The primary disadvantages of geothermal energy are its inability to be used anywhere and its costly construction. While geothermal energy is practical in some areas, it's a poor choice in most locations.
Geothermal energy requires extensive drilling or being located on an area where the Earth's mantle is close to the surface. Another disadvantage many experts point out is the relatively low amount of energy that comes from the Earth's core compared to the amount of heat that radiates onto the planet through sunlight. Geothermal plants are fairly simple, but their construction costs and unpredictable nature makes them less popular than other energy sources.
Geothermal energy is not as well studied as other forms of generating energy, so the industry largely revolves around untested designs. If the industry becomes more popular, the cost of producing new plants will likely drop. However, no two potential geothermal locations are the same, and all plants will need to be adjusted to deal with local conditions. Solar energy is the most popular alternative method of generating power, and it is expected to receive more funding in the coming years. Geothermal energy research, on the other hand, receives considerably less interest from scientists and industry experts.