies, gaining progressively attention in the global food production sector. Teaming up photovoltaic with agriculture or aquaculture, namely, the agrivoltaics and aquavoltaics (AquaPV ), create novel energy-food (land or water) nexus offering mutual benefits potentially (Jing et al., 2022). AquaPV is a concept emerged with combining electricity production and aquaculture. The goal of AquaPV is the efficient use of water with the dual use for both food and energy generation. The AquaPV approach aims to maintain parameters such as water and air temperature, light availability, water pH, dissolved oxygen, feeding system, and predator pressure, and improve the system by exploiting synergies between aquaculture and FPV systems. While solar panels above the water or on its surface provide the electrical energy, the aquatic organisms living within the water below provide a sustainable food source.
Light characteristics are very specific in an aquatic environment and light is extremely variable in nature. ‘Receptivity’ of fish to light profoundly changes according to the species and the developmental status (Beouf and La Bail, 1999).
Fish move within their environment and often their environment moves around them, affecting the light that the fish receives (Sumpter, 1992) . Moreover, light shows interesting characteristics in the aquatic envi ronment. In fact, ‘quality’ (the different wavelengths which are absorbed by water to various extents) , ‘quantity’ (different intensities) and ‘periodicity’ (daily cycles, which vary seasonally according to latitude) should also be considered. Fish behaviour can be affected even by artificial light stimuli. A common reaction of fish groups to the presence of artificial light is to school and move towards the light source (Ben-Yami, 1976). Functional explanations for such a reaction include predator avoidance and enhancement of feeding efficiency (Pitcher and Parrish, 1993). In terms of aquavoltaics, l ight emitting diodes (LEDs) can be installed on the bottom of the pontoon structures in the aquavoltaic system, powered by the PV portion of the system to affect the photoperiod of aquatic life. This design provides a powerful tool for the aquaculturist to increase and further optimize production for specific aquatic species but needs to be tested further, while the effects of energy conversion need to be considered, also. (Pringle et al., 2017). Normally, fish are either more active in light and less active in darkness or vice versa, and this can be altered by daily changes in factors such as temperature or oxygen. Growth of aquatic organisms is linked to light, but it is not unique because species vary in their growth conditions. Fish and larvae, for example, must be reared in specific light ranges depending on the species and stage of development (Boeuf and Le Bail, 1998). Aquavoltaics provide shade on the fish pond water surface, and the blocked light is absorbed by solar panels and converted into usable energy. If uncontrolled, an increase in shading decreases algal growth, general plant life, and microbial density are reduced, affecting the entire food chain down to the fish intended for breeding. With a suitable system approach, aquavoltaics can contribute to sustainable water use and fulfil the concept of the food-water-energy nexus . More research is needed to understand the effects of direct contact with pontoon structures and solar arrays on aquatic life.
References
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