Geothermal is the least costly, least polluting means of generating regional electrical power. Period. Too often geo is confused with fracking. Once a geo plant is established, there is no wastewater. Deep steam is used to drive a conventional turbine, a secondary process condenses the steam through a chain of "heat pumps" till it condenses and is re-flowed into the earth.
MIT 2006:
http://geothermal.inel.gov/publicationsfuture_of_geothermal_energy.pdf
http://geo-energy.org/events/Air%20Emissions%20Comparison%20and%20Externality%20Analysis_Publication.pdf
Externalities are those activities required to support a process. Mine/refine, store, transport, store, burn, maintain is a chain of forgotten impacts that cost money AND pollute the environment. Geo has none of these. All energy comes 24/7 from right beneath the plant. Wind and solar - for regional supplies are variable (sun/wind) and require constant, dispersed maintenance & support. Put WWS on the roof ... ok. Put 20,000 train engines with 350 foot props on Washington monuments, and you've got problems.
In Santa Rosa, CA solids are removed from conventional sewage & storm water processing and piped into the several-times boiling deep wells. It's less costly than hauling it to other types of post-treatment plants. And it's cleaned with heat rather than chemistry.
Investment is the issue. The fossil fuel-- or commodities -- industrial complex (CIC), a fuzzy understanding of the potential and necessary integration of alternatives, random political $bones thrown at CIC and "alternatives", and lack of serious, science-based policy research are the major impediments to responsible, CO2-free production of regional electricity over the next few decades.
