Hot Dry Rock technology -HDR

The technology is based on the temperature difference in rocks below the earth’s surface to produce geothermal energy. The layer of hot dry rocks, which has no natural water aquifer, is artificially split, resulting in an increased rock surface. Water under great pressure is circulated in the drilled wells: it is pumped into one of the drills, after boiling water comes up as steam through the other well. Water thus transformed into steam drives conventional turbine generators to produce electricity. The process needs a substantial amount of water as about 20% is lost during the process.

 

The utilization of hot dry rocks was pioneered in the USA and Great Britain. The first HDR system was established in 1977 at Fenton Hill. A well 3000 m deep was drilled and successfully tested using 140°C water through a binary cycle power plant of 60 kWe. Research and development into HDR and the reduction of its costs might be the solution for the general and large-scale production of geothermal energy in the future.

Geothermal Heat Pumps – Earth Heat Exchanger Systems

A geothermal heat pump works on a similar principle to that of a refrigerator: it makes use of a working fluid to facilitate heat transfer.

The construction of a GHP is fairly simple. It has three major parts: a heat pump to move heat between the building and the fluid in the earth circuit, an earth circuit for transferring heat between the fluid and the earth, and a distribution subsystem for delivering heating or cooling to the building.

In winter the GHP extracts heat from the ground, which is warmer than the outside air, while in the summer it transfers heat to the ground, which is colder than the fluid in the earth circuit. Since the ground temperature remains more or less constant it enables the heat transfer to be realized.

With the help of a GHP the heat stored in the ground can be used for heating, cooling and producing hot water. Although the GHP consumes electricity, the power is only used to transfer thermal energy between the ground and the building. So most of the energy is free and only the transfer must be paid for. In this way a GHP might reduce costs by 50-55%. In addition to being energy and cost-efficient, other advantages of heat pumps include the following: it can be used almost everywhere, it conserves fossil fuel resources, provides clean heating and does not emit pollutants by burning fuels.

GHPs can be categorized as:

-        closed loop systems

-        open loop systems

The loops can be installed in three ways:

-        horizontally

-        vertically

-        in a pond