تاثیر کوتاه مدت گواهینامه های سبز و انتشار تجاری CO2 در بخش حرارت مرکزی سوئد

Swedish district-heating (DH) systems use a wide range of energy sources and technologies for heat-and-power generation. This provides the DH utilities with major flexibility in changing their fuel and technology mix when the economic conditions for generation change. Two recently introduced policy instruments have changed the DH utilities’ costs for generation considerably; the tradable green-certificate (TGC) scheme introduced in 2003 in Sweden, and the tradable greenhouse-gas emission permit (TEP) scheme introduced in the EU on January 1, 2005. The objective of this study is to analyse how these two trading schemes impact on the operation of the Swedish DH sector in terms of changes in CHP generation, CO2 emissions, and operating costs. The analysis was carried out by comparing the most cost-effective operation for the DH utilities, with and without, the two trading schemes applied, using a model that handles the Swedish DH-sector system-by-system. It was found that the volume of renewable power generated in CHP plants only increased slightly owing to the TGC scheme. The TGC and the TEP schemes in force together, however, nearly doubled the renewable power-generation. CO2 emissions from the DH sector may either increase or decrease depending on the combination of TGC and TEP prices. The overall CO2 emissions from the European power-generation sector would, however, be reduced for all price combinations assuming that increased Swedish CHP generation replaces coal-condensing power (coal-fired plants with power generation only) in other European countries. The trading schemes also lower the operational costs of the DH sector since the cost increase owing to the use of more expensive fuels and the purchase of TEPs is outweighed by the increased revenues from sales of electricity and TGCs.

District heating (DH) is the dominant source of heat for buildings in Sweden, with a current market share of about 47% [1]. This position has been achieved through the creation of hundreds of local DH systems all over Sweden during the past six decades. Compared with many other countries with major DH sectors, the use of fossil fuels (oil, coal, and natural gas) in the Swedish DH sector is very limited. The major reasons for this are the lack of such resources domestically in Sweden and the active Swedish policy-making discouraging fossil-fuel use. The set of heat production in the respective DH system is, instead, primarily based on the energy resources available locally, for instance industrial waste-heat, municipal solid-waste and, wood waste from forestry. Fossil fuels are used mainly as complements to these energy sources, for instance in periods of peak demand. Another difference from other countries that use a great deal of DH is that only a small part of the Swedish DH production is based on combined heat-and-power (CHP). The main reason for this is the historically good access to cheap electricity, owing to the dominant resources of hydropower and nuclear power in Sweden, which have made CHP investments unprofitable. A great deal of the heat generated in the Swedish DH sector comes instead from heat-only boilers (HOBs). Electric HOBs and electricity-powered heat-pumps are also commonly used in the DH sector owing to the historic abundance of electricity. The implication of these facts is that the Swedish DH utilities today all utilise several fuels and technologies for DH production. Fig. 1 shows the development of the Swedish DH sector from 1970 to 2003.In the respective DH systems, the different energy-sources and production units are used in combinations that satisfy the demand for heat at the lowest overall cost to the system. This is achieved by operating the production units with the lowest heat-generation cost whenever possible and by operating the production units with the highest heat-generation cost as little as possible (order of dispatch). The heat-generation cost is a function of factors including fuel price, imposed tax rate and conversion efficiency for the plant. To maintain the lowest possible operating costs over time, the order of dispatch has to be reassessed as soon as the financial conditions for operation change, for instance when there are changes in fuel prices, tax rates or the price of electricity (the price of electricity is important in determining the order of dispatch for CHP plants, electric HOBs, and electricity powered heat-pumps). Refurbishing of ineffective plants, fuel switches, or investments in new plants are examples of other ways to adjust production to new financial conditions. The non-homogenous set of DH supply provides the DH utilities with a large number of options. Two recently implemented policy instruments that have changed the economic conditions for the DH utilities considerably are the legally-binding scheme for tradable green certificates (TGCs) that was introduced in Sweden on May 1, 2003 [3], and the scheme for tradable carbon dioxide emission permits (TEPs) that was introduced in the EU on January 1, 2005 [4]. The purpose of the TGC scheme is to create economic incentives for investment and operation of power-generation technologies based on renewable energy sources. The basic idea underpinning the scheme is that every megawatt hour (MWh) of power generated with a TGC eligible fuel is granted a certificate, which may then be sold on a TGC market and, thereby, generates an extra income for the producer in addition to the income from power sales.1 The demand for TGCs is regulated by a quota obligation on power consumption. The TEP scheme is one of the three “flexible mechanisms” in the Kyoto protocol, intended to enable cost-effective greenhouse-gas reductions [5].2 The basic idea with this scheme is that TEPs are allocated to CO2-emitting companies corresponding to the volume of CO2 emissions that is committed to be achieved (an 8% reduction for the EU as a whole). If measures are undertaken by the companies that reduce their emissions, the corresponding surplus of TEPs may be sold to other parties in the trading scheme. These parties will typically be companies that have more costly options for reducing their emissions than the selling companies. It is reasonable to believe that the DH utilities will undertake adequate measures to maintain as low operating costs as possible under these new conditions. Such measures could, for instance, comprise increased use of CHP plants based on TGC eligible fuels and decreased use of fossil fuels (for the companies to be able to sell TEPs). According to the government commission that investigated the effects of the TGC scheme prior to its implementation, existing CHP plants were expected to play a dominant role in the TGC scheme – at least during the early years of the scheme [6]. The potential for extended operation of existing biofuel-based CHP plants in the DH sector was estimated to be about 0.5 TWh/year and the potential for fuel switches from coal to biofuels in existing CHP plants was estimated to be about 1.5 TWh/year. This study did not include effects of co-existence of the TGC and the TEP schemes. The co-existence of the electricity, TEP, and TGC markets in the Nordic countries has been analysed by Unger and Ahlgren [7]. They too, concluded that the existing CHP plants in Sweden would play an important early role in the TGC scheme. A third study calculated the profitable short-term increase in CHP generation from the DH sector owing to the TGC and TEP scheme to about 1.5 TWh/year [8]. This figure, however, represented CHP generation based on all fuels (not only renewable fuels). The effects of the TGC scheme have also been analysed for local DH utilities. In such a study, it was found that wood fuel would be more profitable to use for power generation rather than for heat-only generation, which was the case without the TGC scheme [9]. No studies analysing the effects of the TEP scheme on local DH utilities’ operating regimes have been found in the literature. All the studies above use approaches that describe the Swedish DH sector on an aggregated system level or use methods developed for analyses of local DH systems. In the studies using the MARKAL model [10], the entire Swedish DH sector was described as one large DH system [6] and [7]. In the study using the MARTES model (developed for simulating operation of local DH systems) [11], the approach used was to analyse the largest DH systems in detail and to aggregate the remaining ones into “type systems” according to a certain regime [8]. The fact that the Swedish DH sector comprises hundreds of local DH system, all using several fuels and technologies for DH production, gives us reason to believe that analyses including rough descriptions of the DH sector cannot deliver results with a high degree of accuracy. That the level of aggregation may be important for the outcome of analyses of the Swedish DH sector was shown in [12]. The non-homogenous characteristics of the DH systems also imply that case studies of local DH systems are of limited interest when it comes to assessing the response of the entire DH sector to quantitative changes. The objective of the present study is to analyse the short-term effects of the TGC and TEP schemes on the Swedish DH-sector more accurately than has previously been done.3 The study is carried out using a model that describes the Swedish DH-sector system by system taking the local preconditions of each DH-system into account. The analysis includes, in addition to a reference scenario, three scenarios which examine: (1) the isolated effects of the TGC scheme, (2) the superimposed effects of the TGC and TEP schemes, and (3) the superimposed effects of the TGC and TEP schemes, together with removal of the current CO2 tax.4 The results are presented in terms of changes in volume of power generated in CHP plants, volume of CO2 emitted, and operational costs. The paper is organized as follows: Section 2 explains the construction and application of the model. Assumptions and input data used are also accounted for, and a summary of the scenarios analysed is given. Section 3 includes a presentation of the results and a discussion. The conclusions are drawn in Section 4.

The objective of this study was to analyse how the introduction of TGC and TEP schemes impact on the operation of the Swedish DH-sector in terms of changes in CHP generation, CO 2 emissions and operating costs. The study showed that the increase in renewable power-generation in CHP plants owing to the TGC scheme is in the range of 0.2–0.4 TWh/year, depending on TGC price (two TGC prices were tested, 10 and 20 € / MWh el ). The existing CHP plants in the DH sector are therefore not likely to contribute to any significant extent to the fulfilment of the goal of the TGC scheme (to increase the annual renewable power-generation to 10 TWh by 2010). To significantly increase the renewable power-generation from the existing CHP plants in the DH sector, a TGC price of 27 € /MWh el would be required. At this TGC price, fuel switches from coal to wood fuel become profitable in CHP plants with that fuel flexibility (for the given coal and wood-fuel prices). The effects of the TGC scheme on Swedish CO 2 -emissions are uncertain. CO 2 emissions may well increase since peat CHP plants (generation from which is TGC eligible) will be more profitable to operate. The cost of using electricity-powered heat pumps and electric HOBs will also be higher with the TGC scheme (owing to the quota obligation) to the ben- efit of all other fuels (including fossil fuels). The CO 2 emissions in the European power- generation sector (the net CO 2 emissions) will, however, decrease with the TGC scheme since the increased CHP generation and decreased power-consumption (in electricity-pow- ered heat-pumps and electric HOBs) in the DH sector are assumed to decrease coal con- densing power-generation correspondingly. With the TGC and the TEP schemes jointly in force, fuel switching from coal to wood fuels becomes profitable in CHP plants for all the tested combinations of TGC and TEP prices, owing to the increased cost of using coal. 24 Consequently, the volume of renewable electricity-generation increases greatly, between 1.5 and 1.8 TWh/year depending on the combination of TGC and TEP price, as compared with the reference scenario. This also reduces the Swedish CO 2 -emissions for all tested combinations of TGC and TEP prices. The net CO 2 emissions are reduced to approximately zero. The TGC and TEP schemes applied together, in combination with the abolition of the current CO 2 tax, will remove the financial incentive for fuel switches from coal to wood fuels (except for the price combination 20 € /MWh el and 20 € /tCO 2 for TGCs and TEPs, respectively). Except for this price combination, the volume of renewable power-genera- tion is, then, reduced to the volume with only the TGC scheme applied (scenario 1).The Swedish CO 2 -emissions will also be higher if the CO 2 tax is removed than they were before the TEP scheme was introduced. The incomes from the TGC scheme will reduce the overall operating cost in the DH sector. Jointly applied, the TGC and the TEP schemes will reduce the operating costs for the DH sector further since the increased costs of using more expensive fuels and of buying TEPs are compensated for by the higher income from power sales. Removal of the current CO 2 tax would of course also reduce the operating costs.