Geothermal Power The specification states that you need to be able to: Explain about geothermal energy from volcanic sources around the world and potential 'hot' rock sources in the British Isles. Understand that geothermal energy is an example of a renewable energy resource.

Fossil fuels such as coal, oil and gas are essentially non-renewable resources. However, there are renewable resources that can be gained from the Earth, namely geothermal energy. There are three main varieties of geothermal energy: 1) In volcanic areas 2) Hot Rocks – such as granites in Cornwall 3) Hydrothermal fluids in sedimentary basins - Southampton.

This energy has the most potential and is the most plentiful resource today.  A major advantage is that geothermal power has virtually no environmental impact.   From where does the Earth’s heat come? Engineers estimate that 32 million quads of energy are available only 10 km. below the surface of the U. S. A. Most of this cannot be accessed but land is now being set aside for exploration of this resource.

The simplest manifestation of geothermal energy is just hot water or steam. For example the Geysers of California could produce enough electricity to supply half of San Francisco. Another example is in Western Canada above a subduction zone. Magma is generated and this heats up water that has infiltrated down through fractures.

The water may reach 200  C. This water either reaches the surface as geysers or is tapped into via boreholes. In this example 100, 000 Kg/h of steam at 8 atmospheres pressure turns 255 mega watt turbines to produce 110 mega watts of power. Once the steam has cooled and condensed the water is pumped back underground.

As long as the water is pumped back this form of energy is virtually renewable. Other examples occur in Italy, New Zealand, Mexico, Japan, U. S. S. R. and Iceland. Problems: In a potentially dangerous area. The steam can be corrosive and dangerous. Not common.

These are hot dry rock formations where there is no naturally occurring hot water brought to the surface. In particular such hot rocks are associated with granites that contain a higher proportion of radioactive elements than an average rock. They therefore produce more heat and have a steeper geothermal gradient 40  C/km. Therefore it gets hotter quicker with depth.

Water is circulated through at least 2 drill holes which are joined by man made fractures in the hot rock. Pumping cold water down into the hot granite makes the fractures. In the U. K. a hot rock scheme has been developed in Cornwall using the Cornish granites as the heat source.

In some deep sedimentary basins the water that the sedimentary rocks contain can be abundant enough and hot enough to form convection currents of hydrothermal fluids. These fluids can then be pumped up closer to the surface and tapped as steam.

A pilot scheme has been developed in Southampton where water at 70  C has been found at 1.6- km depth. Other potential areas are in East Yorkshire/Lincolnsh ire and the Midland Valley of Scotland.