So, I was on Yahoo answers recently and the following question came up:
"What is the viability of renewable energy sources for future energy production?"
See the question here
In the midst of answering this question, Yahoo told me that my answer was too long. So naturally, I've posted the full answer here:
Talk about a loaded question!
The viability of renewable energy sources depends greatly on use of energy (duh, I know). The more efficient we as a society become in our use of energy, the more viable renewables become. Additionally, as conventional sources of energy (coal, nuclear, gas-powered) rise in cost (as they are doing), again renewable energy becomes more viable. For example, in Ontario, where I live, the average price of energy is about 13 cents per kilowatt hour. The cheapest I've seen wind energy in an "on-the-grid" situation is .65 cents an hour. So as of right now, wind energy is really only useful as a supplement to existing energy, not as a primary source. Couple that with the fact that wind power is intermittent (not consistently outputting power), it's not as reliable as the current sources of non-renewable energy either.
Solar power is more viable then wind energy because it generates more power, but again the cost is prohibitive. For a house to set up solar panels costs a fortune, and the technology still hasn't progressed enough to fully offset the use of conventional "on the grid" power. Again, on small scale it's only viable as a supplement to energy sources. Although one advantage (if one has the money) to solar is that once the panels are set up, the costs are relatively low to maintain. There's also a lot of farms that are converting land use from agriculture to what's known as a "solar farm", which is subsidized in some regions in North America (I can't say much about the rest of the world, because I honestly don't know). Subsidizing is a way to lower the cost to the business and consumer on a startup basis, but it costs the government a ton and that in turn ends up being put onto our taxes. So it's not a perfect solution either.
One renewable that I feel holds potential is geothermal. Geothermal involves drilling a two holes into the ground of various depths (usually a 1km or more, though), one that sends water down and one that returns steam. The idea is that the water is sent down, and because of the thermal heat underneath the earth, the water gets heated until it becomes steam, which is sent back up the second pipeline - that steam at the end hits a turbine which spins and creates power. (That's a crude explanation, but it's along the lines). These can be implemented in houses, and they have potential for much larger, plant-like production as well. This technology is relatively new, so it's again expensive to install initially, but there's huge benefits to it. I've talked with an owner of a housing company that installed geothermal in his own home, and he puts 4 units of energy back into the grid for every 1 that he uses. That holds a lot of promise, in my opinion. This technology also seems to have the most potential to be decentralized and installed in new houses; think of it like it having the potential to become as standard as a home furnace or water heater.
Of course, all renewable sources of energy have downsides to it; some we know, some we don't fully understand yet. Part of the reason we're in such dire straights is from thinking that there was no impact from our previous energy sources, but the sad reality is that everything we do will have some negative effect. Renewables just seem to have the least effect.
Ultimately, most of what I've put here is about decentralized power sources - there's a lot going on in the centralized power sources (think power plants); Centralized power sources are far and above generate the majority of our current energy, and will be relied on heavily in the coming years as energy demands are expected to rise exponentially (due to population increases and more countries developing into second and first world nations). Renewable is something that is in it's infancy - it requires a lot of investment from companies and governments as well as research and development for it to achieve a level of viability that our current, non-renewable sources have.
There's also things we can do with our current, non-renewable sources of energy that may improve it's impact - such as carbon capture technology with coal-fired power plants. I read up a lot on that subject because coal is plentiful and geopolitically stable (unlike nuclear, which has a lot of risks associated with it's development); coal's main problem is that it's dirty when it burns - but carbon capture is a method of cleaning up that pollution output and turning it into a byproduct that's used already in industry. I highly recommend you read Mark Jaccard's book "Sustainable Fossil Fuels", because it brings up a lot of interesting points that may help you better understand the current energy situation we are in. If you google "Sustainable Fossil Fuels", the first result that comes up is actually an online version of the book that you can read (nothing like free reading!)
Anyway, I know this answer was long and if I used terms that you already understood (or didn't), I'm sorry. I do hope that this helps you (I assume you've got an assignment on this or something, and that's why you were asking?)