There are a lot of misconceptions present in this thread, as a mechanical engineer I have taken many classes on nuclear, solar, wind, and fossil fuel energy. First off, solar energy will probably never be our only source of energy due to the intermittance of sunshine, however, there is certainly enough solar radiation impacting our earth that we could get much of our energy from that. That being said, solar radiation should probably be used for other things like space heating where it is much more effective than converting it to electricity through photovoltaics. A combination of solar and wind power will likely make up some portion of our future renewable energy as all rivers that can be dammed have been, with the backbone being a large nuclear system.
The fact is you can't make coal 'clean', that is propaganda (The united states is the middle east of coal). Yes, you can do things like cap emmissions from the plant, pump them into the ground, add scrubbers to the exit stacks, etc. But all of this still leads to a lot of pollution. It's kindve like going to mcdonalds ordering a supersized big mac meal and then getting a diet coke, yeah your shaving a few calories but you're still going to get fat.
The power plant with the most minimal impact on the environement is nuclear, plain and simple, the output of a nuclear plant similarily sized to that of a coal plant is tremendous. The only pollutant from a nuclear power plant is warm water. As far as radioactive material is concerned it is something like since the nuclear age began we haven't even created enough nuclear waste to fill up a football stadium, for all intensive purposes burying it deep in the mountains in the southwest deserts of the US is a fine solution. Meltdowns at this point are a non issue because the nuclear plants that are currently being built in the US, and the ones that are planned are so robust that if a meltdown did occur it would be totally self contained. These plants have 100 feet concrete foundations so that if a meltdown did occur it would basically melt onto itself, but with computer checks and all of those things a meltdown would be extremely unlikely with all the checks and balances put in place. 40 years after the chernoble meltdown wildlife has returned to the area, so the effects may not even be as disastrous as we might think.
The best combination of energy would be solar, wind, and nuclear. Solar works best in the summer, obvious more sunshine, whereas wind power works best in the winter when the winds are at there greatest due to large temperature gradients around the planet. And you fill the remaining load with Nuclear power. This will be our future because energy demand is going up every year, while peak energy demand is going up faster, what this means is that during the peak (june and july) we have brownouts. Because our baseline power supply can not meat the peak demand. To meet this demand is where solar can shine (bad pun) The peak in energy is due to air conditioning so it is a direct relation between using solar energy at that time.
Now the downside, pollution is a global issue, even if the US gets on board and stops all coal plants tomorrow we may still be past the tipping point because China and other developing nations are adding on average a 500 megawatt coal powerplant per week. It's awfully hard for the US to say to these developing nations that they shouldnt be burning coal when we too are adding coal power plants to our energy grid. The only way we will be able to deal with producing enough energy and helping the environment is to build more nuclear plants. The first step to this is dispelling misconceptions about them, they are not scary, no three eyed fish, and living next door to one would at worst be an eye sore because of the large cooling towers associated with them.
, possible upgrade with clean burning to only +1 
per dam upstream in each city. No flood plains down stream, but no 
similar to Forests (perhaps + 0.5 
