Optimisation models for decision support in the development of biomass-based industrial district-heating networks in Italy

A system optimisation approach is proposed to design biomass-based district-heating networks in the context of industrial districts, which are one of the main successful productive aspects of Italian industry. Two different perspectives are taken into account, that of utilities and of policy makers, leading to two optimisation models to be further integrated. A mixed integer linear-programming model is developed for a utility company’s profit maximisation, while a linear-programming model aims at minimising the balance of greenhouse-gas emissions related to the proposed energy system and the avoided emissions due to the substitution of current fossil-fuel boilers with district-heating connections. To systematically compare their results, a sensitivity analysis is performed with respect to network size in order to identify how the optimal system configuration, in terms of selected boilers to be connected to a multiple energy-source network, may vary in the two cases and to detect possible optimal sizes. Then a factorial analysis is adopted to rank desirable client types under the two perspectives and identify proper marketing strategies. The proposed optimisation approach was applied to the design of a new district-heating network in the chair-manufacturing district of North-Eastern Italy.     

Simulation of solar heating systems—an overview

Process simulation has become an accepted tool for the performance, design, and optimization of thermal processes. Solving the mathematical models representing solar heating process units and systems is one of the most tedious and repetitive problems. Nested iterative procedures are usually needed to solve these models. To tackle these problems, several researchers have developed different methods, techniques, and computer programs for the simulation of very wide verity of solar heating process units and systems.It is of interest in this work to characterize and classify these methods, techniques, and programs in order to better understand their relations, types, structures, and procedures.The simulation problems are outlined; the simulation programs are grouped into two main types; special purpose, and general-purpose programs. Sequential and simultaneous computational sequences are illustrated. Simulator structure, program evaluation, and numerical techniques are summarized.By considering the unit and/or system entropy generation as well as the energy and material balances equations, more realistic models can be obtained. Also, rapid development of computer hardware and software will suggest new techniques and programs to be considered. These progress directions are noted.     

Impact of wind power in autonomous power systems—power fluctuations—modelling and control issues

This paper describes a detailed modelling approach to study the impact of wind power fluctuations on the frequency control in a non‐interconnected system with large‐scale wind power. The approach includes models for wind speed fluctuations, wind farm technologies, conventional generation technologies, power system protection and load. Analytical models for wind farms with three different wind turbine technologies, namely Doubly Fed Induction Generator, Permanent Magnet Synchronous Generator and Active Stall Induction Generator‐based wind turbines, are included. Likewise, analytical models for diesel and steam generation plants are applied. The power grid, including speed governors, automatic voltage regulators, protection system and loads is modelled in the same platform. Results for different load and wind profile cases are being presented for the case study of the island Rhodes, in Greece. The scenarios studied correspond to reference year of study 2012. The effect of wind fluctuations in the system frequency is studied for the different load cases, and comments on the penetration limits are being made based on the results. Copyright © 2010 John Wiley & Sons, Ltd.     

Environmental isotope investigations of New Zealand geothermal systems—A review

Environmental isotope investigations of geothermal systems at the New Zealand Institute of Nuclear Sciences have concentrated in recent years on combining several isotopes with chemical analyses. Geothermal hydrology has been studied by the use of hydrogen and oxygen isotopes with chloride and other water analyses. Rocks and minerals in well cores have added information to the geology and chemistry through the use of oxygen isotope techniques. Oxygen, hydrogen, carbon and sulphur isotope geothermometry have been combined in an attempt to derive temperature profiles with depth. ²²²Rn measurements in soil indicate leakage through faults, while ²²²Rn measurement of well discharges show evidence of underground processes. Future work will include noble gas isotope measurements. Measurements of ¹H and ¹⁴C are reported in an associated paper on tracing of underground water movements.     

A parametric study of closed loop solar heating systems—II

A nondimensional equation describing the closed loop solar heating system with either parallel or series auxiliary heaters is derived. Using European weather data the monthly solar fraction is calculated for variations in the major non-dimensional groups. A correlation is given relating the solar fraction to three non-dimensional parameters M, Kc and Rc. M is the ratio of energy available on the collector aperture to energy demand. To calculate the energy available it is necessary to know the monthly utilizability. Kc is the ratio of the store temperature required for a 100 per cent solar contribution to the average monthly collector peak stagnation temperature. Both these temperatures are referenced to the demand temperature. Rc is the effective “turn over time” of the store, i.e. the number of days to empty the energy contents of the store. The magnitudes of Kc and Rc depend on the load heat exchanger size. Comparisons between the solar fraction predicted with a dimensional hour by hour computer model and that by the correlation are made for two system types. The agreement is good and it is concluded that the correlation can be used as a reliable method to optimise closed loop solar heating systems.     

Consumers’ influence on the thermal performance of small SDHW systems—Theoretical investigations

Usually when SDHW systems are tested and modeled the daily hot-water consumption and consumption pattern are constant during all days of the test period and simulation period. This is not realistic in ‘real life’. Numerical simulations with detailed simulation models have been carried out to investigate the influence on the thermal performance of different hot-water consumptions and consumption patterns. Two different small SDHW systems are taken into the calculation, a low-flow system where the heat storage consists of a mantle tank and a high flow system with an internal heat exchanger spiral in the heat storage. Two different domestic hot water (DHW)-load profiles have been taken into the calculation. One of the DHW-load profiles has three draw-offs at equal time, size and duration every day while the other DHW-load profile is a realistic profile for a Danish family where the hot-water consumption and consumption pattern vary from day to day and furthermore weekends and holidays are taken into account in this profile. Different volumes of the tanks in the two systems are taken into the calculation in order to determine how the thermal performance of the systems is influenced by the tank volume for different hot-water consumptions. Furthermore it is investigated how the thermal performance of the systems are influenced by mixing in the solar tank during draw-offs.     

Chemical equilibria in icelandic geothermal systems—Implications for chemical geothermometry investigations

Chemical geothermometry represents the most important tool for estimating reservoir temperatures in the exploration of geothermal resources. Chemical equilibria between alteration minerals and solution are generally attained in geothermal systems for all major components except chloride. For the interpretation of analyses of natural waters involving geothermometry major emphasis should be placed on assessing the overall water composition with respect to mineral equilibria, rather than attempting to distinguish geothermal waters from shallow waters by a classification involving the relative abundance of major anions and major cations. Generally, cold waters may be distinguished from geothermal waters by low chloride (< 10 ppm), in conjunction with relatively low pH (6–7) and low Na/K ratios (same as the associated rock), calcite undersaturation and low √Ca²⁺ H⁺ activity ratios.     

Liquid phase thermochemical energy conversion systems—An application of Diels-Alder chemistry

Thermochemical energy conversion at moderate or low temperature (> about 400°C) employing liquid phase components throughout a cycle is suggested as a promising concept for high-efficiency conversion of various energy sources (e.g. solar or industrial waste heat) to a convenient chemical form. In particular, we propose liquid phase Diels-Alder cycloaddition chemistry as an important class of reversible reactions for such low or moderate temperature thermochemical energy conversion systems. One of the important attributes of thermally driven Diels-Alder reactions is their concerted mechanism, with consequent high yields and efficiencies relative to liquid photochemical systems. Since the systems we propose involve organic species, with thermal stability concerns above about 400°C, it is important to demonstrate equilibrium shift capability for the highly energetic reactions sought. We have therefore carried out experimental studies with model liquid Diels-Alder systems that clearly demonstrate the degree of control over equilibrium available through substituent entropy effects. For example, K_eq is unity at about 420°C (T*) for the anthracene/maleic anhydride system (in solvent) while a phenyl substituent on the anthracene or isopropyl substituent on the anhydride reduce T* to about 200°C at constant ΔH⁰. These results are of importance as regards subsequent systematic identification of Diels-Alder reactions having ideal thermochemical and physical properties. We also have developed a rapid NMR technique for qualitative screening of candidate reactions, and have applied this technique to the study of various bicyclic diene/fumaric acid ester systems. Our paper further points to the need for better understanding of the catalysis likely required for these liquid phase Diels-Alder reactions.     

Applications of photovoltaic systems—An economic appraisal with reference to india

A simple methodology for analyzing the economic viability of photovoltaic systems is proposed. The methodology is applied to the different near-term applications of photovoltaic systems both in the commercial and the rural sector with reference to India conditions. It is concluded that most of the photovoltaic systems are economically viable provided some long-term financial policy is envisaged and a few technical innovations in the balance of systems are made.     

Small-scale solar PV generating systems—The household electricity supply used in remote areas

The purpose of our research in China is to develop a small-scale solar PV system with the features of higher conversion efficiency, higher reliability, reasonable price and ease of operation, which is composed of a PV panel, battery, controller, inverter, etc. The main research work includes the design of the system, the rational selection and deployment of components used in the system, the cost calculation and the financial evaluation of system.     

Thermoeconomic analysis method for optimization of combined heat and power systems—part II

In this paper, a thermoeconomic functional analysis method based on the Second Law of Thermodynamics and applied to analyze four cogeneration systems is presented. The objective of the developed technique is to minimize the operating costs of the cogeneration plant, namely exergetic production cost (EPC), assuming fixed rates of electricity production and process steam in exergy base. In this study a comparison is made between the same four configurations of part I. The cogeneration system consisting of a gas turbine with a heat recovery steam generator, without supplementary firing, has the lowest EPC.     

Lead-acid battery capacity in solar home systems—Field tests and experiences in Lundazi, Zambia

Batteries in solar home systems can cause problems and costs for the users and/or operators of the systems. In Zambia the Lundazi Energy Service Company (LESCO) operates 150 solar home systems on a fee for service basis. The aim of the study was to investigate how the capacity of lead-acid flat plate batteries had changed after one year of operation under real conditions. The results indicate that the batteries capacity has been significantly reduced in comparison to new unused batteries of the same type. Changes in battery management and maintenance, along with additional education of customers on correct use of SHS is advised in order to improve the life span of batteries in practical use.     

The role of hydrogen for the long term development of sustainable energy systems—a case study for Germany

Based on different current long-term energy scenarios the paper discusses the future perspectives of hydrogen in the German energy system as a representative example for the development of sustainable energy systems. The scenario analysis offers varying outlines of the future energy system that determine the possible role of hydrogen. The paper discusses the possibilities of expanding the share of renewable energy and the resulting prospects for establishing clean hydrogen production from renewable energy sources. Emphasis is given to the questions of an ecologically efficient allocation of limited renewable energy resources that can only be assessed from a systems analysis perspective. Findings from recent studies for Germany reveal a strong competition between the direct input into the electricity system and an indirect use as fuel in the transport sector. Moreover, the analysis underlines the paramount importance of reducing energy demand as the inevitable prerequisite for any renewable energy system.     

The photonic light trap—Improved light trapping in solar cells by angularly selective filters

A photonic light trap, i.e. a combination of an angularly selective filter and a light scattering process in a solar cell, results in potentially very efficient light trapping. Angularly selective filters are investigated theoretically and experimentally. One of the filters is used to realize a photonic light trap for a thin-film solar cell with amorphous-silicon absorber layer on a roughened superstrate. We experimentally demonstrate that the light absorption in this solar cell is enhanced by 25% in a wavelength range of 700–750 nm. Accordingly, the quantum efficiency of the solar cell demonstrates an increase of 25% in the same wavelength range.     

Measuring the benefits and costs of utility conservation and load management programmes

We have learned much less than we could have from utility operation of conservation and load management programmes. Our general ignorance concerning the performance (ie benefits and costs) of these programmes exists because we have not devoted sufficient resources to careful evaluations of past and present programmes. We need to build evaluation into the programme planning and implementation process and we should use actual electricity and gas bills to measure programme performance. Finally, we should conduct well designed experiments to learn what does and does not work.     

Greenhouse gas reduction benefits and costs of a large-scale transition to hydrogen in the USA

Hydrogen is an energy carrier able to be produced from domestic, zero-carbon sources and consumed by zero-pollution devices. A transition to a hydrogen-based economy could therefore potentially respond to climate, air quality, and energy security concerns. In a hydrogen economy, both mobile and stationary energy needs could be met through the reaction of hydrogen (H₂) with oxygen (O₂). This study applies a full fuel cycle approach to quantify the energy, greenhouse gas emissions (GHGs), and cost implications associated with a large transition to hydrogen in the United States. It explores a national and four metropolitan area transitions in two contrasting policy contexts: a “business-as-usual” (BAU) context with continued reliance on fossil fuels, and a “GHG-constrained” context with policies aimed at reducing greenhouse gas emissions. A transition in either policy context faces serious challenges, foremost among them from the highly inertial investments over the past century or so in technology and infrastructure based on petroleum, natural gas, and coal. A hydrogen transition in the USA could contribute to an effective response to climate change by helping to achieve deep reductions in GHG emissions by mid-century across all sectors of the economy; however, these reductions depend on the use of hydrogen to exploit clean, zero-carbon energy supply options.     

Resource of energy efficiency in Russia: scale, costs, and benefits

This paper considers Russian economy-wide energy efficiency potential by sectors and energy carriers. The assessment shows that Russian technical energy efficiency potential exceeds 45% of 2005 primary energy consumption or 294 mtoe (excluding associated gas flaring). This is about the annual primary energy consumption in France, the UK, or Ukraine, half of that in Japan, and over 2% of the global primary energy consumption. Related CO₂ emission reduction potential is 50% of the Russian 2005 emission. Special attention is given to methodological issues in aggregating potentials identified in final energy use and to the evaluation of indirect energy efficiency gains. This study found that the energy efficiency potential doubles, if associated reduction of energy use, as well as technology progress, in energy production and transformation are accounted for. Cost curves for energy efficiency improvements were developed using the incremental cost approach to identify the cost-effective part of the potential.     

Solar electricity generation—A comparative view of technologies, costs and environmental impact

The implementation of solar power plants in regions of high insolation is a promising option for an environmentally compatible electricity supply strategy. Today, approximately 80% of the solar generated electricity is provided by solar thermal power plants, while 20% is supplied by photovoltaic systems. Decision-makers have the choice among the following solar technologies: (1) parabolic trough; (2) central receiver; (3) paraboloidal dish; (4) solar chimney; (5) solar pond; (6) photovoltaic cells. This article compared present solar electricity technologies from the point of view of system analysis, taking into consideration their performance, costs and environmental impact. The study shows that the different approaches cover a wide range from units of a few Watts to utiilty-size plants and from isolated to grid-connected systems. It also shows that there is still a need for intense efforts to integrate those technologies into the existing electricity supply scheme. If a continuous development and market introduction is achieved, solar power plants will contribute substantially to the reduction of global CO₂-emissions. A practical tool for decision-makers is presented that facilitates a first estimate of the performance and costs of such plants under local conditions.     

Supporting the externality of intermittency in policies for renewable energy

We analyse the joint problem of supporting renewables and resource adequacy in a liberalised electricity market and present a detailed model-based comparison of two alternative policies. We undertake this in the context of the British market. We show how, ceteris paribus, the progressive replacement of coal with wind imposes extra costs of reserve and evaluate alternative way to meet this, whether through capacity payments funded by customers, or a reliability requirement on wind generators with capital cost or energy feed-in subsidies. We consider the reality of market concentration and the extent to which pragmatic regulation could allow prices to rise above marginal cost to reduce the extent of direct subsidies and complex market designs. We also evaluate the implied cost of carbon reduction in a progressive replacement of coal with wind, when the security is maintained by extra peaking gas. We find that support through capital allowances rather than the energy market is more efficient.     

Industrial energy use—II: Energy use in a light engineering factory

Detailed information about the use of energy on industrial sites is scarce. This paper describes for a particular site how such information can be obtained from existing records together with limited measurements and approximate mathematical models of processes. an energy balance for the site is constructed. Possibilities for reducing the energy consumption by the use of readily available technologies are considered and a new energy balance calculated under these circumstances. In some instances the proposals would require further effort to provide suitable components and controls. We have indicated where this effort would be needed.