The BRUS II Model

General characteristics of BRUS II

The structure of the energy system in BRUS

Costs in BRUS

Main results and applications

Figure 1: The structure of the energy system in BRUS

Figure 2: Options for changing the energy system in BRUS and the related cost structure

The Brundtland scenario model (BRUS) is a long-term simulation model for the energy demand and supply system. The initial version of BRUS was constructed specifically for the development of the Danish Energy plan, Energy 2000. Compared to this the present version (BRUS II) is updated to reflect the Danish Governments new energy plan (Energy21) and significantly extended, especially what concerns the supply part of the model and the treatment of costs. It applies a bottom-up methodology and calculates energy consumption, emissions of CO₂ and related energy systems costs including investments, operation and maintenance costs and fuel costs. The model facilitates long-term analyses and has explicitly incorporated the important long-term factors of the energy system, e.g. the development of energy technologies and conservation.

General characteristics of BRUS II

BRUS is a technical-economic model with an integrated treatment of energy demand and supply which allows for the calculation of demand-driven scenarios for the total Danish energy system. The main purpose of the model is to analyze cost-effective strategies for the reduction of CO₂. Simultaneously, potential minimizations of exhaustible resources are analyzed.

The main features of the model are:

• Long-term simulation model which projects to the year 2030, but only calculates the years 1994, 2005 and 2030. The model operates partly static and partly dynamic.
• The model is total (in contrast to partial or marginal models), making it possible to introduce significant changes e.g. on the demand side, and even though get reliable results for the total energy system.
• It is subdivided into different sectors of energy demand and supply which are integrated to provide useful and comprehensive tool. Thus it is possible in the model to evaluate demand side changes compared to supply side changes what concerns the consequences for energy, environment and costs.
• Macroeconomic driving parameters for energy demand are directly incorporated in the model, e.g. industrial production as activity parameter for energy consumption in industry.
• Energy demand and the development of energy production capacity are driven from the demand side.
• It is possible to choose different conservation options for thermal insulation in buildings, electrical appliances, and industrial processes.
• It is possible to configure the future energy system by choosing from a large number of energy conversion technologies.

Results from the model are given as gross energy consumption split into different fuels, emissions of CO₂ and finally the capacity and economic consequences of the set up of a specific system.

The structure of the energy system in BRUS

The structure of the energy system in the BRUS model is shown in Figure 1. The model consists of submodules starting with society at large, demand modules for domestic purposes, services and industry, supply modules related to the production of district heating, combined heat and power, condensing plants and renewables and a module for the calculation of CO₂ emissions. Finally, modules exist for calculating production capacity (including the development of new capacity) and economic consequences, shown in Figure 2. The modularity gives possibilities for partial recalculations, thus obtaining quick answers to partial questions.

BRUS is developed in close relation to the unique feature of the Danish energy system. The three supply grids for electricity, district heating and natural gas and the very complex way these grids interact. A very large part of district heating is supplied by combined-heat-and-power plants which gives an interdependence with the production of electricity. At the same time most of the natural gas is used for heating domestic buildings, supplying the same heating marked as district heating, introducing constraints on both these supplies. Finally, an increasing part of natural gas is used in electricity production.

The different submodules in BRUS are shown in Figure 1. The basic assumptions are introduced in the society module: Demographic and economic developments at the macro level, split into production at subsector level, development in energy prices etc.

On the basis of these assumptions, the model proceeds to the energy demand side, divided into three modules : Space heating and electrical appliances, industrial energy consumption, and transport.

The first two modules distinguish between dwellings and buildings used for public and private services, while household electrical appliances and appliances used in services are covered in a specific submodule. Space heating is treated according to:

• building stock and development in building area,
• the structural and geographical development in the building stock,
• insulation standards for different building types and years of construction,
• options for individual or collective energy supply, and
• a range of individual heat supply technologies.

The module calculates net heating energy needs and final energy consumption for space heating.

Appliances are treated according to:

• the stock and development in the number of appliances,
• possibilities for improved efficiency.

Figure 1: The structure of the energy system in BRUS

Industrial energy consumption is treated according to:

• splits into main energy-intensive subsectors,
• development of production (related to a macroeconomic development) and production mix,
• conservation possibilities,
• technology and fuel switching, and
• own production of combined heat and power (CHP).

Energy consumption for transport is not treated explicitly in the model. The existing module may be regarded as a dummy. The main reason for this is that transport is the responsibility of the Ministry of Transportation rather than the Ministry of Energy.

The final energy consumption is calculated by adding up the results from the demand modules of the model.

For the supply part of the model, modules exits for the district heating and electricity networks, for production of district heating, CHP and other electricity production, including renewables. These modules incorporate a large number of existing and future technologies characterized by a number of technical data such as overall efficiency, technology-specific emission factors, production relations between heat and power, system-specific data such as utilization time, etc. The model allows a free choice between a large range of technologies from traditional power plants to fuel cells and small-scale biomass CHP plants.

Gross energy consumption is calculated by considering the requirements for energy conversion and this is compared with the available domestic resources. Using emission factors for the fuels the total emissions of CO₂ are calculated.

Finally, for the chosen system configuration the model calculates the total installed capacity needed (split into different types of plants and technologies). Given the decommissioning of old plants, the model calculates an annual development plan for the extension of the electricity and heat system divided into a certain number of default plant types and sizes. This means that the model is totally recursive in its structure. Thus it is possible to make significant changes on the demand side, implying huge changes in final energy consumption, and even though get reliable results for the total energy system without having to adjust the supply part of the model.

An important aspect of the BRUS model is the incorporation of relevant long-term constants. Examples of these long-term constants are the idling use of energy in piped systems and the constant use of energy for domestic hot water, although the general heating demand is reduced significantly. If these constants are not take into account, results might be misleading or even wrong.

Costs in BRUS

The costs in BRUS are related only to the energy system, and in general treated as an ordinary investment analysis, estimating the total annual costs using data for energy prices, investments and operation and maintenance costs.

Figure 2: Options for changing the energy system in BRUS and the related cost structure.

The structure of the costs in BRUS is shown in Figure 2. The energy demand and the energy supply side are treated in different ways:

• For the energy demand system the cost concept is defined as incremental investment costs. As a starting point a baseline is developed for the demand system, and compared to this the additional costs of using different demand options (e.g. retrofitting of buildings, increased insulation, more energy-efficient appliances etc.) are calculated.

• For the energy supply system the model operates in a conventional way with the total investment costs included in the construction of new electricity plants, oil furnaces etc.

Investment costs calculated in this way are leveled according to the lifetime of the technologies. Annual O&M costs are defined as a percentage of investments. Finally, adding fuel costs an estimate is obtained of the annual average cost over the lifetime of the technologies. Adding these levelised costs together gives an estimate of the average system costs. Finally, the costs of CO₂ reductions are obtained by comparison to a reference case.

The average incremental cost for demand options is calculated using the following relation:

I_ic = C*S^x

where I_ic is incremental investment costs

S is the assumed conservation of energy (%)

C is a constant, equal to I_max/S_max (calculated from technology data)

x is a parameter, estimated using technology data

The above-mentioned technology data are provided by working groups set up to carry out the latest energy plan. Incremental investments for demand options are calculated for the years 2005 and 2030, only.

For the supply side total investment costs are calculated according to the time of construction of new plants. Thus for the supply system development, the model operates on a annual basis for the whole period 1994 to 2030, and the investment is undertaken in the actual year, where the capacity development is needed. This makes it possible to generate the total time-dependent investment profile for the investment-intensive part of the system, although comprehensive model calculations are performed for the years 1994, 2005 and 2030, only.

Main results and applications

The main results of the model are summarised below:

• Total gross energy consumption, subdivided into sectors and types of energy

• The energy related emissions of CO₂ (more pollutants will be included in future versions of the model)

• The annual systems costs, including levelised investment costs, operation and maintenance costs and fuel costs. Implementation costs and hidden costs at the consumer level (if any) are not included.

• Total capacity development and the related investment costs on an annual basis.

The model is constructed to facilitate the development of scenarios. Given a baseline, scenarios are developed using a number of choice-parameters which includes:

• choices at the society level, e.g. the macroeconomic growth and the development of energy prices,

• the long-term structure of the energy system, e.g. are the future system based on a continued utilisation of the existing natural gas network or will more decentralised solutions enter,

• choices of options reducing or changing the energy demand, e.g. the degree of realising insulation potentials,

• choice of technology and fuel substitution at the local, decentralised and centralised supply level

Choices of the above-mentioned parameters define a scenario without changing the baseline assumptions in BRUS.

The BRUS model is constructed using commercial spreadsheet software and its details are specific to the Danish energy system. The methodology and general model structure are however applicable to other national or regional energy systems.

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Last updated: 30 September 1996 by Poul Erik Morthorst. E-mail: p.e.morthorst@risoe.dk