Geothermal energy; lets talk about plugging into the earth!

Have you ever wondered what we can do without energy? Like, is there? I don’t think so. Energy can mean anything ranging from the result of eating food or the burning of fuels. Energy sources are abundant all over the earth and even outside the earth (yes, the sun is outside the earth lol). Over time, man has been able to convert the various sources of energy available on earth into useful power, majorly in the form of electricity. As it is, once you can generate electricity, a lot of things can be done!

Energy sources such as fossil fuels are gradually losing popularity based on the negative effects of their use and maybe the fact that the supply of these fuels is gradually decreasing. I wonder what would happen when all oil wells in the world dry up. Well, that’s not what I am up to today and I guess its too early to digress.

As fossil fuel usage for power generation are gradually approaching the end of the line, we humans (as innovative and genius as we can be) have come up with other sources of energy that can be used for power generation and do not pose the kind of threats that fossil fuels do. Well, you guessed right, I am talking about the renewable sources of energy.

The likes of solar and wind energy have really taken a worldwide stand as the new and sustainably efficient ways of harnessing energy from natural sources and have been successfully used to generate power. Here in Nigeria, solar energy is somewhat the best alternative to power generation as individuals are opting for the option of powering their homes with solar energy, all thanks to the epileptic nature of power supply from the national grid.

A few days ago, a question popped in my head – are solar and wind the only sources of renewable energy? I was quick to answer – no. But I was sure I knew very little about the other sources. Let me say, I have been blinded by solar energy that I didn’t see the others (that was on a lighter note). I quickly took my phone and headed straight to my window, what is with the window you might ask, actually that’s the only spot I can get a good internet connection that will not frustrate me to the point where I might be urged to break my phone lol. So I checked online and I saw the other sources; apart from solar hydro, bio energy and wind, we have tidal and geothermal sources. Out of which the geothermal source of energy piqued my interest (there are no geothermal plants here in Nigeria that I know of and I just couldn’t but ask why).

Today, I would be talking exclusively on geothermal energy and the ways it can be used for power generation and other applications. If you have not taken a critical look at this form of renewable energy, I expect you to be amazed to an extent at the awesomeness of this source of renewable energy – geothermal energy.

_{A GEOTHERMAL POWER PLANT IMAGE SOURCE: WIKIPEDIA public domain}

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I cannot remember when last I did geography but I will do it today!

High school geography taught me that the earth is made of several layers which can be classed into four major layers namely; the crust which is the outer layer, the mantle, the (liquid) outer core and right in the middle is the inner core just like the seed in the middle of a fruit. But it’s not as gentle as a seed, it’s as hot as the sun. So, I think I can say, we have the sun in the earth (whatever that means!). Alright, enough of the jokes.

The earth’s core is about 5500^oC which is just about the same as the temperature of the sun._source The volcanoes are a proof that the innermost part of the earth is as hot as that. This heat is as a result of radioactive decay of materials over time. I wonder how those things got there in the first place but that’s none of my business. With the core being the hottest layer of the earth, it is safe to say that explains why it gets hotter as one goes deeper underground.

Somehow, the heat within the earth finds its way up to the surface in form of molten rock called lava in volcanoes. Or sometimes, water from the surface goes all the way down and gets heated to the surface such as in hot springs, geysers, fumaroles and mud pots (oh, you thought its some spirit that forgot his water heater in the water? Im sorry to disappoint). These naturally occurring phenomena are present in various locations all over the world especially in places with a record of volcanic activity.

By virtue of this I guess it is safe to say that right under our feet is a heat reservoir that doesn’t seem to get used up and at some points on earth, the heat gets in contact with underground water and heats it up sometimes to the point where the water changes to steam at very high pressure. These heat reserves can be tapped into and the heat energy can be used to do useful work such as power generation or space heating or even cooling.

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Geo thermal Energy

The word geothermal was coined from two Greek words; Geo which means earth and Thermos which obviously means heat (or hot). Joining these two words together, we say that geothermal energy is the energy gotten form the heat within the earth.

As said earlier, this heat originates from the core and is self-replenishing thus, can be considered as a renewable source of energy. Places where there are visible proof of the earth’s heat coming to the surface are sometimes referred to as geothermal “hot spots” (no, this has nothing to do with the internet) but that doesn’t mean that other places without volcanic activities or visible heating of water bodies do not have geothermal heat underground. As a matter of fact, the heat of the earth is accessible everywhere on earth. Getting to it is only a function of how deep you go and the makeup of the earth layers at that particular point on the earth.

If you are located at the tectonic plate boundaries (those are the things that move underground and sometimes cause an earthquake) then you are sure to have a good supply of geothermal heat. If you aren’t, don’t be discouraged just yet. Geothermal heat can still be accessed in good (mild) amounts at about 10 to a thousand feet below the ground surface. Reason being that at this depth, the temperature is relatively constant and just sufficient for some applications.

At this depth, with the use of a geothermal heat pump system, geothermal heat can be harnessed and used for indoor heating (and cooling). The geothermal heat pump simply circulates a fluid through piping installed in the space to be heated and the earth. The system is equipped with a heat exchanger which as a result of heat difference, transfers heat to the space to be heated. Geothermal heating systems come in different modes and orientation to fit the application (and space) it is intended for.

The warm (or hot) springs are also useful as the water can be used for indoor cooling or bathing and also in spas (who doesn’t like a warm bath in a natural jakuzzi?), in agriculture for green houses amongst other applications. As a matter of fact, people say the water from warm (or hot) springs have medicinal benefits.

Using geothermal heat for applications such as mentioned above is not a new thing, as a matter of fact, the geothermal heat have been used directly or indirectly for indoor heating as far back as 1892. But as time went by, the possibilities of using geothermal heat to generate electricity was discovered and as I speak (or type), there are numerous geothermal plants all over the world that seamlessly deliver electric power. Let’s take a peep at what happens in there.

_{IMAGE SOURCE WIKIMEDIA COMMONS under the Creative Commons Attribution-Share Alike 4.0 International license.}

Geothermal Energy for Power Generation

Power generation sector cannot fizzle out, it can only improve. The craze for using renewable sources of energy for power generation is all over and countries have seen the numerous economic and environmental advantages of using renewable energy over fossil fuels for power generation.

Let’s take a look at how a steam power plant generates electricity shall we?

The plant uses boilers (which burns some sort of fuel to generate heat) to heat up water until it turns to steam. It is this steam (or steem) that drives the turbines which in turn turns the shaft connected to the generator to produce electricity. You can check this post to see what I mean.

Well, using fossil fuels to generate the heat needed for this method of power generation doesn’t seem to be an environmental friendly approach (is it?) but what if I told you the steam can be gotten without burning anything? Well I expect you to know how by now. That is what the geothermal power plants are based on – using the heat from the earth to generate steem (that was intentional) or even to take steem (yes, once again) from the earth and use it to generate electricity.

Can I say geothermal power plants are steam (lol, not this time) plants without boilers? Maybe yes! Basically the geothermal plants make use of deep “wells” dug into the earth from where steam is captured (directly from the source) and used to drive the generators and produce electricity. The steem is simply collected to the plant and used to drive the turbines for the electricity generators and in the end, the cooled water is returned back to the earth thereby replenishing the ground water reserve and facilitating its stand as a form of renewable energy.

Using geothermal energy for power generation requires high temperature and thus the need for the wells to go deep into the earth and also the need for the plant itself being close to the geothermal site to avoid losses. There are three methods by which geothermal energy is harnessed to generate electric power, have a look.

• Dry steam Geothermal plants
  As I said earlier, steam is needed to drive the turbines and at some points, it is readily available even in the superheated form. These type of geothermal plants use steam directly from the earth to drive the turbines and then condense the vapor at the other end to return it to the earth. This requires two wells – one from which the steam is extracted and the other to return the condensed water thereby completing the cycle.

These types of power plants have been around for a long time and are the first types of geothermal plants with the very first being the dry steam plant set up at Lardrello, Italy in 1904 ^source(I wasn’t born then).

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• Flash steam Geothermal plants
  In cases where steam is not available but there is water at high temperatures of about 182^o the hot water is used to produce another type of steam known as ”flash steam” which is used to drive the turbines.
  Flash steam is created by feeding the hot water into a tank of lower pressure thereby causing the water to vaporize or ”flash” into steam which is what is needed to turn the turbines.

The subsequent process of returning the cooled water via another well also follows just like in the dry steam method. The flash steam method finds application more than the dry steam methods as majority of the geothermal plants of today make use of this method to generate electricity.

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• Binary Cycle Geothermal plants
  On the other hand, a binary geothermal plant does not directly use steam or hot water to turn the turbines, rather, it uses another fluid of a lower boiling point is used (usually pentane or butane). The other fluid (also called the binary fluid or the exchanger fluid) is heated in a heat exchanger by the hot water from the geothermal reservoir. As a result of its lower boiling point, this fluid vaporizes and the steam is used to turn the turbines.The cooler water is then returned to the earth for recirculation as required.

An advantage of the binary cycle method is that it can utilze geothermal water of lower temperatures than the dry or flash methods and thus makes it possible to harvest geothermal energy from regions of lower geothermal temperatures.

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The choice of which ever method solely depends on the type of geothermal reservoir present in the location. For instance, if the well produces steam, the dry steam method can be employed. If it is water at very high temperatures, the flash steam method is possible and for water at lower temperatures, the binary system is fit.

The geothermal energy plants are a way to unlock the hidden energy locked in the depths of the earth and it is a beautiful feeling to know that the technology behind this is still evolving and a system such as the Enhanced Geothermal System (EGS) is a promising one as it presents the possibilities of having geothermal power at regions where there is little or no water to be heated in the earth due to lack of cracks in the underground water system to allow water flow through.

The geothermal method of generating electricity does not come as a totally perfect package thus, just like any other system, it has its advantages as well as disadvantages and they are as follows;

• ADVANTAGES

• It is a relatively environmental friendly method

• It is efficient for heating (and cooling) and power generation

• No fuel is burnt thus, pollution is not experienced

• It is available at all times during the day and night

• DISADVANTAGES

• It is not 100% clean as there are some non environmental friendly emmissions

• Location is an important factor as some regions do not posses a good amount of geothermal resources that are suitable for exploitation

• Start up cost is relatively high

• Reserves can reduce if not properly managed

• There is possibility of earthquakes occurring in regions where power plants are situated

CONCLUSION
If solar energy experts use the slogan – “plugging into the sun”, then we can also call geothermal energy as “plugging into the earth”. It is so amazing to know that energy is readily available around us and all we need is to tap or simply “plug” into the source.

The geothermal method of power generation is another renewable source that is relatively environmentally safe and totally defeats the fossil fuels. Coupled with its other minor applications, geothermal energy is really a good way to receive the energy gifts that Nature gives us. Compared to solar or wind energy, it has the advantage of being available 24/7 unlike solar which is unavailable at night or wind which fluctuates.

In my country (Nigeria) where there is still the problem of steady power supply, a look into this method of power generation will not be a bad one as I am very sure of one proof of geothermal activity in the country, the Ikogosi Warm Springs.

And there you have it guys, one of the various ways by which Nature would never cease to amaze us and ana ever available source of energy waiting for the taking.

REFERENCES
Geothermal energy
Geothermal energy
How geothermal energy works
Geothermal energy
Geothermal heat pumps
What is geothermal energy
Geothermal energy
Geo energy

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