The Use of Geothermal Energy for the Decarbonisation of Heat in Greater Manchester
Lead Research Organisation:
University of Manchester
Department Name: Earth Atmospheric and Env Sciences
Abstract
The earth's climate is warming, and scientific evidence shows that this is due to greenhouse gases like carbon dioxide being emitted during the combustion of fossil fuels such as coal, oil, and natural gas. The more greenhouse gases that are added, the hotter the earth will become, and so reducing their emissions is something we should all care about.
We can reduce emissions by using renewable sources of energy which do not involve the burning of fossil fuels. Generation of electricity using wind or solar has been successful in the UK, although the use of fossil fuels for heat is still widespread as most houses and offices have a gas or oil boiler to provide heating and hot water. One possible low-carbon alternative is to use heat from geothermal energy. This involves harnessing the natural heat present within the earth. The term geothermal energy refers to any heat derived from the ground, from depths of a few metres to multiple kilometres beneath the Earth's surface.
The deeper you travel into the earth the hotter it becomes. In the first 10 meters, layers are warmed by the sun, below this the deeper layers of rock are heated by radiation from the earth's core. The rate of temperature increase with depth is known as the geothermal gradient. Below Manchester the geothermal gradient is around 28 degrees Celsius (degC) per kilometre. For example, if the surface temperature is 10degC then at 1km below Manchester the temperature of will be 38degC (10+28).
To extract this heat, you need water. Heat from the surrounding rock is transferred into water stored within these rocks at depth. If the geology is right this can then be then pumped to surface and used to warm buildings, greenhouses, or swimming pools. If water can flow naturally from the rock, it is described as a permeable aquifer. This permeability may be due to interconnected space (known as porosity) between the grains in the rock, you can think of it as being like a bath sponge. Not all rocks have this space between the grains, they have low or no porosity. Water may still be able to flow through these rocks, however, if they are broken or fractured. Think of hitting a pane of glass placed on the ground. Water would still not flow through the individual pieces but could find its way through the cracks. In the same way, fractured rocks can still be a permeable aquifer. A special group of aquifers occurs in the coal mines below Manchester. These aquifers are not natural, but the permeability is created by the tunnels dug out, by thousands of men, women and children undergoing great hardship to mine coal. What a fantastic legacy if we could then use all their hard work to heat our homes, not with coal, but with warm water extracted from these underground voids.
The main aim of this project is to make maps of these underground aquifers and mines so we can find the best places to drill and extract this geothermal energy. To do this we need to "look" into the earth using methods such as seismic reflection surveying. We send sound waves into the earth and measure the time taken for them to come back, a little like a bat does when hunting for food. This gives us a "picture" of different layers and their position in the earth. We then trace these in three dimensions to show how their depth varies under the whole of Manchester. If we know the depth, we can predict the temperature of the water using the geothermal gradient. In Greater Manchester many holes (called wells) have been drilled to explore for natural resources such as coal, water and natural gas. They give us a direct view of what types of rocks are below our feet, and whether they are able to produce heated water for geothermal energy. By mapping the depth and temperature of these aquifers we can design wells to extract the heat and move forwards in our decarbonisation of Greater Manchester.
We can reduce emissions by using renewable sources of energy which do not involve the burning of fossil fuels. Generation of electricity using wind or solar has been successful in the UK, although the use of fossil fuels for heat is still widespread as most houses and offices have a gas or oil boiler to provide heating and hot water. One possible low-carbon alternative is to use heat from geothermal energy. This involves harnessing the natural heat present within the earth. The term geothermal energy refers to any heat derived from the ground, from depths of a few metres to multiple kilometres beneath the Earth's surface.
The deeper you travel into the earth the hotter it becomes. In the first 10 meters, layers are warmed by the sun, below this the deeper layers of rock are heated by radiation from the earth's core. The rate of temperature increase with depth is known as the geothermal gradient. Below Manchester the geothermal gradient is around 28 degrees Celsius (degC) per kilometre. For example, if the surface temperature is 10degC then at 1km below Manchester the temperature of will be 38degC (10+28).
To extract this heat, you need water. Heat from the surrounding rock is transferred into water stored within these rocks at depth. If the geology is right this can then be then pumped to surface and used to warm buildings, greenhouses, or swimming pools. If water can flow naturally from the rock, it is described as a permeable aquifer. This permeability may be due to interconnected space (known as porosity) between the grains in the rock, you can think of it as being like a bath sponge. Not all rocks have this space between the grains, they have low or no porosity. Water may still be able to flow through these rocks, however, if they are broken or fractured. Think of hitting a pane of glass placed on the ground. Water would still not flow through the individual pieces but could find its way through the cracks. In the same way, fractured rocks can still be a permeable aquifer. A special group of aquifers occurs in the coal mines below Manchester. These aquifers are not natural, but the permeability is created by the tunnels dug out, by thousands of men, women and children undergoing great hardship to mine coal. What a fantastic legacy if we could then use all their hard work to heat our homes, not with coal, but with warm water extracted from these underground voids.
The main aim of this project is to make maps of these underground aquifers and mines so we can find the best places to drill and extract this geothermal energy. To do this we need to "look" into the earth using methods such as seismic reflection surveying. We send sound waves into the earth and measure the time taken for them to come back, a little like a bat does when hunting for food. This gives us a "picture" of different layers and their position in the earth. We then trace these in three dimensions to show how their depth varies under the whole of Manchester. If we know the depth, we can predict the temperature of the water using the geothermal gradient. In Greater Manchester many holes (called wells) have been drilled to explore for natural resources such as coal, water and natural gas. They give us a direct view of what types of rocks are below our feet, and whether they are able to produce heated water for geothermal energy. By mapping the depth and temperature of these aquifers we can design wells to extract the heat and move forwards in our decarbonisation of Greater Manchester.
