Farklı karbon vergisi uygulamalarının piyasa takas fiyatı ve fosil kaynaklı üretim üzerine etkisi
Potential impacts of a carbon tax on the day-ahead market prices and the electricity generation mix
Yazar: ELİFNUR TOMA
Danışman: PROF. DR. ÜNER ÇOLAK
İstanbul Teknik Üniversitesi / Enerji Enstitüsü / Enerji Bilim ve Teknoloji Ana Bilim Dalı / Enerji Bilim ve Teknoloji Bilim Dalı
Derece: Yüksek Lisans, 2020
Konu: Enerji = Energy

Özet:
Fosil yakıtların kullanımı karbon salımına yol açarak iklim üzerinde olumsuz etkilerin oluşmasına neden olmaktadır. Bu olumsuz etkilerin en düşük seviyeye indirilmesi amacıyla farklı azaltım önlemleri uygulanmaya başlamıştır. Türkiye'de de geçtiğimiz on yıllarda karbon salımı büyük bir hızla artmıştır. Bu artışla karbon salımının çevre üzerindeki etkileri daha görünür hale gelmiş ve bu salımı sınırlandırmaya yönelik çeşitli politika seçenekleri gündeme gelmiştir. 
Dünyada uygulanmakta olan iklim değişikliği azaltım politikalarının başında karbon fiyatlandırma mekanizmaları bulunmaktadır. Karbon vergisi ve emisyon ticareti seçeneklerini barındıran fiyatlandırma mekanizmaları artan farkındalık ile dünyada yaygın hale gelmiştir ve birçok ülkenin de yakın gelecekte bu uygulamaları hayata geçirmesi beklenmektedir. Bu nedenle her iki fiyatlandırma mekanizması da birçok uygulama örneğine sahiptir. Yapılan araştırmalarda özellikle elektrik üretiminde karbon vergisi seçeneğinin daha uygulanabilir olduğu gözlemlenmiştir. İlerleyen dönemde Türkiye'de de bir karbon vergisi mekanizmasının uygulanması olası bir seçenektir. 
Olası karbon vergisi uygulanmasında ülkenin enerji politikaları da dikkate alınarak modelleme çalışmalarının yapılması gerekmektedir. Halihazırda Türkiye'nin enerji hedefleri arasında arz güvenliğinin sağlanması, enerjide yerlilik payının artırılması ve karbon salımının sınırlandırılması yer almaktadır. Bu hedeflerin bir arada sağlanabilmesi için karbon fiyatlandırma önemli bir araçtır. Uygulanacak bir karbon vergisi mekanizmasının bu hedeflere etkilerinin ölçülmesi açısından modelleme çalışmalarının yapılması çok önemli olacaktır. Bu tezde de hedefler göz önünde alınarak değişik seviyelerdeki karbon vergisinin, salımı azaltırken hem piyasa takas fiyatında hem de üretimdeki kaynak çeşitliliğinde yarattığı etkilerin analiz edilerek bu boşluğun doldurulması amaçlanmaktadır. 
Tez kapsamında 2020 ile 2035 yılları arası elektrik üretimi sektörü özelinde modelleme çalışmaları yapılmıştır. Bu amaçla üç farklı senaryo oluşturulmuştur. İlk senaryo mevcut hedefler dikkate alınarak oluşturulan Mevcut Politikalar Senaryosu, karbon vergisi uygulamasının olmadığı senaryodur. Bu senaryo, çalışma sonuçlarında karşılaştırma yapılabilmesi için baz senaryo olarak tasarlanmıştır. Karbon vergisinin uygulandığı ilk senaryo olan Düşük Karbon Senaryosu'nda 2025 yılında 8,8 USD/tonCO2 miktarında uygulanmaya başlanan karbon vergisi, 2035 yılında 16,7 USD/tonCO2 seviyesine ulaşmıştır. Son senaryo olarak da Yüksek Karbon Vergisi Senaryosu çalışılmıştır. Bu senaryoda da karbon vergisi uygulaması 2025 yılında başlamıştır. 11,9 USD/tonCO2 olarak başlatılan karbon vergisi simülasyon periyodu sonunda 39,6 USD/tonCO2 seviyesine çıkarılmaktadır. 
Türkiye Elektrik Kurumu'nun 1993 yılında üçe bölünmesiyle birlikte Türkiye Elektrik Piyasası'nda liberalleşme dönemi, 2001 yılında çıkarılan 4628 sayılı Elektrik Piyasası Kanunu ile hız kazanmıştır.  Günümüzde de elektrik piyasasındaki dönüşüm süreci devam etmektedir. Dönüşüm sürecinde olan bir piyasada yeni mekanizmaların ilave edilmesi daha uygulanabilirdir. Bu da karbon vergisinin elektrik piyasasında daha etkili olacağını gösteren bir durumdur. Yapılan reformlar ile Türkiye elektrik piyasası daha karmaşık bir hale gelmiştir. Bu durum da piyasada modelleme çalışması yapılmasını güçleştirmiştir. Bu nedenle Türkiye piyasasına özel olarak geliştirilen modellerin kullanılması gerekmektedir. Bu tezde de uzun zamandır piyasa katılımcıları tarafından da kullanılan uzun dönemli fiyat tahmin modeli AVIEW MARKETSIM yazılımından faydalanılmıştır. APlus Enerji tarafından geliştirilen AVIEW MARKETSIM, fundamental bir model olup saatlik olarak arz eğrisi oluşturarak arz ve talep eğrilerini kesiştirmektedir. Bunun sonucunda saatlik bazda fiyat, üretim, yakıt tüketimi ve salım miktarı hesaplanmaktadır. 
Senaryolar oluşturulurken Türkiye'nin belirlediği uzun dönemli talep gelişimi ve kurulu güç hedefleri dikkate alınmıştır. Bu hedeflerin yanı sıra önemli bir girdi olan yakıt fiyatları için sabit bedel kabul edilmiştir. Senaryolar arası farklılık gösteren tek girdi karbon vergisi olduğundan dolayı bu parametrenin etkilerini ölçmek mümkün olmuştur. 
Yapılan modelleme çalışmaları sonucunda karbon vergisi uygulaması ile ülkenin enerji hedefleri sağlanırken karbon salımında da önemli azaltımlar yapılabileceği gözlemlenmiştir. Öte yandan, bu azaltım sağlanırken elektrik fiyatları ve yerli kaynak kullanımı üzerinde de etkilerin olduğu görülmüştür. Bir karbon vergisi mekanizması planlanırken Türkiye'nin enerji hedefleriyle ilgili bütün bu etkilerin bir arada değerlendirilmesi gerekmektedir.

Abstract:
Climate change, which is mainly caused by the rising utilization of fossil fuels, is one of the most prominent and widespread problems in the world. Greenhouse gases, global warming, and climate change terminologies are alternatively used to describe the problem and a lot of studies were made to describe these phenomena and chart their interrelation. In 1807, Joseph Fourier was recorded as the first person to investigate the components effective on the Earth's surface temperature. The relation between minimal changes in the volume of atmospheric gases and the climate was first mentioned by Eunice Foote or John Tyndall, even though there is no consensus on the subject. The other important milestone is the quantitative analysis of the relationship between carbon intensity and earth surface temperature that was calculated by Svante Arrhenius in 1896. Greenhouse gases are gases that naturally exist in the atmospheric layers. However, it is important for these gases to be kept at certain levels to avoid disturbing the ecological balance. 
The human induced effects on the chemical balance of Earth are currently well-known, decades after Charles David Keeling was the first to measure carbon dioxide intensity in the atmosphere in 1958. Greenhouses gases consisting of water vapor, carbon dioxide, methane, nitrous oxide, ozone, and halocarbons can persist in the atmosphere through long periods of time; therefore, their effects will also be felt by the next generations. 
On the other hand, the direct and indirect costs that arise from the effects of climate change are borne by the society as a whole. Such costs are referred to as externality costs, with the term coined by Arthur C. Pigou.  Pigou defined two parties of the externality problem: the party that creates the cost and the party that bears the cost. The parties who are responsible for creating costs do not pay to eliminate their harmful effects and the other party has to pay an additional cost for these effects. The problem of carbon emissions can be regarded as a negative externality because the cost is paid by the society as a whole. These kinds of problems can be addressed by finding ways for the parties that are responsible for these costs to internalize them. As a solution, Pigou suggested that this be accomplished through taxation that is applied by the government because two sides are not able to solve this problem without intervention. On the other hand, opposing Pigou, Ronald Coase suggested a market mechanism to be utilized. Coase's assertion is that markets can solve this problem more efficiently without government intervention.
The ongoing academic studies on climate changes have shown that stringent measures should be taken to decelerate the increase in the volume of components that are responsible for climate change. In order to reach this aim, several international organizations were formed in the last decades. Kyoto Protocol was the first international agreement signed for the purpose of mitigating carbon emissions in the world. Under the agreement, the main parties that agreed to mitigation pledges were developed countries. The Paris Agreement which was signed in 2015 became another important step for the climate change struggle as nearly all of the countries in the world made climate change mitigation commitments for the first time. The main target of the Agreement is to keep the increase in global average temperatures below 2°C and to make the best effort to limit the increase to 1.5 °C. Turkey has also became a signatory to the Agreement but the Agreement is still to be ratified by the Grand National Assembly of Turkey mostly due to issues related to climate change financing. 
Although there are several mitigation policies active in Turkey, carbon emissions continue to increase. In Turkey, the total emission amount is increasing year by year, with the exception of 2018. The energy sector is responsible for most of the total emissions in the country, with 71.2%. On the other hand, carbon dioxide is the foremost among different types of greenhouse gases in Turkey, accounting for 80.0%. When these figures are evaluated in tandem, it becomes apparent that a possible carbon emission mitigation scheme in the energy sector would be able to limit the total greenhouse gas emissions in Turkey. 
The Turkish electricity market has been undergoing a transformation since 1993 when the liberalization process was initiated. As of 2020, there are several organizations that are important for the market including the Minister of Energy and Natural Resources, the Electricity Market Regulatory Authority, the Turkish Electricity Transmission Company, the state-owned Electricity Generation Company, and Energy Exchange Istanbul. Currently, several electricity trading options are available in the market including short, mid, and long-term time horizons. Electricity trade can be made either as financial or physical trade. Financial electricity trade is carried out through the Istanbul Stock Exchange, while physical electricity markets are operated by Energy Exchange Istanbul, EPİAŞ, and Turkish Electricity Transmission Company, TEİAŞ. In the scope of this study, the prices that are formed in the day-ahead market are considered because these prices are taken as reference prices for the whole electricity market. In the day-ahead market, electricity price is determined at the intersection point of supply and demand in the hourly merit order. Therefore, supply and demand sides are both effective on price formation. In the day ahead market, electricity generation companies bid according to their marginal costs which are calculated with fuel costs, efficiency, and other costs. Therefore, extra costs regarding electricity generation will affect their marginal costs and their bids in the market. On the other hand, changes in temperature, economic growth, and efficiency are effective on-demand side.  
New investment opportunities in the market accelerated with ongoing liberalization and total installed capacity reached 91 GW as of the end of 2019. According to the installed capacity, natural gas power plants have the highest share with 25.9 GW, while reservoir hydropower plants have the second highest share. Total electricity generation from reservoir hydropower plants was higher compared to natural gas power plants' generation thanks to unusually high precipitation in 2019. Increase in natural gas tariffs was also another factor that influenced natural gas power plants' share in 2019. On the other hand, coal power plants were responsible for 37% of total electricity generation in 2019. Coal power plants in the country can be classified under two categories: local coal and imported coal. Local coal power plants receive incentives from the government in a bid to increase domestic source utilization in the country. As of 2017, renewable power plants, especially solar, started to contribute to the generation mix in the country, significantly. Renewable energy sources are evaluated under the Renewable Energy Support Mechanism that provides feed-in tariffs to these power plants in US dollar terms.
There are several policy targets pursued by the Turkish energy policymakers. Electricity demand in the country is expected to grow rapidly in the coming decades with the industrial development of the country. This situation is expected to exacerbate several problems faced in the electricity market. In this context, the main targets of the Turkish energy policy include reducing the dependence on imported energy sources, mitigating greenhouse gas emissions, and providing electricity to end-users with affordable prices. Some of these targets have conflicting aspects with each other; therefore, it will be a significant challenge to reach all of these targets simultaneously.
For example, increasing electricity generation from local coal power plants would positively affect the domestic source utilization in the country but have a significantly adverse effect on carbon emissions. When electricity generation from coal power plants and total emission amounts are evaluated together, it is apparent that there is a high correlation between them. In order to address such conflicts, it is necessary for Turkey to develop the suitable strategies and policies to accommodate all of the energy targets at the same time. The formulation of such policies would require comprehensive modelling studies to be carried out in order to assess the effects of alternative policy options. Such a policy choice for Turkey is to adopt a carbon pricing scheme. Carbon pricing can potentially be an important tool in reaching country's targets. 
In this regard, this study aims to provide a roadmap for policymakers by assessing the effects of employing a carbon tax scheme in Turkey. For this purpose, simulation studies are carried out for the period between 2020 and 2035. Within the study, three scenarios are simulated including a scenario without any carbon taxation, a scenario with a moderate amount of carbon taxation (from 8.8 USD/tonCO2 in 2025 to 16.7 USD/tonCO2 in 2035), and a scenario with a more ambitious carbon tax (from 11.9 USD/tonCO2 in 2025 to 39.6 USD/tonCO2 in 2035). The results of each scenario are analysed in terms of their impact on import dependency in the country, carbon emissions and electricity prices. 
Due to the unique characteristics of the Turkish market, a specialized modelling methodology should be developed in order to make modelling studies in the country. In this regard, the AVIEW MARKETSIM software is used in study which has been in-use by different parties in the market for a significant time. AVIEW MARKETSIM model uses a fundamental methodology and forecast hourly electricity prices by matching supply and demand curves in the market for each hour. Among other outputs, the model provides hourly prices, generation, fuel consumption and carbon emission amounts. 
In the formation of the scenarios, the long-term demand and installed capacity targets set by the government are taken into account. Fuel prices are taken as constant throughout the simulation period. The only input that changes across scenarios is the level of carbon taxation which enables the effect of this parameter to be clearly visible. 
According to the simulation results, electricity prices in 2035 increase to 57.5 USD/MWh in the Base Case Scenario without a carbon tax, to 64.5 USD/MWh in the Low Carbon Scenario and to 73.9 USD/MWh in the High Carbon Scenario. Additionally, the share of electricity generation from imported fuels in 2035 is 41.4% in the Base Case Scenario, 45.5% in the Low Carbon Scenario and 46.0% in the High Carbon Scenario. On the other hand, carbon emissions are significantly decreased in the two scenarios which employ carbon taxation. In the Low Carbon Scenario, the total carbon dioxide emissions resulting from electricity generation in 2035 is 225.7 mton CO2, while the same figure is 213.4 mton CO2 in the High Carbon Scenario. These figures show a significant decrease compared to the Base Case Scenario results which point to 245.6 mtonnes of CO2 emissions in 2035. 
These results show that significant carbon emission mitigation in the country can be possible through the implementation of carbon taxation measures. However, this mitigation would also result in higher electricity price and increased utilization of imported fuel sources. All these effects should be considered in combination when devising policies for the Turkish energy market. 
It must be noted that different renewable energy capacity assumptions are not employed for different scenarios under the scope of this study. Such studies should be made in the future to assess the potential effects of renewable energy generation in the market. In case of an increased renewable energy capacity in the country, it would be possible to realize the two targets of climate change mitigation and decreasing the import dependency in the market at the same time.