Geothermal Energy

How it works

Geothermal simply means 'Earth's heat'. The centre of the Earth is extremely hot, current estimates are 5,500C at the core just over six and a half thousand kilometres below the crust. This is about as hot as the surface of the sun.

It is not surprising therefore, that even the upper 3 metres of the Earth's surface stay at a nearly constant 10-16C throughout the year.

There are three main ways of tapping geothermal energy:

Direct use

Geothermal heat found near the surface of the Earth can be used directly for heating buildings (District Heating - the system that supplies communities with hot water or heating - being the most well known) and for a number of commercial and industrial uses.

Geothermal heat pumps

The relatively constant temperature of the top 15 metres of the Earth's surface (or ground water) can be used to heat or cool buildings indirectly. The pump uses a series of pipes to circulate fluid through the warm ground. In the winter when the ground is warmer than the buildings above, the liquid absorbs heat from the ground, which is then concentrated and transferred to the buildings. This can also be used to heat domestic water. In the summer, when the ground is cooler, the pump transfers heat from the buildings back into the ground.

Electricity production

There are three types of power plant that can convert geothermal energy to electricity, depending on the temperature of the geothermal fluid used. All three use a turbine that is driven by steam, which then drives a generator to produce electricity.

The past

Humans have used geothermal energy for thousands of years, using hot springs initially for cooking and building reservoirs around springs to create shrines and bathing complexes such as those built at Bath by the Romans.
The world's first District Heating system was built in 1892 in Idaho, USA and piped hot water from springs to town buildings. The first geothermal power plant was built in Ladarello in Italy in 1904.
The dramatic rise in oil prices in the late 1970s prompted the Department of Energy in the UK to look for alternative energy sources. A number of deep geothermal aquifers were identified.
One scheme in Southampton has been developed privately and was launched in 1986 and provides a heating and chilling system for a number of domestic and commercial consumers.

The advantages

By using geothermal energy, no fossil fuel burning is required. Geothermal power plants emit only excess steam and very few trace gases (1000-2000 times less carbon dioxide than fossil fuel power plants), they take up very little land compared to traditional fossil-fuel plants and advanced drilling techniques minimise the impact of drilling wells.
The electricity produced is also more 'available', as fossil-fuelled power plants produce electricity 65-75% of the time compared to 90% from geothermal power plants. While geothermal resources are not spread uniformly, geothermal heat pumps can be used nearly anywhere.

The costs

When a heat pump is used to provide domestic heating, the savings on electricity can outweigh the cost of installing and running the system. Where geothermal energy is used in agriculture (such as to heat greenhouses) heating costs can be cut by up to 80%. The cost of electricity from geothermal power plants is slowly becoming competitive with that from traditional power plants.

The future

The next step in using heat trapped inside the earth, is to drill deeper and circulate water through the hot dry rock found 3 - 5 miles under the surface, or to venture even deeper and try to utilise the hottest source of all - the molten and semi-molten magma that makes up the Earth's core.

(post by rosehanizar & noor sakinah)