The sun, nuclear reactors, hydrogen fuel cells. All zero emissions.
Fuel cell is just an energy storage device like a battery. It takes more energy to separate the the hydrogen than you get from it.
Solar will not keep up anywhere to the demand of everyone driving electric cars and photovoltaic solar panels don't last long enough and have "EMISSIONS" in the manufacturing of them and the recycling.
Nuclear has "EMISSIONS" in the mining and refining plus you have the radioactive waste from the power generation and a huge amount when a power plant is decommissioned.
Wind is one of the cheapest but the way wind pulses and isn't a steady load it is very hard on the equipment that must continually be replaced and that has "EMISSION" also.
Even your bicycle is not "ZERO EMISSIONS" because of manufacturing and wear items like tires put particulates into the air.
Hydro electric is very efficient with the least wear but we haven't built a new dam in years and I personally don't want anymore dams built.
Tidal has big hopes but salt water and sea life are hard on equipment.
Co-gen from waste water treatment sounds good on paper but human waste is way too corrosive and every plant that tries it ends up burning off the methane and running the plant on natural gas because it isn't cost effective.
I think that the big push right now should be more HYBRIDS with the government fleet leading the way. The technology and fueling infrastructure is there. Why does my mail carrier still drive an out-dated AM General mail car that stop at my shop, start up, drive 40 ft and shut off again, and continue that 5 times just on my block? UPS has tested hybrid trucks and they could move them around inside the warehouse without ever starting the IC engines. It seemed like it would be a great fit for all their stop and start driving but they dropped it.
I also say change the way we drive. get rid of stop signs, traffic lights, and toll booths. keep the vehicles(weight) moving. make better public transportation and ,at least around here, better car pool lanes. Also lets build some tunnels trough the mountains rather than having a semi truck effectively lift 80,000 lbs up and over the sierra passes.
Good judgement comes from experience. And experience? Well that comes from poor judgement.