Electricity for heating and storage: geothermal energy development

With the development of geothermal resources exploration in recent years, in addition to the above high-temperature geothermal fields formed at plate boundaries, many high-temperature geothermal fields have also been discovered in the interior of the plate, representative of which are the Republic of China Basin (> 200℃) in the northeast margin of the Tibetan Plateau, Landau in Germany (> 160℃) and Cooper Basin in Australia (> 200℃).

Utilization of geothermal power

Geothermal power generation is one of the most important ways of utilizing geothermal energy. At present, the mainstream geothermal power generation technologies include back-pressure power generation, condense-type power generation, flash evaporation power generation, dual-working medium power generation, full-flow power generation, and flash dual-working medium power generation, etc. Which power generation method is adopted mainly depends on the local geothermal resource endowment.

Geothermal power generation has a hundred years of history, in 1904, in Tuscany, Italy, the first use of geothermal power to drive small generators to generate electricity, generating power of 0.55kW, can provide five 100W electric lighting power. In 1913, the world's first geothermal power station was built in this geothermal field, with an installed capacity of 250kW. In 1958, New Zealand built the Waira Thermal Power plant, the first hot water expansion flash geothermal power station. In 1960, the first geothermal power plant in the United States with an installed capacity of 11MW was built in the Geysers geothermal field in California and has been running smoothly for 30 years.

According to the statistics of the International Renewable Energy Organization (IRNEA), by the end of 2021, the total installed capacity of geothermal power generation in the world was 15644MW, which was 3832MW more than that in 2015 (Figure 2), and the world's geothermal power generation is mainly medium and high temperature geothermal resources.

China's high-temperature geothermal resources are mainly distributed in Tibet. In 1977, China's first megawatt-level high-temperature geothermal power plant was successfully generated in Yangbajing, Xizang Province, and the installed capacity of Yangbajing geothermal power station reached 27.18MW at its peak. At the end of 2018, the first phase of 16MW construction of Xizang Yangyidi Thermal Power Station was completed, and the full load was connected to the grid at the end of February 2019. Up to now, the accumulated installed capacity of geothermal power generation in China is about 59.6MW, however, due to various reasons, less than 20MW is currently in actual operation.

Because the exploitable high temperature geothermal resources need to be further explored and the key technologies of dry hot rock power generation still need to be broken through, medium and low temperature geothermal power generation is expected to become an important direction of the future development of geothermal power generation, but medium and low temperature geothermal power generation should be combined with other geothermal utilization methods to improve energy utilization efficiency and economy.

Iceland uses 116℃ geothermal for power generation, with an installed capacity of 0.6MW, and the 76℃ tail water generated after power generation is used for heating, achieving the cascade utilization of geothermal resources. The Chenna geothermal power station built in Alaska in the United States uses geothermal water at 74 ° C to generate electricity, and the geothermal water flows into the evaporator of the organic Rankine cycle generator set, and the heat exchange with the organic working medium in the evaporator is reduced to 54 ° C and flows into the recharge well, and the unit can provide 250kW of electricity. Japan has built ORC power stations with an installed capacity of 100kW~5MW using medium and low temperature geothermal.

In the 1970s, China's first geothermal power station built in Fengshun County, Guangdong Province, the use of geothermal water temperature of 92 ° C, its unit 3 has been running for nearly 40 years, Jiangxi Yichun has created the use of 67 ° C geothermal water for power generation precedent.

Direct utilization of geothermal energy

The direct utilization of geothermal energy includes geothermal heating, geothermal cooling, geothermal drying, hot spring bathing and ground source heat pump. After long-term development, the direct utilization of geothermal resources has evolved from a small single-purpose utilization to a large-scale comprehensive utilization project. At present, more than 80 countries in the world directly use geothermal energy for heating (or cooling) buildings, or for industry and agriculture.

Among them, Iceland is a well-known example of the efficient development and utilization of geothermal energy. Although it is close to the Arctic Circle and has low temperatures all year round, more than 90 percent of households nationwide use geothermal heating due to its abundant geothermal resources. Reykjavik, the capital of Iceland, has a hundred years of geothermal heating history, and the urban area mainly uses geothermal heating, which has the reputation of "smoke-free city".