Efficiency is an overused/misused concept. It is just a measure of the closeness to maximum energy exchange of a process. So when you burn coal, the best modern engineering can extract from this “burn” is ~33% (given conventional systems) because to get “electricity” (the energy we want) from the coal we have to create steam which then spins a turbine (and in each step there are losses in conversion). Geothermal systems are actually less efficient in converting heat to electricity (see article, ref 1; though much more efficient in extracting heat, as in, geothermal heat pumps which are much better than conventional gas-powered furnaces). And solar arrays are in the same ball park as geothermal systems with efficiencies of ~15-20%.
However, the big difference between the coal and the others is the fact that while the sun provides us light for free and the Earth provides us heat for free (24/7 as well), the coal comes by way of extraction from distant areas. (Solar photovoltaic panels and geothermal components require the extraction of materials from distant lands as well, but once this initial extraction is done and manufacturing is completed, they operate for 25+ years.) Also, sun and Earth heat will continue into the distant future while coal is limited in quantity (as it takes too long to replenish). Additionally, when one burns coal, waste products are produced, many which are quite toxic to humans and life, most notably, mercury, PAHs and sulfur dioxide (ref 2).
Thus, while efficiencies of renewable energy forms may be less efficient than fossil fuel forms, the key benefits derived from RE’s are:
(1) the pollution created in using them (over a 25-year cycle) is so much less;
(2) the RE energy sources are on-site (or close by) at the point of use;
(3) the RE sources are plentiful and renewable.
Additionally, and importantly, given the nature of geopolitics right now, RE resources also create more jobs (ref 3) and can be more decentralized (which allows people to have more control over their operation and production; I say “can” because this requires forethought and intentionality regarding democratic input and collective ownership, something still missing from most RE installations).
Given all of these benefits (here is the Union of Concerned Scientists’ take on these, ref 4), investors are finally taking notice in a big way and, as expressed best by a recent (April 2016) Bloomberg article, “Wind and Solar are Crushing Fossil Fuels” (ref 5). So, don’t be squeamish at all advocating vehemently for RE creation/expansion in your neighborhood/community. Everything is now on the side of RE (economics, environmental concerns, and social/health factors). The time is right, to “flip the switch.”