I think the most sustainable and green energy sources are:

1) Ocean thermal energy conversion (OTEC).

2) Tidal energy conversion (ETC)

3) Wave energy conversion (WEC)

4) Wind power

I didn't mention solar photo voltaic PV) because the raw materials for making the wafers may not be sustainable in the future.

Hope this helps answer your question.

Professor Yehia Khalil

Yale University

USA

I think Tidal energy, Wind, and Photovoltaic will be the key players...

All renewable energy promote sustainability and the advance in technology of each type will be decisive from economic and environmental  point of view.

In my opinion, the trend of using  solar energy will increase dramatically in the near future especially in the Mediterranean countries.

I think,

The most dominant energy will be sustainable;

For 50 years: Wind and Solar

For 100 years: Wind, Solar, Wave and Hydrogen.

@Yehia F. Khalil,

Thank you professor Yehia for your answer. in a moment i am surprise that the OTEC & ETC will be the dominate energy in future, that means the scientist will resolve the energy conversion and transmission , the greatest obstacle for losing energy , other things that's also means the superconductor will be used widely in that time.

Thank you again for the best answer and information ..

Mustafa Al-Azzawi

@Pavan Kumar A. V.

Thank you Mr. Kumar for your answer, i totally agree with you of OTEC has good chance to be the future energy. but i don't think solar or wind will. the new word will change and may the wind energy and solar energy will not be cover the that consumption.

Thank you again..

Mustafa Al-Azzawi

@Samah K Alghoul

Thank you so much for your answer Dr. Alghoul , i think the solar energy will be widly used but i am not sure will be the dominated in future because the silicon consumption.

Thank you so much for your answer and i notice, the disagreement will reinforce the topic.

Mustafa Al-Azzawi

@Seyfi şevik

Thank you very much Dr. Seyfi şevik , your totally right i think the same , but what you mean of Hydrogen ? is that hydrogen nuclear fusion?

best regards ,

Mustafa Al-Azzawi

You're right. Hydrogen is an interesting element. I have written in terms of sustainable energy. Ok. A question from me. Is hydropower a renewable energy? 

Hi Seyfi şevik,

I understand now you mean the hydrogen power energy it self, yes it very attractive if you can get extracted it with efficient enough from Air, there's studies that extracting hydrogen from photolysis. The other part of your question is the hydropower is totally clean and renewable energy till now.

Let me answer the following question that was posed:

Is hydrogen a renewable energy source?

My answer is that it all depends on how hydrogen is generated. For example, if hydrogen is generated by reforming methane gas with steam, then it is non-renewable since methane gas is a depletable source of energy (i.e., unsustainable).

However, if the source of hydrogen is wind turbines integrated with water electrolyzers, then this hydrogen technology is sustainable.

I teach these topics in my engineering courses at Yale University including the Green Energy Systems (GES) course which I introduced as an online course at Yale University.

Hope this helps answer your question.

Professor Yehia Khalil

Yale University

USA

Dear Prof Yehia F. Khalil,

Thank you again for sharing your experience and ideas, exactly that was my previous answer. I 'am trying to develop new technique that's depends on photolysis to extracting Hydrogen from water from years, and i am surprise i saw paper talk about that technique in few weeks ago. I have other idea cold solve this issue which is "Photosynthesis" its still need much investigation, its stimulated of leaves that totally could work if we use nanotechnology. 

Thank you again

Mustafa