Geothermal energy and applications

Geothermal energy is heat energy stored inside the earth. It comes from the heat left from the earth's formation and from the decay of radioactive elements in the crust. The temperature rises by about 25–30 °C per km of depth, and in volcanic or tectonic areas hot water and steam are found near the surface (hot springs, geysers). It is renewable on human timescales and available all the time (24 hours).

In Nepal there are many hot springs (for example Tatopani in Myagdi, Sindhupalchowk and Rasuwa), but the resource has been used mainly for bathing and tourism. The geothermal potential is estimated at about 30 MW (not yet exploited), and feasibility studies have been carried out at some sites.

Applications

1. Electricity generation

• Dry steam, flash steam and binary-cycle power plants. Large producers: USA, Indonesia, Philippines, Iceland.

2. Direct use of heat

• Space heating and district heating (Iceland)
• Greenhouse heating and agriculture; crop and fruit drying
• Fish farming (aquaculture)
• Industrial process heat, drying of timber, food processing
• Bathing, spas and tourism (balneology)

3. Geothermal heat pumps

• Use the almost constant ground temperature (10–15 °C) at 2–100 m depth for heating in winter and cooling in summer in buildings.

4. Others: snow melting, and extraction of minerals (lithium, silica) from brines.