Currently, burning fossil fuels is the main source of energy here and around the world. Those fuels emitting greenhouse gasses are considered by most associated scientific organizations in the world as contributing to a potential global catastrophe in the making. With this, we are critically dependent on electricity for almost every necessity we have in our standard of living.
A very important concept in electricity production is the term baseload. This term is often used when concluding the need for nuclear energy to be in the mix of clean electricity sources for modern society. Baseload electricity is simply the minimum total electricity used throughout the year at any given time and region. This means that all sources combined, the baseload amount of electricity needs to be supplied continually as the very minimum. At different times of the year and throughout each day, only more electricity than that baseload minimum will be needed. So more capacity is required to meet the day to day variations in peaks and lulls from society demands on the electrical energy grid.
Familiar renewable energy sources such as wind and solar panels are not able to contribute to baseload energy needs without some form of energy storage. Without reliable storage capabilities having low conversion loss, these solar based sources would not be able to start contributing to the baseload. This would be based on average solar availability although industrial scale storage systems do not currently exist, some are in development and do show promise.
Another common difficulty with wind and solar panel energy sources is the large area typically required to be committed for the energy generation capabilities. This means that to a first approximation, the energy which can be generated from 100,000 acres of land devoted to wind turbines and solar panels could be generated by a fossil or nuclear powerplant on only 100 acres of land. Specific examples will vary substantially but if an environmentally friendly option requires not taking up vast sections of land, then wind and solar panels might have to be concluded as not actually being environmentally friendly.
Common baseload energy sources are fossil fuels, coal, natural gas and oil. In limited locations, building damns in rivers or drilling for geothermal heat sources can also provide a contribution to baseload energy supplies. Burning biomass or growing other organic material as an energy source are other developing technologies which could contribute to baseload.
As consumers we all tend to also be interested in which one will cost me less in my monthly utility bill, currently this latter answer is burning natural gas as a baseload supplier. This does not produce multiple trainloads of ash waste as does burning coal but it still does emit greenhouse gases.
One often overlooked aspect of energy production is the amount of energy required to install the power generation capacity per total amount of energy eventually produced by that installed capacity. If this is to be considered in grading environmentally friendly electricity production, then a look at how the various sources stack up may be worthwhile.
Which energy source has the lowest overall greenhouse generation per Watt created in its lifetime? The answer to this select question appears to be nuclear power, an enormous amount of electricity is produced in a small area with a single power plant with very little waste generation per amount of electricity produced. Hydroelectric also compares quite favorably behind nuclear in this regard. Still if the grading criteria is shortened simply to consumer cost per Watt and energy produced per total life cycle energy installation and removal, the two winners would be nuclear and hydroelectric power supplies (the larger the scale the better).
To those who are convinced all radiation is evil, the main detractor for nuclear power seems to be the issue of nuclear waste. True, like all power sources there is some waste and like so many other things, it needs to be handled safely and disposed of properly for the entire cycle to meet consensus based standards.
It might be a red herring to point out that some coal has sufficiently large quantities of naturally occurring radioactivity that when burning this coal to make electricity, there is more radioactivity per Watt generated in the waste of those rare forms of coal than that created by a nuclear power plant. More to the point, "safety is as safety does", if you do something safely then by definition it is safe. In other words, everything involves some form of risk, it is incumbent upon us to manage those risks accordingly.
The true bottom line is that when it comes to making electricity, there is no such utopia where this can be done without some impact to the environment and no waste generation. Everything we do generates some waste and has some cost and it really just comes down to a cost benefit analysis. What costs are you willing to pay and for what benefits?