Here are the hard facts: coal is the primary workhorse of electricity, and new coal plants have an average cost of $2500 per kW. Using the costs of a new coal plant as our benchmark, the cheapest alternative energy to implement is natural gas. In comparison, coal produces an average of 2.3 times more C02 than natural gas, and new natural gas plants cost 30% less than new coal plants.

Natural gas appears to be the best solution moving forward—at least, in terms of cost—but natural gas still creates carbon waste. Also, due to a glut of building natural gas plants in the U.S., current facilities are running at less than 40% efficiency. That makes any future investments unlikely due to surplus capacity.

Then there is the remote possibility of unproven clean coal plants at 1.3 times the cost of coal…or the possibility of nuclear plants at double the cost. Nuclear may play a role eventually, but it is expensive and a plant takes more than ten years to construct. And lest we forget, nuclear power plants have a short shelf life of only 40 years (per the U.S. Atomic Energy Act) with a potential extension of 20 years. There’s also the issue of having no safe haven for the stockpiling or storage of nuclear waste by-products.

Not many renewable alternatives can take over for coal plants, either. Hydroelectric plants (which use water and gravity) are no longer a viable option: they require massive construction efforts and sizeable water flows to function. In the U.S., there are few—if any—locations left. Decreasing rainfalls and more droughts have had an adverse affect on hydro efficiencies; in the U.S., this resource has been tapped to capacity.

Other clean energy technologies might be viable, but they’re currently too expensive to implement on a large scale. Wind energy sounds very reasonable at only 0.9 the cost of coal, but when we factor in wind-efficiency vacillations of 25%, the realized cost becomes a staggering 3.4 times that of coal. Solar fares worse: thin film costs twice what coal does (at that level, it’s comparable to nuclear power), but when overcast days and night efficiency losses are factored in, the realized cost becomes 8.7 times that of coal. Solar thermal may be cheaper than thin films at a rate of 1.7, but with an average efficiency of only 15%, it becomes the most costly at 11.3 times the cost of coal. Geothermal has the best cost chance (a factor of 1.5 times); however, after 30 years of use, it is still plagued with the same problems: drilling issues, difficulties in finding suitable locations to utilize its power, and its hazardous potential to cause earthquakes.