Combined Heat And Power Technologies Research Articles

Reliability-oriented optimal sizing of power-to-gas and combined heat and power technologies in integrated electricity and natural gas transmission systems

Integration of electricity and natural gas systems is a promising solution to enhance the overall efficiency and reliability of the energy systems. The combined heat and power (CHP) and power-to-gas (P2G) technologies are first-rate options to integrate an electrical power system with a natural gas network. Accordingly, unlike previous works that considered only one technology in their studies, this paper proposes an optimization framework to determine the optimal sizing of both CHP and P2G technologies in the integrated electricity and natural gas systems. In addition, although previous researches proved the impacts of the P2G and CHP units on energy system reliability, this criterion has been neglected in optimal sizing of these technologies. To narrow research gaps, this paper employs a detailed energy flow model along with a sequential Monte Carlo-based reliability evaluation method within the proposed optimization framework. The proposed optimization problem aims to minimize the investment, operation, and reliability costs subject to economical and operational constraints. The proposed method is tested on an integrated IEEE 24-bus electrical power system and 20-node Belgian natural gas system. The simulation results demonstrate the effectiveness and applicability of the proposed reliability-oriented sizing method and prove how considering the reliability cost in the objective function can reduce the total cost.

A cost-effective and ecological stochastic optimization for integration of distributed energy resources in energy networks considering vehicle-to-grid and combined heat and power technologies

Electric vehicles (EVs) have the potential to decarbonize the transport sector and contribute to the attainment of the global Net-Zero goal. However, to achieve sustainable decarbonization, EVs’ power for grid-to-vehicle (G2V) operations should be sourced from carbon-free or low carbon power generating sources. Whilst the adoption of renewable energy sources (RES) in EVs’ G2V process has been extensively explored, combined heat and power (CHP) technologies are underexamined. Hence, this paper deploys harmonized natural gas and fuel cell CHP technologies alongside RES and battery energy storage systems (BESS) to facilitate EVs’ G2V and vehicle-to-grid (V2G) operations. While the BESS supports V2G operations and stores excess power from the CHP and RES, the CHP’s by-product heat could be employed in heating homes and industrial facilities. Furthermore, to maximize environmental and economic benefits, the CHP technologies are designed following the hybrid electric-thermal load strategy, such that the system autonomously switches between following the electric load strategy and following the thermal load strategy. The proposed optimization problem is tested using three different case studies (CSs) to minimize the microgrid’s (MG) operating costs and carbon dioxide (CO2) emissions in a stochastic framework considering the RES generations, the load consumption, and the behaviour patterns of charging/discharging periods of EVs as the uncertain parameters. The first CS tests the proposed algorithm using only CHP technologies. Secondly, the algorithm is examined using the CHP technologies and RES. Finally, the BESS is added to support and analyse the impacts of the V2G operations of EVs on the MG. Furthermore, the life cycle assessment is investigated to analyse the CO2 emissions of distributed generations. The results show a 32.22%, 44.49%, and 47.20% operating cost reduction in the first, second, and third CSs. At the same time, the CO2 emissions declined by 29.13%, 47.13% and 47.90% in the various corresponding CSs. These results demonstrate the economic and environmental benefits of applying CHP with RES in facilitating G2V and V2G operations towards achieving a decarbonized transport sector.

Advances on a free-piston Stirling engine-based micro-combined heat and power system

As a promising supplement to traditional central electric generation technologies, a distributed combined heat and power (CHP) system is conducive to renewable energy deployment and mitigation of carbon emissions. Among the candidate technologies, the free-piston Stirling engine (FPSE)-based CHP technology is competitive in micro- or small-scale applications. In this work, the performance of a FPSE-based micro-CHP system is improved through a combination of numerical optimization and experimental validation. First, by using a third-order model and thermoacoustic analysis, the impact of regenerator length, displacer moving mass, and force factor of the alternator on the free-piston Stirling generator (FPSG) inside acoustic field, supplied thermal power and exergy loss is studied numerically. The numerical results indicate a rational increase of the force factor, the regenerator length as well as the displacer moving mass is positive for improving the CHP performance. Based on the numerical optimization, the FPSG prototype is updated accordingly, and adequate measurements of the internal acoustic field of the FPSG have been deployed. Then, a series of experiments are conducted to evaluate the CHP performance of the refurbished FPSG prototype. The experimental results show that the highest CHP efficiency reaches 95.7%, the output electric power is 4.03 kW, and the corresponding thermal-to-electric efficiency is 32.2% when the average temperature of supply and return water is as high as 75 °C. Compared with the work before upgrade, the output electric power and CHP efficiency are improved significantly by 39% and 9.4%, respectively. An insight into the impact of the temperature difference between supply and return water indicates that it has a slight impact on electric power generation, especially under higher charge pressure. In contrast, thermal production exhibits an apparent negative correlation with the temperature difference.

Off-design modeling of a microturbine combined heat & power system

There is increasing interest in decision support software tools that evaluate the techno-economic potential of distributed energy system technologies for deployment in combined heat and power (CHP) applications, such as commercial buildings, microgrids, and connected communities. This trend is particularly evident among end-users looking to integrate renewable resources with more traditional CHP technologies for on-site generation and enhanced resiliency. However, many of these software tools do not account for part-load and off-design characteristics of prime mover and heat recovery equipment, resulting in lower accuracy for both the optimal selection and sizing and the economic value proposition of integrated hybrid renewable energy-CHP systems. Microturbine technology is an attractive distributed energy resource whose performance is sensitive to both part-load and off-design (i.e., excursions of ambient conditions away from the design point temperature and pressure) operating conditions but is widely unreported. In the present work, we address this deficiency by developing a detailed, thermodynamic model of a commercial 200 kW microturbine CHP system and paramaterizing results for incorporation into the Renewable Energy Optimization (REopt) tool developed by the National Renewable Energy Laboratory. The details of the microturbine model, including model benchmarking and validation, are presented. Microturbine off-design modeling includes part-load analysis, assessment of ambient sensitivities, and mapping heat recovery heat exchanger response to hot water grade requirements. The model is then exercised in several illustrative examples to depict the numerous factors which alter electric power, electric efficiency, and hot water recovery. Model results show, for example, predictions of a 4 percentage point electric efficiency range occurring between intake air temperatures of -18 to 50 °C. Likewise, the model closely predicts the 25 % loss in heat recovery while at -18 °C and the 8 % gain in heat recovery while at 35 °C. An additional case shows how heat recovery may increase or decrease by 9.5 % of the design value when changing the return water temperature plus-or-minus 22 °C. In particular, the impact of ambient conditions on best-possible microturbine performance is conveyed through hourly simulations of the system subjected to the weather of different geographic locations within the United States. • A model of a 200 kW microturbine configured for hot water recovery is developed. • Part-load modeling approach and simulation results for both electric efficiency and waste heat recovery are detailed. • Off-design performance as functions of ambient temperature and pressure is explored. • Heat recovery performance maps as functions of return and supply hot water temperatures are developed.

CHP performance under the warming climate: a case study for Russia

Vulnerability of the cogeneration technologies towards the climate change is addressed. Climate and energy modeling approaches were combined to simulate operation of a modern binary-cycle combined heat and power (CHP) plant across Russia. It has been shown that a heating loads decrease combined with an increase of the extreme cold temperatures is determining a crucial vulnerability mechanism for CHP technologies development under the climate change. A heating load criterion was elaborated to describe a dependence of the CHP performance on the local climate conditions. The proposed criterion was applied to generalize results of the fulfilled numerical modeling. It has been found that the climate-related CHP efficiency deterioration observed since the middle of the 20th century attained 0.3–0.9% points across Russia contributing to the current crisis of the CHP technology nationwide and increasing carbon intensity of the cogeneration sector. Peak heating demand management has been discussed as a potential adaptation strategy. The CHP efficiency drop may be leveled by an adjustment of the extreme cold temperature values according to the observed climate dynamics when designing the CHP plants.

A Review of Small–Medium Combined Heat and Power (CHP) Technologies and Their Role within the 100% Renewable Energy Systems Scenario

The energy transition towards a scenario with 100% renewable energy sources (RES) for the energy system is starting to unfold its effects and is increasingly accepted. In such a scenario, a predominant role will be played by large photovoltaic and wind power plants. At the same time, the electrification of energy consumption is expected to develop further, with the ever-increasing diffusion of electric transport, heat pumps, and power-to-gas technologies. The not completely predictable nature of the RES is their well-known drawback, and it will require the use of energy storage technologies, in particular large-scale power-to-chemical conversion and chemical-to-power re-conversion, in view of the energy transition. Nonetheless, there is a lack in the literature regarding an analysis of the potential role of small–medium CCHP technologies in such a scenario. Therefore, the aim of this paper is to address what could be the role of the Combined Heat and Power (CHP) and/or Combined Cooling Heat and Power (CCHP) technologies fed by waste heat within the mentioned scenario. First, in this paper, a review of small–medium scale CHP technologies is performed, which may be fed by low temperature waste heat sources. Then, a review of the 100% RE scenario studied by researchers from the Lappeenranta University of Technology (through the so-called “LUT model”) is conducted to identify potential low temperature waste heat sources that could feed small–medium CHP technologies. Second, some possible interactions between those mentioned waste heat sources and the reviewed CHP technologies are presented through the crossing data collected from both sides. The results demonstrate that the most suitable waste heat sources for the selected CHP technologies are those related to gas turbines (heat recovery steam generator), steam turbines, and internal combustion engines. A preliminary economic analysis was also performed, which showed that the potential annual savings per unit of installed kW of the considered CHP technologies could reach EUR 255.00 and EUR 207.00 when related to power and heat production, respectively. Finally, the perspectives about the carbon footprint of the CHP/CCHP integration within the 100% renewable energy scenario were discussed.

State-by-State comparison of combined heat and power to photovoltaic installations at manufacturing facilities with heat and power loads

Manufacturing facilities with large electricity and steam loads commonly meet those loads with a grid and boiler (GB) system configuration. In this study, two alternatives, a natural gas turbine cycle driven combined heat and power (CHP) system configuration and a grid boiler system augmented with photovoltaics (GB-PV), are investigated sustainable manufacturing in reference to the GB system configuration. For this purpose, their discounted payback period (DPP), carbon dioxide (CO2) and nitrogen oxides (NOx) emission reductions, and primary fossil energy impacts are calculated. The major contribution of this study is that it directly compares the application of both CHP and PV technologies at an assumed manufacturing facility in all 50 states of the United States. This highlights the location-specific impacts of the facility. The examined manufacturing facility utility requirements are 5 MW of power and over 12,000 kg/h of 250 kPa and 400 K saturated steam. A DPP of less than 25 years, the technology lifetime, is found in 44 states for the CHP system configuration and 6 states for the GB-PV system configuration. GB-PV and CHP cost-effectively reduce CO2 in 44 and 38 states, respectively. CHP is better for NOx reduction, whereas GB-PV is better for primary fossil energy reduction.

Heat pipelines and climate camps: Coal mining's in/visible infrastructure

Heat pipelines installed for combined heat and power (CHP) connect cities to their coal mining hinterlands. In Germany, CHP technology assures that coal fired power plants can continue producing electricity even during times when renewable sources are overproducing, thereby thwarting the low-carbon energy transition. Using a case study of Leipzig and surrounding coal mines, this article draws attention to the socio-material path dependency of this technology. Local anti-climate change protesters emphasise heavily the impacts of mines and power plants, presencing the risks of coal combustion. What they often fail to take into account, however, is CHP technology and heat pipelines.

Comparative analysis of different CHP systems using biogas for the cassava starch plants

Energy demands of a cassava starch plant (CSP) were investigated and modeled. Four combined heat and power (CHP) systems using biogas were evaluated and compared, including energy self-support, economic feasibility and environmental impacts. Assessment results indicated that CHP system with reciprocating internal-combustion engine (ICE-CHP) and micro turbine (MT-CHP) can meet all the energy demands of the CSP. ICE-CHP technologies obtained the best profit, followed by MT-CHP, B/T-CHP and common system. The four systems are economically feasible, ICE-CHP showed better economy than MT-CHP system. Both ICE-CHP and MT-CHP systems have the lowest environmental impacts comparing to other CHP systems in view of emissions. ICE-CHP should be suggested firstly considering the short payback period (4.57 year), the lowest environmental impacts and 100% of energy self-support. Boiler/Turbines CHP (B/T-CHP) will not be adopted as it is unable to supply all the electricity needs of the CSP. Plant availability shows the greatest impact on the payback period. If the investment cost of MT-CHP decreases by more than 12.7%, MT-CHP would have better economy than ICE-CHP. The results are helpful for the management of CSP to select the suitable CHP technology.

A review of Stirling-engine-based combined heat and power technology

Small- and micro-scale combined heat and power (CHP) technologies offer great potential for reducing energy costs and CO2 emissions in residential and small commercial buildings. Among various CHP technologies, Stirling engines, particularly free-piston ones, show great promise in residential applications because of their remarkable advantages of low emissions, maintenance, noise, and vibration, theoretically high thermal-to-electrical efficiency, and flexibility of fuel sources. This paper presents a comprehensive review of Stirling-engine CHP in terms of different heat sources, tri-generation systems, status of commercial development, techno-economic issues, and challenges and future trends. The techno-economic assessment indicates that the relatively low on-site operational efficiencies and considerable investment costs are the main issues that hinder the further development of Stirling-engine CHP systems, and suggestions for future development are made accordingly. For successful commercial dissemination of Stirling-engine CHP, it is essential to improve the on-site electrical efficiency, reduce the capital cost of systems, and develop renewable-energy-powered and free-piston Stirling-engine-based CHP systems against the background of grid decarbonization and carbon neutrality.

Techno-Economic Assessment of CHP Systems in Wastewater Treatment Plants

Wastewater treatment plant (WWTP) utilization of combined heat and power (CHP) systems allows for the efficient use of on-site biogas production, as well as increased annual savings in utility costs. In this paper, a review of biogas energy recovery options, CHP prime mover technologies, and the costs associated with biogas cleaning give a broad summary of the current state of CHP technology in WWTPs. Even though there are six different prime mover technologies, the main ones currently being implemented in WWTPs are micro turbines, fuel cells and reciprocating engines. Different prime movers offer varying efficiencies, installation costs, and biogas impurity (H2S, siloxanes, HCl) tolerances. To evaluate the long-term savings capabilities, a techno-economic assessment of a CHP installation at a case study WWTP shows the payback, annual savings, and initial costs associated with the installation of a CHP system. In this case, a study a payback of 5.7 years and a net present value of USD 709,000 can be achieved when the WWTP generates over 2,000,000 m3 of biogas per year and utilizes over 36,000 GJ of natural gas per year.

Prospects of Fuel Cell Combined Heat and Power Systems

Combined heat and power (CHP) in a single and integrated device is concurrent or synchronized production of many sources of usable power, typically electric, as well as thermal. Integrating combined heat and power systems in today’s energy market will address energy scarcity, global warming, as well as energy-saving problems. This review highlights the system design for fuel cell CHP technologies. Key among the components discussed was the type of fuel cell stack capable of generating the maximum performance of the entire system. The type of fuel processor used was also noted to influence the systemic performance coupled with its longevity. Other components equally discussed was the power electronics. The thermal and water management was also noted to have an effect on the overall efficiency of the system. Carbon dioxide emission reduction, reduction of electricity cost and grid independence, were some notable advantages associated with fueling cell combined heat and power systems. Despite these merits, the high initial capital cost is a key factor impeding its commercialization. It is, therefore, imperative that future research activities are geared towards the development of novel, and cheap, materials for the development of the fuel cell, which will transcend into a total reduction of the entire system. Similarly, robust, systemic designs should equally be an active research direction. Other types of fuel aside, hydrogen should equally be explored. Proper risk assessment strategies and documentation will similarly expand and accelerate the commercialization of this novel technology. Finally, public sensitization of the technology will also make its acceptance and possible competition with existing forms of energy generation feasible. The work, in summary, showed that proton exchange membrane fuel cell (PEM fuel cell) operated at a lower temperature-oriented cogeneration has good efficiency, and is very reliable. The critical issue pertaining to these systems has to do with the complication associated with water treatment. This implies that the balance of the plant would be significantly affected; likewise, the purity of the gas is crucial in the performance of the system. An alternative to these systems is the PEM fuel cell systems operated at higher temperatures.

Analytical Study to Use the Excess Digester Gas of Wastewater Treatment Plants

Abstract This study presents an analytical method that can be used to enhance the power production rate and the energy-saving at wastewater treatment plants. The digester used at wastewater treatment plants produces digester gas by anaerobic digestion, with which biofuel production can be achieved. Biofuels can be used to meet some of the energy requirements of the wastewater treatment facility through combined heat and power (CHP) gas engines (cogeneration). Using micro gas turbine (MGT), a CHP technology can be introduced in wastewater treatment plants (WWTPs). The combination of MGTs and absorption chillers is a promising technology as it produces electricity, heating, and cooling simultaneously. The study demonstrated how the waste heat of MGTs could be used to drive absorption chillers. In this analytical study, a detailed technical and economic analysis is provided on the trigeneration system, i.e., the integration of MGTs and absorption chillers driven by waste digester gas of the wastewater treatment plants. It can meet the heating and cooling demands of the plants, which promote the reduction of utility costs. The technology presented is also useful for other thermal energy users.

Modeling of combined heat and power generation in the context of increasing renewable energy penetration

Combined heat and power (CHP) can achieve fuel efficiencies of up to 90% and is thus considered as economically advantageous and ecologically sound compared to uncoupled power and heat generation. This advantage is exploited only if CHP plants are operated as much as possible at their optimal operation point. Increasing penetration by variable renewable energy sources and more flexible technologies challenge this optimal operation. With decreasing residual power loads the required share of power in the CHP output combination decreases and a mix of alternative technologies by uncoupled power and heat generation, power-to-heat, and storage, can become more efficient than CHP. Using a cost-minimizing investment and dispatch model individual CHP technologies are examined in stylized energy systems with increasing renewable energy penetration. Findings: whereas fuel efficiency of CHP and the share of cogenerated residual power increases, this improvement is offset by decreasing full load hours.

Flexibility of combined heat and power plants: A review of technologies and operation strategies

With an increasing penetration of renewable energy, combined heat and power (CHP) plants play an important role in connecting different energy sectors of an integrated energy system (IES). Technical flexibility is an essential ability for CHPs to provide secure and economic operation of the IES, as well as to implement a profitable arbitrage in different markets. Operation strategies (OSs) are adopted to utilize the existing technical flexibility in an optimal way. The delivered flexibility is evaluated in terms of the system performance and operation profits. In this paper, a literature review on technical flexibility and characteristics of different CHP technologies is summarized. Moreover, the applications of CHP system flexibility in the IES are discussed from the perspectives of plant owners, system operators and demand side. Literature classified by cost-based and price-based OSs is studied for system operators and generation plant owners respectively. Characteristics of the OSs in terms of the CHP modeling, optimization objectives, constraints and algorithms, etc. are discussed and compared. The study is beneficial to achieve more economic operation of the IES and more profitable operation of the CHP system by system operators and plant owners. Future research work regarding this topic is investigated in the last part.

Development of an advanced free-piston Stirling engine for micro combined heating and power application

Combined heat and power (CHP) systems play an important role in meeting energy requirements and reducing the environmental impact of power generation. Recently, free-piston Stirling engines (FPSE) have attracted much attention as a promising CHP technology due to the characteristics such as high efficiency, high reliability, and quiet operation. In this study, a conceptual CHP system integrated with a FPSE was developed. In order to reduce flow separation and thermal losses in the FPSE, an integrated assembly of the pressure vessel, heat exchangers, and new foil type regenerator was designed. To achieve this integrated design, additive manufacturing was used to fabricate these key components and improve the overall FPSE efficiency by removing the design limitation of traditional fabrication methods while decreasing manufacturing cost. Finite element analysis and computational fluid dynamics were conducted to determine the optimal flow distribution and engine structure. Dynamic and rocking mode analyses of displacer assembly were performed. One dimensional thermodynamic modeling of the Stirling engine using Sage software was performed to estimate the system performance. The results indicated that the CHP system could provide 1 kWe electrical power at nearly 38% fuel to electricity efficiency and 1.1 kW of thermal energy at 80 °C. The mapping results of the FPSE show that it has excellent partial power efficiency. Thus, it is concluded that the CHP system based on a FPSE is much more efficient and cost-effective than other CHP system designs and is suitable to provide electrical power and heat for residential applications.

An Improved Heating System with Waste Pressure Utilization in a Combined Heat and Power Unit

An improved heating system integrated with waste pressure utilization (WPU) for combined heat and power (CHP) cogeneration was proposed. The new heating system efficiently utilized the excess pressure of the extraction heating steam to drive the WPU turbine and generator for producing electricity, achieving higher energy efficiency and lower fuel consumption of the CHP unit. The results of the detailed thermodynamic analysis showed that applying the proposed concept in a typical 300 MW coal-fired CHP unit could reduce the standard coal consumption rate by 9.84 g/(kW·h), with a thermal efficiency improvement of 1.97% (absolute value). Compared to that of the original heating process, the energy efficiency of the proposed process decreased by 0.55% (absolute value), but its exergy efficiency increased dramatically by 17.97% (absolute value), which meant that the proposed configuration could make better use of the steam energy and contribute to the better performance of the CHP unit. As the unit generation load and supply and return-water temperatures declined and the unit heating load rose, the WPU system would generate more electricity and its energy-saving benefit would be enhanced. This work provides a promising approach to further advance the CHP technology and district heating systems.

Combined vs separate heat and power production – Primary energy comparison in high renewable share contexts

Natural Gas Combined Cycle (NGCC) units are currently the most efficient power plants based on fossil fuels. When used for Combined Heat and Power (CHP) production, serving District Heating (DH) systems, they have been usually promoted by stating their lower primary energy consumption compared to separate production of power and heat with conventional technologies. However, a significant increase of the share of Renewable Energy Sources (RES) in power generation and Heat Pumps (HP) for heat production in buildings could undermine this assumption. This paper evaluates a case study in Northern Italy, by comparing the real operation of three NGCC plants serving a DH network against the separate production of power (from real data of the National electricity mix) and heat (considering two scenarios based on natural gas boilers and heat pumps). The analysis is performed on hourly data over a two-years’ time frame, to highlight the variations across the hours of the day and the seasons. To perform a comprehensive analysis, the entire system performance is considered, by comparing the useful energy supplied to the users to the primary energy consumption. The results show how the primary energy savings of fossil CHP technologies are strongly related with the available alternatives, which have been going through a significant evolution in last years. The separate production of heat and power can now be performed with competitive technologies, which benefit from the high share of RES in electricity production. Therefore, the comparison between combined and separate production is influenced by the high variability of the electricity generation mix, which needs to be carefully considered.

Effects of environmental emissions on optimal combination and allocation of renewable and non-renewable CHP technologies in heat and electricity distribution networks based on improved particle swarm optimization algorithm

Combined heat and power (CHP) units are efficient from view point of source energy, however, for maximum utility company economic profit, it is necessary to account for all revenues and expenditures. The goal of this study is to examine the effects of considerations for environmental emissions in optimal combination and allocation of renewable and non-renewable CHP technologies including fuel cells (FC), internal combustion engines (ICE), and micro turbine (MT) in heat and electricity distribution networks based on improved particle swarm optimization algorithm, where the economic profit of utility company as the CHP owner and operator is maximized over the operation horizon. When all three technologies are available, the optimal combination and allocation results show that FC-CHP and MT-CHP are the preferred technologies and, the environmental emission costs do not allow for ICE-CHP technology to be included in the combination and, the yearly utility company economic profit is increased by 10.39, 28.37, and 13.95% due to optimal combination and allocation of CHP units in comparison with optimal allocation of FC, ICE, and MT technologies on individual basis, respectively. Also, by analyzing various HPRs, it is determined that the yearly utility company economic profit is increased when HPR is decreased.

Effect of feeding frequency and organic loading rate on biomethane production in the anaerobic digestion of rice straw

World energy demand is growing and the negative effects of greenhouse gases (GHGs) and climate change are being felt more acutely. Accordingly, technologies that reduce GHG releases and produce renewable energy, such as anaerobic digestion (AD) with combined heat and power (CHP) systems, are potentially attractive for agricultural wastes, including rice straw (RS). Asia produces over 500 Mt of RS per year that is usually burned, wasting potential energy, causing air pollution and GHGs, and having negative health impacts. Therefore, making RS AD options more attractive is urgently needed. This paper shows biomethane (CH4) yields from infrequently fed RS AD units, which match better with RS harvest production cycles, can be very efficient at specific CH4 production without the need for co-digestion. Using Biomethane Potential (BMP) data to guide AD reactor conditions, five feeding frequencies (FFs) were operated for over 250days in bench-scale units, ranging from five feeds per seven days (5/7; frequent) to one feed per 21days (1/21; infrequent), using OLRs of 1gVS/L/d and 2gVS/L/d. Highest specific methane yields (148±6.3mL CH4/g VS/d) were observed at 1/21 FF and the lower OLR. In contrast, highest volumetric yields were seen for a FF of 1/7 at 2gVS/L/d (276±10.6mL CH4/L/d), although AD units failed at this OLR for FFs of 1/14 and 1/21 due to volatile fatty acids accumulation. This study shows RS AD is feasible without co-digestion, producing biogas that can be coupled with CHP technology to provide renewable energy. However, less frequent feeding regimes performed better than more frequent feeding regimes, suggesting infrequently-fed batch AD units may be a better option for biomethane production, especially for rural locations.