Hi there Miyz , I'm certainly not the top expert in this field but hence this is a more general question not a specific math one, I think I would or could share my 2 cents .
Well there is a saying that everything has a price tag in this life not only in our economic/political system in the world but also in nature and in the universe as a whole.
Basically what I mean by that is that everything comes with a price and effort.
Well oil as we all know has been the backbone of the world for the whole 20th century and still continues to be a large part even when the prices have tripled over the years and still going up while the reserve going down.But basically oil was easy to refine and pretty much easy to use in everyday life like internal combustion fuels, lubricants, greases plastic products literally pretty much everything you can see around you.
Well what can one possibly think about a energy source that is maximized and slowly dying , nothing good I guess.
Well biofuels and other stuff I don't let an expert speak but as much as I think not that much of an alternative because to produce them means taking up huge agriculture spaces for that alone and the cost in the end +the huge demand in the world market I don't think it will go on that good.
Solar power , well I think the solar cells have a long road to develop so that they could increase the output per square/m .The good thing is that you can design them into building glass walls and roofs and all other places to make a intelligent and usable architecture but still I don't think that could power the whole typical office tower demand of electricity not even half.
Wind power pretty much like solar minus the visual looks of it which may look cool in the countryside but not that much usable in a or near a city.the whole thing takes up lots of space , needs constant wind to operate , doesn't produce significant amount of electricity i think it's not that much of alternative at all.
There are these cogeneration stations of different type most of them use the gas produced from chemical reactions in old city dumpsters to burn them and use that to turn a turbine -generator producing electricity and since the gas would emerge anyway from the dumpster I think it is a very good idea to use it for a purpose.The same goes to burning and reproducing old plastics and trash from the city dumpsters that are specially sorted out and used in these special stations where they are being burnt a gas is extracted and used to again heat water steam/turbine/generator cycle or different types as there are a few ways how they operate.I think this is a good way of utilizing the otherwise left alone trash.
http://en.wikipedia.org/wiki/Cogeneration
Seee the wiki page and search google for this type of energy it is becoming more and more widely used .
Well then there is nuclear, fission as you know has been around for quite a long time , the reactor designs gotten better , safer, but the uranium also is limited but the good thing is that as you may know it produces a huge amount of power to size/weight ratio so we still have plenty for some 100 years or so , and then again we have more of it deposited in the nuclear bombs of countries like China, Russia , Uk ,USA.
Fusion... Readupon it there is a lot to search in google but in few words , good things come with hard work and a lot of effort.The most complicated to achieve nuclear reaction on earth.They are building the Iter and even Iter will be more like a test ground for further more practical ways of fusion electricity than a ready commercial reactor.Although they estimate that Iter should put out more than is required to put into sustain the fusion plasma , the magnetic field keeping it and all the equipment.
By the way well as you may know we can achieve fusion and have done it but the bad thing is that it has been in a shape of a bomb or thermonuclear weapon where all you need is a second destruction force capable of turning cities into deserts not harnessing power for civil peace purposes.Which in the case of fusion is much much much times 10 harder.
@Berkeman your fast.Well yes it does sound like a school essay thing but then again I don't think it's that destructive to give him some general ideas of what's going on like i tried in my post , as the further search and understanding is left upon him as to from what I just said is far far less to make a good essay.
Also @Miyz it would be highly appreciated if you would write some thoughts on your own and answer berkemans and other questions to make a thoughtful discussion and not just take the few notes and run away.