Unlocking the potential of biogas systems for energy production and climate solutions in rural communities

The study addresses the challenge that reliable, on-demand renewable energy systems are often lacking in developing regions, leading to continued reliance on fossil fuels and rising carbon emissions. Biogas, with 55–65% methane, offers a viable path to control methane and replace fossil fuels, potentially achieving comparable energy-return-on-investment when ecological costs are considered. In rural China, approximately 800 million people lack access to natural gas or biogas. Existing centralized models (e.g., CHP or biomethane upgrading) face economic and technical barriers for deployment in developing areas, while village-scale systems often suffer intermittent supply and methane leakage due to mismatched production and consumption. The core research question is how to design and deploy an efficient community biogas production and distribution system (CBPD) that supplies biogas on demand, minimizes methane leakage, and maximizes climate and energy co-benefits. The proposed solution focuses on achieving a consumption-to-production ratio (CPR) close to 1 through coordinated control on both plant and user sides, supported by storage, operational optimization, and demand management.

The paper reviews current biogas utilization models, notably EU practices emphasizing CHP and biomethane upgrading with real-time grid injection, which require advanced monitoring and automation and face feasibility challenges in developing contexts. In rural developing regions, incomplete utilization and intermittent supply limit biogas’ contribution to energy access and climate benefits. China’s manure and crop straw have a methane potential of 73.6 billion m³ per year, enough to cover household demand, and high-quality biogas systems are among the most effective strategies to reduce methane emissions from organic waste management (e.g., replacing anaerobic lagoons). Prior work highlights operational requirements (feeding strategies, temperature control), monitoring of methane emissions, and policy and market constraints affecting decentralized bioenergy projects. The authors frame CBPD as a practical, decentralized alternative that can better align local feedstock availability and stable demand while addressing methane leakage.

The authors propose an upgraded CBPD and evaluate it with empirical data from five rural Chinese systems supplying biogas directly to households. The optimization framework has four steps: (1) data-driven identification of biogas demand rate, modeling consumption patterns including routine and intermittent uses; (2) quantification of biogas production capacity and dynamics based on fermentation temperature, organic loading, reactor configuration, and feeding schedules, using existing models and data fitting; (3) storage capacity design to buffer mismatches, including safety margins accounting for operational deviations and usage variability; (4) coordinated operational strategies on plant and user sides, including active adjustments in feeding timing/amount and user-side incentives/regulation, combined with professional operation to minimize leakage. Data collection: Hourly biogas production and consumption (and methane content) were measured at each CBPD using calibrated transit-time ultrasonic flow meters with dehydration systems; one meter upstream of storage (production) and one on the main supply line. Data cleaning removed outliers and suspected leakage periods based on thresholds (e.g., improbable nocturnal consumption, extreme values relative to daily averages), retaining only days with both production and consumption quality data. Modeling and calculations: Mass balance of storage Q(t) relates production q(t), consumption g(t), emissions e(t), and heating demand h(t) to maintain fermentation temperature. Storage capacity Q_storage is sized as a multiple (safety factor k) of peak residual gas during a feeding interval. GHG emissions (E_CBPD) account for methane slip and fossil fuel replacement benefits using methane content r, biogas density p, substitution fractions C_j, and emission factors E_j (rural household weighted mean 0.0739 kg CO2-eq/MJ). Net GHG with heating (E_CBPD,net) deducts biogas needed for maintaining fermentation temperature based on caloric value (21.54 MJ/m³ at 60% CH4) and 70% heat efficiency. Climate impacts on heating needs are estimated using outdoor solar-air temperature computed from bulb temperature and solar radiation. The RPD metric (ratio of regional manure methane potential to rural biogas demand) evaluates provincial deployment feasibility. Methane mitigation from manure management optimization uses IPCC methodology with methane conversion factors (MCF) for baseline systems; upgraded CBPD assumes zero methane emissions from manure management. National contribution to the 1.5 °C target is estimated by comparing mitigation against required national emission decrement.

- A four-step, demand-driven CBPD optimization enables CPR close to 1 by fitting production to consumption, optimizing storage, and coordinating plant- and user-side operations. - Empirical production dynamics show a ~1.5-day lag after feeding, with production peaking around hours 39–48 and then declining until the next feeding; consumption follows daily cycles aligned with mealtimes. - Under current empirical operations (baseline CPR 67.5%), assumed methane loss of 32.5% eliminates fossil-fuel substitution benefits, yielding net positive emissions of 1.39 kg CO2-eq d⁻¹ customer⁻¹. - Upgrading CBPD with adequate storage and optimized operation to achieve CPR = 1 converts this to net negative emissions of −1.01 kg CO2-eq d⁻¹ customer⁻¹ per customer (considering fossil fuel replacement and avoided leakage). - Operator training and operational tuning can reduce storage required to achieve CPR = 1 by 11.6% (by increasing user-side consumption at peaks) and 9.5% (by decreasing plant-side production amplitudes), respectively. - Sensitivity analyses indicate that a 1.79× increase in storage capacity ensures robustness across most conflicted supply–demand scenarios. A coordinated strategy with allowable fluctuation ranges and cycle-to-cycle adjustments prevents error accumulation. - Climate analysis across cities shows net mitigation remains substantial with heating penalties in colder climates: e.g., Nairobi’s additional heating reduces mitigation by ~9%; Harbin in January achieves −0.38 kg CO2-eq d⁻¹ customer⁻¹; six other cities show −0.88 to −0.95 kg CO2-eq d⁻¹ customer⁻¹. - Nationally in China, upgraded CBPDs could eliminate 62.4% of rural inhabitants’ carbon emissions from household energy use and contribute 3.77% toward China’s 1.5 °C commitment when including manure management methane reductions and fossil fuel substitution. - Current rural biogas use corresponds to only 25.4% of manure methane potential at observed consumption rates, indicating large untapped potential; even considering fuel substitution only, further manure-based biogas use could reduce national fossil-fuel combustion emissions by 0.9–1.7%.

The upgraded CBPD directly addresses the research question by demonstrating a practical, decentralized system that synchronizes biogas production with demand (CPR ≈ 1), thereby maximizing energy access while minimizing methane leakage. Coordinated plant-side feeding strategies, right-sized storage with safety margins, and user-side incentives create a flexible, self-adjusting system capable of real-time balancing. This approach reduces reliance on centralized grids and complex CHP/biomethane systems that face feasibility challenges in developing regions. The findings show robust decarbonization across diverse climates, with manageable penalties in cold regions, and substantiate the potential for large-scale rural deployment in China to meaningfully advance national climate targets. Broader implications include improved manure management, enhanced circular agriculture via nutrient recycling, and policy pathways for operator training and storage optimization subsidies to secure reliable operations and sustained emissions reductions.

The paper presents an upgraded, demand-driven CBPD that attains CPR ≈ 1 through data-driven consumption modeling, tuned production (feeding timing/amount), appropriately sized storage, and coordinated operational strategies on plant and user sides. Empirical evaluation across five rural Chinese communities shows that aligning biogas supply with demand and minimizing leakage turns currently positive emissions into net negative emissions per customer, with robustness achieved via modest storage amplification and operator training. Climate analyses confirm viability across prevailing conditions, and national-scale deployment could substantially reduce rural household emissions and contribute ~3.77% toward China’s 1.5 °C target when including manure management methane abatement. Future work should refine feedstock logistics and co-fermentation strategies, enhance predictive control to minimize storage needs, explore time-of-use demand management, and integrate with other renewables (e.g., solar, heat pumps) to form resilient, stand-alone rural energy systems.

- Feedstock availability and characteristics vary spatiotemporally; results depend on region- and practice-specific logistics, stakeholder incentives, and transport distances, which can erode net mitigation. - The RPD assessment was conducted at the provincial level; finer spatial resolution (e.g., town-level) could yield more accurate deployment planning and storage designs. - Operational success hinges on skilled management of feeding schedules and amounts; misoperation can cause temporal congestion, mismatches, and leakage. - Cold climates impose additional heating requirements to maintain fermentation temperature, reducing net mitigation in some periods. - The empirical analysis draws on five CBPDs; broader datasets across diverse contexts would strengthen generalizability and parameterization for predictive control.