No solution can easily replace fossil fuels -- especially gasoline and diesel and other liquified hydrocarbons. It's surprising, but diesel for example packs a huge amount of energy, both per unit volume and per unit mass. Nothing comes close, at this time. Batteries are far away, even with the most modern varieties. And hydrogen takes up huge volumes, even compressed at 5000 psi, and even cryogenically cooled. And it takes an incredible amount of energy to extract it from water (it's actually easier to get hydrogen from fossil fuels, which is how most of the hydrogen is produced, right now.) Hydrogen will cost you almost 200 MJ/kg -- that's 200 million Joules for one kilogram. Even with the best in fuel cells, this converts back to 60% of 123 or about 73 MJ/kg. And then you get only a part of that with the electric motor of the car. Guess where all that extra energy will come from... yup... fossil fuels.
Batteries, 1MJ/kg, 1MJ/liter
5000 psi pressurized H₂, 2MJ/kg, 2MJ/liter
Hydrides, 5MJ/kg, 4MJ/liter
Liquid/20K-cryo-H₂, 8MJ/kg, 8MJ/liter
Gasoline/diesel, 38-46MJ/kg, 27-36MJ/liter
That table tells a lot about gas/diesel. We already have the systems in place, they are relatively safe to use, and they are far more convenient by quite some span.
Nuclear power dangers fall into multiple bins. If you reprocess the fuel, you get plutonium stockpiles... bad... the US stopped that in the 1970's because of those concerns. You can remix the plutonium into MOX, but efficiency requires a new kind of fast reactor... which means we need to build them... successfully. That still waits to be done on any scale at all. You can go to thorium, either in the LFTR or the breeder reactor IFR type -- but despite experimental successes and the inherent passive safety of IFR, they remain still experimental and the US has been resistant about exchanging the technology to other countries, as well. I have to mention one other thing -- almost every country with commercial nuclear power has some kind of regulatory agency. But they are all pretty much run by the nuclear commercial industry and not run by critical self-examination. In India, for example, the board is selected BY the nuclear industry and paid for by them, as well. In Japan, there have been abundant articles about this problem. And I have personal experience in the US with the NRC and certain MOAs (Memorandum of Agreements) between the NRC and INPO (a private nuclear safety organization) which in effect prevent the NRC from doing its safety inspection job in the US. If you care, examine the Congressional Record from a hearing around 1990 when the Seabrook nuclear power plant received its FPO and was about to start full power operations. It's all in the record at that time. Dr. Pollard discussed it at some length in front of Congress and I've separately researched this. The US NRC works for the operators in the US, quite simply. And the MOAs make it pretty plain, too.
Power generation on the scale of entire societies is very political.
Hydropower is tapped -- we'd have to destroy many wildlife areas and human habitats too to do much more with it. Wind power is still very expensive and besides doesn't provide base-power -- it is intermittent in most places -- and most of the really good wind energy is far out to sea, in the oceans. We don't really know how to do all that just yet. Solar power is creaking along and may possibly get to break-even -- there are many reports that will tell you it already is... but if you take into account degradation of the panels over time (they produce less and less each year of use) and their replacements, as well as damage, transportation and set up, packaging, and all the rest, they still don't cut the mustard just yet. There is some hope there, though. So that's a place I'd look for something serious in a decade or so. Maybe. Certainly, it could supply baseload for a large part of the day, too.