Researchers tested a solar-powered system to gasify dried cattle manure, achieving higher energy recovery than grid-powered systems. Their techno-economic-ecological analysis shows that the approach can reduce emissions and be economically viable, although system usage and operational factors strongly influence profitability.
An international team of researchers has conducted an experimental analysis of solar PV integrated gasification of dried cattle manure.
The gasification of dried cattle manure begins by feeding the dried biomass into a gasifier, where only a limited amount of oxygen or air is supplied. In the reactor, the material is exposed to high temperatures, causing thermochemical reactions such as pyrolysis and partial oxidation, which break down the organic material. As a result, a combustible gas mixture called producer gas or syngas is produced, which consists mainly of carbon monoxide, hydrogen and small amounts of methane, along with residual ash and charcoal left behind as byproducts.
“Our research presents a new approach by integrating solar PV technology with the gasification of livestock manure, especially in confined animal feeding operations (CAFOs),” corresponding author Muhammad Ashraf told pv magazine. “The unique aspect of our work lies in the Techno-Economic-Environmental Assessment (TEEA), which shows that the integration of solar energy significantly improves energy recovery and reduces dependence on electricity from the grid, providing an economically viable and environmentally sustainable waste-to-energy solution for regions with abundant livestock resources, such as Pakistan.”
Ashraf also explained that while the team expected the PV system to improve the system’s energy recovery, the TEEA results were unexpectedly surprising.
“Although we assumed that the cost of raw livestock manure was free, the levelized cost of energy (LCOE) and overall economic feasibility were still affected by load patterns and system usage,” he said. “Even with high energy recovery efficiency – more than 80% biomass conversion and almost 67% energy recovery – the economic benefits in some operating conditions, especially at partial or low system utilization, were not as great as expected.”
Additionally, he noted that factors such as capacity factor, system outages and maintenance are as important as the fuel source itself in determining the overall feasibility of the system. “This outcome challenges the conventional assumption that biomass energy systems with free feedstocks will always be economically viable, especially if they rely on intermittent renewable energy sources such as solar energy,” he said.
Their research began by analyzing different combinations of cow and buffalo dung, measuring their moisture content and volatiles, and analyzing the carbon, hydrogen, nitrogen, sulfur and oxygen compositions. After the tests, the group decided to proceed with one mix of cow dung from different Pakistani cities, one mix of buffalo dung and one mix containing both.
Image: Bahauddin Zakariya University, Sustainable Chemistry for Climate Action, CC BY 4.0
All three raw materials were dried, crushed, sieved and then fed into the gasification system. The system consisted of an electric tube oven, powered by six 400 W mono PERC solar panels. The pilot plant operated at a fertilizer feed rate of 2 kg/hour at four power levels: 500 W, 700 W, 900 W and 1,100 W. These power levels heated the oven to approximately 500 C, 600 C, 700 C and 800 C respectively.
The researchers said the solar PV system showed a net energy recovery of 40.17%, which significantly outperformed grid-based systems, which achieved only 23.03%. They added that the system reduces CO₂ emissions by 1.2 to 1.3 kg per kilogram of dried cattle manure, equivalent to the carbon sequestration capacity of 12 to 13 hectares of forest per year.
Image: Bahauddin Zakariya University, Sustainable Chemistry for Climate Action, CC BY 4.0
Based on the TEEA, the researchers also concluded that the system is economically viable. It has a payback period of 3.75 years and can generate an annual turnover of PKR 98,703 ($352.1) at a processing capacity of 5 kg/day. They added that gasification at 800 C, which provided optimal syngas yields, proved to be scalable.
“We plan further research to scale up this system for larger CAFOs and to investigate its feasibility in different environmental conditions. In addition, we would like to investigate further optimization of the system to improve syngas yield and reduce emissions, especially in the context of different types of biomass,” said Ashraf. “The next phase of research will focus on improving the commercial viability of solar PV integrated gasification systems and evaluating their performance at different scales, including pilot projects in rural and off-grid areas.”
Their findings can be found in “Evaluation of the market feasibility of solar photovoltaic integrated gasification of livestock manure: experimental research”, published in Sustainable chemistry for climate action. Researchers from Pakistan’s Bahauddin Zakariya University, the University of Engineering and Technology, the NFC Institute of Engineering and Technology, China’s Nantong University, Nigeria’s Federal University of Petroleum Resources and the University of South Africa conducted the study.
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