Keep that fire burning: Fuel supply risk management strategies of Swedish district heating plants and implications for energy security

Recent decades have seen a strong increase in bioenergy utilization in Sweden, from 52 TWh in 1983 to 128 TWh in 2013. Much of this increase has been achieved by replacing fossil fuels with different forms of bioenergy in district heating. Increased use of bioenergy is generally seen as key to reducing fossil fuel consumption and greenhouse gas emissions and improving energy security.However, replacing fossil fuels with solid biomass fuels in stationary heat and power generation entails significantly more complicated fuel supply logistics, with geographically scattered material associated with storage difficulties and low energy density. Given these risks and challenges and the key role of biomass-based district heating in the Swedish energy system, disturbances in fuel supply to district heating could potentially be an energy security issue.Through literature studies and interviews with employees at 18 district heating plants, we mapped present and future risks and risk management strategies in district heating supply in the Mälardalen region, south-east Sweden. We found that although small disturbances to fuel supply are not uncommon, the likelihood of heat supply failures due to fuel supply problems is low. Risk awareness is generally high among fuel supply managers, with widespread use of multilevel redundancies and diversification as key risk management strategies. However, fuel supply to plants is highly dependent on functioning truck transport and, consequently, availability of diesel fuel for trucks. Risk management can be strengthened further by implementation of forward-looking risk assessments that are less reliant on past experiences.     

Future use of heat pumps in Swedish district heating systems: Short- and long-term impact of policy instruments and planned investments

Heat pumps constitute one of the major technologies used in district heating systems in Sweden. Totally about 6 TWh of heat are supplied annually by heat pumps, equivalent to 12% of the heat supplied in district heating systems. New policy instruments that have recently been introduced will change the conditions for technologies in the district heating systems. It is likely that the incentives for waste incineration and combined heat and power will be improved. This study estimates how different policy instruments, and new investments in waste incineration and combined heat and power, affect heat pumps in Swedish district heating systems. The results indicate that heat pumps are affected in both a short-term and a long-term perspective, and that heat pumps will play a less important role in district heating systems in the future. Depending on the policy instruments applied in the district heating sector, the long-term use is between 18% and 71% lower than current use. In a long-term perspective, it is in the systems which currently use heat pumps during a large part of the year that new investments in waste incineration and combined heat and power can be expected, resulting in a convergence between different district heating systems regarding how much heat is supplied by combined heat and power and waste incineration, and regarding the annual operating hours for heat pumps.     

Future production and utilisation of biomass in Sweden: Potentials and CO2 mitigation

Swedish biomass production potential could be increased significantly if new production methods, such as optimised fertilisation, were to be used. Optimised fertilisation on 25% of Swedish forest land and the use of stem wood could almost double the biomass potential from forestry compared with no fertilisation, as both logging residues and large quantities of excess stem wood not needed for industrial purposes could be used for energy purposes. Together with energy crops and straw from agriculture, the total Swedish biomass potential would be about 230 TWh/yr or half the current Swedish energy supply if the demand for stem wood for building and industrial purposes were the same as today. The new production methods are assumed not to cause any significant negative impact on the local environment. The cost of utilising stem wood produced with optimised fertilisation for energy purposes has not been analysed and needs further investigation. Besides replacing fossil fuels and, thus, reducing current Swedish CO₂ emissions by about 65%, this amount of biomass is enough to produce electricity equivalent to 20% of current power production. Biomass-based electricity is produced preferably through co-generation using district heating systems in densely populated regions, and pulp industries in forest regions. Alcohols for transportation and stand-alone power production are preferably produced in less densely populated regions with excess biomass. A high intensity in biomass production would reduce biomass transportation demands. There are uncertainties regarding the future demand for stem wood for building and industrial purposes, the amount of arable land available for energy crop production and future yields. These factors will influence Swedish biomass potential and earlier estimates of the potential vary from 15 to 125 TWh/yr.     

Influencing Swedish homeowners to adopt district heating system

Improved energy efficiency and greenhouse gas mitigation could be achieved by replacing resistance heaters with district heating system. In 2005, only about 8% of the Swedish detached houses had district heating system. The expansion of such systems largely depends on homeowners’ adoption decisions. And, to motivate homeowners to adopt district heating, it is essential to understand their decision-making process. In this context, in June 2005 we carried out a questionnaire survey of about 700 homeowners who lived in the city of Östersund in houses with resistance heaters (baseline survey). About 84% of the respondents did not intend to install a new heating system. Since then these homeowners were influenced by (a) an investment subsidy by the Swedish government to replace resistance heaters with district heating, a brine/water-based heat pump, or a biomass-based heating system and (b) a marketing campaign by the municipality-owned district heating company. This paper analyses how these two measures influenced about 78% of the homeowners to adopt the district heating system. For this purpose we carried out a follow-up survey of the same homeowners in December 2006 (resurvey). Results showed that the investment subsidy and the marketing campaign created a need among the homeowners to adopt a new heating system. The marketing campaign was successful in motivating them to adopt the district heating system. The marketing strategy by the district heating company corresponds to the results obtained in the baseline survey.     

District heating and energy efficiency in detached houses of differing size and construction

House envelope measures and conversion of heating systems can reduce primary energy use and CO₂ emission in the existing Swedish building stock. We analysed how the size and construction of electrically heated detached houses affect the potential for such measures and the potential for cogenerated district heating. Our starting point was two typical houses built in the 1970s. We altered the floor plans to obtain 6 houses, with heated floor space ranging between 100 and 306 m². One of the houses was also analysed for three energy standards with differing heat loss rates. CO₂ emission, primary energy use and heating cost were estimated after implementing house envelope measures, conversions to other heating systems and changes in the generation of district heat and electricity. The study accounted for primary energy, including energy chains from natural resources to useful heat in the houses. We showed that conversion to district heating based on biomass, together with house envelope measures, reduced the primary energy use by 88% and the CO₂ emission by 96%, while reducing the annual societal cost by 7%. The choice of end-use heating system was decisive for the primary energy use, with district heating being the most efficient. Neither house size nor energy standard did significantly change the ranking of the heating systems, either from a primary energy or an economic viewpoint, but did affect the extent of the annual cost reduction after implementing the measures.     

District heating in Sweden, 1972–1977

The oil crisis led to renewed interest in combined heat and power production (CHP) and consequently also in district heating. The studies of CHP which have been carried out in various countries indicate that no general conclusions can be drawn about the merits of CHP and that assessments are strongly dependent on local conditions. In the following Carl-Erik Lind gives an account of some of the salient features of the Swedish district heating systems and their development since 1972.     

Vertical integration of local fuel producers into rural district heating systems – Climate impact and production costs

Farmers can use their own agricultural biomass residues for heat production in small-scale systems, enabling synergies between the district heating (DH) sector and agriculture. The barriers to entry into the Swedish heat market were extremely high as long as heat distribution were considered natural monopoly, but were recently lowered due to the introduction of a regulated third party access (TPA) system in the DH sector. This study assesses the potential impact on greenhouse gas emissions and cost-based heat price in the DH sector when farmers vertically integrate into the heat supply chain and introduce more local and agricultural crops and residues into the fuel mix. Four scenarios with various degree of farmer integration, were assessed using life cycle assessment (LCA) methodology, and by analysis of the heat production costs. The results show that full integration of local farm and forest owners in the value chain can reduce greenhouse gas emissions and lower production costs/heat price, if there is an incentive to utilise local and agricultural fuels. The results imply that farmer participation in the DH sector should be encouraged by e.g. EU rural development programmes.     

Biomass fired small-scale CHP in Sweden and the Baltic States: a case study on the potential of clustered dwellings

Sweden as well as the three Baltic states has an abundant supply of biomass, mostly wood waste. Much of it goes into district heating (DH), which has expanded continuously since the first system started 50 years ago. DH now accounts for 43% of the heating consumption and a further expansion is possible in many directions. Firstly existing DH systems can be enlarged, secondly DH can be upgraded to combined heat and power (CHP) to a much larger extent, thirdly new DH (and CHP) systems can be implemented in many smaller places down to 1000 inhabitants or less. The last alternative, biomass and especially pellets fired small-scale cogeneration in combination with local heating networks, is the topic for this paper. It presents a method to estimate the potential for small-scale DH and CHP and results from a “test” area in southeast Sweden. The method estimates local heat demand using databases with individual and statistical property data. It identifies areas with clusters of buildings where the heat demand is enough to implement decentralized small DH networks if possible in combination with small-scale CHP. In the event for Swedish circumstances very sparsely populated test area of 36×48 km² with around 8000 inhabitants, the total heat consumption in residential buildings is estimated to 84 GW h. When we have identified the areas with clusters of buildings, we have set the minimum heat consumption in such an area to 500 MW h. The area size is varied in 250 m steps from 250×250 m² to 1000×1000 m². For the four area sizes, the method then identifies and locates 30, 38, 38,30, respectively, clustered areas with a potential for small-scale DH and CHP worth investing closer.     

Coproduction of district heat and electricity or biomotor fuels

The operation of a district heating system depends on the heat load demand, which varies throughout the year. In this paper, we analyze the coproduction of district heat and electricity or biomotor fuels. We demonstrate how three different taxation scenarios and two crude oil price levels influence the selection of production units to minimize the district heat production cost and calculate the resulting primary energy use. Our analysis is based on the annual measured heat load of a district heating system. The minimum-cost district heat production system comprises different production units that meet the district heat demand and simultaneously minimize the district heat production cost. First, we optimize the cost of a district heat production system based on the cogeneration of electricity and heat with and without biomass integrated gasification combined-cycle technology. We considered cogenerated electricity as a byproduct with the value of that produced by a condensing power plant. Next, we integrate and optimize different biomotor fuel production units into the district heat production system by considering biomotor fuels as byproducts that can substitute for fossil motor fuels. We demonstrate that in district heating systems, the strengthening of environmental taxation reduces the dependence on fossil fuels. However, increases in environmental taxation and the crude oil price do not necessarily influence the production cost of district heat as long as biomass price is not driven by policy measures. Biomotor fuel production in a district heating system is typically not cost-efficient. The biomotor fuels produced from the district heating system have to compete with those from standalone biomotor fuel plants and also with its fossil-based counterparts. This is also true for high oil prices. A carbon tax on fossil CO₂ emissions based on social cost damage will increase the competitiveness of biomass-based combined heat and power plants, especially for BIGCC technology with its high electricity-to-heat ratio.     

Heat Roadmap Europe: Combining district heating with heat savings to decarbonise the EU energy system

Six different strategies have recently been proposed for the European Union (EU) energy system in the European Commission's report, Energy Roadmap 2050. The objective for these strategies is to identify how the EU can reach its target of an 80% reduction in annual greenhouse gas emissions in 2050 compared to 1990 levels. None of these scenarios involve the large-scale implementation of district heating, but instead they focus on the electrification of the heating sector (primarily using heat pumps) and/or the large-scale implementation of electricity and heat savings. In this paper, the potential for district heating in the EU between now and 2050 is identified, based on extensive and detailed mapping of the EU heat demand and various supply options. Subsequently, a new ‘district heating plus heat savings’ scenario is technically and economically assessed from an energy systems perspective. The results indicate that with district heating, the EU energy system will be able to achieve the same reductions in primary energy supply and carbon dioxide emissions as the existing alternatives proposed. However, with district heating these goals can be achieved at a lower cost, with heating and cooling costs reduced by approximately 15%.     

An adopter-centric approach to analyze the diffusion patterns of innovative residential heating systems in Sweden

Innovation and diffusion of renewable energy technologies play a major role in mitigation of climate change. In Sweden replacing electric and oil heating systems with innovative heating systems such as district heating, heat pumps and wood pellet boilers in detached homes is a significant mitigation option. Using an adopter-centric approach, we analyzed the influence of investment subsidy on conversion of resistance heaters and oil boilers, and the variation in diffusion pattern of district heating, heat pumps and pellet boilers in Swedish detached homes. Results from questionnaire surveys of 1500 randomly selected homeowners in September 2004 and January 2007 showed that more than 80% of the respondents did not intend to install a new heating system. Hence, about 37% of the homeowners still have electric and oil heating systems. The government investment subsidy was important for conversion from a resistance heater, but not from an oil boiler. This is because homeowners currently replacing their oil boilers are the laggards, while those replacing resistance heaters are the ‘early adopters’. Economic aspects and functional reliability were the most important factors for the homeowners when considering a new heating system. There is a variation in the perceived advantages associated with each of the innovative heating systems and therefore, the diffusion patterns of such systems vary. Installers and interpersonal sources were the most important communication channels for information on heating systems.     

Heat distribution and the future competitiveness of district heating

The competitiveness of present and future district heating systems can be at risk when residential and service sector heat demands are expected to decrease in the future. In this study, the future competitiveness of district heating has been examined by an in depth analysis of the distribution capital cost at various city characteristics, city sizes, and heat demands. Hereby, this study explores an important market condition often neglected or badly recognised in traditional comparisons between centralised and decentralised heat supply.     

Design of biomass district heating systems

The biomass exploitation takes advantage of the agricultural, forest, and manure residues and in extent, urban and industrial wastes, which under controlled burning conditions, can generate heat and electricity, with limited environmental impacts.Biomass can – significantly – contribute in the energy supplying system, if the engineers will adopt the necessary design changes to the traditional systems and become more familiar with the design details of the biomass heating systems.The aim of this paper is to present a methodology of the design of biomass district heating systems taking into consideration the optimum design of building structure and urban settlement around the plant. The essential energy parameters are presented for the size calculations of a biomass burning-district heating system, as well as for the environmental (i.e. Greenhouse Gas Emissions) and economic evaluation (i.e. selectivity and viability of the relevant investment). Emphasis has been placed upon the technical parameters of the biomass system, the economic details of the boiler, the heating distribution network, the heat exchanger and the Greenhouse Gas Emissions.     

Holistic methodological framework for assessing the benefits of delivering industrial excess heat to a district heating network

In Sweden, over 50% of building heating requirements are covered by district heating. Approximately 8% of the heat supply to district heating systems comes from excess heat from industrial processes. Many studies indicate that there is a potential to substantially increase this share, and policies promoting energy efficiency and greenhouse gas emissions reduction provide incentives to do this. Quantifying the medium and long-term economic and carbon footprint benefits of such investments is difficult because the background energy system against which new investments should be assessed is also expected to undergo significant change as a result of the aforementioned policies. Furthermore, in many cases, the district heating system has already invested or is planning to invest in non-fossil heat sources such as biomass-fueled boilers or CHP units. This paper proposes a holistic methodological framework based on energy market scenarios for assessing the long-term carbon footprint and economic benefits of recovering excess heat from industrial processes for use in district heating systems. In many studies of industrial excess heat, it is assumed that all emissions from the process plant are allocated to the main products, and none to the excess heat. The proposed methodology makes a distinction between unavoidable excess heat and excess heat that could be avoided by increased heat recovery at the plant site, in which case it is assumed that a fraction of the plant emissions should be allocated to the exported heat. The methodology is illustrated through a case study of a chemical complex located approximately 50 km from the city of Gothenburg on the West coast of Sweden, from which substantial amounts of excess heat could be recovered and delivered to heat to the city's district heating network which aims to be completely fossil-free by 2030.     

Optimal flow of regional forest biomass to a district heating system

There has been a growing interest in utilizing forest biomass for energy generation in district heating systems to reduce dependence on fossil fuels. However, variability in forest biomass availability and quality over time and its complex and costly supply chain have made investments in forest biomass energy generation projects less attractive. In this paper, a linear programming model is developed to minimize the delivery cost of forest biomass to the gate of heating plants and determine the optimal monthly flow of biomass to the plants. The model has a 1‐year planning horizon with monthly time steps. It determines (1) the amount of woodchips that should be transported to the plants from supply sources directly and through the terminal storages, (2) the amount of biomass that should be stored at supply sources and at terminal storages, and (3) the amount of biomass that should be chipped at supply sources and at terminal storages. The model was applied to a potential district heating system in Williams Lake, BC, Canada. The results of the optimization model indicated that it would not be economical to carry out the chipping process at the terminal storage. Biomass should be chipped at supply sources, and woodchips should be sent to the terminal storage and/or directly to the plant. Of the total optimum annual flow of woodchips to the plant, 90% is transported directly, while 10% is transported to the plant via the terminal storage. It would cost $43.38 Odt^?1 to deliver forest biomass to the plant. Copyright © 2013 John Wiley & Sons, Ltd.     

Potential of biomass‐fired combined heat and power plants considering the spatial distribution of biomass supply and heat demand

Combined heat and power (CHP) plants fired by forest wood can significantly contribute to attaining the target of increasing the share of renewable energy production. However, the spatial distribution of biomass supply and of heat demand limits the potentials of CHP production. This article assesses CHP potentials using a mixed integer programming model that optimizes locations of bioenergy plants. Investment costs of district heating infrastructure are modeled as a function of heat demand densities, which can differ substantially. Gasification of biomass in a combined cycle process is assumed as production technology. Some model parameters have a broad range according to a literature review. Monte‐Carlo simulations have therefore been performed to account for model parameter uncertainty in our analysis. The model is applied to assess CHP potentials in Austria. Optimal locations of plants are clustered around big cities in the east of the country. At current power prices, biomass‐based CHP production allows producing around 3% of the total energy demand in Austria. Yet, the heat utilization decreases when CHP production increases due to limited heat demand that is suitable for district heating. Production potentials are most sensitive to biomass costs and power prices. Copyright © 2009 John Wiley & Sons, Ltd.     

Conventional and advanced CO2 based district energy systems

District energy systems can potentially decrease the CO₂ emissions linked to energy services, thanks to the implementation of large polygeneration energy conversion technologies connected to buildings over a network. To transfer the energy from these large technologies to the users, conventional district energy systems use water with often two independent supply and return piping systems for heat and cold. However, sharing energy or interacting with decentralised heat pump units often results in relatively large heat transfer exergy losses due to the large temperature differences that are economically required from the water network. Besides, the implementation of two independent supply and return piping systems for heat and cold, results in large space requirements in underground technical galleries. Using refrigerants as a district heating or cooling fluid at an intermediate temperature could alleviate some of these drawbacks. A new system has been developed, that requires only two pipes, filled with refrigerant, to meet heating, hot water and cooling requirements. Because of the environmental concerns about conventional refrigerants, CO₂, a natural refrigerant, used under its critical point, is considered an interesting candidate. A comparative analysis shows that both in terms of exergy efficiency and costs the proposed CO₂ network is favourable.     

Heat supply of agglomeration areas

The technologies of heat supply for agglomeration areas will, in the future, undergo appreciable changes compared to the present status. There will be a strong enhancement of the use of domestic energy sources like solid waste, biogas and biomass or coal. Perhaps the strongest momentum will come from efforts to make use of the large potential of industrial waste heat, which is generally in the same order of magnitude as the demand for heating energy. Since we have different temperature levels here compared to conventional district heating, different technologies will be employed, in particular connected with low temperature applications. Some of them are described in the paper, and the main results of an investigation are reported, where the potential of application in an area of about 400,000 inhabitants were studied.     

Projecting demand and supply of forest biomass for heating in Norway

This paper assesses the increase in demand and supply for forest biomass for heating in Norway in 2020. By then there is a political aim to double the national production of bioenergy from the level in 2008. The competitiveness of woody biomass in central and district heating is analyzed in a model selecting the least-cost heating technology and scale in municipalities given a set of constraints and under different fuels price scenarios. The supply of forest biomass from roundwood is estimated based on data of forest inventories combined with elasticities regarding price and standing volumes. The supply of biomass from harvesting residues is estimated in an engineering approach based on data from the national forest inventories and roundwood harvest. The results show how the production of bioenergy is affected by changes in energy prices and support schemes for bioenergy. One conclusion from the analyses is that the government target of 14 TWh more bioenergy by 2020 is not likely to be met by current technologies and policy incentives. The contribution of the analysis is the detailed presentation of the heat market potentials and technology choices combined with supply functions for both roundwood and harvesting residues.     

Is space heating in offices really necessary?

New office buildings in Sweden are thoroughly insulated due to the Swedish building code. This code, however, does not consider the type of activity occurring in the building. This means that the heating equipment is designed as if no activity at all is going on. In modern offices there is a lot of equipment installed which uses electricity. This electricity is converted into heat which can be utilized for heating the premises, mostly in a direct way but also by the use of exhaust-air heat-pumps or heat exchangers. This paper deals with a modern office building plus office hotel complex located in Linköping, Sweden, about 200 km south of Stockholm. The tenants deal with the design of hard- and software for computers. The lighting and computers in the building use electricity which converts into heat. In this paper, it is shown that this electricity is all that is needed during normal conditions, i.e. when people work in the building. The building is also equipped with a district-heating system, which is designed as if no activity goes on in the building, so subsequently the heating equipment is larger than it need be. In this special case, it might have been better to install an electric heating device for hot-water heating and very cold winter conditions, instead of using district heating. This is so even if district heat is about half the unit price compared with that due to the dissipation of electricity. At present, when district heating is used, no measures for saving heat can be profitable due to the low district-heating price. The fact is that the tenants complain of too much heat instead of too little: the prevailing indoor temperature was about 24° C in January 1990 even though 20° C would have been sufficient. There is subsequently a need for a properly working regulation system. The one currently in use is designed to a modern standard, but is not able to maintain temperatures at a modest level.