The European Green Deal targets to increase significantly the share of renewable energy sources (RES) in the electricity system by 2030. However, the electricity market is a competed sector and the private investors develop RES capacity based on the profitability of the business plan. The RES profitability depends strongly on the long-term future price of the electricity market, which needs to be estimated. Although several studies focus on developing accurate short-time forecasting methods for the day-ahead market, these methods cannot be used for long-term forecasting due to uncertainty of the required inputs, e.g. weather condition and fuel cost, in a long-term future. In these circumstances, this paper developed a methodology to analyse and estimate the long-term day-ahead electricity market. This research used the data of Finnish electricity market to show the performance of the methodology. However, the same methodology could also be applied to other countries.