Supercritical CO2 Based Enhanced Geothermal System

Supercritical CO2 Based Enhanced Geothermal System (EGS) for Green Power Generation toward Achieving Geothermal Development 2025 Target

Energy usage worldwide is increasing. Since industrialization, energy consumption of mankind has increased more rapidly than ever. During the period, the fossil fuel was still main consumption to generate electricity, but it has been noted that fossil fuel as a non renewable energy has also decreased rapidly. 

Energy consumption in Indonesia always impacted to pollutant gasses emission such as CO2 and CO. According to Trends in Global CO2 Emission, 2016 report(PBL Netherlands Environmental Assessment Agency), Indonesia increased its share in total global CO2, emissions from 0.6% in 1990 to 1.2% in 2005 and 1.4% in 2015. Since 1990, the only decline in CO emissions has been recorded for 2008 (0.6%); in 2015, the increase was 4%, which was above the average over the last 10 years (3.4%).

            Recent national focus on the value of increasing our supply of indigenous, renewable energy undersources the need for reevaluating all alternatives, particularly those that are large and well-distributed nationally. One of this alternative is Geothermal Energy. Geothermal energy is renewable energy source that come from the heat of the earth's core. It has been well known that geothermal energy is a domestic energy resource that does not require carbon-intensive fuel to operate power plant. 

Geothermal power can displace the use of fossil fuels, thereby reducing our reliance on foreign fuel markets. Based on the data from Badan Geologi -- ESDM (Geological Agency-Energy and Mineral Resources) (December 2012), the Indonesian geothermal reserve is 16,484 Mega Watt (MW) from the potential of 28, 617 MW. Installed capacities of geothermal power plants is 1,341 MW or 4.7% from the available potential. Meanwhile, hydropower potential (large scale hydropower) reaches 75,670 MW with installed capacities of 5,705 MW or 7.5% from its potential. In the future, geothermal production capacity is targeted for 9500 MW in the year 2025. So throughout 2021 until 2025 the government still requires no less than US$ 9 billion for geothermal projects. However, the government can't provide funds from the state budget only, so that cooperation with the private sector is indispensable. There are a lot of challenges/problems in geothermal energy development. These are devided  in to three categories, which are (i) upstream side problems, (ii) downstream side problems, (iii) supporting side problems.

            One of the upstream side problems is resource or exploration risk. Every project has a risk from many aspect, either from investor or developer. We also need technology to increase result of exploration in once of exploration. One of the alternative solution is using Enhanced Geothermal System (EGS). An Enhanced Geothermal System (EGS) is a man-made reservoir, created where there is hot rock but insufficient or little natural permeability or fluid saturation. In an EGS, fluid is injected into the subsurface under carefully controlled conditions, which cause pre-existing fractures to re-open, creating permeability ((U.S. Department of Energy's (DOE) Geothermal Technologies Office (GTO)). By the data of CO2 emission and geothermal resource in Indonesia, it will be potential to combine both of these. EGS using Supercritical CO2 could be a small solution of environment problem with the electricity supply based on geothermal technology. During period, EGS in Indonesia is still dominated using injection of millions of gallons water. Water is sometimes mixed with small amounts of chemicals to help liquids create and disperse better small cracks in the underground, which eventually extend the life of geothermal power plants. But technical challenges and concerns over the cost and massive use of water are still a concern for countries with minimal water resources.

            CO2 capture and sequestration (CGS) in geological formation and geothermal energy both help in reducing the greenhouse gas emission and thereby help in controlling the climate change (Socolow & Pacala, 2006). The proposes Supercritical (SC) CO2-HDR concept uses supercritical CO2 as the heat transfer fluid and heat contained in the SSCO2 is then transferred to the working fluid on the surface to run a turbine. CO2 injection and associated reservoir pressurization would generate a production fluid stream that initially would be single-phase aqueous, then would transition to two-phase water-CO2 mixtures, and eventually would dry out to produce a single supercritical CO2 phase. 

This phase will contain some dissolved water that may be chemically active. The development of Supercritical CO2based Enhanced Geothermal System (EGS) is supplied by CO2emission from nearest industry with the field. According to thinkgeoenergy.com, exploration for geothermal resources does not need to take years to complete, it does not need to cost millions of dollars and produce speculative results. It was predicted also that this system will not spent much cost of money and years to reach geothermal target in 2025. Indonesia which has 1000-6000 m depth of geothermal source is very suitable for this development. Thus, CO2 will be automatically converted into supercritical CO2 in LHD-5 after 1000 meters. Most of research simulation proved that initial heat that produce is approximately 50% larger with CO2 than comparison to water. Of course, this result can be profitable to be developed in Indonesia field purposed in 2025 target by Government.

            Another challenges of geothermal development is in downstream side problems. The most difficult problem in the downstream side problems is selling price of geothermal electricity. This problem tries to solve by the government with the implementation of Feed in Tariff (FIT) since 2009. According to Hadi Setiawan (2016), minister MEMR Decree 22/2012 also set a fixed price that must be purchased by PLN, although the price is very attractive for the developer (around US$11.5 cent -- US$18.5 cent/kWh) but according to the writer it is not fair for PLN, since PLN cannot negotiate the price. However, in 2014, Minister MEMR issued a new rule about the selling price of geothermal electricity namely Minister MEMR Decree No. 17/2014, which revoke Minister MEMR Decree no. 22/2012. This rule set about the highest benchmark price of geothermal electricity, since this is only the benchmark then there is room for PLN to negotiate the price. The range of the price is US$ 11.8 cent --

US$29.6 cent/kWH depend on the COD time and area. This price is higher than the price set before. According to the writer, this rule is fair enough for both side, developer of geothermal energy and PLN, since the developers have a chance to get high selling price, while PLN has a chance to negotiate the price. This rule also allows the first developers to renegotiate the selling price of electricity to PLN so that this rule is also fair for the first developer.