Alternativ uppvärmning av reningsverket på Utö - En studie av energibesparingsmöjligheterna i syfte att minska uppvärmningskostnaderna
The projects objective is to find an alternative method of heating (the current method being via electric heating) the sewage treatment plant on the island Utö in Stockholm?s archipelago in order to reduce the energy consumption and ultimately the cost for heating the plant. The project is given by ?Skärgårdsstiftelsen? (The Archipelago Foundation) and is a part of the larger EU-project ?Green Islands?.A model for the plants total heating demand is established in order to get a good perception of how much money can be saved using alternative heating methods. The heating demand model gives an annual heating demand of approximately 32 500 kWh and a maximum heating power demand of around 24,7 kW. With an electricity price of 0,95 SEK/kWh, not including sales tax, the current total annual cost of heating is about 30 900 SEK per year.A number of different heating methods are analyzed in the rapport, mainly from an economical perspective, where a short payback time and a high net present value are ideal. The analysis gives three different systems that are regarded as the most appropriate for the plant, seen from both an economical and a practical perspective. The three systems have different initial investment costs depending on how much ?Skärgårdsstiftelsen? is prepared to pay for a new heating system. A less expensive system doesn?t give such a large net cash flow however and therefore a smaller net present value later in the systems life. These three systems are then analyzed closer in a sensitivity analysis in order to determine if the profitability is secure enough to motivate an investment into one of the new heating systems.The initial investment cost for the most expensive system is approximately 133 000 SEK with a payback time of around 5 to 7 years. The net present value is about 33 000 SEK after 10 years and about 79 000 SEK after 15 years. The initial investment cost for the least expensive system is approximately 61 000 SEK with a payback time of around 4 to 5 years. The net present value is about 43 000 SEK after 10 years and about 72 000 SEK after 15 years.The initial investment cost for the third system is approximately 90 000 SEK with a payback time of around 4,5 to 6 years. The net present value is about 43 000 SEK after 10 years and about 80 000 SEK after 15 years. For a lifetime of 15 years, this system is the best economical choice. However, after 15 years the net present value of the most expensive alternative becomes the largest.The sensitivity analysis indicates that the investments are very certainly profitable regardless of potential variations of the most important parameters. Only in the worst-case scenario when all these parameters are set to their worst possible values respectively, the investment turns unprofitable with a net present value below zero after 15 years. It should however be noted that in the best case scenario when all the parameters are set to their best possible values the net present value at 15 years is about 190 000 to 260 000 SEK.The investment would also be advantageous for the environment since the treatment plant?s electricity demand would decrease which ultimately leads to lower carbon dioxide emissions. Dependent on which investment is chosen the total carbon dioxide emissions are reduced by between 0,33 to 0,52 metric tons per year. This value does not however take into account the systems total lifecycle emissions.