Organic Rankine Cycle (ORC) technology is modern and highly energy efficient. It allows electric energy production from renewable sources like geothermal wells, biomass, Sun and waste heat energy. Organic Rankine Cycle technology is based on Rankine cycle with high-molecular-mass organic fluid. Key is in organic fluid which evaporates on significantly lower temperature and pressure than water in classic Rankine cycle. This system is described in first part of study with accent on biomass and geothermal ORC systems.
Second part of study is based on two Croatian wells and finding solutions how to apply ORC technology for electric energy production. However both wells are characterized by low geothermal water temperature (about 60 °C) and small heat power. ORC technology demands at least 100 °C of geothermal water temperature.
This study offers two solutions. First one is based on drilling the well hole deeper, this procedure provides higher geothermal water temperature and more heat power. Other solution is based on second energy source. More heat power and higher temperature of organic fluid can be achieved by including biomass boiler in system. Furthermore, heat pump is also required. It lifts heat energy from geothermal well on higher temperature level. With biomass boiler and heat pump in system, deeper drilling of well is not required.
Investment costs of proposed solutions are high. Plant with overall thermal power 1,000 kW and electric power about 200 kW cost approximately € 3,180,000.00. One third of investment costs is for reinject drillhole and completion of production drillhole, that is the main reason for so high investment costs. Many parts of plant have to be custom made and there is a lot of special work so it is very difficult to estimate costs precisely.