Will renewable energy ever be able to replace fossil fuels completely?

Given that the amount of fossil fuel is finite then even if left alone the market will naturally replace it incrementally as it becomes more scarce. It must eventually either reach a point where utilization is no longer practical at all or limited to such specific niche applications that it can effectively be considered out-of-use as a meaningful source of energy.

In practical purposes though this may not mean replacement with the energy sources traditionally considered as fully renewable. Utilization of ground based solar will continue to increase as the cost of generation decreases though there are some potential practical as well as theoretical limits to this as an energy source - as with wind power. That is to say that there is a finite amount of solar energy which reaches the surface of the Earth that would prohibit indefinite expansion of solar generation even if there were not more practical obstacles that would be reached before that point.

Wind power generation faces the same sort of theoretical limits and similar practical limits in terms of indefinite expansion as a source of energy. The idea that they might significantly impact weather patterns before being built to such an extent as would be impractical is somewhat ridiculous but then again so is extending exponential growth in terrestrial energy demand ad infinitum I suppose. Really that only seems applicable if we consider civilization into the future for thousands or more years.

What is reasonable to understand however is that the materials we produce devices to harness renewable energy are somewhat finite themselves. It is quite reasonable to think that any individual renewable energy technology may reach a point where scarcity of component materials increases the differential cost of building more capacity to the point where it ceases to be economically feasible just as such scarcity will eventually render fossil fuels undesirable.

So yes fossil fuels will eventually be completely replaced. It may not be for a hundred or more (or hundreds if it is more gradual) years under natural market driven behavior, but it is inevitable. Whether it is replaced entirely by renewable energies at some given point, even if only temporarily, is less certain. Depending on population growth and the development of aneutronic fusion in that incredibly long time frame it is entirely possible that some new but not renewable sources of energy will grow to represent a significant portion of production. In the more near term there is also the possibility of more and more economical bio-engineered forms of compatible replacement fuels. These be renewable but not quite as clean as some might desire - though given that they could work with existing inexpensive technologies and be grown in something as cheap as algae they may increase in usefulness and represent a significant portion of the market for some time in the future.

I do feel confident however that in 200 or more years time we will be using a combination of orbital and land based solar, wind, tidal, and lithium fusion power for the vast majority if not totality of our energy needs. The finite availability of aneutronic fusion fuels (those that produce no radioactive waste in terms of irradiated reactor components) would however require significant exploitation of resources elsewhere in our solar system.

That depends on what one defines "fossil" fuel as. Actual fossil fuels, will run out some day. But that day is somewhat far off. (relatively). There are great advancements in carbon based fuels for combustion that are indeed renewable. Which is not where most folks go when the say "renewable". Most think sun / wind / tidal, etc.

As an example, here is a company that makes a diesel replacement using waste CO2.

There is also the issue of petroleum as a lubricant, Organic oils were used around the turn of the last century, but they go rancid, and they may not be up for our high tolerance machinery today.

There will most likely be many and varied renewables to replace petroleum and coal. Adn they will replace fossil fuels, if you are open minded enough in your definition of "fossil".

The amount of solar energy that falls on the Earth is 174 Petawatts of which half makes it's way to the surface. The total energy use from all energy sources including fossil fuels is 15 Terawatts so there is thousands of times more solar energy available then energy we currently use from fossil fuels. Fossil fuels are also solar energy, it's just ancient solar energy collected over millions of years and collected at extremely low efficiencies at that (far less than 0.5% efficiency). The difference is that nature has been in the business of collecting solar energy through photosynthesis for millions of years and no one had to pay for any of that while we would have to pay for our more efficient photovoltaic panels.

Technically, solar energy could easily replace fossil fuels and eventually will. Economically, mother nature did all the work for us with fossil fuels and there's nothing cheaper than someone else paying the price.

Sure. In fact, we could already do this if we wanted to--the technology is there. But we could've gone to the moon in the 50s if we wanted to, technologically, but it took the Apollo Project to do that. What I mean is, we *can* but it would currently be very expensive and difficult to make a complete switch.

A better bet is to continue developing better renewable technologies, and in the mean time lessen the dependence on fossil fuels by reducing oil usage (coal is in much greater supply than oil) through using substitutes or alternatives (e.g. electric cars) and by replacing coal and gas-powered energy with nuclear energy. Though nuclear energy is not renewable, we could run the whole world on it for about a century, and it would be pretty clean. Hence, nuclear energy is a good choice to "bridge the gap" while renewable energy technology improves and becomes gradually easier and cheaper to implement.

Yes of course it will because fossil fuels are running out and becoming more and more expensive to find and extract. There will come a point when fossil fuels are so expensive that renewable energy will be the preferred method for everyone not just the environmentally conscious.

Not likely, although wind, solar and hydro will always be around they can't be relied on 24/7. In drought years hydro production goes down, obviously solar only works during the day and wind often has lulls during portions of the day as well. Many of these are also seasonally affected, days are shorter in the winter, less rain in the summer (at least in my area). There are areas of the nation and planet that have a good mix of these, but other areas that have only 1 or 2. There are also tidal and geothermal, but they are even more geographically limiting. So if we run out of fossil fuels we will likely have to rely on nuclear.

no because fossil fuels make too much money. Renewable energy is a great idea by our society is corrupt and greedy. It cannot make as much money as exploitation for fossil fuels, so it will never completely replace fossil fuel use (until all our natural resources are gone)

No. It defies the laws of nature.

An engineer knows you cannot get something for nothing.

The ecology is a finely balanced system.

If we remove energy from wind, solar radiation, tides and waves we upset this balance, destroy the environment and do more harm than supposed CO2 ever could, which it doesn't.

John W is right about fossil fuel being stored up solar energy, but wrong about the cost - 4 coal miners died in Wales last week.

Keep in mind fossil fuels are responsible for much more than energy in machines, we make our fertilizers, tires, plastics and many other products that may not be so easy to replace with alternative sources. When you buy your food at the store think of how much fossil fuels went into producing a product, packaging it, and delivering it so that you may transport it and cook it using electricity or gas.

I think so. Solar power, wind power, nuclear energy, human energy (walking, riding a bicycle instead of driving), hydro-electricity, etc... yes I believe it's possible. Plus, fossil fuels are rapidly declining. The sad thing is that humans probably won't start really mastering renewable energy technologies until we have used up all the fossil fuels. Humans can be silly like that.