System design of a DC based micro grid - A comparison study on the Andaman Islands

Abstract: The world today stands at a cross roads when it comes to energy and electrical grids. A large part of the worlds population still lacks access to reliable working electricity 24 hours a day. Much of this is in remote and poor parts of the world. For much of the 20th century large centralized AC grids have been the norm to provide people with electricity. But for remote parts of the world including island communities this have been problematic, because of the difficulty and high cost of extending the main AC grid to them. With the introduction of large amounts of renewable energy into our grids in combination with the increasing use of DC appliances inside our homes, the idea of using DC as the main way for transmission and distribution in the form of isolated microgrids has gained traction. This thesis as a part of bilateral research project between the Swedish Energy Agency and India’s Ministry of New and Renewable Energy, looks at a renewable energy based DC microgrid on the Andaman Islands in India. With the background being an earlier pre study that recommended an island called Rutland Island as a pilot site. With the aim to propose a suitable design for both long term and reliable electrical supply, while at the same time looking at the current state of DC grids and the possible future. This is done by testing two different microgrid designs based on two different scenarios, the current energy consumption of the Rutland community and an average Indian per capita energy consumption. The thesis concludes that for a DC microgrid of this size, cables are an important aspect, but as a whole including the economic analysis DC/DC converters and batteries are more important, especially if aiming for the future design with Lithium-ion batteries instead of Lead-acid. Both components are still expensive but with their increasing use, especially Lithium-ion batteries in the car industry, prices should come down like they have for other renewable energy products like solar panels and wind power turbines. For the grid on Rutland Island the thesis recommends to aim for the future and use a larger grid design with Lithium-ion batteries. The most deciding factor being that even the larger and more future oriented design had almost 30% lower price per kWh than the pre study calculations.