Net Energy Use Research Articles

Hybrid microalgal biofuel, desalination, and solution mining systems: increased industrial waste energy, carbon, and water use efficiencies

This work reviews retrofitting new waste energy, carbon and water intensive technologies into existing industrial facilities (including electricity generators) to increase net energy, carbon, and water use efficiencies. The three applications reviewed are microalgal ponds consuming flue gasses and providing thermal power station cooling services, thermally driven membrane distillation desalination, and hydrometallurgical solution mining processes to indirectly remove water contaminants, and additional power station cooling. The aim of this work is to explore the unique challenge of site-specificity of retrofitting any or all of the reviewed technologies within existing facilities for commercial operations. The theoretical basis behind higher aggregated efficiencies is essentially vertical integration of infrastructure, energy, and material flows, reducing total costs, net waste, and associated potential environmental contamination. Whilst solution mining and some thermal desalination technologies are not necessarily new in isolation, new technical developments enable these technologies to use waste heat and waste water by operating in parallel with industrial facilities, and effectively subsidise microalgae biofuel water pumping and dewatering. This research determines three fundamental developments are required to enable wide-scale industrial co-located vertical integration efficiencies: (1) fundamental engineering, (2) monitoring system innovation, and (3) technology/knowledge transfer.

What Is the Most Environmentally Beneficial Way to Treat Commercial Food Waste?

Commercial food waste represents a relatively available high-quality feedstock for landfill diversion to biological treatment. A life-cycle assessment was performed for commercial food waste processed through aerobic composting systems of varying complexity, anaerobic digestion, and landfills with and without gas collection and energy recovery, as well as a bioreactor landfill. The functional unit was 1000 kg of food waste plus 550 kg of branches that are used as a bulking agent. For each alternative, global warming potential, NO(x) and SO(2) emissions, and total net energy use were determined. Anaerobic digestion was the most environmentally beneficial treatment option, leading to -395 kg net CO(2)e per functional unit. This result was driven by avoided electricity generation and soil carbon storage from use of the resulting soil amendment. The composting alternatives led to between -148 and -64 kg net CO(2)e, whereas the landfill alternatives led to the emission of -240 to 1100 kg CO(2)e. A traditional landfill with energy recovery was predicted to have lower emissions than any of the composting alternatives when a fertilizer offset was used. There is variation in the results based on uncertainty in the inputs, and the relative rankings of the alternatives are dependent on the soil amendment offset that is used. The use of compost to offset peat has greater emission offsets than the value of compost as a fertilizer.

Developments in greenhouse gas emissions and net energy use in Danish agriculture – How to achieve substantial CO 2 reductions?

Greenhouse gas (GHG) emissions from agriculture are a significant contributor to total Danish emissions. Consequently, much effort is currently given to the exploration of potential strategies to reduce agricultural emissions. This paper presents results from a study estimating agricultural GHG emissions in the form of methane, nitrous oxide and carbon dioxide (including carbon sources and sinks, and the impact of energy consumption/bioenergy production) from Danish agriculture in the years 1990–2010. An analysis of possible measures to reduce the GHG emissions indicated that a 50–70% reduction of agricultural emissions by 2050 relative to 1990 is achievable, including mitigation measures in relation to the handling of manure and fertilisers, optimization of animal feeding, cropping practices, and land use changes with more organic farming, afforestation and energy crops. In addition, the bioenergy production may be increased significantly without reducing the food production, whereby Danish agriculture could achieve a positive energy balance.

Energy Chain Analysis of Passenger Car Transport

Transport makes up 20 percent of the World’s energy use; in OECD countries this has exceeded 30 percent. The International Energy Agency (IEA) estimates that the global energy consumption will increase by 2.1 percent annually, a growth rate that is higher than for any other sector. The high energy consumption means that transportation accounts for nearly 30 percent of CO2 emission in OECD countries and is also one of the main sources of regional and local air pollution. In this article, we analyze energy consumption and greenhouse gas emissions from passenger car transport using an energy chain analysis. The energy chain analysis consists of three parts: the net direct energy use, the energy required for vehicle propulsion; the gross direct chain, which includes the net direct energy consumption plus the energy required to produce it; and, finally, the indirect energy chain, which includes the energy consumption for production, maintenance and operation of infrastructure plus manufacturing of the vehicle itself. In addition to energy consumption, we also analyze emissions of greenhouse gases measured by CO2-equivalents. We look at the trade-offs between energy use and greenhouse gas emissions to see whether some drivetrains and fuels perform favourable on both indicators. Except for the case of electric cars, where hydropower is the only energy source in the Norwegian context, no single car scores favourably on both energy consumption and greenhouse gas emissions.

Compensation for differential energy balance across a building incorporating solar energy systems

In order to compensate for imbalance in solar energy between different sides of a building, and the resultant difference in energy availability and (heating/cooling) demand, methods using offsetting were developed to adjust occupiers’ energy bills. In the case of solar electricity generation, a model was considered, in which all the power is routed through common meter(s), so that total electricity generated is recorded. Equal proportions of this metered energy can then be deducted from occupiers’ individual meter readings, to give the net energy use for which each user is billed. Computer-based models were used to calculate the imbalance on those energy demands, which are affected by solar gain, i.e., space heating and cooling. The offset was calculated, such that all users pay the same bill for a given thermostat setting, and are charged more or less, for settings which result in higher or lower energy consumption respectively. Several case studies were performed, in which one building parameter was changed between successive trials. It was found that the offset was different in each case. Therefore, it is necessary to calculate the offset separately for each location, and for each building, depending on those parameters related to solar and thermal energy exchange.

The relationship between net energy use and the urban density of solar buildings

There is a paradoxical relationship between the density of solar housing and net household energy use. The amount of solar energy available per person decreases as density increases. At the same time, transportation energy, and to some extent, household operating energy decreases. Thus, an interesting question is posed: how does net energy use vary with housing density? This study attempts to provide insight into this question by examining three housing forms: low-density detached homes, medium-density townhouses, and high-density high-rise apartments in Toronto. The three major quantities of energy that are summed for each are building operational energy use, solar energy availability, and personal transportation energy use. Solar energy availability is determined on the basis of an effective annual collector efficiency. The results show that under the base case in which solar panels are applied to conventional homes, the high-density development uses one-third less energy than the low-density one. Improving the efficiency of the homes results in a similar trend. Only when the personal vehicle fleet or solar collectors are made to be extremely efficient does the trend reverse and the low-density development results in lower net energy

Energy flow of agro-fruit ecosystem in the Loess Plateau of Shaanxi Province

以黄土高原中南部延安市宝塔区飞马河村、南沟村和淳化县西坡村为对象，研究了农果复合系统的能流特征。研究结果表明：农业、果业、畜牧业、人类子系统和复合系统能量产投比分别为3.58、1.86、3.17、0.41和1.17；人类子系统是复合系统中最大的耗能系统，年平均净消耗能量1 281×10¹⁰ J；农业子系统年均提供经济产品（粮食和饲料）能量347×10¹⁰ J，其中系统内部利用97%，系统外市场销售3%；果业子系统年均提供经济产品（果品）能量414×10¹⁰ J，其中系统内部利用45%，系统外市场销售55%；畜牧业子系统年均产能538×10¹⁰ J，占系统产能总量的14%。从能量流动角度看，黄土高原农果复合系统是一个在市场支持下的以畜牧业为纽带的自给型农业、商品型果业的初级生态农业系统。复合系统产业结构调整应遵循“稳定农业、发展畜牧业和强化果业”的发展方针。

How Much Energy Do Different Toplighting Strategies Save?

Skylights can introduce considerable heat gains and losses that may offset the benefits of electric light savings and cause an increase in yearly net building energy use. The design of a toplight system needs to take into consideration different toplighting types, including aperture size and orientation, electric lighting control, and, most important, the local climate. This study examines the impacts of a variety of toplighting strategies and glazing types on the total yearly energy loads for a prototypical open office space situated in five different climates. Coordinated modeling with both an advanced daylight and electric lighting simulation program and a building thermal simulation program based on hourly weather data for an entire year enable the reliable estimation of annual lighting energy use in response to dynamically changing daylight conditions, and address the interaction between lighting energy and total building energy. This study shows that different toplighting strategies designed to meet...

Life cycle assessment of seawater neutralised red mud for treatment of acid mine drainage

One feature that has not been analysed in the re-use of bauxite residue (or “red mud”) is the comparison of its environmental benefits with competing products. The life cycle assessment (LCA) described in this article compares the use of seawater neutralised red mud to treat acid mine drainage (AMD) at Mount Morgan in Queensland, Australia with that of lime. The aim of the LCA is to evaluate the environmental merits of each neutralant by comparing the carbon dioxide emissions and the net energy use over their respective life cycles. Both life cycles involve the collection and processing of raw materials from Gladstone in Central Queensland, their transportation to Mount Morgan (about 150 km away) and finally their application in a wastewater treatment plant. This plant, which currently uses lime as its treatment media, increases the pH of the acidic open cut pit water to acceptable levels for discharge. The results of the analysis revealed that seawater neutralised red mud would, over the entire life cycle, generate 20% of the carbon dioxide emissions and use 44% of the electricity compared with that of lime. This amounts to a saving of about 3500 kg of carbon dioxide for every 1000 m 3 of pit water treated. However, as red mud is a much weaker neutralant compared with lime on a weight basis, significantly more red mud is required to perform the same duty; as a result the fuel usage in the red mud scenario is 12 times that compared with lime, which is primarily due to increased transportation requirements for red mud. The results of a sensitivity analysis demonstrated that even if the seawater neutralised red mud neutralisation capability was half the expected value, seawater neutralised red mud would still generate only 35% of the carbon dioxide and use 44% of the electricity compared with that of lime. The fuel usage for seawater neutralised red mud would, however, be nearly 24 times greater than that for lime.

Effect of Feeding Propionibacteria on Milk Production by Early Lactation Dairy Cows

This experiment was conducted to determine the effect of a direct-fed microbial agent, Propionibacterium strain P169 (P169), on rumen fermentation, milk production, and health of periparturient and early-lactation dairy cows. Starting 2 wk before anticipated calving, cows were divided into 2 groups and fed a control diet or the control diet plus 6×1011cfu/d of P169. Cows were changed to a lactation diet at calving, and treatments continued until 119 d in milk. Rumen fluid samples were taken about 1 wk before calving, and at 1 and 14 wk after calving. Cows fed P169 had lower concentrations of acetate (mol/100mol of total volatile fatty acids) at all time points, greater concentrations of propionate on the first and last sampling points, and greater concentrations of butyrate on the first 2 time points. Concentrations of glucose in plasma and milk and plasma concentrations of β-hydroxybutyrate were not affected by treatment. Cows fed P169 had greater concentrations of plasma nonesterified fatty acids on d 7 of lactation. The high nonesterified fatty acids at that time point was probably related to the high production of milk during that period by cows fed the additive. Cows fed P169 during the first 17 wk of lactation produced similar amounts of milk (44.9 vs. 45.3kg/d, treatment vs. control) with similar composition as cows fed the control diet. Calculated net energy use for milk production, maintenance, and body weight change was similar between treatments, but cows fed the P169 consumed less dry matter (22.5 vs. 23.5kg/d), which resulted in a 4.4% increase in energetic efficiency.

Sustainability of Transportation and Other Infrastructure Systems

This is the second of two special issues we have organized on the broadly defined concept of sustainability of infrastructure. Our view of infrastructure ~and the resulting call for papers! is instinctively broad, including buildings, transportation, energy, information and communication technologies, and various utilities. The first issue ~September 2004! focused on sustainable energy systems. The current issue is centered on the sustainability of building and transportation infrastructure, discussing highways, bridges, stormwater facilities, as well as buildings in terms of environmental implications and energy use. Jonsson’s forum article leads the issue with a discussion on sociotechnical infrasystem services. Infrasystems are large technical systems with a public character. His discussion considers social innovations and a framework for managing infrasystems based on needs and conveniences. Zapata and Gambatese perform an abbreviated life-cycle energy assessment of asphalt and concrete pavements. They note some sources of life-cycle energy use, as well as differences in the leading life-cycle stages. Jeon and Amekudzi summarize sustainability initiatives for transportation systems. They note the shortcomings in existing measures and propose frameworks consistent with sustainability as potentially useful for transportation agencies to adopt. Keoleian et al. compare bridge deck systems using conventional and alternative ~engineered cementitious composites! materials. They find that the new material yields significant environmental and energy benefits over the life cycle. Matthews and Williams broadly consider the energy implications of telecommuting in the United States and Japan. Beyond the usual focus on transportation system impacts, they include net energy use of residential and commercial buildings. They conclude that when these categories are considered, total energy benefits are small.

Comparison of ecological effects and costs of communal waste management systems

The selection of an appropriate “optimal” recycling alternative has to take into consideration both the ecological and economic effects of the entire life-cycle. The aim of this paper is to compare different waste management systems by means of a life-cycle assessment (LCA) and a cost comparison. The analysis uses data regarding the amount of household waste generated, collected and treated in a selected area in Austria. For this purpose, model-based scenarios with recycling and separate collection as well as scenarios without recycling were created. The database covers the amounts of household waste generated in the different collection schemes, the transport distances by private delivery and by regional waste management companies and data on the waste treatment processes that are widely employed throughout Austria and Germany. The resulting life-cycle inventories have been assessed according to three impact categories relevant to this topic—the global warming potential (GWP), the acidification potential (AP) and the net energy use (NEU). The results include ecological impact analyses and cost comparisons for the overall waste management systems and the waste management systems for the individual waste types—waste paper, plastic packaging, metal packaging and waste glass. Finally, a sensitivity analysis should prove the validity of the results for regions with transport distances differing from those in the area under analysis.

Comparison of the energy performance of fibre sorghum, sweet sorghum and wheat monocultures in northern Italy

Four monocultures (fibre sorghum, sweet sorghum and wheat at high and low nitrogen doses) were compared at a field-scale over 3 years (1997–1999) in terms of net energy, net energy ratio and energy use efficiency. Two nitrogen fertilisation levels were assessed for wheat (80 and 120 kg ha −1 of N) to evaluate the energy use efficiency of the applications. For all the crops, fuels, lubricants and farm inputs together formed around 92% of the total input, mainly due to nitrogen fertilisation. A year×crop significant interaction was found for all considered parameters. In fact the monoculture did not lower the biomass yield of both sorghum types, while it involved a drop in wheat yield starting from the second year (third considering that wheat was also cultivated in the same field in 1996). The average (1997–1999) net energy supplied by the monoculture of sweet sorghum was 17, 40 and 50% higher than those of fibre sorghum and wheat at high and low nitrogen doses respectively. The energy use efficiency (EUE, i.e. the energy (MJ) requirement to produce a kg of dry matter) ranged from 0.78 to 0.96 for fibre sorghum, from 0.69 to 0.85 for sweet sorghum and from 1.00 to 1.23 and 0.91 to 1.33 for wheat at low and high nitrogen levels respectively. With ethanol as the end-product of the 3-year monoculture of sweet sorghum, the production process would be a bit less favourable in term of energy balance: the net energy yield would be 90% of that obtained by dry matter gasification (with an efficiency of 50%). If straw was not processed, ethanol from wheat was generally unfavourable. On average of the two nitrogen doses, net energy ratios were 0.99, 1.05 and 0.97 in the first second and third year respectively. If bagasse was not considered also sweet sorghum had a very low net energy ratio, but always higher than wheat (1.14, 1.12 and 1.24 over the 3 years).

Effect of tillage, residue management and crop establishment techniques on energetics, water use efficiency and economics in soybean (Glycine max)wheat (Triticum aestivum) cropping system

In Indo-Gangetic plains of India, the returns from crop cultivation are shrinking gradually owing to escalation of input costs. Under such situation, conservation agriculture systems have gained importance to make farming prof- itable by cutting down the variable cost and enhancing resource-use efficiency. The studies were conducted dur- ing 2009-10 to 2010-11on energy relations and irrigation water use efficiency (IWUE) involving sequential tillage (i.e to skip the tillage either in kharif to soybean or in rabi to wheat) in soybean (Glycine max (L.) Merr.)wheat (Triticum aestivum L. emend. Fiori and Paol) system in order to evaluate the performance under sequential tillage. The energy relations viz. input energy, output energy, net energy and energy use efficiency were statistically simi- lar in most of the cases except energy-use efficiency for both soybean and wheat due to different sequential tillage and crop establishment techniques. Residue management treatments significantly influenced the energy relations in both the crops. Wheat + soybean residue recorded highest gross energy (235.9 and 269.9 103 MJ/ha), while the reverse with net energy and energy use efficiency where the no residue (control) obtained 189.0 and 206.4 103 MJ/ha; 8.69 and 10.4 103 MJ/ha respectively during the year 2009-10 and 2010-11 in the soybean-wheat sys- tem. IWUE in wheat recorded significantly higher with bed system of crop establishment either adopting conven- tional tillage-bed (CT-Bed) (209.1 kg/ha-cm) or skipping CT-Bed with zero tillage-bed (ZT-Bed) (312.6 kg/ha-cm) in rabi season during the year 2009-10 and 2010-11, respectively.

Considerations for the Specification and Statistical Estimation of Differences Among Animals in the Partial Efficiencies of Feed Energy Utilization

The partial efficiencies of feed net energy use for lactation, maintenance, weight change, and pregnancy are important components of production system efficiency. If heritable variation in these efficiencies can be identified, the efficiencies may become important selection criteria in livestock. Estimates of the partial efficiencies of interest have been obtained using multiple regression procedures and data from nutrition experiments. Such experiments utilize variation among animals, not necessarily within animals. Variation within animals is necessary to estimate partial efficiencies for individuals. Within-animal multiple regression yields interpretable and meaningful estimates of the partial efficiencies of energy use only when 1) the model is correctly and completely specified, 2) values of the independent variables are uncorrelated, and 3) autocorrelation among observations is accounted for correctly. To obtain independent variation in weight, weight composition, weight change, pregnancy, and milk yield may not be feasible within animals, especially in field data. Analyses of residuals from prediction equations based on among animal estimates of the partial efficiencies may provide some information as to the amount of genetic variation available, but they are difficult to interpret. Alternatives, such as random coefficients models, may help in addressing the problems.

Glazing energy performance and design optimization with daylighting

This study systematically explores the influence of glazing systems on component loads and annual energy use in prototypical office buildings. The DOE-2.1B building energy simulation program, which contains an integrated daylighting model, is used to determine fenestration energy performance in diverse climates. The sensitivity of total energy use to orientation, window area, glazing properties (U-value, shading coefficient, visible transmittance), window management strategy, installed lighting power, and lighting control strategy are all described. We examine the conditions under which daylighting reduces net anual energy use as well as those conditions under which energy use may increase. Combinations of wall and fenestration properties that minimize net energy requirements as a function of climate and orientation are described.

Real-Time Irrigation Decision Analysis Using Simulation

ABSTRACT AMETHODOLOGY is developed in which a dynamic crop simulation model is used to evaluate the expected profit and yield benefits for irrigating on any day of the season. The algorithm uses current season weather prior to the decision date and several years of historical weather data for the rest of the season. The user interacts with the computer, if necessary to update crop, soil, and economic information. Direct comparisons of expected net profit, water use, yield, and energy use are made for two options of the decision to (a) irrigate today or (b) wait one or more days to re-evaluate the need to irrigate. A soybean crop growth model (SOYGRO) was used to demonstrate this concept for soybean growing in sandy soil in a humid region. The model was first used to determine an optimal strategy based on 17 years of historical weather data. The sequential use of the real-time decision model during the 1978 growing season was shown to improve this long term strategy by about 5%. This algorithm allows users to input current product prices, fuel costs, and wather conditions to provide within-season adjustments to irrigation schedules that were formulated using long-term weather conditions and out-dated economic data.