Tests were conducted at an off-grid location in India, and the proposed method includes using thermal storage of excess heat from photovoltaic modules for space and water heating. The optimal configuration of the system is given by the combination of a 224 kW photovoltaic system equipped with phase change materials, a 206 kW wind turbine, a 420 kW biogas generator, a 633 Ah battery and a 170 kW converter.
The excess heat generated by solar panels can be used for space heating.
Image: O'Connor School of Law/Flickr
Scientists at the University of Portsmouth in the UK have developed a system design for integrating large-scale wind, solar, biogas and energy storage into off-grid locations.
The feature of the proposed design is that the excess heat from the photovoltaic module is stored in the phase change material. The researcher explained: "This heat energy can be converted into space and water heating-this is usually the largest energy consumption in a household."
Phase change material (PCM) is a substance that can store heat energy and can stabilize temperature. When their physical state changes, such as during melting and freezing, they can absorb or release a large amount of so-called "latent heat."
The system consists of PV units equipped with PCM on the back of solar modules; wind turbines; a battery; and a biogas plant. PCM is used to cool the panel and store excess heat. "The heat storage capacity of PCM depends on its melting temperature and its latent heat capacity," the scientists emphasized. "Calcium chloride hexahydrate has a melting point of about 30 degrees Celsius and a latent heat capacity of 191 kJ/kg. It is used as PCM."
When photovoltaic and wind power cannot meet all demands, batteries are used as secondary energy sources, and their capacity must be based on the power, battery efficiency, and energy demand required for a day. Wind turbines, photovoltaic systems, and battery packs are connected to the DC bus, and biogas generators and electrical loads are connected to the AC bus. A converter is needed to convert AC power to DC power and vice versa.
The system design was tested in a hotel in Chennai, India, where the climate is hot and humid. "The electrical load curve is the main influencing factor in the design and optimization of integrated hybrid energy systems," the British group emphasized. "Therefore, it is very important to understand how the load changes during weekdays and weekends so that the hybrid system can maximize resource utilization and minimize system costs." The electrical loads of buildings include computers, fans, lights, electronic equipment, and machinery.
Control algorithms are used to maximize wind and solar power generation, reduce battery usage, and minimize biogas operations to reduce carbon emissions. The optimal configuration of the system is given by the combination of a 224 kW photovoltaic system equipped with PCM, a 206 kW wind turbine, a 420 kW biogas generator, a 633 Ah battery and a 170 kW converter.
The current net cost of this configuration is US$1.43 million, and the research team estimates its levelized energy cost (LCOE) to be US$0.094/kWh. Comparing these values with the values of the same system design without PCM storage, it is found that these values are much lower.
"For an off-grid system based on photovoltaic-wind-biogas-generator-battery, the integration of phase change materials and photovoltaic panels can save US$220,000 in net present cost and reduce the energy of the system from US$0.099/kWh to $0.094/kWh," the researcher said. "We conducted this research in areas without power grids, so our future research needs to investigate how to transform it into areas with power grids."
A complete description of the system design can be found in a paper recently published in the Energy Journal on Optimizing a New Hybrid Wind Bio-Cell Solar Photovoltaic System Integrated with Phase Change Materials.
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