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The construction of an energy balance sheet for a power plant or other energy conversion facility is a relatively straightforward task. |
This approach can be applied to any process where there are multiple inputs and outputs, and where some of the inputs and outputs have different forms (e.g. heat versus work). |
In this section we will deal with the first stage in the overall system, namely the power generation itself. |
Here we focus on backpressure power plants, which are widely used for both base-load and peaking applications. |
In this section we will look at how energy balances can be constructed for different types of refineries. |
We will now deal with a more detailed analysis of the refining process, focusing on the various stages involved. |
Energy has always played an important role in human and economic development and in society’s well-being. For example, fuelwood has been used from time immemorial to make fire, and the first civilisations were already making use of wind in sailing overseas. Wood was then abundant and free. People lived in small tribes and it was only when villages and small cities emerged that fuelwood became a traded commodity. |
The situation is different for wind; sailing boats still use wind freely. Millers continue to use wind freely to grind the grain in windmills. It is the appearance of the first wind turbines which prompted companies to measure the output of the wind force, i.e. the electricity generated, rather than the wind itself. |
Modern society uses more and more energy for industry, services, homes and transport. This is particularly true for oil, which has become the most traded commodity, and part of economic growth is linked to its price. |
However, neither oil nor any of the other fossil fuels, such as coal and natural gas, are unlimited resources. The combined effect of growing demand and depleting resources calls for a close monitoring of the energy situation. |
Strange as it may appear, it is precisely at a time when more and more energy is produced, traded, transformed and consumed, when energy dependency is increasing, and when greenhouse gas emissions are high on the international agenda, that it becomes more and more difficult to provide a timely and reliable picture of the energy situation in many countries. |
Having a clear view of the situation implies detailed and reliable data on the different parts of the production and consumption chain. This involves proper reporting mechanisms, sound check procedures and adequate resources, in other words, mature and sustained energy statistics. |
This trend needs to be reversed urgently. Policy makers have to be aware of the seriousness of the situation and of the impact on the decision-making process. Data users need to be aware of some of the quality issues when using data. Statisticians need to make every effort to sustain and strengthen the statistics systems and to adapt them to the rapidly changing energy environment. |
So there is a vast programme of actions ahead of us. One of the priorities should be to raise the level of expertise in basic energy statistics so that definitions and methodology can be applied. |
The Manual's objective is not to provide an answer to all the questions linked to energy statistics. Its purpose is to provide the basics to the layman in energy statistics. |
The Manual contains seven chapters: The first one presents the fundamentals of energy statistics, five chapters deal with the five different fuels (electricity and heat; natural gas; oil; solid fuels and manufactured gases; renewables and waste) and the last chapter explains the energy balance. Three technical annexes and a glossary are also included. |
For the five chapters dedicated to the fuels, there are three levels of reading: the first one contains general information on the subject, the second one reviews issues which are specific to the joint IEA/OECD-Eurostat-UNECE questionnaires and the third one focuses on the essential elements of the subject. |
Although there are references to the joint IEA/OECD-Eurostat-UNECE questionnaires in several places, the Manual can be used by statisticians and energy analysts from all countries. |
Most of the text is relevant to general energy statistics concepts, regardless of the format and contents of any particular questionnaire. At the end of the day, electricity is the same all over the world. The same applies to flows such as “power plants” or “transmission losses”, as well as to units such as megawatts and gigawatt hours. |
It is the hope of the International Energy Agency and of Eurostat that the Manual will facilitate the understanding of the fundamentals of energy statistics. We also hope that through this Manual a better understanding of statistics will raise expertise and lead to better energy statistics. |
As a first step, the energy statistician must be able to move comfortably between the units of measurement for fuels and energy and have a working knowledge of the main fuel conversion processes. Equally, the statistician will need to know the conventions and definitions used for the collection and presentation of energy statistics. This knowledge is loosely referred to as the methodology. |
There are a few basic concepts and defined terms which are essential to know since they are widely used in the discussion of fuels and energy. This chapter will introduce these notions as often as possible in a question-and-answer mode. The questions include: What do people mean by “fuels” and by “energy”? What are primary and secondary energy commodities? What is a commodity flow? How are energy data presented? |
An English dictionary defines a fuel as any substance burned as a source of heat or power. The heat is derived from the combustion process in which carbon and hydrogen in the fuel substance combine with oxygen and release heat. The provision of energy as heat or power in either mechanical or electrical form is the major reason for burning fuels. The term energy, when used accurately in energy statistics, refers only to heat and power but it is loosely used by many persons to include the fuels. |
Both electricity and heat may be produced in a primary or secondary form. Primary electricity is discussed later in the chapter on electricity. Primary heat is the capture of heat from natural sources (solar panels, geothermal reservoirs) and represents the arrival of “new” energy into the national supplies of energy commodities. Secondary heat is derived from the use of energy commodities already captured or produced and recorded as part of the national supplies (heat from a combined heat and power plant, for instance). |
Primary energy commodities may also be divided into fuels of fossil origin and renewable energy commodities. Fossil fuels are taken from natural resources which were formed from biomass in the geological past. By extension, the term fossil is also applied to any secondary fuel manufactured from a fossil fuel. Renewable energy commodities, apart from geothermal energy, are drawn directly or indirectly from current or recent flows of the constantly available solar and gravitational energy. For example, the energy value of biomass is derived from the sunlight used by plants during their growth. |
Fuels are measured for trading purposes and to monitor processes which produce or use them. The units of measurement employed at the point of measurement of the fuel flow are those which are the best suited to its physical state (solid, liquid or gas) and require the simplest measuring instruments. These units are termed thenatural units for the fuel (the term physical unit is also used). Typical examples are mass units for solid fuels (kilograms or tonnes) and volume units for liquids and gases (litres or cubic metres). |
Electrical energy is measured in an energy unit , kilowatt-hour (kWh). Quantities of heat in steam flows are calculated from measurements of the pressure and temperature of the steam and may be expressed in calories or joules. Apart from the measurements to derive the heat content of steam, heat flows are rarely measured but inferred from the fuel used to produce them. |
Once it is expressed in its natural unit, a fuel quantity may be converted into another unit. There are several reasons for doing so: comparing fuel quantities, estimating efficiency, etc. The most usual unit is an energy unit because the heat-raising potential of the fuel is often the reason for its purchase or use. Use of energy units also permits the summing of the energy content of different fuels in different physical states. |
The actual methods used to measure calorific value are not important for this Manual but the presence of water in fuel combustion will influence calorific value and this is discussed in the next section. |
Most fuels are mixtures of carbon and hydrogen and these are the main heating agents. There may be other elements which do not contribute, or contribute only slightly, to the calorific value of the fuel. Both the carbon and the hydrogen combine with oxygen during combustion and the reactions provide the heat. When the hydrogen combines with oxygen, it forms water in a gaseous or vapour state at the high temperature of the combustion. |
The derivation of net calorific values for solid fuels is further complicated because they often contain water trapped within the fuel in addition to the water which will be formed from the hydrogen they contain. The reduction in net calorific value as a result of the additional water is uncertain because the dampness of the fuel may vary according to weather and storage conditions. |
In summary, the net calorific value of a fuel is the total heat produced by burning it, minus the heat needed to evaporate the water present in the fuel or produced during its combustion. |
A commodity flow can be recorded at the main points between its arrival and disappearance, and the important criterion for a successful statistical account of the flow is that the commodity must not change its characteristics during its lifetime and that the quantities must be expressed in identical units for each source of supply and type of use. The characteristics which matter are those which affect its energy-producing capacity. |
A similar flow diagram exists for heat and electrical or mechanical power. A discussion of these energy commodities needs to be conducted carefully as they are abstract in nature and their treatment in energy statistics is partly a matter of convention. The conventions affect both the assumed nature of the primary energy and the value given to its production. |
Consider the energy obtained from any device driven mechanically by air or water (wind, hydro, wave, tidal power, etc.). In almost all cases the mechanical force present in the moving parts of the apparatus is used to generate electricity (there are of course a few exceptions such as pumping water from wind mills). |
no other outlet for the mechanical power before it is used for electricity generation the energy form used to represent hydro wind and tidal power is the electricity they generate No attempt is made to adopt the mechanical energy as the primary energy form as it would have no utility in energy statistics The primary electricity produced from these devices is sometimes referred to as non-thermal electricity as no heat is required for its production Energy from photovoltaic PV cells which convert sunlight directly to electricity is considered as primary electricity and included with the sources of non-thermal electricity In any case the efficiency of a PV cell is relatively low |
Primary heat arises from geothermal reservoirs nuclear reactors and solar panels converting incoming solar radiation to heat The form for nuclear energy is not the heating value of the nuclear fuel used as this is difficult to establish unambiguously Instead the heat content of the steam leaving the reactor for the turbine is used as the primary energy form |
Setting a figure for the production of primary electricity and heat is closely related to the definition of these two forms of energy in the different conditions of their exploitation In general the statistical production point is chosen to be a suitable measurement point as far downsteam as possible from the capture of the energy flow before the energy flow is used For example for hydroelectricity this will be the electricity generated at the alternators driven by the water turbines For nuclear reactors it will be the heat content of the steam leaving the reactor there are a few cases where some steam is taken from reactors and used for district heating purposes as well as electricity generation Where this does not occur the steam input to the turbine may be used |
This imputation is done by back-calculating from the gross electricity production, using the thermal efficiency of the plant. An identical approach may be used to estimate the geothermal heat input to turbines when direct measurement of the heat in the geothermal steam flow cannot be made. However, in this case a fixed thermal efficiency is used. |
The trading of fuels between buyers and sellers in different countries raises anumber of issues for reporting statistics of imports and exports. |
Attempts to measure the production of biofuels are complicated by the absence of clearly defined production points. |
Setting the figure for production of fuelwood and a few other biofuels is also complicated because they are only part of a much larger production for non-fuel uses. |
Imports and exports of commodities are the quantities entering and leaving a given country as a result of purchases and sales made by persons living in that country. The import or export is considered to take place when the commodity crosses thenational boundary, whether or not clearance by the customs authority has taken place. |
In order to keep the external trade figures for fuels and energy consistent with major economic indicators, the purchases should be, at least partly, for domestic use. This requires that quantities passing through a country “in transit” should not be included in import or export figures. Equally, the correct identification of trade origins and destinations not only serves to isolate transit trade but provides essential information on the country's dependence on foreign supplies. |
Trade origins and destinations are usually available for the fuels shipped as cargoes (fuels which can be easily stocked) but similar information for network energy commodities is more difficult to obtain. Gas or electricity meters will give accurate figures for physical quantities crossing national borders but no information on origins and final destinations. |
Also, in newer electricity markets, the country of origin may not be available. The territorial scope of the data collection which supports the energy statistics is clearly important for its use and its consistency with other economic statistics. The energy statistician should ensure that this statistical boundary is known and stated in the bulletins or statistical digests. |
The coverage of national consumption data is also influenced by the manner in which the data are collected. Consumption data are generally collected by a mixture of two types of surveys: direct surveys of consumers, or surveys of fuel suppliers in which the supplier classifies deliveries according to the economic activity or the type of customer. |
For example, a Spanish electricity company may sell electricity to a Belgian consumer and arrange for the supply to be made from France. With network energies traded in open markets, clear differences can emerge between the commercial trade flow and the physical flow. |
For national and international statistical purposes, therefore, it is not practicable to insist on a precise identification of origins and destinations for electricity. Instead, reporting should be based on the physical flows and the countries of origin and destination will be neighbouring countries. It follows that, for electricity, transit quantities will be included. |
Over the past two decades the international gas market has developed considerably through the introduction of new pipelines and the use of liquefied natural gas (LNG) transport where pipelines are not practicable. Unlike the production of electricity, the production of natural gas is dependent on the existence of natural reserves and this introduces the issues of gas supply dependence of a country or region on another. |
International marine bunkers Deliveries of oils to ships for consumption during international voyages (bunker oils) represent a special case of flows of oil from the country. The oils are used as fuel by the ship and are not part of the cargo. All ships, irrespective of the country of registration, should be included but the ships must be undertaking international voyages. |
Fundamentals included in the national fuel statistics. Stocks held by other consumers are included only if figures for consumption by the consumers are based on surveys of consumption at consumers' premises. |
Unlike the other “flow” elements of the statistical account (consumption, imports, production, etc.) which relate to the complete reporting period, stocks have values (levels) which may be measured at specific instants of time. The stock levels at the beginning and end of the reporting period are known as the opening stock and closing stock respectively. |
Not all stocks on national territory should be included in national stock levels. The criterion for deciding which stocks may be included is their availability to meet any excess of demand for the fuel over supply or vice versa. |
There is a large variety of types of stocks, especially for petroleum products, and great care should be taken when allocating the quantities to the relevant stock category. The types of stocks for crude oil and petroleum products include, for instance, those held by governments, by major consumers, by stockholding organisations, stocks held on board incoming ocean vessels, stocks held in bonded areas, etc. |
Fuel transformation or fuel conversion changes a primary fuel, by physical and/or chemical means, into a secondary energy commodity which is better suited than the primary to the uses for which the secondary commodity is intended. The various processes of fuel conversion and energy production are described in detail in Annex 1. Examples are the manufacture of coke from coal in coke ovens or the generation of electricity from steam produced by burning fuels. |
Although both examples are considered by energy statisticians as transformation processes, it is important to note that they are fundamentally different. The manufacture of coke is an example of a true conversion process which is essentially a separation process. In this case, most carbon from the coal is left within the coke, and the hydrogen in the coal with some carbon goes into coke-oven gas and some oil products. |
The production of heat in heat plants is also the direct result of combustion and is identical in nature to heat-raising by final consumers. However, the production of heat (steam) for sale is considered a transformation activity because, by including it in the transformation sector, the heat sold will appear within the total heat supply and its consumption by final users recorded. |
the practice were not adopted then heat produced and sold by manufacturing enterprises would not appear in the balance with the consequence that the fuel consumption by enterprises would be overstated and the heat used by final consumers understated. |
final energy consumption covers deliveries of commodities to consumers for activities that are not fuel conversion or transformation activities as defined elsewhere in the balance structure the energy commodities are considered consumed and not transformed into others in short they disappear from the account |
quantities shown are intended to represent the energy needs of the economic activity under which they are classified within the industry sector for example consumption of energy commodities will be for final use without transformation into other commodities |
the statistics contained within this part of the commodity balances are mainly taken from reports of deliveries made by energy industries to enterprises classified by principal economic activity or by direct survey of consumers |
industrial enterprises use energy commodities for heat raising for own use for non energy purposes transport electricity generation and production of heat for sale fuels used for the last three categories are not part of final energy consumption and are usually reported elsewhere in a questionnaire |
quantities recorded as consumption by the chemical industry branch represent use of fuels for heat-raising and for feedstock use although quantities used for the latter are usually also shown elsewhere in the questionnaires. Feedstock use is discussed in the following section on Non-energy uses of fuels. |
similarly, figures for final energy consumption by iron and steel manufacture cover only the combustion requirements for heating coke ovens, blast furnaces and metal finishing. Quantities of coal and coke undergoing transformation are reported within the transformation sector. |
road it is common for all road transport fuels to be shown as supporting the transport activity. some will be used however off-road for digging lifting and agricultural or forestry needs. small but significant quantities will be used for pleasure craft and powered garden equipment. consumption for these diverse uses can be obtained only by survey. none of these off-road quantities should be included as road transport. |
air where separate data are available for deliveries of fuel to aircraft undertaking international flights the figures are shown in international civil aviation see the discussion under International marine bunkers above. in the absence of separate data all deliveries should be attributed to domestic air. |
inland navigation all fuel consumption for transport of goods or persons on inland waterways and for national sea voyages should be included. a national sea voyage is one which starts and ends in the same country without any intermediate foreign port of call. note that an extensive part of the voyage may take place in international waters for example le havre to marseilles. fuel consumed by fishing vessels of all types inland coastal or deep-sea should be included under consumption for agriculture. |
Agriculture Energy use for forestry and fishing, including deep-sea fishing, should be included here. However, fuels delivered for deep-sea fishing are sometimes omitted from this sector and included in international marine bunkers statistics when they should not. A small part of the deliveries of gas/diesel oil for road transport is consumed within this sector as “off-road” use of the fuel. |
Residential Statistics of energy consumption in households are collected in a variety of ways in different countries. Gas and electricity consumption data are usually derived from meter-readings made by the utility companies. Consumption of stockable fuels may be obtained by calculating the difference between all deliveries and those to economically active sectors to which deliveries are recorded. Some countries also conduct surveys of household energy consumption which serve to reveal any bias in delivery-based statistics. |
The petrochemical industry represents, by far, the most important user of fuels for non-energy purposes. It converts fossil fuels (oil, natural gas and coke-oven by-products) and biomass carbon to synthetic organic products. |
To collect reliable statistics is one thing. To disseminate this information in a clear and comprehensive manner is another thing. |
The most commonly used format for the presentation of energy commodity data isthe balance in which both the sources of supply for each commodity and its usesare shown in a single column. |
The balance format is appropriate for energy commodities provided that theyare homogeneous at each point in thebalance. |
Almost all consumption of electricity is for power, heat and electronic use resulting in the disappearance of the electrical energy as heat. |
Other sources of production are rare and the heading is present to cover sources of fuels which are recovered from fuels already produced but not counted or saved. For example, waste coal may be later recovered for use. |
Imports have already been discussed with Exports in the section External trade. It may seem strange to include exports as a source of supply and there are economic models of energy use which treat exports as a part of demand. However, the energy balance seeks to show the supply of fuels used within the country and so exports are subtracted to calculate the total domestic supply. |
Stock change is the difference between opening and closing stock levels. A stock draw is an addition to supply and so will be entered with a positive sign. The converse applies for a stock build. In both cases, stock change = opening – closing stock levels. |
Transfers between commodities are not major flows and arise primarily from the reclassification of commodities. A product may cease to meet its specification and will be reclassified as another commodity of lower quality. The “transfers” row may also be used as a practical device to bring different commodities into another single commodity grouping. For example, in the Eurostat balances, separate balances for hydro and wind electricity show transfers of the production to the electricity balance where the disposal of all electricity is shown. |
The figures reported under Transformation input are the quantities of the fuels used for the manufacture of secondary fuel products and the fuels burned to generate electricity and heat for sale. |
These are further divided into Electricity-only plants, Combined heat and power plants (CHP) and Heat-only plants. These types of plants may be operated by enterprises which are producing the electricity and/or heat for sale as their main business or by enterprises which are not producing the energy as their main business but primarily for their own consumption. |
The two types of plants produce gases which are used on site and may be sold to users off site. A coke of lower quality than that used for blast furnaces is produced in a few countries during the manufacture of town gas in gas works. Coke manufacture also produces light oils and tars. |
Petroleum product manufacture from the refining of crude oils and treatment of semi-finished products is mainly conducted within petroleum refineries. The quantities of oils reported as entering the refineries for the fuel conversion process will provide the materials for the products manufactured (including non-fuel products) and fuel use within the refinery. |
The presentation of the figures in the balance does not distinguish between the various economic sectors within which the use occurs except in a very limited manner. Usually the non-energy use by the petrochemical industry is identified. However in the IEA balances feedstock use in the petrochemical industry is included as a separate line in the final energy consumption. |
At least four transport modes are identified: road, rail, air and national navigation. The IEA, in addition, includes pipeline transport (transport of materials by pipeline); Eurostat treats this consumption as part of the energy sector own use. |
The amounts of fuels included under these headings cover the fuel use for propulsion only. Fuel used by transport enterprises for other purposes must not be included here but under “Commerce and public services” (see “Other sectors” below). |
Usually, the quantities for transport are easily identified because fuels for road engines and aircraft differ from heating fuels, but some confusion is possible where engines use gas/diesel oil and care may be required to separate the vehicle and enterprise use. |
Energy use for pipelines is usually electricity, or where gas is transported, some of the gas is used to drive the compressors. It is important that this gas use be correctly reported and not considered to be part of the distribution losses. |
There are differences between international organisations and countries in their choice of headings under “Other sectors” although all activities are included somewhere. |
The heading “Agriculture” covers agriculture, forestry and fishing. Oil consumption for fishing should include all fishing vessels, including those engaged in deep-sea fishing. It is therefore important to ensure that oils delivered to deep-sea fishing vessels are not included in the quantities reported as “International marine bunkers”. |
National statisticians should pursue large statistical differences in order to establish which data are wrong or incomplete. |
Unfortunately, it will not be always possible to correct the data and, in this case, the statistical difference should not be changed but left to illustrate the size of the problem. |
The fundamental concepts and principles that govern the energy sector's overall performance are presented in this section. |
The transformation of raw materials into various forms of energy is a crucial step in the energy sector's overall performance. |
The final consumption of energy by different sectors, such as industry and households, is an essential part of the energy sector's overall performance. |
electricity is used in almost all kinds of human activity ranging from industrial production household use agriculture commerce for running machines lighting and heating |
the start of industrial use of electricity can be set in the year 1879 when thomas alva edison invented and publicly presented the light bulb since then the use of electricity has been growing and gaining importance in everyday life |
electricity is produced as primary as well as secondary energy primary electricity is obtained from natural sources such as hydro wind solar tide and wave power secondary electricity is produced from the heat of nuclear fission of nuclear fuels from the geothermal heat and solar thermal heat and by burning primary combustible fuels such as coal natural gas oil and renewables and wastes |
after electricity is produced it is distributed to final consumers through national or international transmission and distribution grids |
heat as electricity is an energy carrier primarily used for warming spaces and industrial processes the history of heat is almost as long as the history of humankind and started with the discovery of fire |