Hello Agyemand,

In my opinion, the most sustainable renewable energy device is Solar Panel.

Solar Panel can harvest Solar Energy, the Primary Energy Resource of our Planet.

Solar Panel has no moving mechanical parts that can be damaged. 

Solar Panel requires very little maintenance, operates silently (no noise) and no pollution. 

Solar Panel can be easily installed and deployed as many prefer size and site options: Solar Home System, Micro Grid, Mini Grid and Smart Grid. 

http://www.conserve-energy-future.com/Advantages_SolarEnergy.php

http://energyinformative.org/benefits-of-solar-panels/

All have their negative aspects. Solar blocks the sun from the ground below, so it depends how solar panels are deployed. To get a substantial amount of power from solar, the area covered needs to be quite large. And, over time, solar panels degrade, become less efficient, and need replacement.

Wind affects the wind patterns, which may also have consequences.

Both solar and wind also require storage, because neither is consistently available. That may mean batteries. Or, they require some more traditional power grid to coexist.

Nothing is ever free. I like bio in the sense that it requires lots of consistently planted vegetation. Ultimately, the more vegetation we have, the better Mother Nature's own CO2 sequestration methods work. Just think that if we had not deforested the planet to the extent that we have done, there would be NO problem with CO2.

Desmond,

All renewable sources have pros and cons as the others have discussed. I would like to introduce a more fundamental point.

With perhaps the exception of biogas and biofuels, most renewable sources are extremely site specific ! That is, they are not options at all in certain parts of the world.

Further, even though a particular source may be possible, it may not always be economically viable ! For example there are parts of India where wind turbines simply won't work (the wind is not strong enough !) and certain parts where they don't make economic sense in terms of capital investment vs. energy output. And then there are certain parts where they are so economically viable that wind becomes an obvious option.

To summaries, the reply to your question should be a very subjective one.

-Sanjay

It depends of location where they are to be installed. It would be better to install Solar modules near equatorial reasons. Also, good to install it in hilly reason where sunshine is more. Wind mills are good near seashores as there is considerable wind velocity available regularly.

https://en.wikipedia.org/wiki/Solar_energy

http://energyinformative.org/potential-of-solar-energy/