Decarbonization of the electricity, heating, and transport sectors on Samsø

Lyngsø, Tilde (2021) Decarbonization of the electricity, heating, and transport sectors on Samsø. Masters thesis, Aarhus University.

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    In 1997 Samsø was named the renewable energy island of Denmark, and it has lived up to that name, achieving carbon neutrality in just ten years. This was done by installing wind turbines and receiving extra CO2-quotas from the export of 70% of the island’s renewable electricity generation to the mainland. In 2007 the island opened an Energy Academy dedicated to energy savings and the transition to renewable energy, continuing to set new goals for the island after it met the initial targets. The next goal the island has set for itself is to become completely independent of fossil fuels. A necessary step if the island wishes to stay carbon-neutral without the extra CO2 quotas, which will stop in 2030 when the Danish electricity sector is expected to become carbon neutral. Currently, the island’s need for fossil fuels is practically limited to the transport sector and a significant part of the private heating demand. Removing fossil fuels from private the heating sector requires persuading the residents to replace the remaining oil burners. While this is not an easy task, a wide range of alternative heating sources make it seem like a simple project compared to the transport sector, which more challenges. With the share of electric cars in the private transport sector slowly increasing on its own, the main task is to find a way to meet the demand for heavy transport like ferries, tractors, and trucks without relying on fossil fuels. Constructing a biogas plant on the island could be part of the solution to this problem. However, this would lay claim to some of the local biomass, which is currently being used to fuel the district heating sector. As the island wishes to avoid depending on the biomass import for the biogas plant, it is relevant to explore alternative heat sources for the district heating sector. An obvious choice is large-scale heat pumps, a CO2-neutral option, as long as renewable sources generate the electricity. In this thesis, a technical-economic analysis is performed to determine if the electrification of the district heating sector is cost-competitive with the current biomass burners. The operation of the electrified district heating plant is examined in detail, and it is investigated how sensitive the optimal capacities are to external factors, such as annual variations, component costs, and varying electricity cost. With the electrification of the heat and transport sector, the electricity demand on the island will increase. To examine how this increase in demand affects the energy system on Samsø, the energy generation and consumption on the island is modelled as a "Smart Energy System". Here, the coupling between the electricity, heat and transport sectors allows the system to balance the production and demand in all three sectors by using the storage in the transport and district heating sector. The inclusion of the connection to Jutland in the model allows the island to import electricity when necessary and to export electricity to the mainland when production exceeds local demand. In this project, the following questions are examined: Is the production cost for an electrified district heating plant cost-competitive with biomass burners? What are the effects of increasing synergy between the energy sectors on Samsø? Can Samsø benefit from increasing its renewable capacities? All systems are modelled for a full year in hourly snapshots, and an optimisation algorithm is applied to determine the capacities and operation, which result in the lowest system cost while meeting the required demands every hour. When optimising the district heating plant in Ballen-Brundby for an air-sourced heat pump, the plant’s electrification results in a direct heat production cost equal to the current cost of 35 AC/MWh. With a ground-sourced heat pump, the production cost is slightly lower at 33 AC/MWh, but this solution has a higher investment cost. The lowest overall system cost is therefore found when using an air-sourced heat pump. When the district heating plant is based on an air-sourced heat pump, the recommended configuration consists of a heat pump of 1.2 MWthermal, along with a resistive heater of 1.0 MW. The resistive heater functions to cover the peak load in the colder months to reduce the capacity of the expensive heat pump. The system also includes heat storage of 21 MWh, which mainly functions to balance the electricity cost, allowing the system to increase the heat production when the electricity price is low and discharge the storage in the morning and evening when the electricity price is high. A coupling of the energy sectors on Samsø results in a decrease in electricity export as the annual electricity demand on the island increases. The conversion to an electrified district heating sector also increases the annual system cost, as the expense of the capital and marginal costs associated with the district heating sector are now included. When the transport sector is included, the island residents cover the associated capital costs, but the system covers the increase in electricity demand. However, the system also gets the advantage of using the batteries in the electric vehicles to store electricity, which can later be discharged into the grid. This advantage reduces the annual system cost by an average of 2%, as the system is allowed to import electricity when the spot price is low and sell it at a profit later. When looking at the energy system for Samsø, the renewable resource quality is higher than the Danish average. However, despite the higher than average wind quality, the installation of more wind is not cost-competitive with the current electricity market, even as the cost of wind turbines decreases towards 2050. The same cannot be said for solar PV, where the current cost is on the verge of making solar panels cost-optimal. This is revealed by the fact that the capital cost of solar is too high to warrant an increase in solar panels for a year with an average amount of sunny hours. However, it is cost-optimal to increase the solar panels on Samsø by 45 MW for a slightly above average year. The same is seen when the associated cost decrease in the future, where the expected cost in 2030 makes it cost-optimal to increase the islands solar panels by 55 MW. The reduction in installation costs associated with renewable energy makes it beneficial for the island to increase the link capacity to the mainland by 2040. In both 2040 and 2050, the increase in link capacity is 10 MW or 25%, allowing the system to install the maximum permitted solar capacity of 81.3 MW. Nevertheless, reaching the limit for solar panels does not result in an increase in on- or offshore wind turbines unless the cost of wind turbines is reduced significantly beyond expected values.

    Item Type: Thesis (Masters)
    Creators: Lyngsø, Tilde
    Projects: SMILE
    Date Deposited: 16 Jun 2021 11:46
    Last Modified: 14 Sep 2021 09:06

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