When we talk about renewable sources of energy we mainly refer to water, sunlight and wind, but there are others: some countries of the world exploit the high temperatures present inside the Earth through geothermal energy, which can be used efficiently for example where there are volcanic activities. This is the case of Iceland, which is located along the junction line between two tectonic plates, and even more so of Kenya, the country that most of all relies on geothermal energy to power homes, offices and companies (used to produce 38 percent of total electricity, more than any other country in the world).
The credit goes to the Rift Valley, the long valley known for the archaeological finds of ancient hominins, including those of the Australopitheca Lucy
The Rift Valley was formed by the separation of two African tectonic plates: the process began 30 million years ago and will still last tens of thousands of years. The moving away of the plates means that in this part of the planet the surface part of the earth's crust is thinner than elsewhere: for this there are numerous active and extinct volcanoes, there is seismic activity and it is also easier to obtain geothermal energy because the streams from the center of the Earth encounter fewer obstacles. In particular, it happens that the liquid water present in the subsoil comes into contact with very hot rocks, transforming into steam, which can escape to the surface even in a natural way, through geysers or thermal springs.
In other parts of the world you have to dig for miles and miles before you reach layers of rock hot enough to produce geothermal energy, while in the Kenyan Rift Valley you don't have to go too deep. The steam is used to drive turbines and produce electricity; once it has condensed and returned to liquid water, it is re-injected into the subsoil to heat up again.
The largest facility where this process takes place is the Olkaria Geothermal Power Plant, located in Hell's Gate National Park, about 120 kilometers northwest of Nairobi. In the next few years, Olkaria will become the largest geothermal power plant in the world, according to a BBC Future article.
The power plant consists of five large plants and a series of smaller structures connected to them, each built near a point where it is easy to obtain geothermal energy, the so-called geothermal wells.
The first attempts to exploit geothermal energy in the Olkaria area were made in the 1950s, but initially the technologies available to the Kenyan public electricity company, the Kenya Electricity Generating Company (KenGen), were not sophisticated enough to achieve good results. The first plant of the current power plant, Olkaria I, was built in 1981 and was not only the first geothermal power plant in Kenya, but also in the whole of Africa.
The power plant has since been expanded several times and a new expansion, Olkaria VI, is now under construction. According to estimates by the electricity company, it will bring the plant's maximum electrical power to 791 megawatts: to get an idea, it is the power needed to power a medium-sized western city, and, according to KenGen estimates, 27 percent of the electricity installed today in Kenya. When Olkaria VI is completed, Kenya will overtake Italy – currently seventh in the world – for geothermal energy production.
The Olkaria power plant produces energy from about 300 geothermal wells scattered around the Hell's Gate park, and the geologists and geophysicists who work for KenGen are always looking for places to build more: they look for what is called “geothermal grass”, areas in where the grass grows high, thanks to the high humidity of the soil. Once a point has been identified where it might be worth digging a new well, various analyzes are carried out: the excavation operations are very expensive and, given that some wells prove to be too weak to be used to produce electricity, we must proceed with caution.
In the Olkaria area, after building a new well, they wait two months to connect it to the power plant network. First, the flow of steam that can be produced is measured; then, if the flow is constant and sufficiently powerful, the steam is channeled to one of the main plants of the power plant (from Olkaria I to Olkaria V) or to one of its branches built for the purpose.
Since many wild animals, including giraffes, live in Hell's Gate park, the pipes through which the steam is passed are built several meters above the ground. The smallest wells are between 2 and 3 kilometers deep and produce around 5 megawatts each: that's enough power to power around 50,000 homes in Kenya.
However, wells continue to be dug, as a quarter of Kenya's population still does not have access to electricity. Blackouts are very common in the country which, among other things, damage industrial production and prevent students from studying in the evenings.
For Kenya, trying to increase electricity production by exploiting geothermal energy has at least two advantages.
The first is that it takes little time to build a new geothermal well to be connected to an existing plant such as those of Olkaria. The second is that smaller plants, those built close to a single well, take up little space – much less than what would be needed to produce the same amount of energy with wind or photovoltaic – and can be disassembled and moved into the if the well in question is no longer convenient to use.
There are drawbacks though.
Even if a single geothermal well takes up little space, the approximately 300 scattered around the Olkaria area, together with the pipes and roads that connect them, have profoundly changed the territory. For this reason, over the years KenGen has asked for the displacement of 1,181 Masai, an ethnic group that lives between Kenya and Tanzania, along with their homes, churches and schools. Another 500 Maasai families living around the Suswa crater, south of Olkaria, fear that with the expansion of the plant they will have to move themselves.
The Masai are mostly herders, but some work in the small tourism sector created around visits to craters, caves and areas inhabited by wild animals. In recent years, the work around these activities has been an important source of income for the Maasai, who now fear that the expansion of geothermal plants will harm tourism. The wells are in fact noisy and not very beautiful to see.
Another problem related to the expansion of geothermal plants is the pollution they produce.
As for carbon dioxide (CO2), that is the main gas that causes global warming, and other polluting gases such as nitrogen oxide, there are no major problems: we are talking about much lower quantities than those due to production. of energy from coal or natural gas thermoelectric power plants. A greater problem is instead that created by the water that is re-injected into the subsoil to keep the wells active: it can contain high concentrations of toxic elements, such as arsenic, lithium, mercury and sulfur, and if injection is done badly there is a risk that these substances pass to the aquifers from which the water of the aqueducts is taken.
Another disadvantage of exploiting geothermal energy is that digging wells can cause earthquakes. They are not frequent, but they can also be quite strong: in 2017 the activities of a geothermal power plant in South Korea caused a 5.5 magnitude earthquake.
