Load structure

An energy system may serve a load characterised by demands of one or more forms of energy to be delivered at one or several different locations. In other words, loads may range from very specific and spatially confined energy demands (e.g. for performing one specific task such as food refrigeration) over several stages of intermediate size systems (such as individual buildings with requirements of heating, hot water and electricity for appliances, building blocks, industrial facilities, entire cities or agricultural districts) to the total demands of regional areas, nations and further aggregated communities, with a complex combination of energy needs.

Considering the loads on a regional or national level, it is customary to divide the loads into a number of sectors, such as energy demands of industry, agriculture, commerce, service and residential sectors, and transportation. Each sector may require one or more types of energy, e.g. heat, electricity or a "portable source" capable of producing mechanical work (typically a fuel). The distribution of the loads on individual sectors depends on the organisation of the society and on climatic conditions. The latter items influence the need for space heating or cooling, the former includes settlement patterns (which influence the need for transportation), building practices, health care and social service levels, types of industry, etc. A systematic way of treating energy demands is described in the following, with a concrete ex ample of its application, to be used in the example of system simulation following in section 6.3.3.

The development of energy demands is sometimes discussed in terms of marginal changes relative to current patterns. For changes over extended periods of time, this is not likely to capture the important issues. Another approach, called the "bottom-up model" is offered by looking at human needs, desires and goals and building up first the material demands required for satisfying these, then the energy required under certain technology assumptions (Kuemmel et al., 1997, appendix A). This approach is based on the view that certain human needs are basic needs, i.e. non-negotiable, while others are secondary needs that depends on cultural factors and stages of development and knowledge and could turn out differently for different societies, subgroups or individuals within a society. The basic needs include those of adequate food, shelter, security and human relations, and there is a continuous transition to more negotiable needs that incorporate material possessions, art, culture and human interactions and leisure. Energy demand is associated with satisfying several of these needs, with manufacture and construction of the equipment and products entering into the fulfilment of the needs, and with procuring the materials needed along the chain of activities and products.

In normative models such as the scenarios for the future, the natural approach to energy demand is to translate needs and goal satisfaction into energy requirements consistent with environmental sustainability. For market-driven scenarios, basic needs and human goals play an equally important role, but secondary goals are more likely to be influenced by commercial interest rather than by personal motives. It is interesting that the basic needs approach is always taken in discussions of the development of societies with low economic activity, but rarely in discussions of industrialised countries.

The methodology suggested here is to first identify needs and demands, commonly denoted human goals, and then to discuss the energy required to satisfy them in a chain of steps backwards from the goal-satisfying activity or product to any required manufacture, and then further back to materials. This will be done on a per capita basis (involving averaging over differences within a population), but separately for different geographical and social settings, as required for any local, regional or global scenarios.

The primary analysis assumes a 100% goal satisfaction, from which energy demands in societies that have not reached this can later be determined. The underlying assumption is that it is meaningful to specify the energy expenditure at the end-use level without caring about the system responsible for delivering the energy. This is only approximately true. In reality, there may be couplings between the supply system and the final energy use, and the end-use energy demand therefore in some cases becomes dependent on the overall system choice. For example, a society rich in resources may take upon it to produce large quantities of resource-intensive products for export, while a society with less resources may instead focus on knowledge-based production, both doing this in the interest of balancing an economy to provide satisfaction of the goals of their populations, but possibly with quite different implications for energy demand. The end-use energy demands will be distributed on energy qualities, which may be categorised as follows:

1. Cooling and refrigeration 0-50°C below ambient temperature.

2. Space heating and hot water 0-50°C above ambient.

3. Process heat below 100°C

4. Process heat in the range 100-500°C

5. Process heat above 500°C

6. Stationary mechanical energy

7. Electrical energy (no simple substitution possible)

8. Energy for transportation (mobile mechanical energy)

9. Food energy

The goal categories used to describe the basic and derived needs can then be chosen as follows:

A: Biologically acceptable surroundings

B: Food and water

C: Security

D: Health

E: Relations and leisure

F: Activities f1: Agriculture f2: Construction f3: Manufacturing industry f4: Raw materials and energy industry f5: Trade, service and distribution f6: Education f7: Commuting

Here categories A-E refer to direct goal satisfaction, f1-f4 to primary derived requirements for fulfilling the needs, and finally f5-f7 to indirect requirements for carrying out the various manipulations stipulated. Ranges of estimated energy requirements for satisfying needs identified by present societies are summarised in Table 6.1 (Kuemmel et al., 1997), with a more detailed, regional distribution given in Table 6.2 (Serensen and Meibom, 1998). For comparison an analysis of current energy end-uses according to the principles presented above is given in Table 6.3, indicating the present low average efficiencies of the final conversion steps. The assumptions behind the "full goal satisfaction" energy estimates are given in the following.

Table 6.1. Global end-use energy demand based upon bottom-up analysis of needs and goal satisfaction in different parts of the world, using best available currently available technologies (average energy flow in W/cap.) (Kuemmel et al., 1997).

For use in the global scenario for year 2050 described in section 6.4 below, the end-use energy components for each category is estimated on the basis of actual assumed goal fulfilment by year 2050, given in Table 6.4 on a regional basis. This analysis assumes a population development based on the United Nations population studies (UN, 1996), taking the alternative corresponding to high economic growth (in the absence of which population is estimated to grow more). Figures 6.1 and 6.2 show the present and assumed 2050 population density, including the effect of increasing urbanisation, particularly in developing regions, leading to 74% of the world population living in urban conglomerates by year 2050 (UN, 1997).

Biologically acceptable surroundings

Suitable breathing air and shelter against wind and cold temperatures, or hot ones, may require energy services, indirectly to manufacture clothes and structures, and directly to provide active supply or removal of heat. Insulation by clothing makes it possible to stay in cold surroundings with a modest increase in food supply (which serves to heat the layer between the body and the clothing). The main heating and cooling demands occur in extended spaces (buildings and sheltered walkways, etc.) intended for human occu pation without the inconvenience of heavy clothing that would impede e.g manual activities.

Regions:

/ Energy quality:

1. USA, 2. Western Canada Europe, Japan, Australia

3. Eastern 4. Latin 5. China, 6. Average

Europe, Ex- America, India, Africa

Soviet, Mid- SE Asian rest of dle East "tigers" Asia

/ Total

3. Eastern 4. Latin 5. China, 6. Average

Europe, Ex- America, India, Africa

Soviet, Mid- SE Asian rest of dle East "tigers" Asia

/ Total

Space heating*

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Renewable Energy 101

Renewable Energy 101

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.

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