Potential For Improving Efficiency Research Articles

The role of district heating in coupling of the future renewable energy sectors

For the last decades energy efficiency initiatives have avoided enormous amounts of energy consumption, to the favor of the environment and consumer expenditures. Although there is still a big potential for further energy efficiency improvements it is time to move further and start preparing the whole energy system for the challenge of oversupply from intermittent renewable energy sources, particularly in the power sector. In 2015 the maximum one-hour power oversupply from wind turbines alone in Denmark happened the 26th of June, peaking at around 900 MW and the oversupply over a 15-hour period was 10 GWh. Known solutions to make use of oversupply in the power sector are power export, energy storage and halting the power generation. The power export needs to rely on sufficient capacity at local interconnectors, power demand in the importing country and there is an economic gain in the export. Energy storages can range from storing of power in batteries, pumped hydro, synthetic fuels to fuel displacing at other energy sectors. The last option is stopping the turbines, which should be avoided. The optimum energy storage would have large capacity, fast charging, high recovery efficiency and low cost. Scoring high on all criteria’s can be difficult when focusing on a single energy sector. By widening the perspective and start taking advantages of synergies between the energy sectors there is a possibility to score high on all three criteria’s. In this paper the potential of utilizing synergies between the power and heat sectors will be explored by considering the projections for the Danish energy system in 2025. The result of the analysis shows the optimum energy storage of renewable power is achieved through fuel displacement in the heating sector in combination with utility sized heat pumps, electric boilers and large thermal storages.

Efficiency evaluation and improvement potential for the Chinese agricultural sector at the provincial level based on data envelopment analysis (DEA)

In this study, we develop indices for the overall technical efficiency (OTE) and energy-saving target ratio (ESTR) using data envelopment analysis (DEA) to calculate the relative efficiency and energy-saving potential of 30 provinces in China from 1997 to 2014. The results are as follows: (1) the OTE of China is 79.187%, indicating that there is 20.813% potential for improvement. The OTE exhibits decreasing efficiency values from the coastal areas to the inland areas and has clear geographical relationships. The average values of OTE in the east, midland and west are 0.932, 0.694 and 0.703. Theoretically, the total energy savings of CE, HE, ME and BE are 11080.60PJ, 5124.71PJ, 4729.24PJ and 6797.39PJ. (2) Regarding CE, HE, ME and BE, the provinces with the highest comprehensive ranks are Henan, Shanxi, Shaanxi, and Gansu, which simultaneously have the greatest energy-saving potentials and energy-saving targets. (3) The HE has the largest average ESTR of 38.357% and the values for BE, CE, and ME are 25.759%, 23.874%, and 22.143%, respectively. The CE category is the greatest in total energy savings (40.171%), which is followed by BE (24.150%), HE (18.384%), and ME (17.293%).

Long-term U.S transportation electricity use considering the effect of autonomous-vehicles: Estimates & policy observations

In this paper, we model three layers of transportation disruption – first electrification, then autonomy, and finally sharing and pooling – in order to project transportation electricity demand and greenhouse gas emissions in the United States to 2050. Using an expanded kaya identity framework, we model vehicle stock, energy intensity, and vehicle miles traveled, progressively considering the effects of each of these three disruptions. We find that electricity use from light duty vehicle transport will likely be in the 570–1140 TWh range, 13–26%, respectively, of total electricity demand in 2050. Depending on the pace at which the electric sector decarbonizes, this increase in electric demand could correspond to a decrease in LDV greenhouse gas emissions of up to 80%. In the near term, rapid and complete transport electrification with a carbon-free grid should remain the cornerstones of transport decarbonization policy. However, long-term policy should also aim to mitigate autonomous vehicles’ potential to increase driving mileage, urban and suburban sprawl, and traffic congestion while incentivizing potential energy efficiency improvements through both better system management and the lightweighting of an accident-free vehicle fleet.

The remaining potential for energy savings in UK households

Progress on improving energy efficiency of UK homes has stalled in recent years and the question arises how much more potential for further energy savings exist across the housing stock. Whilst there are some high-level estimates of the potential for buildings energy efficiency in the UK, a more granular assessment is needed to understand exactly where this potential lies and what form it takes. Our analysis fills this gap. It is based on the best available evidence on the remaining potential for energy efficiency improvements within UK residential buildings. Using UK government criteria for investment appraisal, we demonstrate that there is a significant resource of untapped energy-saving opportunities in UK homes. Specifically, our estimates suggest that: one quarter of the energy currently used in UK households could be cost effectively saved by 2035; and this could increase to one half if allowance is made for falling technology costs and the wider benefits of energy efficiency improvements. However, these estimates are sensitive to the assumptions made about capital, energy and carbon costs, and capturing this potential will require both significant policy change and large-scale investment.

Energy efficiency improvements of post-combustion CO2 capture based on reactive gas–liquid absorption applied for super-critical circulating fluidized bed combustion (CFBC) power plants

The environmental impact represents a significant constraint for fossil fuel-intensive industrial processes in transition to a low-carbon scenario. This paper is evaluating the potential energy efficiency improvements in reactive gas–liquid absorption process used for CO2 capture from coal-based super-critical CFBC power plants. Two improved configurations for Methyl diethanolamine (MDEA)-based post-combustion CO2 capture were assessed: absorption intercooling and lean vapour recompression as well as the combination of both. The improved MDEA gas–liquid absorption configurations were compared to conventional MDEA and MEA-based systems for post-combustion CO2 capture as well as the CFBC power plant without carbon capture to assess both the energy and cost penalties for CO2 capture. As the results show, the proposed innovative concepts exhibit better specific thermal energy consumptions for solvent regeneration (2.24–2.58 vs. 2.97 MJ/kg CO2), higher net electrical efficiency (34 vs. 32%) and improved economic indicators (e.g. 2403 vs. 2552 €/kW net power as specific capital investment, 39.2 vs. 41.6 €/MWh as O&M costs, 79 vs. 84 €/MWh as cost of electricity) compared to the conventional MDEA and MEA cases.

Electrical energy demand management in Russia

One of the modern and effective tools for energy efficiency improvement at the level of national economies is management of the demand for electrical energy consumption. The mechanism of management of the demand for electrical energy consumption has a significant potential for energy efficiency improvement for the Russian economy, but due to structural features of the Unified Energy System of Russia, the Electrical Energy Demand Management Program is at the stage of concept development. A model of management of the demand for electrical energy consumption for Unified Energy System of Russia has been developed taking into account structural features of the electric power system. Peculiarities of the economic structure of Russia, which influence the formation of the structure of the country’s electric power complex, have been revealed. They were taken into account when developing requirements for the electrical energy demand management system in the Unified Energy System of Russia. The basic features are the multilevel form and hierarchy of the structure; they have been investigated in the process of developing the demand management model. The classification of electric power industry entities, related to processes of electric energy circulation and the influence on the management of the demand for electrical energy consumption, has been developed with economic interests of each entity within the framework of the demand management model. The electrical energy demand management model, which is based on the hierarchical structure of demand management, has been developed and covers the whole complex of management functions and takes into account features of demand management at each management level. The model allows to significantly improve the efficiency of management of the demand for electrical energy consumption, to ensure the quality of management.

Energy Efficiency in Logistics: An Interactive Approach to Capacity Utilisation

Logistics operations are energy-consuming and impact the environment negatively. Improving energy efficiency in logistics is crucial for environmental sustainability and can be achieved by increasing the utilisation of capacity. This paper takes an interactive approach to capacity utilisation, to contribute to sustainable freight transport and logistics, by identifying its causes and mitigations. From literature, a conceptual framework was developed to highlight different system levels in the logistics system, in which the energy efficiency improvement potential can be found and that are summarised in the categories activities, actors, and areas. Through semi-structured interviews with representatives of nine companies, empirical data was collected to validate the framework of the causes of the unutilised capacity and proposed mitigations. The results suggest that activities, such as inflexibilities and limited information sharing as well as actors’ over-delivery of logistics services, incorrect price setting, and sales campaigns can cause unutilised capacity, and that problem areas include i.a. poor integration of reversed logistics and the last mile. The paper contributes by categorising causes of unutilised capacity and linking them to mitigations in a framework, providing a critical view towards fill rates, highlighting the need for a standardised approach to measure environmental impact that enables comparison between companies and underlining that costs are not an appropriate indicator for measuring environmental impact.

Potential efficiency improvement of Cu (In, Ga) Se2 thin-film solar cells by the window layer optimization

In this paper, an initial model based on a CIGS experimental device has been established. Afterwards, the conventional i-ZnO layer replaced by ZnO1-xSx or Zn1-yMgyO layers as window layer and the solar cell performance analyzed. The estimated optical bandgap (Eg) of Zn1-yMgyO material is linearly enhanced from 3.3 eV for pure ZnO to 4.1 eV for Zn0.6Mg0.4O. Also, Eg for ZnO1-xSx material is variable between 2.83 eV–3.76 eV that is wider than pure ZnO. The AlZnO/ZnO1-xSx/CdS/CIGS structure when 0.4 < x < 0.6 and the AlZnO/Zn1-yMgyO/CdS/CIGS structure when 0.055 < y < 0.2 are the proposed solar cells with 21.15% efficiency.

Potential energy efficiency improvements for the Brazilian iron and steel industry: Fuel and electricity conservation supply curves for integrated steel mills

The iron and steel sector is the second-largest energy consumer and main emitter of greenhouse gases in the Brazilian industry. We present a unique, detailed analysis of the energy performance of a sample of five integrated mills with internal coke production that account for over half of the crude steel produced in Brazil and identify economically viable energy efficiency measures. The analysis indicates that the specific total energy consumption of this sample of mills increased by about 13% between 2004 and 2014 and that the corresponding figure for electricity consumption was 18%. Performance and cost data on best energy practices for iron and steel production processes applicable in Brazilian mills are used to develop fuel and electricity Conservation Supply Curves. The economic potential identified for fuels was 3.02 GJ/t of crude steel, which can be achieved with nine energy efficiency measures, mainly in the iron making, sintering and steel making processes. The findings also indicate that these mills could become net exporters of electricity with an economic potential of 1.51 GJ/t of crude steel if four energy efficiency measures were implemented, particularly in the O2 production and coke making processes.

Assessment of long-term energy efficiency improvement and greenhouse gas emissions mitigation potentials in the chemical sector

The industrial sector accounts for more than one-third of global energy consumption and greenhouse gas (GHG) emissions. In the sector, the chemical industry makes up nearly 30% of global industrial energy consumption. In this study, a framework is developed to apply bottom-up energy modelling for analyzing energy efficiency improvement and GHG mitigation potential in the chemical sector. Also, techno-economic and policy analyses are used to analyze the applicability and economic performance of different mid- to long-term energy efficiency measures. The comprehensive, data-intensive, and technology-rich model is flexible and can be used to study the GHG mitigation potential in different regions. A case study was conducted for Alberta, one of the biggest industrial hubs in Canada, using the Long-range Energy Alternative Planning model. Twenty-eight GHG mitigation scenarios in the petrochemical and fertilizer industries (the two major chemical industry sub-sectors) were developed. The costs of implementing each mitigation measure were calculated and used to develop cost curves. The results suggest that cumulative mitigation potential from the chemical industry would be 7.1 and 29.7 megatonnes CO2 equivalent in the periods ending 2030 and 2050, respectively. We also found that more than 75% of the emissions reductions are achievable with negative cost.

Advanced exergy analysis of a carbon dioxide ammonia cascade refrigeration system

In the present research study, a cascade NH3/CO2 refrigeration system is modeled and comprehensively assessed. Engineering Equation Solver (EES) as a potential tool is used for the simulation purpose. In order to validate the simulation code, the exergy destruction and COP is compared with an experimental data from the literature. In addition, advanced exergy analysis is applied to the system in order to determine the magnitude and location of the endogenous/exogenous and avoidable/unavoidable exergy destruction rates. The results of the advanced exergy analysis provide a very good insight for thermal engineers for system design, analysis and assessment of energy systems. The results identify that the proposed system has significant potential for efficiency improvement. The results of the advanced exergy analysis suggests that CO2-Throtteling valve, CO2-compressor and cascade heat exchanger are the components where improvements are necessary while conventional exergy analysis cannot provide such recommendations.In addition, advanced exergy analysis results indicate that improvement of the components has the ability to improve the system efficiency for about 42.13%. while this improvement for exergy destruction rate is 23.81 kW.

Exergetic optimization of double stage Organic Rankine Cycle (ORC)

The present work focuses on the exergetic optimization of double stage Organic Rankine Cycle (DS ORC) for waste heat recovery. A model of a DS ORC, consisting of a high temperature (HT) stage serially connected to a low temperature (LT) stage is developed, while different combinations of working fluids with variable critical temperatures are considered in each stage. The optimization variables are the evaporation pressures in the HT and LT stages, as well as the evaporator pinch point and condenser temperature in the HT stage. The aim is to explore the exergetic efficiency improvement potential of DS ORCs compared to the single stage cycles and establish optimization guidelines for maximizing their total power output for heat source temperatures ranging from 100 °C to 300 °C. Compared to single stage ORCs, DS ORCs can lead to a relative increase of the exergetic efficiency by up to 25%, depending on the heat source temperature and the working fluids considered. Meanwhile, DS ORCs are especially favorable when the heat source temperature is far lower or between the critical temperatures of the fluids used in their two stages.

Combining Thickness Reduction and Light Trapping for Potential Efficiency Improvements in Perovskite Solar Cells

In this contribution it is shown that the efficiency of perovskite solar cells based on CH3NH3PbI3 can be increased further by combining thickness reduction of the perovskite layer and light trapping. A physical model for the current/voltage curve of pin solar cells is used to reveal the beneficial impact of thinning on cell efficiency. If interface recombination is kept at moderate levels, the model shows that there is a potential efficiency increase above 20% relative (+3% absolute) when thickness is reduced from 500 to 200 nm, provided total light absorption is maintained. A rigorous optical model is employed to calculate light absorption on typical state–of–the–art layer stacks patterned with sinusoidal grooves on ITO coated glass. The results suggest that solar light absorption in a flat, 500 nm thick film, can be matched by a 200 nm thick perovskite layer on a sinusoidal texture, while using 300 nm leads to several sinusoidal parameter combinations delivering the same light absorption. Since the structuring step must be compatible with low cost processing, it is shown that direct laser interference patterning (DLIP) is capable of delivering +3% absolute efficiency increase, while offering a typical photovoltaic module cost reduction of 10%.

Artificial selection for improved energy efficiency is reaching its limits in broiler chickens

Modern broiler chickens are a major animal husbandry success story, both in terms of efficient resource utilisation and environmental sustainability. However, continuing artificial selection for both efficiency and rapid growth will be subject to both biological limits and animal welfare concerns. Using a novel analytical energy flow modelling approach, we predict how far such selection can go, given the biological limits of bird energy intake and partitioning of energy. We find that the biological potential for further improvements in efficiency, and hence environmental impact reduction, is minimal relative to past progress already made via artificial selection. An alternative breeding strategy to produce slower-growing birds to meet new welfare standards increases environmental burdens, compared to current birds. This unique analytic approach provides biologically sound guidelines for strategic planning of sustainable broiler production.

A New Amplification Regime for Traveling Wave Tubes With Third-Order Modal Degeneracy

Engineering of the eigenmode dispersion of slow-wave structures (SWSs) to achieve desired modal characteristics, is an effective approach to enhance the performance of high power traveling wave tube (TWT) amplifiers or oscillators. We investigate here for the first time a new synchronization regime in TWTs based on SWSs operating near a third order degeneracy condition in their dispersion. This special three-eigenmode synchronization is associated with a stationary inflection point (SIP) that is manifested by the coalescence of three Floquet-Bloch eigenmodes in the SWS. We demonstrate the special features of "cold" (without electron beam) periodic SWSs with SIP modeled as coupled transmission lines (CTLs) and investigate resonances of SWSs of finite length. We also show that by tuning parameters of a periodic SWS one can achieve an SIP with nearly ideal flat dispersion relationship with zero group velocity or a slightly slanted one with a very small (positive or negative) group velocity leading to different operating schemes. When the SIP structure is synchronized with the electron beam potential benefits for amplification include (i) gain enhancement, (ii) gain-bandwidth product improvement, and (iii) higher power efficiency, when compared to conventional Pierce-like TWTs. The proposed theory paves the way for a new approach for potential improvements in gain, power efficiency and gain-bandwidth product in high power microwave amplifiers.

Exergy approach for advancing sustainability of a biomass boiler

An exergy analysis of the district energy plant at University of Idaho, Moscow, Idaho, USA is presented. Exergy flows through the components of the steam cycle through the biomass boiler are quantified to identify major sources of exergy destruction. A mathematical model is developed to determine sources of exergy destruction using measurements taken. The largest sources of exergy destruction are the boiler and furnace at 35% and 33% of the overall exergy losses, respectively, followed by the campus heating equipment at 5.7% and pressure reducing valve (PRV) at 3.5%. Parametric studies reveal that decreasing boiler steam pressure levels to reduce exergy destruction in the PRV results in increased exergy destruction rates in the boiler. Increasing boiler steam pressure levels instead reduces exergy destruction, but has negligible effects on the overall exergy efficiency of the complete cycle. This indicates that the PRV is limiting potential improvements in the boiler exergy efficiency.

Comparison of Free Energy Loss Analysis and Synergistic Efficiency Gain Analysis for PERC Solar Cells

The optimization of a solar cell requires a detailed knowledge of the efficiency limiting power losses. The free energy loss analysis (FELA) and the synergistic efficiency gain analysis (SEGA) both allow for studying these power losses. We compare both approaches for industrial passivated emitter and rear solar cells. The resistive losses calculated with both approaches are in good agreement with each other. In contrast, we find deviations of more than 20% for losses because of charge carrier recombination. From an analytical description of both methods, we conclude that these deviations are caused by a shift of the maximum power point voltage in an improved cell which is not considered in the FELA. The deviation of the losses critically depends on the specific loss channel investigated. In contrast with implied front-side power gains which are usually underestimated, rear-side or absorber gains can be over or underestimated by the FELA depending on the magnitude of the power loss. These differences follow from the Fermi level splitting which is affected differently by recombination currents at different locations. For an accurate determination of the efficiency improvement potential of individual recombination loss channels, we therefore recommend to perform a SEGA.

Alcohol fuels for spark-ignition engines: Performance, efficiency and emission effects at mid to high blend rates for binary mixtures and pure components

The paper evaluates the results of tests performed using mid- and high-level blends of the low-carbon alcohols, methanol and ethanol, in admixture with gasoline, conducted in a variety of test engines to investigate octane response, efficiency and exhaust emissions, including those for particulate matter. In addition, pure alcohols are tested in two of the engines, to show the maximum response that can be expected in terms of knock limit and efficiency as a result of the beneficial properties of the two alcohols investigated. All of the test work has been conducted with blending of the alcohols and gasoline taking place outside the combustion system, that is, the two components are mixed homogeneously before introduction to the fuel system, and so the results represent what would happen if the alcohols were introduced into the fuel pool through a conventional single-fuel-pump (dispenser) approach. While much has been written on the effect of blending the light alcohols with gasoline in this way, the results present significant new findings with regard to the effect of the enthalpy of vaporization of the alcohols in terms of particulate exhaust emissions. Also, in one of the tests, two mid-level blends are tested in a highly downsized prototype engine – these blends being matched for stoichiometry, enthalpy of vaporization and volumetric energy content. The consequences of this are discussed and the results show that this approach to blend formulation creates fuels which behave in the same manner in a given combustion system; the reasons for this are discussed. One set of tests using pure methanol alternately with cooled exhaust gas recirculation and with excess air shows a significant increase in thermal efficiency that can be expected as the blend level is increased. The effect on nitrous oxide emissions is shown to be similarly beneficial, this being primarily a result of the enthalpy of vaporization of the alcohol cooling the charge coupled with the lower adiabatic flame temperature of the alcohol. Whereas it is normally a beneficial characteristic in spark-ignition combustion systems, one disadvantage of a high value of enthalpy of vaporization is shown in another series of tests in that, in admixture with gasoline, it is a driver on flash boiling of the hydrocarbon component in the blend in direct injection combustion systems. In turn, this causes the particulate emissions of the engine to increase quite markedly over those of ethanol–gasoline blends at the same stoichiometry. The paper shows for the first time the dichotomy of the potential efficiency improvement with the challenge of particulate control. This effect poses a challenge for the future introduction and use of such high blend rate fuels in engines without particulate filters. Although it must be stated that the overall particulate emissions of the methanol–gasoline blend are lower than for gasoline, the effect is only present at extremely low load, and that there is a likelihood that particulate filters will be adopted in production vehicle anyway, nullifying this issue.

Charging properties of a compact energy storage device for transport air conditioning applications

Air conditioning system in transport applications is a great challenge due to the frequently fluctuated load which causes comfort degradation and even healthy concern. In our previous study, a compact energy storage device filled with PCM was designed and experimentally tested which showed great potential for thermal comfort improvement and efficiency improvement. In this study, charging properties of the energy storage device for train air conditioning systems are experimentally investigated. Time evolutions of PCM temperature during the charging process are presented. The charging performances including charging time, transient charging rate, thermal efficiency and exergy efficiency are revealed. The results show that the designed device has excellent heat transfer behaviors with exergy efficiency up to 78%. The designed device is feasible to be used in transport air conditioning systems due to the quick charging.

Proposed suitable electron reflector layer materials for thin-film CuIn1−xGaxSe2 solar cells

This paper investigates the electrical properties of electron reflector layer to survey materials as an electron reflector (ER) for chalcopyrite CuInGaSe solar cells. The purpose is optimizing the conduction-band and valence-band offsets at ER layer/CIGS junction that can effectively reduce the electron recombination near the back contact. In this work, an initial device model based on an experimental solar cell is established, then the properties of a solar cell with electron reflector layer are physically analyzed. The electron reflector layer numerically applied to baseline model of thin-film CIGS cell fabricated by ZSW (efficiency = 20.3%). The improvement of efficiency is achievable by electron reflector layer materials with Eg > 1.3 eV and −0.3 < Δχ < 0.7, depends on bandgap. Our simulations examine various electron reflector layer materials and conclude the most suitable electron reflector layer for this real CIGS solar cells. ZnSnP2, CdSiAs2, GaAs, CdTe, Cu2ZnSnS4, InP, CuO, Pb10Ag3Sb11S28, CuIn5S8, SnS, PbCuSbS3, Cu3AsS4 as well as CuIn1-xGaxSe (x > 0.5) are efficient electron reflector layer materials, so the potential improvement in efficiency obtained relative gain of 5%.