Modelling and optimization of the smart hybrid renewable energy for communities (SHREC)

The future energy system in community level should be more ‘smart’ to secure reliability, enhance market service, minimize environmental impact, reduce costs and improve the use of renewable energy source (RES). Therefore, this paper proposes an energy integration system – smart hybrid renewable energy for communities (SHREC). It considers both thermal (heating and cooling) and electricity market in a large community level and highlight the interactions between them through utilizing RES, combined heat and power (CHP) and energy storages. A planning model based on CHP modelling is developed for the SHREC system. A linear programming (LP) algorithm is developed to optimize the SHREC system in a weekly period and the results are compared with an existing energy optimization software. We also demonstrate the model in a sample SHREC system during three typical weeks with cold, warm and mid-season weather in the year 2011. The results indicate that the developed modelling and optimization method is more efficient and flexible for the smart hybrid renewable energy systems.     

Off-grid electricity generation with renewable energy technologies in India: An application of HOMER

Renewable energy-based off-grid or decentralised electricity supply has traditionally considered a single technology-based limited level of supply to meet the basic needs, without considering reliable energy provision to rural consumers. The purpose of this paper is to propose the best hybrid technology combination for electricity generation from a mix of renewable energy resources to satisfy the electrical needs in a reliable manner of an off-grid remote village, Palari in the state of Chhattisgarh, India. Four renewable resources, namely, small-scale hydropower, solar photovoltaic systems, wind turbines and bio-diesel generators are considered. The paper estimates the residential, institutional, commercial, agricultural and small-scale industrial demand in the pre-HOMER analysis. Using HOMER, the paper identifies the optimal off-grid option and compares this with conventional grid extension. The solution obtained shows that a hybrid combination of renewable energy generators at an off-grid location can be a cost-effective alternative to grid extension and it is sustainable, techno-economically viable and environmentally sound. The paper also presents a post-HOMER analysis and discusses issues that are likely to affect/influence the realisation of the optimal solution.     

Analysis of wind power generation operation management risk in China

The Chinese government has made an important effort to diversify the country's energy mix and exploit different sources of renewable energy. Although China's installed wind power capacity has undergone a dramatic expansion over the past six years, the electricity generated from wind power has not increased as expected. Meanwhile, operational risks, such as high generation cost, mismatch between capacity and generation, intermittent wind power generation, power grid construction lag, deficient policy, and operation mechanism, have become increasingly prominent. If not controlled, these risks will negatively affect wind power development in China. Therefore, this paper established a quantitative analysis model of wind power operation management risk from two aspects, feed-in tariff and grid electricity (electricity being connected to the grid), based on an analysis of wind power operation management risk in China. Moreover, this study quantitatively assessed the risk of the operational management of a wind farm in Inner Mongolia. Finally, corresponding risk control strategies for the healthy development of wind power generation in China were proposed.     

A new future for carbohydrate fuel cells

The development of renewable energy sources to reduce our dependence on limiting fossil fuel reserves continues to be a critical research initiative. Utilizing the abundant high energy content of carbohydrates contained in biomass (cellulose and hemicellulose) must be considered to be an important contribution to our overall energy budget. Carbohydrate-derived furan-based liquid fuels and especially ethanol are becoming important added components forming gasoline blends to lower overall fossil fuel use. Alternate renewable energy processes that more efficiently use the carbohydrate energy content are desirable and would lower the overall carbohydrate input requirement for energy production. Recently, new catalysts have shown the feasibility of efficiently transporting the 24 electrons in glucose to fuel cell electrodes making possible the direct conversion of the stored energy in carbohydrates into electricity with the benign formation of carbonate and water as products. The conversion of glycerol, a byproduct of biodiesel production, into three-carbon carbohydrates provides another opportunity to produce electricity from an abundant carbohydrate source. New developments in catalyst systems promise to make carbohydrate fuel cells an important part of future energy strategies.     

Viability of off-grid electricity supply using rice husk: A case study from South Asia

Rice husk-based electricity generation and supply has been popularized in South Asia by the Husk Power Systems (HPS) and the Decentralised Energy Systems India (DESI), two enterprises that have successfully provided electricity access using this resource. The purpose of this paper is to analyze the conditions under which a small-scale rural power supply business becomes viable and to explore whether larger plants can be used to electrify a cluster of villages. Based on the financial analysis of alternative supply options considering residential and productive demands for electricity under different scenarios, the paper shows that serving low electricity consuming customers alone leads to part capacity utilization of the electricity generation plant and results in a high cost of supply. Higher electricity use improves the financial viability but such consumption behaviour benefits high consuming customers greatly. The integration of rice mill demand, particularly during the off-peak period, with a predominant residential peak demand system improves the viability and brings the levelised cost of supply down. Finally, larger plants bring down the cost significantly to offer a competitive supply. But the higher investment need and the risks related to monopoly supply of husk from the rice mill, organizational challenges of managing a larger distribution area and the risk of plant failure can adversely affect the investor interest. Moreover, the regulatory uncertainties and the potential for grid extension can hinder business activities in this area.     

Assessing sustainable forest biomass potential and bioenergy implications for the northern Lake States region,USA

Forestlands in the United States have tremendous potential for providing feedstocks necessary to meet emerging renewable energy standards. The Lake States region is one area recognized for its high potential of supplying forest-derived biomass; however, the long-term availability of roundwood harvests and associated residues from this region has not been fully explored. Better distribution and temporal availability estimates are needed to formulate emerging state policies regarding renewable energy development. We used a novel predictive methodology to quantify sustainable biomass availability and likely harvest levels over a 100-year period in the Lake States region. USDA Forest Inventory and Analysis estimates of timberland were combined with published growth and yield models, and historic harvest data using the Forest Age Class Change Simulator (FACCS) to generate availability estimates. Monte-Carlo simulation was used to develop probability distributions of biomass harvests and to incorporate the uncertainty of future harvest levels. Our results indicate that 11.27–15.71 Mt y⁻¹ dry roundwood could be sustainably harvested from the Lake States. Assuming 65% collection rate, 1.87–2.62 Mt y⁻¹ residue could be removed, which if substituted for coal would generate 2.12–2.99 GW h of electricity on equivalent energy basis while reducing GHG (CO₂e) emission by 1.91–2.69 Mt annually. In addition to promoting energy security and reducing GHG emissions, forest residues for energy may create additional revenues and employment opportunities in a region historically dependent on forest-based industries.     

A re-look at the biochemical strategies to enhance butanol production

Butanol produced from renewable feedstock is defined as an emerging biofuel and biochemical. Research efforts made during the last three decades on biochemical production of butanol via conventional ABE (acetone-ethanol-butanol) fermentation has tried to bring biobutanol close to competition with petrobutanol. However, each new effort of development has been often countered by new challenges, confining biobutanol production mostly to the laboratory scale. This review provides a systematic, comparative analysis of different steps in biochemical production of butanol and identifies the counteractive aspects and challenges to overcome. A special emphasis is given on process inhibitors, applied detoxification techniques, chemical supplements and research & development in industry in order to enhance and update ABE fermentation and make it cost effective. Biobutanol future lies in utilization of inexpensive cellulose enriched lignocellulosic hydrolysates and hyper-butanol producing bacteria, combined with specific detoxification techniques and followed by efficient continuous fermentation technologies together with in situ product recovery.     

Environmental assessment of electricity generation from an Italian anaerobic digestion plant

A standard ISO Life Cycle Assessment study was carried out to evaluate the environmental sustainability of electricity production from an anaerobic digestion (AD) plant using a mixture of dedicated energy crops, agricultural residues and livestock effluents as input materials. The functional unit was 1 MJ of electricity. System boundaries were from cradle to grave and covered all the phases from energy crops cultivation to the production of biogas and its use in a Combined Heat and Power plant to produce electricity. Liquid and solid digestate storage and spreading on agricultural land were included. Primary data were collected from the AD plant for all the above phases. Since heat produced is used only internally, no allocation was applied in the study. As regards digestate management, CH₄ emissions were calculated from literature, whereas four literature methods were applied for calculation of nitrogen emissions with the goal to perform a sensitivity analysis on LCA results. ILCD Handbook impact assessment methodologies were used. Results show that the main hotspots are energy crops cultivation and the management of digestate, mainly because of both nitrogen and methane emissions, affecting Global Warming, Acidification, Marine and Freshwater Eutrophication. Finally, a detailed Monte Carlo analysis, was carried out to evaluate the results uncertainty. The study represents the state of the art about the environmental performance of the AD plant with the use of sensitivity and uncertainty analysis, which both improve the reliability of results, and allows drawing general conclusions on how to mitigate the environmental impacts of AD process.     

Climate change impacts of power generation from residual biomass

The European Union relies largely on bioenergy to achieve its climate and energy targets for 2020 and beyond.We assess, using Attributional Life Cycle Assessment (A-LCA), the climate change mitigation potential of three bioenergy power plants fuelled by residual biomass compared to a fossil system based on the European power generation mix. We study forest residues, cereal straws and cattle slurry.Our A-LCA methodology includes: i) supply chains and biogenic-CO₂ flows; ii) explicit treatment of time of emissions; iii) instantaneous and time-integrated climate metrics.Power generation from cereal straws and cattle slurry can provide significant global warming mitigation by 2100 compared to current European electricity mix in all of the conditions considered.The mitigation potential of forest residues depends on the decay rate considered. Power generation from forest logging residues is an effective mitigation solution compared to the current EU mix only in conditions of decay rates above 5.2% a⁻¹. Even with faster-decomposing feedstocks, bioenergy temporarily causes a STR(i) and STR(c) higher than the fossil system.The mitigation potential of bioenergy technologies is overestimated when biogenic-CO₂ flows are excluded. Results based solely on supply-chain emissions can only be interpreted as an estimation of the long-term (>100 years) mitigation potential of bioenergy systems interrupted at the end of the lifetime of the plant and whose carbon stock is allowed to accumulate back.Strategies for bioenergy deployment should take into account possible increases in global warming rate and possible temporary increases in temperature anomaly as well as of cumulative radiative forcing.     

Evaluation of ground energy storage assisted electric vehicle DC fast charger for demand charge reduction and providing demand response

In 2012 there was approximately 2400 electric vehicle DC Fast Charging stations sold globally. According to Pike Research (Jerram and Gartner, 2012), it is anticipated that by 2020 there will be approximately 460,000 of them installed worldwide. A typical public DC fast charger delivers a maximum power output of 50 kW which allows a typical passenger vehicle to be 80% charged in 10–15 min, compared with 6–8 h for a 6.6 kW AC level 2 charging unit. While DC fast chargers offer users the convenience of being able to rapidly charge their vehicle, the unit's high power demand has the potential to put sudden strain on the electricity network, and incur significant demand charges.Depending on the utility rate structure, a DC fast charger can experience annual demand charges of several thousand dollars. Therefore in these cases there is an opportunity to mitigate or even avoid the demand charges incurred by coupling the unit with an appropriately sized energy storage system and coordinating the way in which it integrates. This paper explores the technical and economical suitability of coupling a ground energy storage system with a DC fast charge unit for mitigation or avoidance of demand charges and lessening the impact on the local electricity network. This paper also discusses the concept of having the system participate in demand response programs in order to provide grid support and to further improve the economic suitability of an energy storage system.     

Resource and revenue potential of California residential load participation in ancillary services

Increasing penetrations of intermittent renewable energy resources will require additional power system services. California recently adopted an energy storage mandate to support its renewable portfolio standard, which requires 33% of delivered energy from renewables by 2020. The objective of this paper is to estimate the amount of energy storage that could be provided by residential thermostatically controlled loads, such as refrigerators and air conditioners, and the amount of revenue that could be earned by loads participating in ancillary services markets. We model load aggregations as virtual energy storage, and use simple dynamical system models and publicly available data to generate our resource and revenue estimates. We find that the resource potential is large: 10–40 GW/8–12 GWh, which is significantly more than that required by the mandate. We also find that regulation and spinning/non-spinning reserve revenues vary significantly depending upon type of load and, for heat pumps and air conditioners, climate zone. For example, mean regulation revenues for refrigerators are $11/year, for electric water heaters are $24/year, for air conditioners are $0-32/year, and for heat pumps are $22–56/year. Both consumer choices, such as appliance settings, and policy, such as the design of ancillary service compensation and appliance standards, could increase revenue potentials.     

Can slurry biogas systems be cost effective without subsidy in Mexico?

Biogas from pig slurry in Mexico has potential to produce 21 PJ per year, equivalent to 3.5% of natural gas consumption in 2013. In this paper, three different scenarios are analysed: mono-digestion of pig slurry in a finisher farm (scenario 1); co-digestion of pig slurry and elephant grass in a finisher farm in situ (scenario 2) and co-digestion of pig slurry and elephant grass in centralised biogas plants (scenario 3). The digesters proposed are anaerobic high density polyurethane (HDPE) covered lagoons. HDPE centralised plants can have capital costs 5 times cheaper than European biogas plants. The economics of utilisation of biogas for electricity generation and as biomethane (a natural gas substitute) were investigated. Economic evaluations for on-site slurry digestion (Scenario 1) and on-site co-digestion of elephant grass and pig slurry (Scenario 2) showed potential for profitability with tariffs less than $US 0.12/kWh_e. For centralised systems (Scenario 3) tariffs of $US 0.161/kWh_e to $US 0.195/kWh_e are required. Slurry transportation, energy use and harvest and ensiling account for 65% of the operational costs in centralised plants (Scenario 3). Biomethane production could compete with natural gas if a subsidy of 4.5 c/L diesel (1 m³ of biomethane) equivalent was available.     

GIS-based assessment of sustainable crop residue potentials in European regions

In this paper a novel model based on a geographic information system (GIS) is presented for the assessment of sustainable crop residue potentials. The approach is applied to analyse the amount and the spatial distribution (1 km × 1 km grid cells) of cereal straw, root crop and oil plant residues for five European regions, considering spatially differentiated environmental sustainability issues, i.e. organic carbon content in topsoil, soil erodibility, and protected areas. The maximum sustainable residue potential varies strongly between the regions and residue types. In the scenarios Basis and Restrict, it accounts for 45–59% and 24–48% of the theoretical potential respectively without considering competing uses. Among the crop residues, cereal straw shows the highest energy potential in all regions under investigation. In terms of wet mass it accounts for 3.7 Mio. t_wet/a in North Rhine-Westphalia, 1.6 Mio. t_wet/a in Île-the-France, 1.2 Mio. t_wet/a in Wallonia, 0.9 Mio. t_wet/a in West Midlands, and 0.3 Mio. t_wet/a in South Netherlands (scenario Basis). Our survey shows that spatially differentiated potential estimations and the inclusion of crop residues other than cereal straw are urgently needed to improve the present rough estimations for crop residues which can be used in a sustainable way. The rather high spatial resolution of our analyses particularly allows for the support of regional stakeholders and prospective investors when it comes to questions of regional availability of biomass resources, transport distances to biomass conversion plants, and identification of suitable plant sites and sizes, respectively.     

Biosynthesis of β-caryophyllene,a novel terpene-based high-density biofuel precursor,using engineered Escherichia coli

β-caryophyllene is a common sesquiterpene compound currently being studied as a promising precursor for the production of high-density fuels. Acute demand for high-density fuels has provided the impetus to pursue biosynthetic methods to produce β-caryophyllene from reproducible sources. In this study, we produced β-caryophyllene by assembling a biosynthetic pathway in an engineered Escherichia coli strain of which phosphoglucose isomerase gene has been deleted. The 1- deoxy-d-xylulose 5-phosphate (DXP) or heterologous mevalonate (MVA) pathways were employed. Meanwhile, geranyl diphosphate synthase, glucose-6-phosphate dehydrogenase and β-caryophyllene synthase genes were co-overexpressed in the above strain. The final genetically modified strain, YJM59, produced 220 ± 6 mg/L of β-caryophyllene in flask culture. We also evaluated the use of fed-batch fermentation for the production of β-caryophyllene. After induction for 60 h, the YJM59 strain produced β-caryophyllene at a concentration of 1520 mg/L. The volumetric production fermented in the aerobic fed-batch was 0.34 mg/(L·h·OD₆₀₀) and the conversion efficiency of glucose to β-caryophyllene (gram to gram) was 1.69%. Our results are the first successful attempt to produce β-caryophyllene using E. coli BL21(DE3), and provide a new strategy that is green and sustainable for the production of β-caryophyllene.     

Ash reduction strategies in corn stover facilitated by anatomical and size fractionation

There is growing interest internationally to produce fuels from renewable biomass resources. Inorganic components of biomass feedstocks, referred to collectively as ash, damage equipment and decrease yields in thermal conversion processes, and decrease feedstock value for biochemical conversion processes. Decreasing the ash content of feedstocks improves conversion efficiency and lowers process costs. Because physiological ash is unevenly distributed in the plant, mechanical processes can be used to separate fractions of the plant based on ash content. This study focuses on the ash separation that can be achieved by separating corn stover by particle size and anatomical fraction. Baled corn stover was hand-separated into anatomical fractions, ground to <19.1 mm, and size separated using six sieves ranging from 9.5 to 0.150 mm. Size fractions were analyzed for total ash content and ash composition. Particle size distributions observed for the anatomical fractions varied considerably. Cob particles were primarily 2.0 mm or greater, while most of the sheath and husk particles were 2.0 mm and smaller. Particles of leaves greater than 0.6 mm contained the greatest amount of total ash, ranging from approximately 8 to 13% dry weight of the total original material, while the fractions with particles smaller than 0.6 mm contained less than 2% of the total ash of the original material. Based on the overall ash content and the elemental ash, specific anatomical and size fractions can be separated to optimize the feedstocks being delivered to biofuels conversion processes and minimize the need for more expensive ash reduction treatments.     

Enhancement of lipid productivity in green microalgae Chlorella sp. via fast neutron irradiation

Microalgae is becoming a promising candidate for biofuel production and energetic lipid production, which urges the need to develop efficient methods for improvement of the lipid production. In this study, the neutron irradiation was employed to improve lipid production under different dosage irradiation. Effects of different dosages (No.1:8.14 × 10⁹, No.2:5.64 × 10⁸, No.4:9.42 × 10⁷ n/cm²) were compared by investigating associated algae cell growth, total lipid production, metabolization and enzyme activity. Dosages No.2 and No.4 improved the lipid content without negative influence on the growing, whereas irradiations shortened the period of biomass accumulation. The neutron irradiation in No.2 accelerated the synthesis of lipid from the carbohydrate transition process. In addition, the neutron irradiation not only increased the total lipid production by 20% but also speeded up the reaction rate to reach the maximal total lipid production in 28 days. Our results can provide a better understanding of the lipid production in microalgae Chlorella sp. by neutron irradiation, which are critical for evaluation of neutron irradiation based technologies for the sustainable and renewable biofuel production.     

Biopower from direct firing of crop and forestry residues in China: A review of developments and investment outlook

This paper reviews developments in the direct-fired biomass power sector and provides an up to date investment outlook by calculating the Net Present Value of new investments, and the appropriate level of Feed-in-Tariff needed to stimulate future investment. An overview is provided of support policies, historical growth in installations, and main market players. A number of data sources is combined to build a database with detailed information of individual biopower projects. This data is used to describe technological and market trends, which are used in a cash flow model to calculate the NPV of a typical project. The NPV for new projects is estimated to be negative, and investment should be expected to stall without proper policy intervention. Increasing fuel prices, local competition over biomass fuel resources, lower than expected operational performance and a downturn in carbon markets have deteriorated the investment outlook. In order to ensure reasonable profitability, the Feed-In-Tariff should be increased, from the current level of 90.9 € MWh⁻¹, to between 97 and 105 € MWh⁻¹. Where possible, government organizations should help organize demand for the supply of heat. Local rural energy bureaus may help organize supply networks for biomass fuels throughout the country, in order to reduce seasonal and local fuel scarcity and price fluctuations.     

Biomass for residential and commercial heating in a remote Canadian aboriginal community

Most residents of Canada's 300 remote communities do not have access to natural gas and must rely upon higher cost and/or less convenient heat sources such as electric heat, heating (furnace) oil, propane, and/or cord wood. This research sought to determine the techno-economic feasibility of increasing biomass utilization for space and hot water heating in remote, off-grid communities in Canada and abroad using a two-option case study approach: 1) a district energy system (DES) connected to a centralized heat generation energy centre fuelled by wood chips; and 2) a decentralized heating option with wood pellet boilers in each individual residence and commercial building. The Nuxalk First Nation Bella Coola community was selected as a case study, with GIS, ground surveys, and climate data used to design DES routes and determine heat demand. It was determined that biomass has the potential to reduce heat costs, reduce the cost of electricity subsidization for electrical utilities, reduce greenhouse gas emissions, and increase energy independence of remote communities. Although results of the analysis are site-specific, the research methodology and general findings on heat-source economic competitiveness could be utilized to support increased bioheat production in remote, off-grid communities for improved socio-economic and environmental outcomes.     

Thermodynamic and exergoeconomic analysis of energy recovery system of biogas from a wastewater treatment plant and use in a Stirling engine

The aim of this research it is to show how the biogas biomethanisation from primary and secondary treatment of activated sludge from a wastewater treatment plant (WWTP), can be an alternative renewable energy option from fossil fuels, which offers competitive advantages and points out new horizons for the use of this fuel. This will allow to achieve some important priorities of energy plans in EU countries: to reduce the organic matter deposited in landfills and CO₂ emissions and to find viable solutions to minimize the environmental impact of sewage sludge (SS).This study analyses the biogas combustion and energy recovery processes from a thermodynamic, thermoeconomic and exergetic point of view.The results show that the boiler of the process is the main source of irreversibility and exergy destruction. Moreover, the energy and exergy economic value of exhaust gases from the combustion chamber, are significant and worthwhile to be exploited. For this reason, the present study explores the applicability and suitability of integrating a Stirling engine in such process. The study reveals that it is possible to create a small micro-cogeneration system which leads to sustainable waste management and energy savings in the treatment plant itself.