To be direct: your question sounds a bit like: "Do my homework for me". There is plenty of literature on the subject. A Google scholar search is always a good start if you want to do the work yourself:

scholar.google.com/scholar?q=global+potential+for+renewable+energy&btnG=&hl=de&as_sdt=0%2C5

I very much think is not a foolish idea to think about it, in as far as we continue to exploit different renewable energy resources and improve the efficiency of existing technologies. 

To be direct: your question sounds a bit like: "Do my homework for me". There is plenty of literature on the subject. A Google scholar search is always a good start if you want to do the work yourself:

scholar.google.com/scholar?q=global+potential+for+renewable+energy&btnG=&hl=de&as_sdt=0%2C5

I think the answer of your question may be yes or no. For present situation of fossil energy reserve and technological development it is not possible to exploit all energy needed globally from renewable. But time may come when most if not all energy can be harnessed from renewables.

At least we should all work to reach that goal.

There are already some example where the energy consumed is 100% renewable. The challenge is to focus on energy efficiency together with renewable energy, otherwise one would install renewable energy and just keep on consuming more energy. One also has to think about the available RE sources on site, in the vicinity, in the region, in the country, etc... Finally, it all depends on the price of oil, if one keeps thinking about cost, otherwise you have to start considering other reasons for shifting to RE.

I think energy conversion efficiency is the key issue to be addressed. Take for example the solar energy conversion to electricity ( PV panels). The present efficiency is well below 20 %. Another key issue is efficiency of utilisation of energy and transmission losses.  

Except of RES usage, energy efficiency improvement is very important. I think that education about rational usage of energy is also very, very important. Education about rational energy usage should start already in primary school.

Since nuclear power is now unlikely to increase its present modest share, renewable energy (RE) will have to provide for most energy in the future. The reserve depletion and greenhouse gas emissions will necessitate a major shift from fossil fuels as the dominant energy source. However when the energy costs of energy are considered, it is unlikely that RE can provide anywhere near a 1000 EJ by 2050 (projected energy demand in 2050). The overall technical potential for RE may fall if climate change continues.

Definitely as pointed by Ahmad, the cost of RE at present is not a very encouraging factor. But a day will come, when all the fossil sources vanish and the only alternative left will be RE, it may be solar, wind or some other so far untapped source. When one cannot supply the demand, one way is to decrease the demand. As rightly pointed by Danijel Topic, rational usage of energy is one method.  

Tell me what the population will be in year XXXX, and the standard of living you want to achieve in terms of energy use per capita, then you can pose your question.  Is there any doubt we can use renewables as our sole source of energy (and food), as long as we have a mass population die off and return to Neolithic level living conditions?  So without laying out those conditions you can't address the question you pose.

The question is also tied to whether or not nuclear energy is allowed in the renewable mix.  It seems the public (in countries where the public opinion is taken into consideration) has decided that nuclear is not an option, at least as far as NIMB is involved, and arguably rightfully so after Chernobyl and Fukushima are concerned.  Our governments have generally shown they cannot be relied upon to properly regulate the industry.  If we add in the issue of nuclear proliferation and terrorism, nuclear is a non-starter.  In any event it is an expensive source of power when all costs are factored in.

Note:  These are my personal opinions, not a GTI company position.

Efficiencies enhancements (both in generation and utilization), responsible consumption, smart grids, chemical conversion/storage.

No doubt renewables are potential sources of energy they are season/region specific.Requires huge  storage and can't meet whole energy requirements. 

The world receives yearly  from the sun about 10'000 times the energy use of mankind. It is therefore possible to  cover the entire global energy requirements from renewable energy sources originating from solar radiation (direct radiation, wind, hydro, biomass, etc.). Geothermal energy (heat contained in the globe) can also be considered as renewable at human views, and coud be therefore added!

We are in a learning world and as the day passes by, we learn more and more. There is point being criticized for asking question we do not anything about. Based on your question, there are ways we could meet the entire global requirements from renewable energy sources. The very first point to this is for us all to know exactly what renewable energy sources (RES) are and the fundamentals of energy from that source and the benefits it is having for the developmental needs of our environment. That is when we talk about climate change and the after effect of the associated problems from the use of fossil fuels. From there we can proceed further to finding the possibilities of meeting the entire global energy requirements. 

Dear Jethro Betcko,

If some body puts a question, it is not that he has not done any home work. Some questions are meant to initiate a debate and exchange of ideas, which I think is a way to enrich ourselves. I think we have to respect exchange of ideas.

Dear Dennis Leppin, the population, the energy requirement, the standard of living etc.. for any year can be forecasted. There are methods of forecasting on longterm and short term basis reported in literature. Every country will have its own forecasts of its energy requirement. 

As Alain Roulet rightly pointed out, the solution lies in solar energy. But yes there are hurdles.....intermittancy of availability, cost of production, cost of storage  etc. The key for success lies in enhancing the energy conversion efficiency and rational usage of energy.

We are in a learning world and as the day passes by, we learn more and more. There is NO point being criticized for asking question we do not anything about. Based on your question, there are ways we could meet the entire global requirements from renewable energy sources. The very first point to this is for us all to know exactly what renewable energy sources (RES) are and the fundamentals of energy from that source and the benefits it is having for the developmental needs of our environment. That is when we talk about climate change and the after effect of the associated problems from the use of fossil fuels. From there we can proceed further to finding the possibilities of meeting the entire global energy requirements.

There are some studies initiated towards the question. And some are giving a positive results too. One can refer the link attached.But , yes, there are many hurdles. 

https://www.researchgate.net/go.Deref.html?url=http%3A%2F%2Fwww.sciencedaily.com%2Freleases%2F2015%2F02%2F150205083032.htm

Succinctly : the possibility that renewable energy can meet the various requirements in global scope can be met in a coordinated and differentiated use of the same, in a smart grid approach , starting from the knowledge and the critical , efficient and profitable use of local energy potential, e.g: in an area wind energy more available; or biomass or energy from manure or solar energy ... and strengthening this method on a wide geographical basis.

It is not foolish at all to ask and there are excellent possibilities. It should have been that way to start with. No air pollution should have been allowed in the beginning. It was a criminal act to pollute the air/water/oceans and hide the effects from the public for so long.