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Abstract This paper addresses the question of the stability of the demand for the factors of production at the aggregate level for United States manufacturing over the period 1947 through 1976. The results are conclusive. The demand for capital and labor have remained virtually constant over the period of investigation while the relative importance of the factors affecting the demand for energy has changed in a statistically significant fashion.

Abstract There was a rapid development of coal to synthetic natural gas (SNG) projects in the last few years in China. The research from our previous work and some other researchers have found coal based SNG production process has the problems of environmental pollution and emission transfer, including CO 2 emission, effluent discharge, and high energy consumption. This paper proposes a novel co-feed process of coal and coke-oven gas to SNG process by using a dry methane reforming unit to reduce CO 2 emissions, more hydrogen elements are introduced to improve resource efficiency. It is shown that the energy efficiency of the co-feed process increases by 4%, CO 2 emission and effluent discharge is reduced by 60% and 72%, whereas the production cost decreases by 16.7%, in comparison to the conventional coal to SNG process. As coke-oven gas is a waste gas in most of the coking plant, this process also allows to optimize the allocation of resources.

Abstract The operation of a Carnot heat pump is viewed as a production process with exergy as its output. The short-run economic optimization of the endoreversible heat pump is performed in this paper. The profit of the heat pump is taken as the optimization objective function. Using the method of finite-time exergoeconomic analysis, which emphasizes the compromise optimization between economics (profit) and the utilization factor of energy (Coefficient of Performance, COP) for finite-time (endoreversible) thermodynamic cycles, this paper derives the relation between optimal profit and COP of an endoreversible Carnot heat pump based on a relatively general heat transfer law: q∞Δ(Tn). The COP bound at the maximum profit is also obtained. The results obtained involve those for three common heat transfer laws: Newton's Law (n = 1), the linear phenomenological law in irreversible thermodynamics (n = − 1), and the radiative heat law (n = 4).

Abstract Since the establishment of the market economy in 1993, the residential consumption of commodities, including energy, has been highly influenced by prices in China. However, the contribution of the factors related to prices in residential energy consumption is relatively unexplored. This paper extends the KAYA identity with price and expenditure factors and then applies the LMDI method to a decomposition of residential energy consumption in China from 1993 to 2011. Our results show the following: (1) Though the prices of a majority of residential energy sources in China declined, the effect of energy prices restrained residential energy consumption because the expenditure structure changed during the period. (2) During the research period, the urban energy expenditure proportion experienced two progresses of rising and falling, and the rural proportion, which was stable before 2002, sharply increased. (3) The energy consumption intensity effect, which is the negative of the average energy price effect, contributed to most of the decrease in energy consumption, whereas residential income played a key role in the growth of consumption. According to the conclusions, we suggest further marketization and deregulation of energy prices, the promotion of advanced energy types and guidance for better energy consumption patterns.

Abstract Global warming is said to be caused by the build up of active greenhouse gases in our atmosphere and carbon dioxide — released on the combustion of fossil fuels is thought to be the most important of these. Agricultural crops, grown specifically for use as a fuel source, might play an important role in reducing our consumption of fossil fuel sources through substitution. However, in order to fully qualify as a “beneficial crop” it must be clearly shown that production entails a net benefit in terms of energy output to energy input i.e.; it has a positive energy balance. This paper considers the difficulties in assessing both carbon and energy budgeting. It describes a recently developed computer model which attempts to define the energy and carbon inputs and outputs of the leading UK energy crop, that is of short rotation coppice (SRC). Preliminary results show that SRC, when displacing fossil fuel, has a very positive energy yield with the added benefit of carbon saving in terms of offset emissions. The computer model takes account of direct and indirect energy and carbon inputs to the crop, allowing the model user to determine the sensitivity of individual cropping operations including establishment, fencing, harvesting operations, rotation and cutting cycle variations, the impact of field size, transport distance from the farm to the point of utilisation, the energy cost of storage and drying. Each management decision influences the final energy or carbon ratio of the SRC crop. Such complexity makes a definitive statement on the energy/carbon ratio for crop production difficult, however if a standard management system is adopted (as described later) the energy ratio of growing SRC for fuel may be assigned. In the case examined here a ratio of 30 : 1 (energy units produced : used) is reported. However, this ratio is sensitive to variation in crop yield and management efficiency and so, although the ratio is positive, this should not encourage a wasteful attitude to crop management systems. In terms of carbon balances, the most important consideration is the substitution value of the material in relation to fossil fuels. In this paper, figures presented refer to wood substituted for coal use and pertain to a field area of 1 hectare (ha). If field size is increased up to 3ha, then the energy and carbon ratios improve by approximately 15 %.

One possible way to further reduce levelized costs of electricity of concentrated solar thermal energy is to directly use water/steam as the primary heat transfer fluid within a concentrated collector field. This so-called direct steam generation offers the opportunity of higher operating temperatures and better exergy efficiency. A technical challenge of the direct steam generation technology compared to oil-driven power cycles is a competitive storage technology for heat transfer fluids with a phase change. Latent heat thermal energy storages are suitable for storing heat at a constant temperature and can be used for direct steam generation power plants. The calculation of the economic impact of an economically optimized thermal energy storage system, based on a latent heat thermal energy storage system with phase change material, is the main focus of the presented work. To reach that goal, a thermal energy storage system for a direct steam generation power plant with parabolic troughs in the solar field was thermally designed to determine the boundary conditions. This paper discusses the economic impact of the designed thermal energy storage system based on the levelized costs of electricity results, provided via a wide parametric study. A state-of-the-art power cycle with a primary and a secondary heat transfer fluid and a two-tank thermal energy storage is used as a benchmark technology for electricity generation with solar thermal energy. The benchmark and direct steam generation systems are compared to each other, based respectively on their annual electricity yields and their levelized costs of electricity at two different sites. A brief comparison of a passive and an active latent heat storage system is included. Finally, specific target costs for the new direct steam generation thermal energy storage system are determined based on the results of the parametric study.

Abstract This work presents an analysis of the inherent potentialities and characteristics of the sugarcane industries that produce sugar, bioethanol, biogas and bioelectricity and that are being described as “Biorefineries”. These Biorefineries are capable of producing bio-energy under diverse forms, intended for their own internal consumption and for external sales and marketing. A complex model and simulation are carried out of the processes of a sugarcane industry, with the data characteristic as well as the production costs, prices of products and considerations on the energy demand by basic processes. A Mixed-Integer Linear Programming (MILP) optimization problem formulation and an analysis of optimal solutions in short-term operation are described, taking into account the production cost functions of each commodity and the incomes obtained from selling electricity and other products. The objective is to maximize the hourly plant economic profit in the different scenarios considered in a real case study.

Abstract This article identifies the sources and determines the convergence and causes of energy efficiency in Africa. In terms of contribution, it provides the first cross-country evidence. This study applies the stochastic fixed effect, true fixed effect and the Kumbhakar-Heshmati (K-H) models using a panel data of 22 countries for the period 1988–2014. The result reveals that: (1) the problem of energy efficiency in Africa is more structural in nature. Removing transient inefficiency and minimizing persistent inefficiency will save 5.7% and 84% of total energy consumption, respectively. Thus, energy security and carbon emissions will benefit more from policies aimed at the long-term than the short-term; (2) overall energy efficiency is low and hyoid in nature. While it declined from 1988 to 2006, the trend has reversed after 2006; (3) economic growth, urbanization and population density promote efficiency but price, foreign direct inflows and service and industry output reduce it; (4) energy efficiency convergence is conditional in nature, driven by country-specific factors such as the level of technology; (5) energy intensity is not a good measure of energy efficiency and should not be used as a policy indicator for energy efficiency enhancement.

Increasing attention has recently been drawn to energy consumption in manufacturing plants. Facing the challenges from reducing emissions coupled with rising raw material prices and energy costs, manufacturers are trying to balance the energy usage strategy among the total energy consumption, economy, and environment, which can be self-conflicting at times. In this paper, energy systems in manufacturing environments are reviewed, and the current status of onsite energy system and renewable energy usage are discussed. Single objective and multicriteria optimization approaches are effectively formulated for making the best use of energy delivered to the production processes. Energy supply operation suggestions based on the optimization results are obtained. Finally, an example from an automotive assembly manufacturer is described to demonstrate the energy usage in the current manufacturing plants and how the optimization approaches can be applied to satisfy the energy management objectives. According to the optimization results, in an energy oriented operation, it takes 35% more in monetary cost; while in an economy oriented operation, it takes 17% more in megawatt hour energy supply and tends to rely more on the inexpensive renewable energy.