Energy Analysis

How to Obtain the Energy Services We Desire

Ann Vikkelso, M.Eng., Copenhagen Environment and Energy Office

Consumption of energy is not an objective itself. Huge energy consumption is not necessarily a sign of high material living standard. It is instead the so-called energy services - light, a warm living room, food, etc. - we are satisfied by.

It is important that we discuss our demands and become clear about which energy services we want to fulfil. Then we can evaluate which is the best way to obtain the desired energy services - for example we do not need an electrical hairdryer to get dry hair.

Energy Chains


Figure 4.1 Schematic presentation of the energy chain through society, from primary energy to energy service. From resource to object /1/.

Energy chains can be set up on how to obtain different energy services. Figure 4.1 shows an energy chain for energy services in general. The starting point - primary energy - can be fossil fuels, renewable energy, uranium, etc. This is converted into secondary energy (e.g. wind turbine producing electricity), which is used by the consumer (e.g. in a low energy light bulb), or in industry for producing goods (e.g. a low energy light bulb), which also ends with the consumer.

It is important to evaluate the chain in total, if we want to decrease energy consumption. A good example is fresh air in Danish cowsheds which is traditionally provided by large ventilation systems. It is of course possible to lower the energy consumption by improving the motor and ventilator. But another possibility, at experimental stage, is to replace the ventilator with an automatically controlled damper, thus totally skipping one link the electricity consuming ventilator /1/, figure 4.2.


Figure 4.2 Example of significant reduction of power consumption for cowshed ventilation obtained by evaluating the total energy chain, not only improving the motor and ventilator.

Another example is electrical lighting. In figure 4.3 the last part of the energy chain for light on a desk is shown (it is not taken into consideration how power is produced). Obviously the source of light (incandescent lamp, low energy light bulb, ...) is not the only thing influencing the light efficiency. It is also of great importance what kind of shade is chosen, and if it is kept clean, etc.


Figure 4.3 Energy chain for light on a desk /1/.

Life-cycle Analyses

If we want to compare the environmental impact from different technologies, a life-cycle analysis also called cradle to grave analysis - must be made. It consists of an evaluation of resource consumption and environmental impact caused by production, operation and phasing-out of the technology.

A check list on the content of life-cycle analyses can be set up /2/:

* Construction

Material flows

Energy

Transport

Emissions and environmental impacts

Work environment

* Operation

Energy and resource consumption

Transport

Emissions and environmental impacts

Work environment

Life span

* Phasing-out

Energy and resource consumption

Transport

Reusability

Emissions and environmental impact

Work environment

Low energy refrigerators are a good example of why it is important to consider the above mentioned factors in an analysis. Low energy refrigerators produced in Denmark have a thicker insulation layer than ordinary new refrigerators. The insulation used at the moment contains CFCs, which severely contribute to the green house effect and deplete the ozone layer. Fine enough, that the green house effect decreases due to decreased electricity consumption (simultaneously decreases coal consumption in Denmark), but this is partly counterbalanced by the CFC emission that slowly comes from the insulation. Though it must be mentioned that the total effect is positive, and methods for destruction of the CFC in the insulation material are nearly ready /21. Likewise refrigerators without CFCs are on the way.

General Energy Analyses


Figure 4.4 Total fossil energy consumption related to construction and operation of a wind turbine, a photovoltaic power station, and a coal-fired power plant, per produced kWh electricity during the whole life-cycle /3/.

General energy analyses are limited to factors influencing the energy consumption, but still cover the full life-cycle for a certain technology. In a total energy analysis energy consumptions are compared to achieve a certain out-come (electricity, heat, lighting, etc.). When the energy consumption at the different stages is evaluated, it is important to remember all kinds of energy use; including energy used: for mining of raw materials, by sub-contractors, for running pumps in renewable energy installations, for fuel transport, etc.

In figure 4.4 and 4.5 renewable energy technologies are compared to fossil. It is visible, when comparing fossil (primary) energy consumption for construction and operation, that renewable energy technologies are much less polluting.


Figure 4.5 Total fossil energy consumption related to construction and operation of a solar heating system and an oil furnace, per produced GJ heat during the whole life-cycle /3/.

Energy Pay Back Period

Another method for evaluating renewable energy technologies and conservation technologies is the calculation of the energy pay back period (EPP). EPP is the time it takes, to save the same amount of fossil (primary) energy as the amount of energy (calculated as fossil energy) used for producing the technology.

Most renewable energy and conservation technologies are paid back within a few years, while their life span is generally longer than 20 years. Especially wind turbines are a good energy investment, as the EPP is only 3-4 months for wind turbines placed at medium-good sites in Denmark, figure 4.6.


Figure 4.6 Energy pay back period (EPP) for various technologies. Calculated from information in /2/. Notes: EPP is 0, because more energy is used for producing the replaced incandescent bulbs. 2) Depends on insulation standard and in-glazed area. a) Compared to ordinary standard, according to the Danish building code.

Literature

  1. Energi og ressourcer (Energy and Resources), Niels 1. Meyer and Jorgen S. Norgard. Polyteknisk Forlag, 1989. ISBN 87-502-0675-3.

  2. Renere teknologi pa energiomradet (Cleaner Technology in the Energy Sector), Annette Gydesen et al. Physical Laboratory 3, Technical University of Denmark, 1990.

  3. Vedvarende energi i Danmark (Renewable Energy in Denmark), Niels I Meyer et al., 1990. ISBN 87-418-5891-3.