Geothermal energy is heat from inside the earth. The middle of the earth has a temperature at around 7000 degrees celsius, which is reduced towards the crust. In average the temperature is reduced by 25-30 degrees for each kilometer outwards, but could be substantially higher. The energy is utilized by drilling a hole down through the crust and pump a media that is absorbing the heat and delivering this to a heat cycle. The heat is either utilized for the production of electricity, district heating or by heat exchange to heatpumps.

Technology
In order to utilize the heat for power production it is necessary to drill deep wells of 3-5 kilometres where the temperature is around 225-300 degrees celsius, depending on local conditions.The most attractive geothermal resource is wells that produces dry steam. The steam are abel to run a standard turbine connected to a generator. Other pressure and temperature conditions in the well requires pre-treatment of the steam before directing it into a turbine.

Scientists have a goal to drill all the way down to 10 000 metres or more to fully exploit the geothermal heat. If they get this far, they are able to reach the so called super critical water that has a temperature above 375 degrees celsius and a pressure at 220 bar. At these conditions, the harvesting of energy will increase 10-fold, making geothermal energy compete with energy created in a nuclear power plant, but with a very important difference: the geothermal energy is clean and renewable.

The oil companies of today are drilling down to depths of 5000 metres and 170 degrees, but the challenges related to the drilling are increasing exponentially at temperatures above this level. The steel becomes brittle, the plastic is melting and the eletronic instruments break down. These challenges have to be solved in order to utilize deep geothermal heat.

Utilization
The countries with the highest power production from geothermal energy is USA (2 020 MW), the Phillipines (1 931 MW) and Mexico (953 MW).

Utilization of high temperature sources for heating and process heat is the oldest form of geothermal energy utilization. The total installed capasity worldwide is 12 103 MW(th), and the total production was 49 TWh in 2005. Swimming facilities, district heating, fisheries and industry is the largest utilizators.

The utilization of geothermal energy differs around the globe, and is dependent on the local conditions. Iceland is covering 87 percent of their building heat demand by geothermal energy.

Norway is only utilizing geothermal energy as ground heat in combination with heat pumps, but the field is experiencing a growing interest. In 2005 Europes largest thermal energy storage was completed in Oslo, Norway, consisting of 180 wells down to 200 metres. New knowledge about energy wells has lead to an increased installation rate of buildning heat pumps in Norway, as these systems are experiencing high efficiency when they deliver both heating and cooling.

Research at NTNU, SINTEF and IFE
Because of its long traditions within oil drilling in the North Sea, Norway is in a very special position within development of geothermal energy.

NTNU is cooporating with Rock Energy with a pilot system for the collection of heat from 5.5 kilometres depth to the district heating system in Norway. It is advantegous to build this system in Oslo as the thermal gradient is much higher there than other parts of Norway. NTNU is researching around the thermal aspects of the system.

SINTEF is working on the development of drilling equipment from the oil industry, to make it become suitable for deep geothermal energy drilling. The research is in its startup phase and a lot of investment is being made in order to develop a network within Norway.

More information
Norwegian Center for Geothermal Energy Research
U.S. department of Energy, Geothermal Technologies Program

Contacts
Professor Bjørge Brattli , 73 59 48 21 (NTNU)
Researcher Inge Røinaas Gran, 73 59 39 65 (SINTEF Energy)
Researcher Are Lund, 98 24 34 85 (SINTEF Materials and Chemistryi)
PhD-student Henrik Holmberg, 73 59 26 71 (NTNU)