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Fraunhofer ISE, TMU build ‘aquavoltaic’ system for microalgae production

Source：pv-magazine

The system can reportedly reduce electricity costs in aquaculture. It consists of an open raceway pond, a mechanical paddle wheel, a motor and power transmission system, a motor speed control circuit, a 100 W photovoltaic module, and 12-V battery with a capacity of 60 Ah, an inverter, and a 10-A charge controller.

Scientists from Germany's Fraunhofer Institute for Solar Energy Systems (Fraunhofer ISE) and the Tarbiat Modares University (TMU) in Iran have designed a PV system for microalgae and electricity co-production.

They explained that aquaculture facilities have commonly high electricity costs accounting for approximately 40 % of their total energy costs, with around 0.5 % of global GHG emissions being attributable to aquaculture. “The cultivation of microalgae in open pond systems, when integrated with PV technology, can improve energy efficiency, and reduce water evaporation, further aligning aquaculture practices with climate change mitigation goals,” they stressed.

The research group described the proposed technology as a “small aquavoltaic” system consisting of an open raceway pond, a mechanical paddle wheel, a motor and power transmission system, a motor speed control circuit, a 100 W photovoltaic module, and 12-V battery with a capacity of 60 Ah, an inverter, and a 10-A charge controller.

The key element of the system, the polyethylene raceway pond, was conceived with an open design to allow access to sunlight and air. Usually, these ponds have a shallow design to reduce evaporation and contamination, as well as to favor continuous water circulation.

The academics set the optimum water depth for microalgae production in the pond at 0.3 m. “By controlling this specific water depth together with other parameters such as rotation speed and reaction time, it is possible to create favorable conditions for both microalgae production and electricity generation in the aquavoltaic system,” they further explained.

The performance of the system was assessed through a series of experimental tests conducted from May 9 to May 15, under different weather conditions. The main parameters were solar radiation, air temperature, and wind speed.

The analysis showed that the shading caused by the solar panel has a “significant” impact on controlling the temperature and pH range in the microalgae production pond. The module, however, was able to cover approximately 98.6 % of the aquaculture facility's annual electricity demand.

The team also conducted a techno-economic analysis on a system hosting the cultivation of Spirulina, blue-green algae containing vitamins, minerals, antioxidants, and proteins, and found it was able to achieve 7% lower electricity costs compared to a reference system powered by grid electricity.

“The cost of Spirulina produced with the aquavoltaic system in the fifth year was calculated at $0.4975/g at a %5 interest rate and $0.331/g at a %10 interest rate,” the scientists emphasized. “In addition, the cost per liter for Spirulina produced with the aquavoltaic system was calculated at $0.7133/g.”

The details of the system can be found in the paper “Development and experimental performance evaluation of a small-scale aquavoltaic system for microalgae production,” published in Results in Engineering. “The current study underlines that aquavoltaics could have the potential to further increase the production of microalgae and thus reduce production costs,” the researchers concluded.

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