Large-scale Bioenergy Research Articles

An Assessment of Potential Resources for Biomass Energy in Nigeria

Nigeria is a developing country with an insufficient supply of energy to meet the continuously growing demand. However, there are several biomass resources available within the country. This paper presents a desk review, which investigates the potential resources for biomass energy generation within the country. Energy policies to aid biomass use as an energy source within the country were also reviewed. Biomass resources identified within Nigeria include forest residues, agricultural residues, human and animal wastes, aquatic biomass, and energy crops. However, several of the resources, particularly agricultural residues, have competing uses, such as livestock feed and soil rejuvenation. An estimation of the technical energy potential of the biomass resources revealed that about 2.33 EJ could be generated from the available resources in Nigeria. Agricultural residues have an energy potential of about 1.09 EJ, with cassava, maize, oil palm, plantain, rice, and sorghum being the major contributors. Animal wastes, municipal solid waste, and forest residues have energy potentials of 0.65, 0.11, and 0.05 EJ, respectively. The potentials of wood fuel and charcoal are 0.38 and 0.05 EJ, respectively. The study found that despite the available potential and existing policies, not much has been done in the implementation of large-scale bioenergy within the country. However, there has been laboratory and research-scale investigations. The review suggests that more policies and stronger enforcement will aid bioenergy development within the country. From the review, it has been suggested that the agricultural sector needs to be developed to generate more biomass resources. More research, development, and implementation have to be carried out on biomass resources and bioenergy generation processes. The production of non-edible energy crops in marginal lands should also be considered prime to the development of bioenergy within the country.

A spatial equilibrium analysis of using agricultural resources to produce biofuel

In order to alleviate the potential damage from climate change and fulfil the requirements contracted in the Paris Agreement (COP 24), China has promulgated the mandatory regulation on ethanol-blend gasoline to reduce current levels of CO2 emissions. Since large-scale bioenergy development involves various aspects such as feedstock selection (energy crops, crop wastes), technology alternatives (conventional and cellulosic ethanol, pyrolysis), government subsidy (land use, energy crop subsidy) and carbon trade mechanism, an analysis that integrates economic, environmental, and social effects is necessary to explore the optimal biofuel strategy and social effects. This study proposes a price endogenous, partial equilibrium mathematical programming model to investigate how the selection of bioenergy crops and bioenergy technologies influences the amount of net bioenergy production, carbon sequestration, government subsidies, and cultivation patterns. We show that the conjunctive use of agricultural wastes can be an effective addition to current biofuel production. The results also indicate that at high gasoline and emissions prices, more land used for the energy crop program results in a significant change in government expenditure. In addition, net emissions reduction and emissions offset efficiency can vary substantially when different bioenergy techniques are adopted.

Extra CO2 capture and storage by carbonation of biomass ashes

Eight biomass ashes (BAs) produced at 500 and 900 °C were studied to definite their composition, phase transformations, carbonation-decarbonation behavior, and CO2 capture and storage (CCS) potential. Light microscopy, powder X-ray diffraction, scanning electron microscopy, as well as differential-thermal, thermo-gravimetric and chemical analyses were used for that purpose. It was found that most of the BAs studied have high contents of alkaline-earth and alkaline elements represented by carbonates, bicarbonates, oxyhydroxides, chlorides, sulphates, phosphates, and inorganic amorphous material, and such minerals and phases have a key role for CCS by BA. There is an intensive formation of newly formed carbonates as a result of solid–gas reactions between alkaline-earth and alkaline oxyhydroxides and volatile CO2 formed during biomass combustion. Subsequently, additional post-combustion carbonates and bicarbonates are formed by both solid–gas and solid-liquid reactions between the unreacted oxyhydroxides and carbonates in BA and CO2 occurring in air and water during BA storage. The decomposition temperature of carbonates is mostly at 600–900 °C and the mass loss measured in this temperature range approximately determines the CO2 volatilization from the carbonates in BAs. The measured CO2 volatilization (or CCS) for the BAs studied is between 1 and 27% (mean 11%). It was emphasized that the biomass energy can be not only carbon-neutral, but also with some extra CCS potential due to fixation and immobilization of atmospheric CO2 in BA. Therefore, the future large-scale bioenergy production can contribute enormously for reducing CO2 emissions and can decrease or eliminate the application of expensive technologies for CCS.

Freshwater requirements of large-scale bioenergy plantations for limiting global warming to 1.5 °C

Limiting mean global warming to well below 2 °C will probably require substantial negative emissions (NEs) within the 21st century. To achieve these, bioenergy plantations with subsequent carbon capture and storage (BECCS) may have to be implemented at a large scale. Irrigation of these plantations might be necessary to increase the yield, which is likely to put further pressure on already stressed freshwater systems. Conversely, the potential of bioenergy plantations (BPs) dedicated to achieving NEs through CO2 assimilation may be limited in regions with low freshwater availability. This paper provides a first-order quantification of the biophysical potentials of BECCS as a negative emission technology contribution to reaching the 1.5 °C warming target, as constrained by associated water availabilities and requirements. Using a global biosphere model, we analyze the availability of freshwater for irrigation of BPs designed to meet the projected NEs to fulfill the 1.5 °C target, spatially explicitly on areas not reserved for ecosystem conservation or agriculture. We take account of the simultaneous water demands for agriculture, industries, and households and also account for environmental flow requirements (EFRs) needed to safeguard aquatic ecosystems. Furthermore, we assess to what extent different forms of improved water management on the suggested BPs and on cropland may help to reduce the freshwater abstractions. Results indicate that global water withdrawals for irrigation of BPs range between ∼400 and ∼3000 km3 yr−1, depending on the scenario and the conversion efficiency of the carbon capture and storage process. Consideration of EFRs reduces the NE potential significantly, but can partly be compensated for by improved on-field water management.

Energy and Environmental Aspects of Using Eucalyptus from Brazil for Energy and Transportation Services in Europe

The international market of woody biomass for bioenergy is expected to have a major role in future global scenarios aligning with a 2 or 1.5 °C target. However, the quantification of the environmental impacts of energy and transportation services from novel technologies and biomass production systems are yet to be extensively studied on a case-specific basis. We use a life cycle assessment approach to quantify environmental impacts of four bioenergy systems based on eucalyptus plantations established in abandoned pastureland in Brazil. The alternative bioenergy systems deliver energy and transportation services in Europe (cradle-to-gate analysis), including modern technologies for production of heat, electricity (with and without carbon capture and storage), and advanced liquid biofuels. We find that all bioenergy systems can achieve sizeable climate benefits, but in some cases at increased pressure in other impact categories. The most impacting activities are biomass transport stages, followed by eucalyptus stand establishment, and pellet production. An estimate of the potential large-scale bioenergy deployment of eucalyptus established in marginal areas in Brazil shows that up to 7 EJ of heat, 2.5 EJ of electricity, or 5 EJ of transportation biofuels per year can be delivered. This corresponds to a climate mitigation potential between 0.9% and 2.4% (0.29 and 0.83 GtCO2 per year) of the global anthropogenic emissions in 2015, and between 5.7% and 16% of European emissions, depending on the specific bioenergy system considered. A sensitivity analysis indicated that the best environmental performance is achieved with on-site biomass storage, transportation of wood chips with trucks, pellets as energy carrier, and larger ship sizes. Our quantitative environmental analysis contributes to increased understanding of the potential benefits and tradeoffs of large-scale supply of biomass resources, and additional research can further improve resolution and integrate environmental impact indicators within a broader sustainability perspective, as indicated by the recently established sustainable development goals.

Global energy sector emission reductions and bioenergy use: overview of the bioenergy demand phase of the EMF-33 model comparison

We present an overview of results from 11 integrated assessment models (IAMs) that participated in the 33rd study of the Stanford Energy Modeling Forum (EMF-33) on the viability of large-scale deployment of bioenergy for achieving long-run climate goals. The study explores future bioenergy use across models under harmonized scenarios for future climate policies, availability of bioenergy technologies, and constraints on biomass supply. This paper provides a more transparent description of IAMs that span a broad range of assumptions regarding model structures, energy sectors, and bioenergy conversion chains. Without emission constraints, we find vastly different CO2 emission and bioenergy deployment patterns across models due to differences in competition with fossil fuels, the possibility to produce large-scale bio-liquids, and the flexibility of energy systems. Imposing increasingly stringent carbon budgets mostly increases bioenergy use. A diverse set of available bioenergy technology portfolios provides flexibility to allocate bioenergy to supply different final energy as well as remove carbon dioxide from the atmosphere by combining bioenergy with carbon capture and sequestration (BECCS). Sector and regional bioenergy allocation varies dramatically across models mainly due to bioenergy technology availability and costs, final energy patterns, and availability of alternative decarbonization options. Although much bioenergy is used in combination with CCS, BECCS is not necessarily the driver of bioenergy use. We find that the flexibility to use biomass feedstocks in different energy sub-sectors makes large-scale bioenergy deployment a robust strategy in mitigation scenarios that is surprisingly insensitive with respect to reduced technology availability. However, the achievability of stringent carbon budgets and associated carbon prices is sensitive. Constraints on biomass feedstock supply increase the carbon price less significantly than excluding BECCS because carbon removals are still realized and valued. Incremental sensitivity tests find that delayed readiness of bioenergy technologies until 2050 is more important than potentially higher investment costs.

Life cycle water use of a biomass-based pyrolysis polygeneration system in China

Water is essential for bioenergy production. Characterized as low carbon technology, crop-based bioenergy technology witnesses rapid development, inevitably putting pressure on global water resources. Therefore, it is crucial to carefully assess bioenergy technology’s overall impact on scarce water source for a sustainable bioenergy future. In this regard, this study aims to evaluate the life cycle water use of bioenergy from agricultural residues via the first pilot moving-bed pyrolysis polygeneration system in China. By using a tiered hybrid life cycle assessment, both direct and indirect water use are calculated. Results show life cycle water use is 3.89 L H2O/MJ and agricultural process dominates the total water use. Scenarios analysis shows different feedstock allocation ratios during agricultural production have striking influence on water use intensity. In addition, the choice of feedstock is another important influential factor. Under the 2020 Scenario in China’s 13th Five Year Plan, if all the bioenergy target could be met by polygeneration the estimated annual water use will be 6.6 billion m3, in magnitude up to around ten times the total water consumption in Denmark in 2013. In global scenario of potential feedstock available in 2060, the estimated water use for bioenergy produced by polygeneration will be 179–369 billion m3. Although the water use intensity of bioenergy production from agricultural residues by polygeneration is lower than that for other biomass conversion pathways, it is still higher than water intensity of conventional fossil energy products. Large-scale bioenergy production will have macroscopic effects on water demand. Finally, suggestions such as selecting high water-efficient biomass feedstock and reinforcing water-saving irrigation management to minimize water use in agriculture stage are proposed.

Potential impacts of agricultural land use on soil cover in response to bioenergy production in Canada

The introduction of a market for agricultural biomass to feed large-scale second generation bioenergy (cellulosic ethanol) or other bio-products has positive implications for food producers and bio-product industries but may impact soil quality. In order to assess the potential impact on Canada’s agricultural lands, we integrated land use and soil capability maps and land management information to introduce several scenarios of crop residue harvest rates and land use conversions. The implications for soil quality, as represented by soil cover, were assessed for each scenario. The results showed that average soil cover at the national scale would decrease by more than 1 day if 40% of annual crop residues (by mass) were harvested, but the negative impacts could be resolved by increased adoption of conservation tillage methods. Additional biomass could be produced by converting low quality agricultural land to perennial biomass crops, but this would result in increased intensity of food production on high quality land. The total area of high and low quality land within the agricultural region of Canada is roughly equal, and the amount of high quality land currently used for perennial crops is about the same as the amount of low quality land used for annual crops, and ‘balancing’ production with capability would result in a net increase in both food and biofuel feedstock, with little impact to soil quality. About 6.73 M ha of high quality land is covered by forest, shrub and grass, and conversion of this land to agricultural production would have a negative impact on soil quality. The study indicates considerable potential for production of both food and biofuel feedstock on Canada’s agricultural lands through careful land use planning. Our analysis using soil cover as an indicator of environmental sustainability also indicates that land use planning should be cautious to prevent soil degradation. Particularly, regional variability of land use and soil capability distribution requires region specific land use policy for sustainable biofuel feedstock production.

Large-scale bioenergy production: how to resolve sustainability trade-offs?

Large-scale 2nd generation bioenergy deployment is a key element of 1.5 °C and 2 °C transformation pathways. However, large-scale bioenergy production might have negative sustainability implications and thus may conflict with the Sustainable Development Goal (SDG) agenda. Here, we carry out a multi-criteria sustainability assessment of large-scale bioenergy crop production throughout the 21st century (300 EJ in 2100) using a global land-use model. Our analysis indicates that large-scale bioenergy production without complementary measures results in negative effects on the following sustainability indicators: deforestation, CO2 emissions from land-use change, nitrogen losses, unsustainable water withdrawals and food prices. One of our main findings is that single-sector environmental protection measures next to large-scale bioenergy production are prone to involve trade-offs among these sustainability indicators—at least in the absence of more efficient land or water resource use. For instance, if bioenergy production is accompanied by forest protection, deforestation and associated emissions (SDGs 13 and 15) decline substantially whereas food prices (SDG 2) increase. However, our study also shows that this trade-off strongly depends on the development of future food demand. In contrast to environmental protection measures, we find that agricultural intensification lowers some side-effects of bioenergy production substantially (SDGs 13 and 15) without generating new trade-offs—at least among the sustainability indicators considered here. Moreover, our results indicate that a combination of forest and water protection schemes, improved fertilization efficiency, and agricultural intensification would reduce the side-effects of bioenergy production most comprehensively. However, although our study includes more sustainability indicators than previous studies on bioenergy side-effects, our study represents only a small subset of all indicators relevant for the SDG agenda. Based on this, we argue that the development of policies for regulating externalities of large-scale bioenergy production should rely on broad sustainability assessments to discover potential trade-offs with the SDG agenda before implementation.

VOC off-gassing from pelletized steam exploded softwood bark: Emissions at different industrial process steps

Formation of hazardous gases during transport and storage of biomass for large-scale bioenergy production is an important safety concern. While off-gassing has been addressed in numerous studies for raw woody biomass, very few describe it in the context of biomass for bioenergy production pre-treated by thermal technologies such as steam explosion. Volatile Organic Components (VOCs) are expected to be altered by the treatment, but until now there is no research published on VOC profiles of steam exploded materials in industrial scale. In the present study, VOCs emitted from the products were evaluated by sampling from different production steps from steam explosion of softwood bark, and following the production chain including also pelletization. Off-gasses were actively sampled using Tenax TA absorbent and analyzed by GC–MS. The VOC formation dependency of operation and storage conditions at different process steps was evaluated by multivariate statistical analysis. We showed that the different process steps along the production line was the main influencing factor for VOC off-gassing amounts, with highest VOC levels directly after the steam explosion process. Treatment severity mainly altered the relative composition of VOC profiles with more terpenes emitted from milder treatment, whereas more severe treatment shifted VOCs composition to contain more furans, e.g. furfural. In summary, treatment by steam explosion leads to potentially problematic VOC off-gassing profiles from the material, and levels vary considerable along the production line. The findings are important from a fuel handling and working environment perspective.

Current and future technical, economic and environmental feasibility of maize and wheat residues supply for biomass energy application: Illustrated for South Africa

This study assessed the feasibility of mobilising maize and wheat residues for large-scale bioenergy applications in South Africa by establishing sustainable residue removal rates and cost of supply based on different production regions. A key objective was to refine the methodology for estimating crop residue harvesting for bioenergy use, while maintaining soil productivity and avoiding displacement of competing residue uses. At current conditions, the sustainable bioenergy potential from maize and wheat residues was estimated to be about 104 PJ. There is potential to increase the amount of crop residues to 238 PJ through measures such as no till cultivation and adopting improved cropping systems. These estimates were based on minimum residues requirements of 2 t ha−1 for soil erosion control and additional residue amounts to maintain 2% SOC level.At the farm gate, crop residues cost between 0.9 and 1.7 $ GJ−1. About 96% of these residues are available below 1.5 $ GJ−1. In the improved scenario, up to 85% of the biomass is below 1.3 $ GJ−1. For biomass deliveries at the conversion plant, about 36% is below 5 $ GJ−1 while in the optimised scenario, about 87% is delivered below 5$ GJ−1. Co-firing residues with coal results in lower cost of electricity compared to other renewables and significant GHG (CO2 eq) emissions reduction (up to 0.72 tons MWh−1). Establishing sustainable crop residue supply systems in South Africa could start by utilising the existing agricultural infrastructure to secure supply and develop a functional market. It would then be necessary to incentivise improvements across the value chain.

Balancing biofuel production and biodiversity: Harvesting frequency effects on production and community composition in planted tallgrass prairie

Native perennial grasslands have been proposed as a source of feedstocks for the production of second-generation lignocellulosic biofuels in the Midwestern USA. Although the consequences of some management decisions for biomass production and plant community composition are well understood (e.g. fertilization), less is known about the effects of harvesting frequency. We compared a once- and twice-annual harvesting regime at two restored prairies in southwestern Michigan established with identical seed mixtures as part of a large-scale bioenergy experiment. We determined biomass production and species composition in experimental plots and also measured the availability of light, inorganic nitrogen and soil moisture. The plant communities that established at the two sites differed markedly in composition and there was little evidence of convergence after five years. At the site dominated by warm-season C4 grasses, single harvests generally produced more biomass than double harvests. By contrast, biomass production was unaffected by harvesting at the more diverse site. Contrary to our prediction that a summer harvest would increase diversity, we found small and subtle effects on plant community composition. This may be due in part to the timing of our harvest treatment. Our results suggest that a single, end-of-season harvest is the best practice for maximizing biomass production in prairies, especially at sites where warm-season grasses dominate. However, at more diverse sites, two harvests can produce the same total biomass and may support other beneficial ecosystem services. This study indicates that in the short term, double harvests are unlikely to affect plant species diversity or community composition in prairie plantings.

Comparing the life cycle impacts of using harvest residue as feedstock for small- and large-scale bioenergy systems (part I)

In part I of our two-part study, we compare the timing-adjusted GHG (greenhouse gas) balance and life cycle impacts of potentially using harvest residue (unmerchantable small-diameter roundwood) in an existing large (211 MWe) wood pellet-fired (formerly coal-fired) power plant in Ontario, Canada, versus a hypothetical small (250 kWe) wood chip gasification plant that recovers heat in addition to producing electricity. Although the large, retrofitted power plant has a higher electrical efficiency, the small plant has lower environmental impacts (TRACI 2.1), mainly due to the benefits of drying the biomass inputs with recovered heat, having a shorter fuel shipping distance, and reduced biomass processing. The small plant emits 38 g of fossil fuel-derived CO2 eq./kWh, versus 134 g/kWh from its large-scale counterpart. Although these GHG emissions are insignificant relative to the forest carbon emissions from gasification and combustion (1.3–1.4 kg CO2/kWh), the harvest residue would have decomposed over time had it been left on the forest floor. After 100 years, forest carbon storage decreases by 3.8–4.1 kg from the sustained production of 1 kWh of electricity per year. The decline in carbon storage delays net GHG mitigation by 4 (small-scale system) to 7 years (large-scale system) when displacing electricity from coal.

Opportunities and Challenges in the Design and Analysis of Biomass Supply Chains.

The biomass supply chain is one of the most critical elements of large-scale bioenergy production and in many cases a key barrier for procuring initial funding for new developments on specific energy crops. Most productions rely on complex transforming chains linked to feed and food markets. The term 'supply chain' covers various aspects from cultivation and harvesting of the biomass, to treatment, transportation, and storage. After energy conversion, the product must be delivered to final consumption, whether it is in the form of electricity, heat, or more tangible products, such as pellets and biofuels. Effective supply chains are of utmost importance for bioenergy production, as biomass tends to possess challenging seasonal production cycles and low mass, energy and bulk densities. Additionally, the demand for final products is often also dispersed, further complicating the supply chain. The goal of this paper is to introduce key components of biomass supply chains, examples of related modeling applications, and if/how they address aspects related to environmental metrics and management. The paper will introduce a concept of integrated supply systems for sustainable biomass trade and the factors influencing the bioenergy supply chain landscape, including models that can be used to investigate the factors. The paper will also cover various aspects of transportation logistics, ranging from alternative modal and multi-modal alternatives to introduction of support tools for transportation analysis. Finally gaps and challenges in supply chain research are identified and used to outline research recommendations for the future direction in this area of study.

Bioenergy and Biodiversity: Key Lessons from the Pan American Region.

Understanding how large-scale bioenergy production can affect biodiversity and ecosystems is important if society is to meet current and future sustainable development goals. A variety of bioenergy production systems have been established within different contexts throughout the Pan American region, with wide-ranging results in terms of documented and projected effects on biodiversity and ecosystems. The Pan American region is home to the majority of commercial bioenergy production and therefore the region offers a broad set of experiences and insights on both conflicts and opportunities for biodiversity and bioenergy. This paper synthesizes lessons learned focusing on experiences in Canada, the United States, and Brazil regarding the conflicts that can arise between bioenergy production and ecological conservation, and benefits that can be derived when bioenergy policies promote planning and more sustainable land-management systems. We propose a research agenda to address priority information gaps that are relevant to biodiversity concerns and related policy challenges in the Pan American region.

Comparing the life cycle costs of using harvest residue as feedstock for small- and large-scale bioenergy systems (part II)

In part II of our two-part study, we estimate the nominal electricity generation and GHG (greenhouse gas) mitigation costs of using harvest residue from a hardwood forest in Ontario, Canada to fuel (1) a small-scale (250 kWe) combined heat and power wood chip gasification unit and (2) a large-scale (211 MWe) coal-fired generating station retrofitted to combust wood pellets. Under favorable operational and regulatory conditions, generation costs are similar: 14.1 and 14.9 cents per kWh (c/kWh) for the small- and large-scale facilities, respectively. However, GHG mitigation costs are considerably higher for the large-scale system: $159/tonne of CO2 eq., compared to $111 for the small-scale counterpart. Generation costs increase substantially under existing conditions, reaching: (1) 25.5 c/kWh for the small-scale system, due to a regulation mandating the continual presence of an operating engineer; and (2) 22.5 c/kWh for the large-scale system due to insufficient biomass supply, which reduces plant capacity factor from 34% to 8%. Limited inflation adjustment (50%) of feed-in tariff rates boosts these costs by 7% to 11%. Results indicate that policy generalizations based on scale require careful consideration of the range of operational/regulatory conditions in the jurisdiction of interest. Further, if GHG mitigation is prioritized, small-scale systems may be more cost-effective.

Bioenergy Development Policy and Practice Must Recognize Potential Hydrologic Impacts: Lessons from the Americas.

Large-scale bioenergy production will affect the hydrologic cycle in multiple ways, including changes in canopy interception, evapotranspiration, infiltration, and the quantity and quality of surface runoff and groundwater recharge. As such, the water footprints of bioenergy sources vary significantly by type of feedstock, soil characteristics, cultivation practices, and hydro-climatic regime. Furthermore, water management implications of bioenergy production depend on existing land use, relative water availability, and competing water uses at a watershed scale. This paper reviews previous research on the water resource impacts of bioenergy production-from plot-scale hydrologic and nutrient cycling impacts to watershed and regional scale hydro-economic systems relationships. Primary gaps in knowledge that hinder policy development for integrated management of water-bioenergy systems are highlighted. Four case studies in the Americas are analyzed to illustrate relevant spatial and temporal scales for impact assessment, along with unique aspects of biofuel production compared to other agroforestry systems, such as energy-related conflicts and tradeoffs. Based on the case studies, the potential benefits of integrated resource management are assessed, as is the need for further case-specific research.

Infrastructure Support for Bioenergy Development in Cities

Worldwide, bioenergy production is increasing. However, there is still a lack of understanding of the types of infrastructural modifications necessary to support further bioenergy development in ways that are both cost effective and environmentally sustainable. This paper provides an overview of the infrastructure support crucial for enabling large-scale bioenergy production in cities. Three waste-to-bioenergy pathways to produce biodiesel from waste oils, syngas from plasma gasification of municipal solid waste (MSW), and bioenergy from algae are reviewed. (i) To produce biodiesel from waste oils, a cost-effective feedstock collection system is key as feedstock cost, including transportation cost, is the single largest contributor to total cost. (ii) To promote the production of syngas from MSW by plasma gasification, a decentralized approach is recommended in the near to medium term. This is because at present, there is still little experience operating large MSW plasma gasification plants. A decentralized approach creates opportunities for public-private partnerships, leading to investments to gain operational experience. Soft infrastructure in the form of a well-developed recycling program or legislation is also necessary to ensure the gasification does not compete with recycling for recyclables. (iii) To produce bioenergy from algae, two infrastructures are vital. The first is infrastructure to integrate wastewater treatment and algae cultivation with nutrients and carbon dioxide recycling. The second is infrastructure to create large surface areas from sides of buildings and/or rooftops that are well exposed to sunlight for algae growth. Provided these infrastructures are in place, the three pathways, combined, have the potential to supply up to 12–16 % of Hong Kong’s electricity demand if converting the energy products from the pathways to electricity. Further, the pathways create new interdependencies between the waste and energy sectors. The interdependencies, while synergistic, could lead to new vulnerabilities such that a failure of one sector will cause a failure in the other as well. Care must be taken when designing systems to minimize this.

Bioenergy in energy transformation and climate management

This study explores the importance of bioenergy to potential future energy transformation and climate change management. Using a large inter-model comparison of 15 models, we comprehensively characterize and analyze future dependence on, and the value of, bioenergy in achieving potential long-run climate objectives. Model scenarios project, by 2050, bioenergy growth of 1 to 10 % per annum reaching 1 to 35 % of global primary energy, and by 2100, bioenergy becoming 10 to 50 % of global primary energy. Non-OECD regions are projected to be the dominant suppliers of biomass, as well as consumers, with up to 35 % of regional electricity from biopower by 2050, and up to 70 % of regional liquid fuels from biofuels by 2050. Bioenergy is found to be valuable to many models with significant implications for mitigation and macroeconomic costs of climate policies. The availability of bioenergy, in particular biomass with carbon dioxide capture and storage (BECCS), notably affects the cost-effective global emissions trajectory for climate management by accommodating prolonged near-term use of fossil fuels, but with potential implications for climate outcomes. Finally, we find that models cost-effectively trade-off land carbon and nitrous oxide emissions for the long-run climate change management benefits of bioenergy. The results suggest opportunities, but also imply challenges. Overall, further evaluation of the viability of large-scale global bioenergy is merited.

Seasonal energy storage using bioenergy production from abandoned croplands

Bioenergy has the unique potential to provide a dispatchable and carbon-negative component to renewable energy portfolios. However, the sustainability, spatial distribution, and capacity for bioenergy are critically dependent on highly uncertain land-use impacts of biomass agriculture. Biomass cultivation on abandoned agriculture lands is thought to reduce land-use impacts relative to biomass production on currently used croplands. While coarse global estimates of abandoned agriculture lands have been used for large-scale bioenergy assessments, more practical technological and policy applications will require regional, high-resolution information on land availability. Here, we present US county-level estimates of the magnitude and distribution of abandoned cropland and potential bioenergy production on this land using remote sensing data, agriculture inventories, and land-use modeling. These abandoned land estimates are 61% larger than previous estimates for the US, mainly due to the coarse resolution of data applied in previous studies. We apply the land availability results to consider the capacity of biomass electricity to meet the seasonal energy storage requirement in a national energy system that is dominated by wind and solar electricity production. Bioenergy from abandoned croplands can supply most of the seasonal storage needs for a range of energy production scenarios, regions, and biomass yield estimates. These data provide the basis for further down-scaling using models of spatially gridded land-use areas as well as a range of applications for the exploration of bioenergy sustainability.