One of the most preferred sources of renewable energy right now for electricity is probably geothermal energy. This is especially true for areas in which there is a lot of volcanic activity. As much as it is popular because of it's continued renew-ability and that there is a lot of it, sometimes the way that it is extracted for the power does come with some disadvantages.
One of the big disadvantages for this kind of power if the location of the power plants. You just can't put one of these power plants just any place that you fee like putting one. These sites need to be where there is some sort of volcanic activity in the area. So, the risk then is having a power plant that is in an area that has high risk of quakes and eruptions. This will pose risk to those that work on the site as well. This also means if something goes wrong due to the activity that power could be lost for thousands of people as well and for quite some time on top of that.
Another disadvantage is the fact that some plants can actually be a serious risk to the environment with the pollution that some of these plants produce when they are converting the power into electricity. Although the source they use is heat, we need to understand that the heat or steam that comes from the earth will often have sulfur dioxide and carbon coming from it. These two things are major contributors to the increase in the so called greenhouse effect. Geothermal energy does release somewhat less emissions as nuclear and coal plants do but since there are very little controls over geothermal power, some of these plants might let off large amounts of sulfur and this could be dangerous to anyone that might live near by.
The top disadvantage to geothermal power would be the cost of building one of these plants. According to a financial study of recent, it has been reported that a geothermal plant and their sites are one of the most expensive types of plants to produce energy right now. Scientist need to be involved, they need to test the area and see where it would be suitable to place a plant and this alone can take years and then after they find the right spot for drilling they need to figure out if the area is going to give enough heat to even power the plant. Then after that is done of course there is the cost of the construction and all of the start up costs. Usually a new geothermal plant costs billions of dollars to build.
As much as most think that geothermal is renewable it's important to note that another drawback is the fact that any one area will only put off enough resources to last 10 years after that the plant could then run out and be unable to continue producing electricity needed to power the area in which depends upon it.