Down To Earth Geothermal Energy Facts



It's always good to know the facts about any topic or event and geothermal energy facts are no exception. In every field the internet is full of misinformation, some of it based on ignorance or some of it deliberate.

When it comes to home alternative energy, the main theme of our site, it is important to know and understand where geothermal energy fits in the renewable energy sector and what practical uses it can have for the community generally and individual homeowners in particular.

Important Geothermal Energy Facts

Geothermal energy is a fascinating field, perhaps because of its origins, deep within the earth and because many of us have seen visible evidence of its power through volcanic eruptions, geysers and hot springs.

However, such physical evidence is only part of the picture and we need to broaden our understanding if we are ever going to make use of the enormous potential of geothermal energy in our daily lives.

Geothermal facts - what it is and where it comes from

The word “geothermal” literally means “heat from the earth”.

How does that come about?

The earth is made up of an inner core which is a solid metal core, mostly iron and nickel and where temperatures reach up to 5000°C (9000°F). This is surrounded by an outer core which is liquid, again mainly iron and nickel and at similar high temperatures.

image of earth's core structure

Source: British Broadcasting Commission

The next layer is the mantle which is the largest segment of the earth's core, being some 2900 kilometers (1800 miles) thick. The composition of the mantle is a mixture of semi-molten and hard rocks.

The outer layer, where we all live, is called the crust and is relatively thin, varying from 0-50 kilometers (0-30 miles) thick.

The heat from the inner core travels by convection, up through the layers. Some of the material melts to form “magma” and some of this magma may even reach the surface, as happens when a volcano erupts, for example. Mostly, though the magma remains below the surface and heats up the surrounding rocks.

In effect we get a temperature gradient, sometimes called the “geothermal gradient”, where a tremendous amount of heat stored in the earth's various layers. Even in the crust the temperatures can reach 200-400°C ( 390 -750°F) where it joins the mantle.

Geothermal facts -how we get it

It's interesting to reflect on how people have used it in the past. For centuries people have used geothermal energy in the form of hot water for bathing, cooking and heating and medicinal purposes.

In modern times we drill down to find geothermal reservoirs and then we pipe the hot water to the surface and use it generate electricity.

There are three types of power plants that are used to generate electricity and these are described below with the aid of graphs sourced from the US Department of Energy.

  • A “dry steam” plant accesses a reservoir where there s steam but very little water. The steam is piped to the surface and used to drive a turbine to generate electricity.

    image of dry steam geothermal plant

  • A “flash” plant is one where there is lots of water and little steam. The water is at high temperature, often between 150°C – 370°C (300°F-700°F). It doesn't turn into steam because of the pressure at its location. However, once it is brought to the surface the change in pressure allows it to “flash” into steam and so produce electricity.
  • image of flash plant geothermal

  • A binary plant is where the water temperature in the geothermal reservoir is not high enough to have a flash point to generate steam. In this type of plant thewater is passed through a heat exchanger containing a liquid with a lower boiling point than water. The liquid then flashes to a vapor which is used to drive the turbines. The condensed liquid is then returned to the ground to be reheated. This is referred to as a closed loop system.
  • image of binary geothermal plant

  • Another type of operation involves finding areas of hot rock where there is no water reservoir but where water can be pumped down and mixed with the hot rock, heated and then returned to the surface for steam generation.

The following excellent video explains in detail how a geothermal power plant actually works.

Geothermal energy facts – where we find it.

The quantity of geothermal energy being used around the world is on the increase. The following table illustrates this very well. The data is taken from the International Geothermal Association and covers 24 countries.

year20052010
CAPACITY8,933MW10,715MW
GENERATED55,709GWh67,246GWh

This represents a 20% increase in the five year period. What is even more interesting is that there is a growing number of countries who are in the process of developing geothermal energy plants – in 2010 this stood at 70 countries.

This data highlights the growing interest in the potential for geothermal energy toservice the power and heating needs in a way that meets the highest standards for environmental pollution.

Geothermal energy facts – what we use it for

The most obvious use is for electricity generation that can then be fed into national grids. It's a great resource because of its low emissions of any harmful pollutants or greenhouse gases.

However, it's use for heating purposes is where it becomes really flexible as the following list of uses shows:

  • direct bathing in hot pools or spas containing geothermal water. The usage is mainly for relaxation for tired muscles but also for other medicinal purposes
  • heating of driveways, roads and footpaths in key areas to prevent icing
  • providing warmth for vegetable and seed crops in commercial and private nurseries
  • geothermal heat energy is used in aquaculture to stimulate growth and development.
  • space heating in buildings is a major use in many countries where the water is passed through heat exchangers and then distributed throughout the buildings
  • various industries use geothermal hot water for drying, for example, the timber industry.
  • geothermal heat pumps are a hugely under utilized resource for the family home. Once we go down a couple of meters the ground temperature is relatively stable and this factor is used to provide a dual purpose system – heating in the winter and cooling in the summer.
  • Finally to conclude our article on geothermal energy facts, we thought you would enjoy this little snippet, produced below. It's taken from the website of Iceland's tourist association:

    There are twenty heated public pools in the Reykjavík Capital area. I‘ll repeat that: twenty. Most of them are outdoors, very affordable (around two euros for an adult) and open from very early in the morning until late in the evening all year round. We use the pools a lot to keep healthy and fit, relax, meet the neighbors to catch up on the latest gossip and simply splash about. When the sun comes out so do the locals – on fair weather days the pools fill up with Icelanders of all ages, shapes and sizes. It‘s an essential part of the Reykjavik experience so you should definitely go - and bring the family. We usually do.

    Icelanders don‘t let a minor thing like geographic location impede on their lifestyle choices, so we‘ve also gone and made a heated bathing beach. Nauthólsvík is located on the south coast and has been certified as a Blue Flag beach (see chapters 10 and 11). The lagoon and nearby pool are heated with run-off water from the city’s geothermal heating system, and are connected to the coastal footpath.

    Now isn't that something? Twenty heated outdoor pools and a heated beach!

    Bring on geothermal energy.

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