Electricity for heating and storage: geothermal energy development

The "14th Five-Year Plan" period is a key period for China to promote high-quality economic development and achieve the phased goal of "dual carbon". Under the environment of strengthening the control of atmospheric haze, actively responding to the trend of global warming, and proactively assuming the responsibility of greenhouse gas emission reduction, geothermal energy has become one of the important new energy sources that all over the country compete to develop and utilize.

Since 2010, the global utilization of geothermal energy has grown rapidly, and the installed capacity and annual utilization heat of geothermal direct utilization are about 108GWt and 283,580 GWH, respectively. China has long maintained the first place in the world in terms of geothermal direct utilization. Ground source heat pump systems account for about 72% and 60% of the installed capacity and utilized heat of global geothermal direct utilization, respectively.

From 1995 to 2020, heat pump systems show an exponential growth trend of about 16% per year, and this trend is expected to continue in the future. By 2020, the total installed capacity of global geothermal power generation will be 15.9GWe, with an annual generating capacity of 73,550 GWH. From 2010 to 2020, the average annual growth rate of geothermal power generation is about 4%.

On the basis of summarizing the current situation of global geothermal energy development and utilization, this paper reviews the development trend and new technology research and development direction of global geothermal energy development and utilization from the aspects of geothermal resource distribution, geothermal power generation utilization, geothermal direct utilization and geothermal energy storage.

At the same time of summarizing the global experience in geothermal development and utilization, aiming at the existing problems and technical level of geothermal energy development and utilization in China, this paper puts forward policy suggestions and future development directions that are conducive to promoting and promoting the development and utilization of geothermal energy in China.

Geothermal resource distribution

The total amount of global geothermal resources is abundant, but the spatial distribution is extremely unbalanced. High-temperature geothermal resources are mainly distributed in discrete plate boundaries and converging plate boundaries. The distribution of high-temperature geothermal resources is generally controlled by the tectonic-thermal background of the Earth, and their spatial distribution is correlated with global plate boundaries, seismic zones and volcanic zones. The most prominent features are high heat flow, strong high-temperature hydrothermal activities, and frequent active volcanoes and seismic activities.

The four global high-temperature geotropics are: the Pacific Rim, the Atlantic Mid-Ridge, the East African Rift, and the Mediterranean-Himalayan belt (Figure 1); The medium-low temperature geothermal resources are widely distributed within the plate, mainly in orogenic belts, intermontane basins and mesocenozoic sedimentary basins.

The circum-Pacific geotropics are the most widely distributed geotropics in the world, spreading along the subduction/collision boundary between the Pacific plate, the American plate and the Eurasian plate. The most notable features are high heat flow, young orogeny and frequent active volcanism. According to the geographical distribution, it is further divided into three geothermal subzones: East Pacific mid-ridge, West Pacific island arc and Southeast Pacific suture line.

The reservoir temperature is generally 250-300 ℃, and the representative geothermal fields are Gaithers in the United States (288℃), Cerro Prieto in Mexico (388℃), Datun in Taiwan, China (293℃), Matsukawa in Japan (250℃), and Bachman in the Philippines (300℃). 

The Mediterran-Himalayan geotropics, composed of the Tethys suture zone, are located at the junction of the collision of the Eurasian plate with the African plate and the Indian plate, and are characterized by crustal thickening, young orogeny, modern volcanism, magma intrusion, and high heat flow. The heat storage temperature is generally 150~300 ° C, and the representative geothermal fields are Yangbajing (262 ° C), Yangyi (192 ° C), Tengchong (250 ° C), Kangding (180 ° C), Radriro (245 ° C) in Italy and Kzerdeir (200 ° C) in Turkey.

Most of the mid-Atlantic ridge geotropics lie on the ocean floor, with the surface of the ocean spreading north-south. The heat storage temperature is generally 200~300 ° C, and the representative geothermal fields are Henyr, Iceland (230 ° C), Reykjavik (286 ° C), Namafyar (280 ° C) and so on.

The East African Rift tropical zone is mainly located within the African plate and spreads along the continental rift system, with the Red Sea-Gulf of Aden mid-ocean ridge spreading zone at its northern end. It is characterized by high heat flow, intense modern volcanism and extensive faulting activity. The heat storage temperature is mostly higher than 200℃, and the representative geothermal fields are Dallol in Ethiopia (> 200℃) and Olkaria in Kenya (287℃).