Balancing Europe: Can district heating affect the flexibility potential of Norwegian hydropower resources?

Renewable Energy 141 (2019) 646e656

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Balancing Europe: Can district heating affect the flexibility potential of Norwegian hydropower resources? Kristine Askeland*, Kristina N. Bozhkova, Peter Sorknæs The Technical Faculty of IT and Design, Department of Planning, Aalborg University, Aalborg, Denmark

a r t i c l e i n f o

a b s t r a c t

Article history: Received 3 December 2018 Received in revised form 25 March 2019 Accepted 30 March 2019 Available online 1 April 2019

As Europe moves towards renewable energy, hydropower stands out as a renewable technology that can provide supply side flexibility through dispatchable electricity production. Several studies have investigated the flexibility hydropower can provide with a particular focus on the Nordic hydropower resources. Of all European countries, Norway has the largest hydropower resources and storage capacity. However, Norway also has a highly electrified heating sector, which means high electricity demand during winter when reservoirs are low. This paper uses EnergyPLAN to analyse how a shift from individual electric heating to district heating affects the flexibility the Norwegian energy system can provide to Europe. The analysis develops a 2015 reference scenario and two scenarios that introduce district heating based on biomass and heat pumps, respectively. Results show that district heating can decrease the maximum load on dammed hydropower facilities, thus freeing up capacity for potential export. Furthermore, the dammed hydropower facilities are able to balance the electricity demands in all hours of the year. However, the shift to district heating also increases forced export to drain reservoirs as domestic electricity demand is reduced. Also, the amount of import the system is able to handle is decreased under the modelled conditions. © 2019 Elsevier Ltd. All rights reserved.

Keywords: Hydropower Smart energy systems District heating Green battery Flexibility Norway

1. Introduction In line with the goals set by the EU to reduce GHG emissions [1] and increase renewable energy shares, the European energy system is currently undergoing a massive transition. Traditional fossil fuel based energy production from dispatchable production units is replaced by variable renewable electricity and heat sources, such as solar and wind, with a naturally fluctuating behaviour. The introduction of large shares of variable renewable energy sources (RES) imposes challenges in terms of matching production and demand, because of variability on both ends. Flexibility and supply security in energy systems with a high penetration of variable renewable energy production therefore needs to be ensured through additional measures. In Ref. [2] the European Commission recognises that an integration of variable renewable energy sources requires additional flexibility measures in the energy system, such as fast reacting generation supply, storage and demand response. Flexibility measures in renewable energy systems have been widely

* Corresponding author. E-mail addresses: [email protected] (K. Askeland), [email protected] (K.N. Bozhkova), [email protected] (P. Sorknæs). https://doi.org/10.1016/j.renene.2019.03.137 0960-1481/© 2019 Elsevier Ltd. All rights reserved.

analysed in literature, and a review of different flexibility measures was presented in Ref. [3]. Potential ways of increasing flexibility include: demand side management, cross sector integration, cross border integration, and energy storages [3]. According to the European Commission, strong, reliable interconnections between countries reduces risks of blackouts and eases the integration of variable renewable electricity generation [4]. In 2014, an interconnection target of 10% of installed electricity generation capacity by 2020 was set by the European Council, which the European Commission recommended be extended to a 15% target by 2030 [5]. However, expansion of interconnection capacity as a means of increasing system flexibility is dependent on spatial variations in production and consumption patterns across borders or differences in energy system characteristics and system flexibility. In Ref. [2] energy storage technologies were highlighted by the European Commission as key enablers in the transition towards renewable electricity production in Europe. Electricity storage technologies include pumped hydropower, flywheels, hydrogen, compressed air and battery technologies, with pumped hydropower being by far the largest available existing storage in the system on a worldwide basis [3]. Relating to both the use of interconnections and storage

K. Askeland et al. / Renewable Energy 141 (2019) 646e656

Abbreviations RES CHP PHES CEEP

Renewable energy sources Combined heat and power Pumped hydro electricity storage Critical excess electricity production

technologies to ensure flexibility in a highly renewable European energy system, Norway has, both within scientific literature and the media been referred to as a ‘green battery’ of Europe [6,7]. Norway is the country in Europe with the largest installed hydropower generation capacity and is by far the largest hydroelectric producer in Europe, accounting for 24% of the annual electricity produced by hydropower in Europe [8]. The ‘green battery’ idea is based on the use of the vast Norwegian hydropower resources to provide flexibility to a variable RES dominated European energy system. In most cases the ‘green battery’ idea refers to the use of pumped storage hydro facilities to store electricity when there is excess production from variable RES in the European energy system and provide production when there is a deficit in production from variable RES compared to the demand [7]. However, the existing pump storage capacity in Norway is limited, making up only 4% of the total dammed hydropower production capacity [9]. The pumped hydro storage facilities in Norway are also mainly used for seasonal storage [10], with continuous production, while the ‘green battery’ idea is based on shorter time intervals for storage and production, of a few days to a couple of weeks [11]. Such facilities are not found in the current Norwegian energy system [11]. While the ‘green battery’ idea utilising pumped hydro facilities has been shown to be technically possible [12], it would require a large expansion of the pumped hydro power capacity, which in turn could face economic, political and environmental challenges. The political feasibility and perception of pumped hydropower and the green battery idea has been investigated in scientific literature. In Ref. [7] Gullberg investigated the political feasibility of Norway as a ‘green battery’ for the European energy system. Through interviews with relevant political actors, interest organisations and industry, the paper investigates the political feasibility both related to the expansion of interconnectors and pumped hydro capacity. It is concluded that the actors are positive towards expansions of interconnectors and pumped hydropower capacity, but that existing policies poses a hindrance for the green battery in the short term, due to decisions being made on individual basis only, and not as strategic changes towards a goal of functioning as a green battery. A similar conclusion was reached by Gullberg et al. in Ref. [13] where technical, economic, environmental and political drivers and barriers for a renewable energy cooperation between Germany and Norway were investigated. While German actors see a cooperation as an opportunity to increase stability in the German electricity system when moving towards variable RES production, Norwegian actors have reservations concerning potential increases in electricity price and environmental impacts from expansion of interconnection and pumped hydropower capacity. Even though these papers point towards a lack of political feasibility towards the ‘green battery’ idea in the short term, Gullberg points out that the existing hydropower resources and interconnection capacity can still contribute to balancing power in the European energy system [7]. Connection to large hydropower resources in the Nordic countries was seen by De Decker and Woyte as one of the drivers in their paper investigating the development of offshore electricity grid infrastructure in Northern Europe [14]. Korpås et al. analysed the

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role of Norwegian hydro power resources for balancing wind power in Ref. [15]. This study concluded that generation constraints and interconnection capacity was the limiting factor for using Norwegian hydropower to regulate variable electricity production from wind power. Furthermore, it was concluded that down-regulation balancing is limited by a low demand and high inflow to reservoirs in spring and summer, while high electricity demands and low reservoir levels limit up-regulation in winter. In Ref. [16] Graabak and Korpås identified state-of-the-art concerning the role of Nordic hydropower for balancing variable renewable electricity production, but the focus of the study was on how it was modelled and not analysing the role of hydropower as such. The role of hydropower in relation to expansion of offshore wind in the North and Baltic seas is investigated in Ref. [17], where it is also concluded that the transmission line capacity is the limiting factor. Common for these studies is the sole focus on the electricity sector and interconnection capacity. However, the flexibility Norwegian hydropower is dependent also on the system behind the interconnectors, as was also indicated in the conclusion by Korpås et al. [15]. The Norwegian energy system is not only dominated by a very high penetration of hydropower production, the country also has a highly electrified heating sector [18] based on individual electric heating, accounting for about 63% of the total heating demand [19]. This leads to a high electricity demand in the cold winter months [20]. This can potentially pose a challenge for using the existing Norwegian hydropower resources to provide flexibility to the European energy system both because of a high load on the generation capacity, but also because of the hydropower reservoir contents are at their lowest in the winter months [20]. The use of individual direct electric heating sources provides limited flexibility in terms of moving the load or reducing the electricity demand over time compared with communal district heating systems [21]. District heating can provide a greater flexibility for the remaining energy system than individual heating solutions, as it e.g. enables larger and cheaper thermal energy storage options and enables the use of several types of heat production units [22]. As such, a potential way of increasing the flexibility that the Norwegian energy system can provide to Europe could be through an expansion of district heating, with production units that allow for an increased sector integration, e.g. electric-driven heat pumps and combined heat and power (CHP) units. In the scientific literature, the concept of cross-sector integration has been discussed as a measure to integrate larger shares of variable RES. In Ref. [3] it was concluded that the integration of variable RES production to a large extent could be handled using the existing energy grids, for example through the integration of electricity and heating sectors. An integration of different energy sectors also forms basis for the smart energy systems concept. The concept was first introduced in Ref. [23] where it was concluded that a large-scale introduction of renewable electricity production needs to be coordinated across sectors through an integration of electricity, heat, and transport sectors. This conclusion was followed up in Ref. [24] where it is argued that the concept allows for the utilisation of synergies between the different sectors and thus enables the integration of a larger share of variable RES electricity production, using the electricity, thermal, and gas grids for storage and balancing. Cross-sector technologies such as heat pumps, electric vehicles, and power-to-gas provide the possibility for exploitation of such synergies [24]. The smart energy system concept has been used for energy system analyses both on country level [25] and European level [26]. Different technologies and subsystems have also been investigated. In Ref. [27] Lund et al. investigated and defined 4th generation district heating in relation to the smart energy systems

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concept, concluding that 4th generation district heating plays a role in these systems by integrating low temperature heat sources and reducing heat losses. Thellufsen and Lund investigated the effects and synergies of energy savings in a smart energy system, and found that a combination of heat and electricity savings resulted in synergy effects that increased the benefits of savings [28]. In Ref. [29] Ridjan, Mathiesen, Connolly and Dui
c found the production of synthetic fuels for transport through the implementation of electrolysers help integration of variables RES in line with the smart energy systems concept. The investigation of hydropower in smart energy systems has been mostly focused on PHES (pumped hydro electricity storage). In Ref. [30] Connolly et al. investigated three practical operation strategies, assessing the maximum profit for PHES for these three. In Ref. [31] several electricity storage measures were investigated, and it was concluded that a cross-sector integration using the smart energy systems is a cheaper and more efficient solution than relying on electricity storage solution for integration of variable RES. Thus, an expansion of district heating and sector integration in Norway may contribute to an increase in the flexibility the country can provide to Europe, without expanding the pumped hydropower capacity. The smart energy systems concept has previously been used to analyse the benefits of using bioenergy, solar thermal and wind in the energy system of Inland Norway to increase the renewable energy share and reduce primary energy consumption [32]. In this analysis, a replacement of direct individual electric heating with heat pumps and biofuels in district heating was found to allow for integration of a larger share of wind power. However, the analysis only focuses on inland Norway and did not analyse the effect an expansion of district heating could have on the potential to provide flexibility outside the country’s borders. As such, this paper analyses how a shift from individual electric heating to district heating affects the potential flexibility the Norwegian hydropower resources can provide to the European energy system. The analysis contributes to the ongoing discussion of Norway as a green battery for Europe. The article is structured around the reference scenario and constructed district heating scenarios. First, the methodology is described. Thereafter, a description of the Norwegian energy system forms basis for the construction of the 2015 reference system model, before the district heating scenarios are constructed and described. Results are presented for all scenarios, including the reference scenario, followed by a discussion of assumptions and results before concluding the analysis. 2. Methods In this section, the methods used for assessing the flexibility the Norwegian energy system can provide in a European context are defined. 2.1. Defining flexibility In order to evaluate the flexibility in the Norwegian energy system and thus the flexibility the Norwegian energy system can provide to Europe, parameters indicating flexibility or inflexibility must be defined. Energy system flexibility is in short related to the energy system’s ability to respond to changes in supply and demand, and thus energy system flexibility is needed to match supply and demand at all times [3]. In traditional energy systems this has been ensured on the supply side of the system, offering flexibility through dispatchable production units able to regulate production with shorter or longer time responses [3]. RES do not have the same flexibility in terms of supply side response, because of the variable nature of

their production pattern dependent on weather conditions. Thus, when large shares of RES is introduced, the flexibility of the energy system changes. Curtailment of RES may be necessary, if there is not enough flexibility in the system to integrate the production from RES, which can have negative consequences for the economy of these units. In scientific literature, there are several definitions of flexibility related to the energy system. When defining flexibility, P.D. Lund in Ref. [3] refers to three different analyses with different definitions of flexibility. Blarke [33] investigated the co-existence between distributed cogeneration and wind power, through comparing heat pumps and electric boilers, looking at what he refers to as an “intermittency-friendly” energy system design. Blarke [33] evaluates the “intermittency-friendliness” of the system using a relocation coefficient, previously defined by Blarke and Lund in Ref. [34] which describes the statistical correlation between plant and grid. Thus, Blarke only evaluates flexibility on the supply side’s ability to meet demands. Huber et al. [35] focuses on metrics such as ramping and response time for evaluating flexibility when assessing power system flexibility requirements for different temporal and spatial scales for different shares of RES. P.D. Lund et al. [3] concludes that metrics for defining flexibility may be different, depending on which aspects of the energy system are addressed, and thus, not all flexibility measures can be evaluated based on the same parameters. In this paper, a national energy system analysis, simulating the operation of the Norwegian energy system on an hourly basis, is conducted. Thus, flexibility must refer to the balancing of supply and demands within the hour, as this is the time resolution for which the analysis is conducted. Furthermore, the analysis includes both the heating and the electricity sector, but in terms of evaluating the flexibility Norway can potentially provide to Europe, this refers to the electricity sector. The ‘green battery’ idea is based on using flexible transmission between Norway and Europe to balance a European energy system with high shares of variable RES. First and foremost, the flexibility the Norwegian energy system can provide to Europe is limited by the capacity of the transmission lines. However, if looking beyond the limitation in transmission line capacity, flexible transmission is also dependent on the flexibility within the Norwegian energy system, as the energy system within the country needs to be not only flexible enough to respond to changes in supply and demand within the country, but also in Europe. The Norwegian electricity production is dominated by hydropower, and the supply side flexibility of the Norwegian energy system is therefore largely linked to the flexibility in the dammed and pumped hydropower resources in the country, but also the electricity demands within the country. When assessing the flexibility Norway can provide to Europe, it is relevant to evaluate both the potential of export of electricity to Europe when there is a lack of electricity production from RES to meet demands, and also the potential to import electricity from Europe when there is excess production from RES. Thus, flexibility needs to be evaluated both for what concerns the ability to increase import and export to Europe. For what concerns export, the flexibility is largely related to the supply side of the energy system responding to changes in demand. Dammed hydropower facilities are flexible in their operation, but their flexibility is limited by the turbine capacities, storage sizes, and inflow to the storages. Thus, the flexibility the Norwegian energy system can provide to Europe in terms of export is to a large extent dependent on the generation capacity in the country as well as the reservoir inflow and content. Therefore, it is important to evaluate the flexibility with a sufficiently detailed temporal resolution, as the flexibility will vary from period to period.

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Furthermore, the flexibility in terms of export also depends on the usage of the hydropower sources, which in turn depends on the production and demands of the remaining energy system. To evaluate the flexibility the Norwegian energy system can provide to Europe in terms of export, the following parameters are defined:
Relation between available generation capacity and maximum export demands o The hydropower generation capacity needs to be able to cover both inland demands and maximum potential export throughout the year.
Export and import o A flexible energy system should be able to match supply and demands in all hours, thus export and import of electricity are signs of inflexibility concerning the flexibility of production units within the country, if choosing a simulation strategy seeking to balance supply and demand within the country. The flexibility the Norwegian energy system can provide in a European perspective in terms of import from Europe, is largely dependent on the demand side of the energy system, but also on the supply side of the system. The supply side of the system needs to be flexible enough to respond to increased supply from Europe. The following parameter can be defined to evaluate the flexibility the Norwegian energy system can provide to Europe in terms of import:
Maximum import without critical excess electricity production o Critical excess production occurs when there is excess electricity production that can not be exported or curtailed [36]. In order to evaluate the potential flexibility that the Norwegian energy system can provide to Europe, and how an expansion of

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district heating will affect this, a reference system model for the year of 2015, with slight modifications, is constructed and simulated in an energy system simulation tool. It has been chosen to use EnergyPLAN, which is described in more detail in the following section. Besides the reference scenario two district heating scenarios are constructed, where part of the heating demand is shifted from individual electric heating to district heating. The difference between the two district heating scenarios is how the heat is produced; one scenario replaces direct individual electric heating with biomass based district heating production, and another replaces it with large scale heat pumps for district heating. Analysing the difference between the reference system and each of the two district heating scenarios shows the potential of district heating for making Norway able to provide increased energy system flexibility to the rest of Europe.

2.2. Simulation tool The energy system simulation tool EnergyPLAN v13.2 is chosen for this study because of its ability to simulate all sectors of the energy system (electricity, heating and transport) on national level on an hourly basis [37], including hydro power, individual heating, and district heating. Furthermore, the tool should be able to integrate a 100% renewable energy system [37] and has been used for analyses of national energy systems [25]. Also, the tool has also previously been used to simulate parts of the Norwegian energy system in Ref. [32]. EnergyPLAN is a deterministic input/output model seeking to optimise the operation of the system on an hourly basis, according to predefined simulation strategies [36]. The model requires inputs of demands, production capacities and distributions. All inputs can be seen in Fig. 1. There are two main simulation options: a technical and a market economic simulation. The technical simulation seeks to minimise fuel consumption while fulfilling the demands within the systems.

Fig. 1. Overview of inputs and connections in EnergyPLAN [36].

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The market economic simulation minimises the operation costs of the system by minimising the short term marginal costs in each hour through identifying the least cost combination of units [37]. In this study, the technical simulation option is used, as the purpose is to assess the technically possible flexibility within the country and thus the flexibility the Norwegian energy system can provide to Europe. Within the technical simulation option, there are four different strategies that can be chosen: 1) Balancing heat demands, 2) Balancing both heat and electricity demands, 3) Balancing both heat and electricity demands (Reducing CHP also when partly needed for grid stabilisation), 4) Balancing heat demands using triple tariff. The second strategy, balancing both heat and electricity demands, is chosen as the analysis focuses on the balance of both the electricity and the heating sector. Strategy 3 and 4 are not deemed relevant for this analysis, as the amount of CHP capacity is very limited and there is no triple tariff for CHP plants. Dammed hydropower is in the EnergyPLAN model defined by the user defining: dammed hydropower capacity [MW-e], dammed hydropower efficiency [%], dammed hydro water supply [TWh/year], dammed hydro storage capacity [GWh], and a distribution for the dammed hydro water supply. In EnergyPLAN, dammed hydropower plays a role in maintaining grid stability. The yearly production from dammed hydropower facilities is calculated based on the water supply to the hydropower storages. The hydropower storage is subject to the condition that the initial content is the same as the end content [36]. Thus, the annual hydropower production is defined by the annual inflow to the hydropower storage, and storages will be drained or filled at the end of the year to match the initial content of the storage. Within the hour, EnergyPLAN will try to balance supply and demand, also from hydropower, however, if the annual hydropower production exceeds the annual demand within the country, excess production needs to be exported.

3. The Norwegian energy system The Norwegian energy system comprises of several sectors. The focus in this paper is on the electricity and heating sector, and thus these will be the ones described in the following. The EnergyPLAN model also includes transport and industrial fuel demands, but these are not evaluated to detail in this paper and therefore not included in the description of the Norwegian energy sector. The total energy consumption in Norway in 2015 was 213,056 GWh [18]. Of this, 61% of the consumed energy was electricity [18].

3.2. Heating sector The Norwegian heating sector is highly electrified and there is widespread use of individual electric heating units. When dealing with a large share of individual electric heating, it is difficult to know the exact heat demand as this is not measured, it will simply be a part of the total electricity demand of the different electricity consumers. For the work presented in this paper it is important to separate the electricity used for heat from the remaining electricity demand. However, only estimations are available for determination of the total heat demand in the country. According to Refs. [40,41] the total heat market in Norway is 50 TWh/year. In a report by Ref. [19] the heat market in 2013 had a fuel distribution as shown in Fig. 2. If assuming that the heat market in Norway is 50 TWh/year and the district heat delivered to consumers in 2015 was 4831 GWh, district heating had a market share of almost 10% in 2015, compared to 7% in 2013. According to statistics, the main heating source in households in 2012 was direct electric heating, having a market share of 53%. Heat pumps had a market share of 21% while district heating had a market share of only 3% [18]. Thus, electricity is the main fuel used for heating in the household sector. It has not been possible to identify statistics for heating sources in industry and service sector, so it is unknown what the main heating sources are for these sectors. In 2015, the total gross production of district heating in 2015 was 5444 GWh. The mix of district heating production in 2015 is seen in Fig. 3. Of the total gross production of district heating, 11% was lost in the network, 55% was delivered to the service sector, 18% to households, and 16% to industry [18]. Under the assumption that the total yearly heat market amounts to 50 TWh, with electric heating amounting to 31.5 TWh, and the share of total electricity demand used for heating amounting to 24.4%, an hourly distribution profile for heat demand is constructed based on the electricity demand profile. Assuming 76.6% of the heat demand is temperature dependent [42], this share is weighted according to the monthly average temperature in the country, while hot water demand is assumed constant throughout the year. This constructed heat demand profile is an estimation at best, and peaks in heat demand may be over- or under estimated. However, due to the lack of alternative distributions and the high share of electricity used in the heating sector, this estimation is deemed

3.1. Electricity sector Because of the large hydropower resources in the country, the Norwegian electricity sector is highly renewable, with 96% of the electricity generation in 2015 generated from hydropower. Wind power accounted for 2% of the electricity production, natural gas for 2% and biofuels and waste for 0.3% [9]. In 2015, the transmission capacity from Norway to Europe was 6095 MW [38]. An expansion of the transmission capacity to the UK and Germany is planned and to be put in operation by 2021, increasing the total transmission capacity to 8895 MW [38]. Norway is part of the Nordic electricity market Elspot. The country is divided into five bidding areas, areas that are related to constraints in the electricity transmission system. Bottlenecks between bidding areas will result in different prices in the different bidding areas [39]. In this paper, potential bottlenecks within the country are not taken into account, and thus inland constraints will not be reflected in the simulation results.

Fig. 2. Heat market fuels in 2013 [19].

K. Askeland et al. / Renewable Energy 141 (2019) 646e656

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Table 1 Electricity demands, installed generation capacities and transmission line capacity. Variable

Value

Reference

Electricity demand [TWh/year] Windpower Generation capacity [MW] Annual generation [TWh/year] Photo voltaic Generation capacity [MW] Annual generation [TWh/year] River hydro Generation capacity [MW] Annual generation [TWh/year] Pumped hydropower Pump back capacity [MW] Reservoir hydropower Generation capacity [MW]

129.012

[20]

865 2.63

[18] [18]

13.6 0.01

[46] [46]

1,352 4.88

[47] [47]

1,350 30,020

[18]

82,224 148.41

[48] [18]

0.35

[49]

7.30

[18,50]

100 24

[51] [50]

8,895

[38]

Fig. 3. Mix of district heating production in 2015 based on data from SSB [18].

adequate for the purpose. The temporal resolution of temperature data could have been finer, but a monthly resolution was chosen as this was the data available for constructing the time series. However, a finer resolution would also have been subject to potentially large uncertainties due to large geographical variations on a daily basis. The constructed profile is used for both the individual heat demand and the district heating demand.

4. Reference system model The reference model is based on data collected for the year, also described in the section above, of 2015 as this was the most recent data available at the time of model construction, with the following modifications:
Interconnection capacity is set to 8895 MW which refers to a situation in 2021 where new transmission capacity of 1400 MW to United Kingdom and 1400 MW to Germany is expected to be in operation [38].
A natural gas power plant at Mongstad is excluded as it is expected to be decommissioned in early 2019 [43]. With the above modifications, the reference model is no longer representative for the year of 2015, and operational patterns for the year of 2015 can not necessarily be replicated, as different production capacities and transmission line capacity can affect the operation of the system. However, the purpose of the reference model is not to replicate the production from a single year, but to construct a starting point for the analysis. The flexibility that can be provided from Norwegian hydropower resources is highly dependent on the transmission line capacity, which is also the conclusion in Refs. [15,44]. However, the technical simulation strategy used in this analysis optimises production according to covering demands and minimising import/export, thus, an increase in interconnection capacity will only lead to a reduction in critical import or export due to potential technical restrictions in the system, such as insufficient generation capacity or excess electricity production. Thus, an increase in interconnection capacity should not affect the operation of the energy system within the country as such. The reference model is available for download at the EnergyPLAN webpage including a detailed description of all model inputs at [45]. The most relevant inputs for the electricity and heating sectors are summarised in Table 1 and Table 2.

Storage capacity [GWh] Annual generation [TWh/year] Waste incineration Annual generation [TWh/year] Electric efficiency [%]

Biomass CHP Generation capacity [MW] Electric efficiency [%] Transmission line capacity Transmission line capacity [MW]

Note

Run-of-river hydro subtracted from statistics.

Estimation based on statistics for waste input and DH production.

Including new transmission line capacity to UK and Germany

The total heat demand given in the table above exceeds the estimated heat demand of 50 TWh by the Norwegian district heating association in Ref. [40]. This is due to the demand found in the individual sector for coal-, oil-, natural gas- and biomass boilers. In the reference scenario, data for these demands are from Ref. [18] and not based on the distribution of the total heat demand in Fig. 2. Furthermore, the efficiencies are general efficiencies, and may be lower in reality. It is also not certain that all fuels are used for heating purposes, but this is what is assumed in the model. However, the difference between the data used for these technologies in the model and the estimations upon which electric heating demand is based, does not affect the results, as the heat demands for these individual technologies are simply represented as a fuel demand. The purpose of constructing a reference model is to have a reference situation to compare scenario results with, in order to evaluate the changes in flexibility from different measures implemented. A technical simulation strategy balancing both heat and electricity demands was used to simulate the operation of the Norwegian energy system on an hourly basis, as described under the methods section. The purpose of the reference model is not to replicate the operation of the Norwegian energy system in 2015, but to have a basis for comparison for different measures analysed in terms of increasing flexibility. For this purpose, it was under the definition of flexibility assessed that the flexibility the Norwegian energy system potentially can provide to Europe, depends on the flexibility within the system itself. Thus, a technical simulation strategy balancing

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Table 2 Heat demands, installed heat generation capacities and annual production. Variable

Value

Heat demand Total heat demand [TWh/year] Individual heating Direct electric heating demand [TWh/year] Electric heat pumps demand [TWh/year] Electric heat pumps COP [] Coal boiler fuel demand [TWh/year] Coal boiler efficiency [%] Oil boiler fuel demand [TWh/year] Oil boiler efficiency [%] Natural gas boiler fuel demand [TWh/year] Natural gas boiler efficiency [%] Biomass boiler fuel demand [TWh/year] Biomass boiler efficiency [%] District heating District heating demand [TWh/year] District heating production [TWh/year] Electric boiler production [TWh/year] Heat pump production [TWh/year] Electric heating capacity [MW-e] Average COP [TWh/year] Waste incineration heat production [TWh/year] Waste incineration thermal efficiency [%] Oil boiler capacity [MW] Oil boiler efficiency [%] Natural gas boiler capacity [MW] Natural gas boiler efficiency [%] Biomass boiler capacity [MW] Biomass boiler efficiency Biomass CHP thermal capacity [MJ/s] Biomass CHP thermal efficiency [%]

Reference

59.38

Note Sum of all heat demands.

24.6 15 2.3 1.81 80 4.89 92 3 100 7.23

[52] [52] [18] [50] [18] [50] [18] [50] [18]

Estimation based on distribution of heat market fuels in Fig. 2.

83

[50]

4.83 5.44 0.67 0.54 325.78 1.34 3.07 63 32.05 92 75.70 92 516.60 87 275 66

[18] [18] [18] [18] [50] [50] [49] [18] [18,50] [50] [18,50] [50] [18,50] [50] [50,51] [50]

Assuming all use of fuel in household is for heating purposes. Assuming all use of fuel in household is for heating purposes. Assuming all use of fuel in household is for heating purposes. Assuming all use of fuel in household is for heating purposes. Most of the demand is for wood furnaces. Based on biomass boilers, not wood furnaces. Not including network losses. Including network losses.

Estimation based on full load hours and efficiencies for electric boilers and heat pumps. Estimation based on average between installed electric boiler and heat pump capacity Estimation based on statistics for waste input and DH production. Estimation based on full load hours and fuel input Estimation based on full load hours and fuel input Estimation based on full load hours and fuel input Efficiency for wood chip boilers. Estimation based on installed electric capacity.

heat and electricity demands while minimising CO2 emissions was chosen, as this shows the technical potential only taking into account import and export when necessary to balance out the energy system within the country. Thus, the results show technically possible solutions. The technical simulation strategy will, however, not necessarily replicate the operation of the Norwegian energy system. This is both due to the technical simulation strategy not operating according to market prices, as is done in reality, but also due to an aggregation of the energy system when analysing on a national scale. Furthermore, predefined priorities and restrictions in EnergyPLAN, for example on the hydropower storage, may contribute to simulation results differing from reality, but it is not known how this potentially differs and if it is the same from year to year. However, as the purpose of this study is not to replicate the operation of the Norwegian energy system for a single year, but to assess technical potentials for providing flexibility to Europe, EnergyPLAN is deemed adequate.

5. District heating scenarios: shifting from individual electric heating to district heating In order to evaluate the change in the potential flexibility that

the Norwegian energy system can provide to Europe, two scenarios that represent a shift from individual electric heating to district heating are constructed. The scenarios both look into a 25% shift away from individual direct electric heating. A 25% shift is based on the scenarios aiming to be representative of a situation where district heating is mostly expanded in densely populated areas such as cities and urban areas. In 2015, 80% of the Norwegian population lived in areas that were classified as urban areas and 29% lived in the four largest cities in the country [53]. Thus 25% is not an unreasonably high level. The effect of the shift is presented in Table 3. The necessary increase in district heating production capacity for the shift from individual direct electric heating to district heating is designed according to the principles for district heating sources as described in Ref. [54] utilising mainly secondary resources for base load, see Table 4. Furthermore, the increase in DH production is kept within the limits of what are given as realistic potentials literature, replicated in Table 4, if these have been identified. For baseload, secondary resources should be utilised. It is chosen not to use biomass CHP’s for baseload, as the heat from such facilities can only be considered a secondary source when the CHP

Table 3 Overview over electricity consumption. Total electricity Total individual electric heating consumption a[TWh/year] demand [TWh/year] Reference 129.012 scenario 25% shift 121.24 a

Electricity demand of individual electric heaters [TWh/year]

Electricity demand of individual heat pumps [TWh/year]

District heating demand [TWh/year]

31.1

24.6

6.52

5.44

23.32

16.82

6.52

14.20

The total estimated electricity consumption, not taking into account increased consumption from district heating production units.

K. Askeland et al. / Renewable Energy 141 (2019) 646e656 Table 4 Fuel potentials and classification of district heating sources. Technology

Potential thermal input [TWh/year]

Classification of district heating source [54]

Biomass CHP Waste incineration Excess heat Geothermal Biomass boiler Solar heating Electric boiler Heat pump

20-22 [55] 4.86 [55] 10 [56] N/A 20/22 [55] N/A N/A N/A

Secondary Secondary Secondary Primary Primary Primary Primary Primary

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As the biomass CHP option is disregarded, the remainder of the increased district heating demand is in the biomass scenario covered by biomass boilers. In the heat pump scenario, heat pumps with a COP of 3 are added to cover the remainder of the demand. In both scenarios, an additional biomass boiler capacity corresponding to 20% of the peak demand is included to ensure security of supply. Thermal storage capacities are increased in both scenarios. The storage is dimensioned to minimise boiler production in the district heating system. The production capacities and storages of the two scenarios are given in Table 5. 6. Results

Table 5 Production and storage capacities for district heating scenarios. District heating unit

DH biomass scenario

DH heat pump scenario

Waste incineration (from reference) [MWth] Excess heat (from reference) [MWth] Heat pump (from reference [MWth] Boilers (from reference) [MWth] Biomass CHP (from reference) [MWth] Excess heat (increase from reference) [MWth] Biomass boiler (increase from reference) [MWth] Heat pump (increase from reference) [MWth] Thermal storage [GWh] Buffer biomass boiler [MWth]

350 21 437 518 275 191 1,484

350 21 437 518 275 191 e

e

1,484

4.3 655

9.3 655

originally is constructed for electricity production purposes. Furthermore, the waste incineration potential is already utilised [55]. Thus, excess heat is the only remaining secondary source to cover baseload demand in the scenarios. Excess heat is therefore used to cover the baseload, which is defined as the minimum load throughout the year. It is chosen to construct two scenarios for covering the remainder of the increased district heating demand: one that replaces direct individual electric heating with biomass based district heating production, and one that replaces it with large scale heat pumps for district heating. The reason for constructing these two scenarios is that they can provide information both on shifting from electricity to other fuel types but also on the effects of shifting from individual to collective heating systems.

The results of the simulation of the scenarios are shown in Fig. 4. There is no CEEP in any of the scenarios, which indicates that it is technically possible to balance the electricity demands in the country with the interconnection capacity included in the model. However, there is a difference in export in the difference scenarios. This is related to the aforementioned restrictions on the hydropower storage, requiring the storage to be at equal capacity at the beginning and end of the year, therefore predefining the annual hydropower production. Therefore, there is an increase in annual export in the DH scenarios, as the inland electricity demand is reduced, and therefore a larger share of the annual electricity produced from hydropower has to be exported to balance the supply and demand within the country. The hourly simulation results for electric load for the different scenarios are plotted in Fig. 5 along with a shaded area representing potential exported electricity for providing flexibility to the European energy system. From Fig. 5 it is seen that in all hours of the year there is free flexible hydropower production capacity in the district heating scenarios, thus making the interconnection capacity the limiting factor for providing flexibility to Europe. In the district heating biomass scenario this is due to shifting away from electricity for heating to biomass, thus reducing peak electricity demands in winter months. Peak electricity demand in winter months are also reduced in the district heating heat pump scenario, both through the utilisation of excess heat but also due to heat pumps having a higher efficiency than individual electric heating. In the reference scenario there are 149 h of the year in which the hydropower generation capacity is the limiting factor for providing electricity for balance in Europe. The results also show that there is no import of electricity,

Fig. 4. Results from simulation of reference scenario and district heating scenarios.

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K. Askeland et al. / Renewable Energy 141 (2019) 646e656

Fig. 5. Electric load and potential export capacity in reference scenario and district heating scenarios.

indicating there is enough inflow of water to the hydropower storages to cover the demand in all hours of the year, which is also expected as there is no increase of electricity demand in any of the DH scenarios. There is an increase in export of electricity in the district heating scenarios, the largest export occurring in the district heating biomass scenario. This is linked to the reduced electricity demand in the country while still having a need to balance the hydropower storage in EnergyPLAN. Thus, a decrease in electricity demand will always lead to either a decrease in import or an increase in export. While the limitations in EnergyPLAN do not reflect how the situation is for hydropower reservoir content in Norway, it is clear that there must be a certain draining of the storage in order to avoid overflow. What concerns import of electricity from Europe, an analysis is made using the hourly import distribution from Nord Pool [20] for 2015 as a fixed import. A second simulation is made for all scenarios, increasing the import in all hours with a factor of 1.84 so the maximum import load in one hour is 8895 MW, matching the interconnection capacity. The results from the analysis are seen in Table 6. The results show, that the increase in import throughout the year, will simply lead to an increase in export throughout the year. The district heating scenarios have a lower electricity demand than the reference scenario, and thus the export is higher in these scenarios. None of the scenarios experience problems with CEEP in the simulations, indicating that within the hour, the energy system has enough flexibility to balance out the supply and demands.

As the flexibility the Norwegian energy system can provide for Europe is not only related to the possibility to use Norwegian hydropower for production when there is a lack of electricity production to meet demands in Europe. The flexibility the Norwegian energy system can provide in a European perspective is also related to the possibility to export from Europe to Norway when there is excess production of electricity from RES in Europe, thus avoiding curtailment of RES. An analysis increasing the fixed import incrementally until CEEP is reached is therefore conducted, to evaluate the maximum import the Norwegian energy system can handle, given a predefined import distribution. The maximum yearly import at which CEEP does not occur for the different scenarios is given in Table 7. The results show that a shift from individual electric heating to district heating will decrease the potential to import electricity from Europe. This is due to the lower electricity demand in the country in the district heating scenarios and the need to export the imported electricity back out in order to avoid overflow. For these results, it is also important to note that the export back to Europe does not take into account whether or not there is a need for electricity in the European energy system. Furthermore, the flexibility in the district heating systems is affected by the storage capability of the systems. For this analysis, thermal storage capacity was implemented based on reducing the use of boilers in the respective scenarios without forced import. When evaluating the amount of electricity import the energy system is able to handle, the storage capacity in the DH system will have an effect, and if storages were sized to maximise import, this could affect the

Table 6 Results of simulation for reference scenario and district heating scenarios with 2015 import and increased import. Scenario 2015 import Reference DH biomass DH heat pump Increased import Reference DH biomass DH heat pump

Electricity demand [TWh/year]

Dammed hydropower production [TWh/year]

Import [TWh/year]

Export [TWh/year]

130.48 123.9 125.29

133.57 133.57 133.57

2.53 2.53 2.53

13.22 19.66 18.34

130.48 123.9 125.29

133.57 133.57 133.57

4.65 4.65 4.65

15.32 21.78 20.46

K. Askeland et al. / Renewable Energy 141 (2019) 646e656 Table 7 Maximum yearly import without CEEP. Scenario

Maximum import without CEEP [TWh/year]

Reference

DH biomass

DH heat pump

13.3

8.2

9.4

results of the import analysis. 7. Discussion The flexibility is analysed separately for what concerns import and export, and results in separate conclusions for what concerns the flexibility when analysing these two parameters. The export in this analysis is dependent on the hydropower reservoir content and limitations for the content set in the simulation tool, EnergyPLAN, while the import is a fixed distribution defined by the user. In reality, the flexibility can not necessarily be evaluated by looking at these parameters separately, both because of Norway’s participation in a Nordic electricity market but also because of limitations in the simulation tool and model, that might not exist in reality. The green battery concept is also more related to the balancing of electricity demands in Europe, by using the Norwegian energy system as a form of electricity storage. Thus, the green battery concept entails that the amount of electricity imported should be exported at other times. Thus, what has in this paper been considered as a sign of inflexibility for export and import separately, might not be considered inflexibility in reality. However, the results from the analyses still offers an insight into what effects a shift from individual electric heating to district heating has on the technical flexibility in the Norwegian energy system. One could argue that, if there are no technical benefits of a shift from individual electric heating to district heating in terms of increasing flexibility, this would also be seen in an analysis taking into account the electricity market conditions and the alternating reality of import and export. This paper analyses the technical possibilities of using the Norwegian energy system to provide flexibility to Europe. This analysis has, however, not taken investment costs and the electricity market into consideration, as this was outside the scope of the study. When analysing whether or not a shift from electric heating to district heating should be made, investment and operational costs need to be taken into account, especially if evaluating whether an expansion of district heating can replace the need for increased hydropower capacity. Furthermore, as Norway is part of the Nord Pool Spot electricity market, the electricity prices are important to consider when evaluating when to import and export electricity to Europe. 8. Conclusion In this paper a reference model for the Norwegian energy system was modelled in the tool EnergyPLAN to provide basis for an analysis of how a shift from individual electric heating to district heating would affect the potential flexibility the Norwegian hydropower resources can provide to the European energy system. To analyse this, two district heating scenarios were constructed and simulated. One scenario based on excess heat from industrial processes and biomass boilers, and one scenario based on excess heat from industrial processes and heat pumps. The results show that the district heating scenarios were able to free up generation capacity so that there in all hours of the year is available hydropower capacity to produce and export electricity to Europe at a level

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corresponding to a maximum interconnection capacity of 8895 MW. However, the analysis also shows that the decrease in electricity demand when shifting to district heating increases export, due to the need for draining hydropower reservoirs to avoid overflow. Export is increased from 13.22 TWh/year in the reference scenario to 19.66 and 18.34 TWh/year in the DH biomass and DH heat pump scenarios. This could be interpreted as a sign of inflexibility that reduces the flexibility service the Norwegian hydropower resources can provide to Europe. However, this conclusion is based on a simulation where bypass is avoided. In reality, bypassing could be an available option as an alternative to export. An analysis using fixed import showed that a shift from individual electric heating to district heating decreased the amount of import the Norwegian energy system can handle, from 13.3 TWh/year to 8.2 and 9.4 TWh/year in the DH bio and DH heat pump scenarios. This happens as both peak and yearly electricity demands in the country are reduced, and there is not enough flexibility in the district heating storages to increase the potential import. Thus, the conclusion of this analysis is that a shift from individual electric heating to district heating does affect the flexibility the Norwegian energy system can provide to Europe, potentially freeing up production capacity. However, the district heating system needs to be designed with flexibility as an aim, as the hydropower dominated system shows signs of inflexibility in terms of regulating production to accommodate both a decrease in electricity demand but also an increase in electricity demand. Acknowledgements The work presented in this paper is a result of the research activities of the project “Renewable Energy Investment Strategies e A two-dimensional interconnectivity approach (RE-Invest)”. The work has received funding from Innovation Fund Denmark under Grant No. 6154-00022B. The reference model, scenarios and parts of the analysis in this paper were initially developed by authors Kristine Askeland and Kristina N. Bozhkova for their master thesis in Ref. [57] under supervision by Peter Sorknæs. References [1] European Commission, Communication from the Commission to the European Parliament, the Council, the European Economic and Social Committee and the Committee of the Regions: Energy Roadmap 2050, 2011 [Online]. Available: https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri¼CELEX: 52011DC0885&from¼EN. [2] EC, In-Depth Analysis in Support of the Commission Communication COM(2018) 773, A Clean Planet for All, A European Long-Term Strategic Vision for a Prosperous, Modern, Competitive and Climate Neutral Economy, November, 2018. [3] P.D. Lund, J. Lindgren, J. Mikkola, J. Salpakari, Review of energy system flexibility measures to enable high levels of variable renewable electricity, Renew. Sustain. Energy Rev. 45 (2015) 785e807. [4] European Commission, “Electricity Interconnection Targets.” [Online]. Available: https://ec.europa.eu/energy/en/topics/infrastructure/projects-commoninterest/electricity-interconnection-targets. [5] European Commission, Communication from the Commission to the European parliament and the council European Energy Security Strategy, 2014. [6] I. Haugan, Norge Kan Bli Europas Grønne Batteri, Gemini, 2015 [Online]. Available: https://gemini.no/2015/05/norge-kan-bli-europas-gronne-batteri/. [7] A.T. Gullberg, The political feasibility of Norway as the ‘ green battery ’ of Europe, Energy Policy 57 (2013) 615e623. [8] International Hydropower Association, Hydropower Status Report, Iha, 2017, pp. 1e83. [9] IEA, Norway - Energy System Overview, 2015 [Online]. Available: https:// www.iea.org/media/countries/Norway.pdf. [10] K.A. Rosvold, Pumpekraftverk, Store Norske Leksikon, 2013 [Online]. Available: https://snl.no/pumpekraftverk. [11] E. Grøv, A. Bruland, B. Nilsen, K. Panthi, M. Lu, Developing Future 20 000 MW Hydro Electric Power in Norway e Possible Concepts and Need of Resources, 2011, p. 36. [12] E. Solvang, A. Harby, Å. Killingtveit, Økt Balansekraftkapasitet I Norske Vannkraftverk, 2011.

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K. Askeland et al. / Renewable Energy 141 (2019) 646e656

[13] A.T. Gullberg, D. Ohlhorst, M. Schreurs, Towards a low carbon energy future renewable energy cooperation between Germany and Norway, Renew. Energy 68 (2014) 216e222. [14] J. De Decker, A. Woyte, Review of the various proposals for the European offshore grid, Renew. Energy 49 (2013) 58e62. € tscher, S. Vo €ller, J. Tande, Balancing of wind power variations [15] M. Korpås, T. Tro using Norwegian hydro power, Wind Eng. 37 (1) (2013) 79e96. [16] I. Graabak, M. Korpås, Balancing of variable wind and solar production in continental Europe with nordic hydropower - a review of simulation studies, Energy Proc. 87 (1876) (2016) 91e99. [17] H. Farahmand, S. Jaehnert, T. Aigner, D. Huertas-Hernando, Nordic hydropower flexibility and transmission expansion to support integration of North European wind power, Wind Energy 18 (6) (2015) 1075e1103. [18] SSB, “Statistics Norway - Energy and Manufacturing.” [Online]. Available: https://www.ssb.no/energi-og-industri. [19] Enova, Markedsutviklingen 2015 - Hovedtrender I Enova Satsningsområder, 2015. [20] NordPool, “Historical Market Data.” [Online]. Available: https://www. nordpoolgroup.com/historical-market-data/. € ller, B.V. Mathiesen, A. Dyrelund, The role of district heating in [21] H. Lund, B. Mo future renewable energy systems, Energy 35 (3) (Mar. 2010) 1381e1390. [22] H. Lund, et al., The status of 4th generation district heating: research and results, Energy 164 (Dec. 2018) 147e159. [23] H. Lund, A.N. Andersen, P.A. Østergaard, B.V. Mathiesen, D. Connolly, From electricity smart grids to smart energy systems - a market operation based approach and understanding, Energy 42 (1) (2012) 96e102. [24] H. Lund, Renewable Energy Systems: a Smart Energy Systems Approach to the Choice and Modeling of 100% Renewable Solutions, 2014. [25] B. Vad, S. Roth, J. Zinck, Aalborg Universitet IDA’S Energy Vision 2050 Søgaard, 2015. Drysdale, Dave; Connolly , David; Østergaard , Poul Alberg. [26] D. Connolly, H. Lund, B.V. Mathiesen, Smart Energy Europe: the technical and economic impact of one potential 100% renewable energy scenario for the European Union, Renew. Sustain. Energy Rev. 60 (2016) 1634e1653. [27] H. Lund, et al., 4th Generation District Heating (4GDH). Integrating smart thermal grids into future sustainable energy systems, Energy 68 (2014) 1e11. [28] J.Z. Thellufsen, H. Lund, Energy saving synergies in national energy systems, Energy Convers. Manag. 103 (2015) 259e265. [29] I. Ridjan, B.V. Mathiesen, D. Connolly, N. Dui
c, The feasibility of synthetic fuels in renewable energy systems, Energy 57 (2013) 76e84. [30] D. Connolly, H. Lund, P. Finn, B.V. Mathiesen, M. Leahy, Practical operation strategies for pumped hydroelectric energy storage (PHES) utilising electricity price arbitrage, Energy Policy 39 (7) (2011) 4189e4196. [31] H. Lund, et al., Energy storage and smart energy systems, Int. J. Sustain. Energy Plan. Manag. 11 (2016) 3e14. [32] D.A. Hagos, A. Gebremedhin, B. Zethraeus, Towards a flexible energy system a case study for Inland Norway, Appl. Energy 130 (2014) 41e50. [33] M.B. Blarke, Towards an intermittency-friendly energy system: comparing electric boilers and heat pumps in distributed cogeneration, Appl. Energy 91 (1) (2012) 349e365. [34] M.B. Blarke, H. Lund, The effectiveness of storage and relocation options in

renewable energy systems, Renew. Energy 33 (7) (2008) 1499e1507. [35] M. Huber, D. Dimkova, T. Hamacher, Integration of wind and solar power in Europe: assessment of flexibility requirements, Energy 69 (2014) 236e246. [36] H. Lund, H. Lund, EnergyPLAN, September, 2017. [37] D. Connolly, H. Lund, B.V. Mathiesen, M. Leahy, A review of computer tools for analysing the integration of renewable energy into various energy systems, Appl. Energy 87 (4) (2010) 1059e1082. [38] NVE, Norway and the European Power Market, 2016 [Online]. Available: https://www.nve.no/energy-market-and-regulation/wholesale-market/ norway-and-the-european-power-market/. [39] NordPool, “Bidding Areas.” [Online]. Available: https://www.nordpoolgroup. com/the-power-market/Bidding-areas/. [40] Norsk Fjernvarme, Svensk Energiminister: - Globalt Kreves Det Energilager, 2016 [Online]. Available: http://www.fjernvarme.no/index.php? pageID¼29&openLevel¼4&cid¼3840. [41] Euroheat & Power, “District Energy in Norway.” [Online]. Available: https:// www.euroheat.org/knowledge-centre/district-energy-norway/. [42] B. Grinden, N. Feilberg, Residential Monitoring to Decrease Energy Use and Carbon Emissions in Europe (Final Report of the Intelligent Energy - Europe Programme REMODECE), 2008, pp. 0e45. [43] K. Rosvold, A. Vinjar, Gasskraftverk, Store Norske Leksikon, 2016 [Online]. Available: https://snl.no/gasskraftverk. [44] H. Farahmand, S. Jaehnert, T. Aigner, D. Huertas-Hernando, T. Aigner, D. Huertas Hernando, Nordic hydropower flexibility and transmission expansion to support integration of North European wind power, Wind Energy 18 (6) (Jun. 2015) 1075e1103. [45] “EnergyPLAN - Existing Country Models.” [Online]. Available: http://www. energyplan.eu/useful_resources/existingcountrymodels/. [46] Norsk Solenergiforening, “Statistikk.” [Online]. Available: http://solenergi.no/ statistikk/. [47] ENTSO-E, “ENTSO-E Transparency Platform.” [Online]. Available: https:// transparency.entsoe.eu/. [48] NVE, Endringer i magasinkapasitet fra 7. mars 2016, 2016 [Online]. Available: https://www.nve.no/nytt-fra-nve/nyheter-energi/endringer-imagasinkapasitet-fra-7-mars-2016. [49] E-mail Correspondence with Roy Ulvang, Avfall Norge, 2017. [50] D. Weir, et al., Kostnader I Energisektoren: Kraft, Varme Og Effektivisering, No. 2, 2015. [51] Norsk Energi, “Årsmøte Norsk Energi.” Norsk Energi. [52] B.S. Torgeir Ericson, Audun Fidje, Jon Erling Fonneløp, Benedicte Langseth, Ingrid H. Magnussen, William W. Rode, Varmepumper I Energisystemet, 2016. [53] SSB, Befolkning, SSB, 2018 [Online]. Available: https://www.ssb.no/ befolkning. [54] S. Frederiksen, S. Werner, District Heating and Cooling, Studentlitteratur, 2013. [55] A.M. Melbye, P.K. Rørstad, M. Killingland, Bioenergi I Norge, 2014. [56] Enova, Potensial for Energieffektivisering I Norsk Landbasert Industri, 2009. [57] K. Askeland, K. Bozhkova, District Heating in Norway e an Analysis of Shifting from Individual Electric Heating to District Heating, Aalborg University, 2017.