Whatever replaces fossil fuels will be more difficult & expensive to use. This follows from the fact that fossil fuels were so easily used by more primitive industrial societies. Look at how our brightest minds struggle to come up with a replacement!
I realize it took you a second to write these three sentences, but I think it reflects a widely held view, a kind of 'knee jerk' energy philosophy that helps bind us to the status quo.
It was not "easy" moving from wood and dung to Oil, Gas, and Coal. It was a centuries long process to dig our current hole of fossil fuel dependence. There are a lot of Fantastically smart people *not* working on developing new energy sources, but instead working on maximizing the value of refined fossil stocks. If the price of heating oil goes up, and the price of propane goes down, modern refineries can adjust to the price change, for example. It took awhile for such science and engineering to develop.
There are a lot of fantastically smart people also trying to ensure the continued value of Fossil energy inventories in the ground as well as plant and equipment, and trying to ensure continued revenue streams for the next decade to come.
The problem for alternatives is the next decade is a moving window, so fossil fuel political actions become a real problem for those whom wish to try to replace fossil fuel with other sources. There are many energy dense sources of energy that could compete with, and eventually exceed Fossil fuel in total energy produced, but in the US, fossil interests are strong, and government focus has been successfully cast with the help of those interests upon very "power diffuse" sources of energy; Such sources will never compete with fossil fuel sources, but may enhance the revenue streams instead. We can think of wind energy being very closely related to natural gas. Wind power will certainly enhance Natural gas revenue streams, not diminish it.
It is not that our "brightest minds" struggle but fail to come up with a replacement, because very little is being done to research them relative to the intelligence and other resources being applied to enhancing and ensuring the continuity of existing revenue streams benefiting politically powerful fossil fuel sources.
If you want to see energy sources more power dense than fossil fuel sources, I hope you're young, because it'll be awhile. It probably won't come from the United states either, because of the political power of fossil fuel interests. Look instead toward China, India, Japan, whom are more either desperate for feeding a growing population, and/or aren't so stymied by a well established fossil fuel political interest.