The City of Helsinki relies strongly on the use of fossil fuels as its main energy source. Coal power with high level of emissions covers one third of the city's energy production. To mitigate the effects of climate change, the city should stop using coal and replace it with the use of renewable energy. The goal of this thesis is to find a way for Helsinki to replace coal by 2030 with energy efficiency improvements and distributed renewable energy. Thesis was an assignment from WWF Finland and it is a part of urban energy campaign called Seize your Power. First of all, the local circumstances have to be understood. This gives a basis to Geothermal Scenario that is formed to replace coal. First step of the Scenario is to reduce the demand of coal power by energy efficiency improvements in buildings. Next, a set of locally functional renewable energy sources is formed based on decreased demand. Main energy source of the Scenario is geothermal energy but also biomass,solar and wind power are utilized. The Geothermal Scenario is then evaluated with costbenefit analysis. Results of Cost-Benefit Analysis show that the net present value (NPV) is negative in short, medium, and long term. The values vary between -200 million and circa -3 billion euros. In the sensitivity analysis, the effects of the changes in prices of emission permit, coal, and bio-SNG as well as discount rate were estimated. The length of time horizon had a huge impact on the results. Non-market values were not included in the analysis.