Abstract

For countries that strive to have near zero carbon dioxide emissions and have to rely on renewable energy sources the technology “Power to gas” is a promising strategy for balancing the electricity supply. Power to gas, hereinafter PtG, involves the conversion of electricity into a gaseous energy carrier, such as hydrogen or methane, using an electrolyser. PtG is a part of the broader “Power to X”, hereinafter PtX, which involves a conversion of electricity into some kind of energy carrier such as gas, chemicals, ammonia or liquid. The purpose of the conversion is often to store “excess” energy from renewable energy sources, usually wind power, in order to use it later. Another technique that has gotten more attention lately and that may be important in the future, with more fluctuating electricity prices due to a larger share of renewable energy in the energy systems, is the so called “Power to gas to power”. Power to gas to power, hereinafter PtGtP, is a technique where electrical energy with the help of an electrolyser is converted and stored in a gaseous energy carrier and later, when there is an electricity shortage, converted back into electrical energy through fuel cells.

The purpose of the study was therefore to investigate the potential for PtX, more specifically PtG and PtGtP in Sweden in terms of profitability. Ptg was investigated considering production of hydrogen and methane where the hydrogen was sold as fuel for vehicles and the methane was injected into the gas grid in Stockholm. The methane production also results in surplus heat which is injected to the district heating network. To investigate this a qualitative case study was carried out on two hypothetical facilities, one from the Swedish company Euromekanik that only produces hydrogen and one from the German company Electrochaea that produces both hydrogen and methane. Euromekanik’s facility was also used for the PtGtP application. The result is mainly based on the electricity prices of 2019. However, electricity prices for 2017 and 2018 as well as Danish electricity prices have also been examined. Simulations of the input- and output flows in the facilities have been performed in MATLAB and profitability calculations have been performed using the net present value method. A sensitivity analysis was conducted in which the values of the most important parameters were varied.

The results regarding Ptg in this study show that the idea that production should take place when the electricity prices are low can be rejected and that the conversion of hydrogen into methane decreases the profitability. Running the Ptg plant all hours of the year and producing hydrogen is therefore the most profitable design of the plant. This leads to a 15 MSEK result after 20 years. The result from the investigation of PtGtP shows that due to the low system efficiency the electricity sold back to the grid needs to have a price 8,83 times as high as the purchasing price to break even. With the pattern and prices on the Swedish electricity market today this technique will not be profitable. However, both these PtG and PtX have a higher value than solely the economic profitability in terms of energy storage and system balancing