Energy Efficient Option Research Articles

Making a case for white light-emitting diodes in the Western Cape

Within the context of the energy crisis in the Western Cape, the Provincial Government and Eskom (the South African power utility) embarked on a retrofit campaign to install 5 million compact fluorescent lamps (CFLs) in a desperate attempt to decrease the generation deficit. There is also increased pressure for investments in new generation capacity, with all options including the Pebble Bed Modular reactor (PBMR), the Open Cycle Gas Turbines (OCGT) as well as renewable resource technologies being pro-posed. Despite all these concerted efforts it is wide-ly regarded that demand-side technologies, with education programs, subsidies and research fund-ing, have greater scope for achieving success as they tackle the root cause rather than the symptom.The light emitting diode (LED) is a new energy efficient option in the lighting sector that has in recent times been deployed extensively by the City of Cape Town’s Transport Network Operations Department. The technology promises superior attributes that include a longer lifespan and higher energy conversion efficiencies, when compared to the traditional incandescents and fluorescents. This paper details the achievements of the LED in its brief history in the local traffic and signals industry as well as its projected impact on the city traffic light department’s future energy and mainte-nance budget. It is then proposed that these mono-chromatic signal LEDs, which is fast evolving into a white LED, holds the best promise in Cape Town as well as the Western Cape’s energy future if adopted for general lighting in the domestic, commercial and industrial market.

Sustainable waste management—what and how?

Historically, ‘developed’ societies have adopted a linear approach to the use of resources, with natural assets being processed, used and ultimately discarded as wastes with little if any thought being given to the capacity of the environment either to maintain the supply of resource at one end or receive the waste at the other. Although governments and the public are now more aware of the problems this creates, the current focus is often on meeting legislative targets rather than the more fundamental goals of sustainable resource management and care for the environment. This paper argues that ‘waste’ should be viewed as part of a resource cycle that includes extracting materials and energy from the environment, refining raw materials and producing goods, consuming and using goods and then eventually returning materials to the environment. Each process has inputs (materials and energy) and outputs (products, energy and waste). Waste outputs from one process can sometimes be used as resource inputs to another, or even the same, process. Sustainability principles require that resources are used with maximum efficiency while they are within the human part of the cycle, and that they are returned to the environment in a way that enables them to be extracted and used again—something that at present happens only rarely, haphazardly and on a geological timescale. Options for sustainable resource management are reviewed and appraised, with reference mainly to household waste. It is argued that the management of interim and residual ‘wastes’ should be based on the most energy or resource efficient option for individual components of the waste stream; this might involve reuse, materials recovery, energy recovery or safe disposal of different components at different stages of the resource cycle.

Elucidation of the intrinsic loss arising from switch output capacitance Coss in ultra-high-speed low-loss power converters

Attempts to drive down the switching losses of hard-switched unipolar devices by increasing gate drive current levels are ultimately limited by the device output capacitance, which thus represents an intrinsic loss. The paper presents an in-depth analysis of the charging and discharging of the output capacitance and the associated loss producing mechanisms. It is shown that energy is stored in the depletion layer of the device during turn-off and then dissipated as heat during the turn-on process. The instantaneous power dissipated in the device is thus different to the instantaneous power loss measured at the device terminals, although the total energy loss over one complete turn-off and turn-on cycle is still faithfully reproduced. An analytical approach to determining the intrinsic switching loss due to the output capacitance is presented and verified by experimental results and by TCAD simulation. It is shown that around 20% of the total switching losses arise from the intrinsic output capacitance loss under fast-switched inductive load conditions. A comparison of Si and SiC FET devices demonstrates the potential for SiC power devices to provide an energy efficient option for very high frequency switching.

Efficiencies of hydrogen storage systems onboard fuel cell vehicles

Energy efficiency, vehicle weight, driving range, and fuel economy are compared among fuel cell vehicles (FCV) with different types of fuel storage and battery-powered electric vehicles. Three options for onboard fuel storage are examined and compared in order to evaluate the most energy efficient option of storing fuel in fuel cell vehicles: compressed hydrogen gas storage, metal hydride storage, and onboard reformer of methanol. Solar energy is considered the primary source for fair comparison of efficiencies for true zero emission vehicles. Component efficiencies are from the literature. The battery powered electric vehicle has the highest efficiency of conversion from solar energy for a driving range of 300 miles. Among the fuel cell vehicles, the most efficient is the vehicle with onboard compressed hydrogen storage. The compressed gas FCV is also the leader in four other categories: vehicle weight for a given range, driving range for a given weight, efficiency starting with fossil fuels, and miles per gallon equivalent (about equal to a hybrid electric) on urban and highway driving cycles.

Impact of cogeneration on integrated resource planning of Turkey

In most developing countries, difficulties in finding sector-specific data on heat rate and power demands make energy planning a hard task. In some countries, although this data is available, it may be four or five years old. In the present work, a new low-cost method is proposed for developing countries aiming at obtaining such data for the industrial sector quickly. Fifty-two textile factories were selected for a survey to represent the industrial sector. The data were processed and used to generate two scenarios of cogeneration applications in the industrial sector; one sized according to the electrical load of the factories, and the other one according to the thermal load. The costs and primary energy requirements of these programs were compared with that of the nuclear alternative. It was found that the most energy efficient and economical option for Turkey was the cogeneration program, the equipment sizing of which was based on the process heat demand of the industrial sector. Turkey would not only save US$ 72.6-billion by deferring the nuclear program, but it will also reduce the total primary energy demand by 11% in 2020.

Navigating the Energy Efficiency Maze

Exciting advances during the past 10 years in building technologies, equipment systems, and techniques have made choosing the right energy-efficient option a confusing and time-consuming task for public works and facilities managers. Through a community-based energy-efficiency program, staff members of the U.S. Department of Energy national laboratories provide technical assistance to local efforts that are striving to save money by saving energy. Having formed more than 200 local and state partnerships, the labs are leading communities to a warehouse of strategies and solutions for their day-to-day energy problems.

Feasibility and benefits of methanogenesis under oxygen-limited conditions

Methanogenic and aerobic (or microaerophilic) biological processes are often considered mutually exclusive and separated as biological wastewater treatment options. However, under oxygen-limited conditions, both aerobic respiration and methanogenesis can be practically accomplished by a single mixed culture. This paper describes sustained batch culture, oxygen-limited methanogenic serum bottle and bench-scale systems. Serum bottle cultures exhibited methanogenic activity similar to or greater than that of a strictly anaerobic culture maintained in parallel. The COD removal efficiencies of anaerobic, oxygen-limited, and aerobic bench-scale reactors receiving 30,000 mg/l of sucrose were all greater than 93%, a system receiving 1 g O 2/L R-day achieved a lower final effluent COD than the strictly anaerobic reactor. After a shock-load of sucrose, the pH recovered in low-aeration batch reactors in 28–34 days, whereas anaerobic pH did not recover after 52 days of observation. In the future, methanogenesis under limited-aeration may be employed as an energy efficient treatment option to achieve low final COD concentrations, minimal biosolids generation, and mineralization of a broad range of specific organic chemicals.

Low Temperature Bleaching of Jute Fabric Using a Peracetic Acid System

Bleaching of jute fabric with peracetic acid is investigated using two different stabilizing agents, sodium tetraborate (borax) and tetrasodium pyrophosphate (tspp). A buffered medium is essential during bleaching in order to improve fiber brightness; a phosphate buffer enhances the bleaching effect obtained with either borax or tspp as stabilizer. A superior bleaching effect is achieved by using tspp as a stabilizer under mildly alkaline conditions (pH 8.0–8.5), and excellent fiber brightness can occur at temperatures as low as 40–60°C. This optimized peracetic acid-tspp bleaching system offers a more energy efficient option for bleaching 100% jute fabric. A further advantage is that it may also be successfully extended to bleaching of jute/cotton blends.

Distributed computer control systems

Energy cost comparison between MSF, MED and SWRO has been conducted. In order to investigate energy consumption differences when combined with a simple cycle Oil-Fired Power Plant (OFPP) or a Combined Cycle Power Plant (CCPP), Yanbu Ph.3 and Ras Al-Khair Ph.1 power and water cogeneration projects are considered as practical heat and mass balance references. With the net power production of 2708.5 MW and the total water production of 124.54 MIGD, the fuel energy differences due to desalination are compared. By calculating the fuel energy requirement for desalination from a cogeneration cycle itself, some controversial issues including evaluating electricity and steam could be avoided. Results show that the required fuel energies for desalination are less by 11–49% when combined with CCPP than with OFPP, owing to the higher efficiency of the combined cycle. Thermal desalination benefits more greatly from the combined cycle's higher efficiency due to a lowered steam value. While SWRO shows a better fuel energy efficiency for most of the studied regime, high Performance Ratio (PR) MEDs combined with CCPP could be a similar energy efficient option if PR is 16.5–19.3, compared to SWRO with CCPP.