Will Renewables Replace Fossil Fuels?

Once again You couldn't be more on topic

It isn't so much about doing without, as it is making the most out of the resources.

The end answer to the title is "Yes". (because fossil runs out)

To the body of the question; technically alternate sources could replace 90% of fossil "tomorrow".

In reality; to have a "24/7 grid" based civilisation - alternate needs storage.

In "economics"; the concept of "National Grid" and Power Companies - has to die first. (e.g. not massive 'owned' PV arrays, but "on every roof")

In "environment"; "Greens" need to get perspective on what impacts what.

In politics: Engineering needs a voice.

Or basically the true answer is; "no" and that point, we're all fucqed.

I agree with that.

Don't know about the rest of the world, but in the USA most folks are not willing to do much to reduce consumption of energy. Many people are probably not even aware that they should, because all many people here are aware of is the sitcom on their 60" TV, who is winning the football/basketball/baseball game, and what Hollywood star has been knocked up by the chauffeur, what's the latest electronic gadget, who's on facebook, did you see the You-tube video of that guy having sex, etc, etc, etc. We are a nation with way too many dummies.

Because of all that, and the fact that our leaders are as dumb as their constituents, I'm going to guess that the economic collapse that is going to come soon WILL REDUCE THE NUMBER OF DUMMIES AND THE POWER USED IN THE USA.

I think at that point those that survive will be forced to wake up and do things a tad differently. Sad that this seems to be the only thing that will wake them up in this country, but it seems to be the case.

I don't know what's your definition of renewables, however, I do believe we can use a 'sustainable' energy source (Enhanced geothermal System (EGS)) to replace fossil fuels completely.

Right beneath our feet we have the safest nuclear power station providing energy sustaining millions of lifeforms in the soil and deepest part of the ocean. This power house will out live any fossil fuels we have. At the moment, only one country - Iceland - has made use of this power house and 99% of its generated electricity is from this 100% carbon free.

This energy can be tapped into http://pubs.usgs.gov/gip/dynamic/inside.html if we can pool all the world's resources together to develop an advanced drilling system that is capable to drill safely and economically to a depth of 10-20 km. It is not free because the drilling will cost money but once we have reach the hot rock, we can generate carbon free and almost inexhausible energy. It is a near-sustainable energy (not sure if it can satisfy the definition of renewables).

Carbon capture, solar PV/thermal, concentrated PV, wave, hydro, tidal energy etc all will become supplementary and can be used to generate Hydrogen to fuel air/space travel. Who needs fossil fuels then?

IMHO, I think three countries will triumph in the EGS/Hot Rod energy technology in 10 years time - the USA, China and France. They have more demonstratable research and commercial development works in this technology than other countries.

Don't know anything about EGS, but aren't there locations where we would not have to drill so deep? Like volcanos, hot springs, etc?

Perhaps the depth is needed to get to a sufficiently large heat sink (source) so our removing the heat has little effect on the rock temperature?

One of the major issues with geothermal energy extraction on a mass scale is that there just aren't that many sites of sufficient potential close enough to sufficient markets to warrant major investments.

This is not new technology. Evidence indicates that humans have been accessing geothermal energy directly since Paleolithic times, and that the Romans used it for home heating where it was readily available. The first known industrial use reportedly dates from 1827 Italy, used directly in a chemical process. Of course, using it to generate usable transportable energy had to await the development of appropriate electrical generators and steam turbines, which had all come together by 1904. Direct home heating appears to have evolved from Roman days to the current approach of a subterranean heat exchanger by 1930 (most previous heating applications appear to have involved naturally occurring surface features such as geysers and hot springs). I would suspect that if this were really an economically feasible process, it would have achieved market penetration similar to air conditioning (a modern technology that dates from roughly the same early 1900's time frame- to be exact, the 902 invention by Carrier).

Now, the deeper one goes, them more likely one is to encounter really harsh environments that play havoc with most materials. Thanks to the oil industry and the space industry, materials that can deal with this deep harsh environment are becoming more readily available. Now, it turns out, there appears to be a serious potential from the redistribution of natural stresses in the rock structure to induce earthquakes (as suspected in such diverse regions as Switzerland and northern California), although drillers are quick to assert that punching holes in sold structures are not the cause of such effects. And, of course, if you chose to live in China, you are not going to be allowed to let this develop into a major social issue...

Looking at the history of man's attempts to tap in to this potential energy source, one gets the distinct impression that, if it was as trivial as the pundits would want us to believe, we would be using it far more extensively than we currently do.

All true. Extracting geothermal energy is not practical everywhere. New technologies do make it practical in more locations but not the wide spread increases some pundits claim.

What intrigues me though is the use of a reversible heat pump with geothermal energy storage in the moderate temperature latitudes where most people live. With the slow migration of heat that happens not far underground the excessive heat of summer can be stored for winter. Of course this approach like everything else has limits that are easy to see. But just like a hybrid vehicle, instead of tossing away energy when it's not wanted saving some of the energy for a later use seems like a good idea. At the very least this is a good attempt to improve efficiency.