Energy system analysis of 100% renewable energy systems—The case of Denmark in years 2030 and 2050

Abstract

This paper presents the methodology and results of the overall energy system analysis of a 100% renewable energy system. The input for the systems is the result of a project of the Danish Association of Engineers, in which 1600 participants during more than 40 seminars discussed and designed a model for the future energy system of Denmark. The energy system analysis methodology includes hour by hour computer simulations leading to the design of flexible energy systems with the ability to balance the electricity supply and demand. The results are detailed system designs and energy balances for two energy target years: year 2050 with 100% renewable energy from biomass and combinations of wind, wave and solar power; and year 2030 with 50% renewable energy, emphasising the first important steps on the way. The conclusion is that a 100% renewable energy supply based on domestic resources is physically possible, and that the first step towards 2030 is feasible to Danish society. However, Denmark will have to consider to which degree the country shall rely mostly on biomass resources, which will involve the reorganisation of the present use of farming areas, or mostly on wind power, which will involve a large share of hydrogen or similar energy carriers leading to certain inefficiencies in the system design.

Introduction

In a recent report from 2007, the United Nations’ International Panel of Climate Change, IPCC, emphasises the many indicators on climate change and recommends that the world society respond to the serious problems. In the US, the European Union and China, policies have been formulated with the objective of decreasing CO₂ emissions. And in many nations around the world, policies to raise the share of renewable energy are being initiated as part of the global response to climate change [1], [2], [3], [4], [5], [6], [7], [8], [9], [10]. In March 2007, the European Union defined a target of 20% renewable energy for year 2020. In Denmark, a target of 30% renewable energy for year 2025 has just been proposed by the Danish Government.

In Denmark, on the one hand, CO₂ emissions per capita have for many years been among the highest in the world on the other, an active energy policy has already led to remarkable results in the decrease of emissions [11]. For a period of 35 years, Denmark has managed to stabilise the primary energy supply, which is the same today as it was before the first oil crises in the early 70s. Furthermore, the share of oil is much smaller today. 20% of the electricity is supplied by wind power and 15% of the primary energy supply is renewable energy including biomass and waste incineration. Moreover, savings and efficiency measures have constituted an important part of the policy, leading to a situation today in which 50% of the electricity is produced by combined heat and power (CHP).

In his opening speech to the Danish Parliament in October 2006, the Prime Minister announced the long-term target of Denmark: 100% independency of fossil fuels and nuclear power. A few months later, the Danish Association of Engineers (IDA) put forward a proposal on how and when to achieve such targets. This proposal was the result of the “Energy Year 2006”, in which 1600 participants during more than 40 seminars discussed and designed a model for the future energy system of Denmark, putting emphasis on energy efficiency, CO₂ reduction, and industrial development. The proposal was presented as the IDA Energy Plan 2030 (see Fig. 1).

The design of 100% renewable energy systems involves at least three major technological changes [12]: energy savings on the demand side [13], [14], efficiency improvements in the energy production [15], [16], and the replacement of fossil fuels by various sources of renewable energy [17], [18]. Consequently, large-scale renewable energy implementation plans must include strategies for integrating renewable sources in coherent energy systems influenced by energy savings and efficiency measures [19], [20], [21], [22], [23], [24], [25], [26].

The design of 100% renewable energy systems has to meet especially two major challenges. One challenge is to integrate a high share of intermittent resources into the energy system, especially the electricity supply [27], [28], [29], [30], [31], [32], [33], [34]. The other is to include the transportation sector in the strategies [35].

This paper presents the methodology and results of the overall energy system analysis of a 100% renewable energy system. The methodology includes hour by hour computer simulations leading to the design of flexible energy systems with the ability to balance the electricity supply and demand and to exchange electricity productions on the international electricity markets.

The results are detailed system designs and energy balances for two energy target years: year 2050 with 100% renewable energy from biomass and combinations of wind, wave and solar power; and year 2030 with 50% renewable energy, emphasising the first important steps on the way. For the first step until 2030, the results include detailed socio-economic feasibility studies, electricity market trade calculations, and sensitivity analyses.

The methodology applied to the design of a future sustainable energy system in Denmark was the combination of a creative phase involving the inputs of a number of experts and a detailed analytical phase involving the technical and economic analyses of the overall system and feed-back on each individual proposal. In a forward and back process, each proposal was formed in such a way that it combined the best of the detailed expert knowledge with the ability of the proposal to fit well into the overall system, both in terms of technical innovation, efficient energy supply, and socio-economic feasibility.

First, the IDA declared 2006 as the “Energy year” in which the organisation aimed at making specific proposals to advocate an active energy policy in Denmark.

Three targets were formulated for the future Danish energy system year 2030:

• To maintain security of energy supply.

• To cut CO₂ emissions by 50% by year 2030 compared to the 1990 level.

• To create employment and to raise export in the energy industry by a factor 4.

The target of maintaining security of supply refers to the fact that Denmark, at present, is a net exporter of energy due to the production of oil and natural gas in the North Sea. However, the reserves are expected to last for only a few more decades. Consequently, Denmark will soon either have to start importing energy or develop domestic renewable energy alternatives.

Based on such targets, the work was divided into seven themes under which the following three types of seminars was held: firstly, a status and knowledge seminar; secondly, a future scenario seminar, and, finally, a roadmap seminar. The process involved around 40 seminars with more than 1600 participants and resulted in a number of suggestions and proposals on how each theme could contribute to the national targets.

The contributions involved a long list of energy demand side management and efficiency measures within households, industry and transportation, together with a wide range of improved energy conversion technologies and renewable energy sources, putting emphasis on energy efficiency, CO₂ reduction, and industrial development. All such proposals were described in relation to a Danish year 2030 “business as usual” reference (see below). Such description involved technical consequences as well as investment and operation and maintenance costs.

In a parallel process, all proposals were analysed technically in an overall energy system analysis using the computer model described below. The energy system analysis was conducted in the following steps:

First, the Danish Energy Authorities’ official “business as usual” scenario for year 2030 was re-calculated by use of the EnergyPLAN model, through which it was possible, on the basis of the same inputs, to come to the same conclusions regarding annual energy balances, fuel consumptions, and CO₂ emissions. Consequently, a common understanding of the reference was established.

Next, each of the proposals for year 2030 (mentioned above) was defined as a change of the reference system and a first rough alternative was calculated including all changes. Such a system leads to a number of imbalances both technically as well as economically, and, consequently, proposals of negative feasibility were reconsidered and suitable investments in flexibility were added to the system.

In the model, the operation of the system is based on a business-economic optimisation of each production unit. Such optimisation includes taxes and involves electricity prices on the international electricity market.

The socio-economic consequences for the Danish society do not include taxes. The consequences are based on the following basic assumptions:

• World market fuel costs equal an oil price of 68 $/barrel (with a sensitivity of 40 and 96 $/barrel).

• Investment and operation costs are based on official Danish technology data, if available, and, if not, on the input from the “Energy Year” experts.

• An interest real rate of 3% is used (with a sensitivity of 6%).

• Environmental costs are not included in the calculation, apart from CO₂ emission trade prices of 20 EUR/ton (with a sensitivity of 40 EUR/ton).

Each individual proposal was analysed technically and a feasibility study was conducted. Since many of the proposals are not independent in nature, such analysis was conducted for each proposal, both in the reference “business as usual” system as well as in the alternative system. One proposal, e.g. the insulation of houses, may be feasible in the reference but not in the alternative system, if solar thermal is applied to the same houses or improved CHP is also part of the overall strategy.

Consequently, several of the contributions and proposals had to be reconsidered and coordinated with other contributions.

The overall energy system analysis and the feasibility studies of the project were carried out by researchers at Aalborg University using the energy system analysis model EnergyPLAN (see Fig. 2). The model has previously been used in a number of energy system analysis activities, including expert committee work for the Danish Authorities [28] and the design of 100% renewable energy systems [12]. However, during the process of analysing the IDA Energy Plan, the model was improved and expanded into the present version 7.0 in order to include all contributions in the analysis. Especially, the analyses of different transportation technologies were improved. Moreover, the modelling of socio-economic feasibility studies including exchange on international electricity markets was expanded.

The energy system analysis of the EnergyPLAN model includes hour by hour simulations of the future Danish energy supply leading to the design of flexible energy systems with the ability to balance the electricity supply and demand and to exchange electricity productions on the international electricity markets. The methodology also includes the design of suitable feasibility studies of national energy systems under conditions of fluctuating world market oil prices, CO₂ quota trade prices, and electricity market prices.

Inputs include energy demands and renewable resources. For relevant demands such as electricity and district heating and relevant sources such as wind power and solar thermal, the inputs are distributed into hour by hour values using actual distribution from historical demands and productions.

More information on the model can be found in [36], [37].

The present version 7.0 of the EnergyPLAN model including input data for the analysis of the IDA Energy Plan and documentation of the model can be downloaded freely from the home page www.EnergyPLAN.eu.

The IDA Energy Plan is compared to both the present situation (of year 2004) and to a “business as usual” reference scenario year 2030, in which the gross energy consumption (primary energy supply) is expected to rise from 850 PJ in 2004 to 970 PJ in 2030.

The IDA Energy Plan is defined as a series of changes to the “business as usual” reference in 2030. The proposal is shown as both an alternative for year 2030 and a 100% renewable alternative for year 2050. The different energy systems include everything, also natural gas consumption on the drilling platforms in the North Sea and jet petrol for international air transportation.

After completing the forward and back process of comparison and discussion between experts and overall systems analysis, the proposals for year 2030 ended up being the following:

• Reduce space heating demand in buildings by 50%.

• Reduce fuel consumption in industry by 40%.

• Reduce electricity demand by 50% in private households and by 30% in industry.

• Supply 15% of individual and district heating demand by solar thermal.

• Increase electricity production from industrial CHP by 20%.

• Reduce fuel consumption in the North Sea by 45% through savings, CHP, and efficiency measures.

• Slow down the increase in transportation demand through tax reforms.

• Replace 20% of the road transportation by ships and trains.

• Replace 20% of fuel for road transportation by biofuels and 20% by electricity.

• Replace natural gas boilers by micro fuel cell CHP, equal to 10% of house heating.

• Replace individual house heating by district heating CHP, equal to 10%.

• Replace future power plants constructed after 2015 by fuel cell CHP plants, equal to 35–40% of the total power plants in 2030.

• Increase the total amount of biomass resources (including waste) from the present 90 to 180 PJ in 2030.

• Increase wind power from the present 3000 to 6000 MW in 2030.

• Introduce 500 MW wave power and 700 MW photovoltaic power.

• Introduce 450 MWe large heat pumps in combination with existing CHP systems and flexible electricity demand in order to integrate wind power and CHP better into the energy system.

It should be emphasised that the proposal of adding heat pumps and flexible demand was an outcome of the overall energy systems analysis process, which also pointed out that the potential of flexible production (low minimum production requirements and ability to change production fast without losing efficiency) from solid oxide fuel cell (SOFC) CHP and power plants should be exploited in the best possible way to overcome balancing problems in electricity and district heating supply.

In order to achieve a 100% renewable energy supply, the following additional initiatives prolonging the 2030 energy system were proposed by the steering committee:

• Reduce the heat demand in buildings and district heating systems by another 20%.

• Reduce the fuel demand in industry by another 20%.

• Reduce the electricity demand by another 10%.

• Stabilise the transportation demand at the 2030 level.

• Expand district heating by 10%.

• Convert micro CHP systems from natural gas to hydrogen.

• Replace oil and natural gas boilers by heat pumps and biomass boilers in individual houses.

• Replace 50% of road goods transportation by train.

• Replace the remaining fuel demand for transportation equally by electricity, biofuels and hydrogen.

• Supply 3 TWh of industrial heat production from heat pumps.

• Replace all CHP and power plants by fuel cell-based or biogas or biomass gasification.

• Supply 40% of the heating demand of individual houses by solar thermal.

• Increase wave power from 500 to 1000 MW.

• Increase PV from 700 to 1500 MW.

• The necessary wind power and/or biomasses resources were calculated as the residual resources and had to be increased as described below.