The economic efficiency of using wind, solar, geothermal and hydro the main renewable energy sources is not a clear cut issue. It depends highly on your particular situation. With oil prices so cheap they are clearly not as good of an option in terms of price per unit of energy output as they were 6 months ago. However there is a lot to consider here.
Hydro is wonderful it has a large onetime ecosystem rearrangement including displacing people but after this point it provides cheap reliable energy when you need it and a reservoir is essentially one of the best batteries we have today. Unfortunately most of the possible large hydro projects have already been built in developed countries.
Wind power is highly dependent on your location. There are many places where it is already an economically competitive energy source and many were it is not or will never be. It does not produce reliable energy however so it must be paired with some energy storage method or a more reliable source.
There are many types of solar energy technologies but mostly I think we are focused on those aimed at producing electricity. If you took all of the solar energy landing on the united states and converted it to electricity at 100% efficiency there is enough energy to meet the entire energy needs of the US roughly 500 times over. Of course solar photovoltaic panels are not very efficient (10-20% in practical uses) and we want sun for other things like growing plants. People are building some large solar plants in places where land is cheap and more people are putting them on their roofs but it is an unreliable source of energy like wind and my understanding is that its usually not very economically practical yet.
There are not very many places where it makes sense to use geothermal energy to create electrical energy. However it can serve as a great heater and cooler in most places.
One of the biggest factors in what energy source is economically practical is government subsidies. There are many more renewable energy projects happening these days because of large government subsidies. Governments can think in the long run and this makes a lot of sense. But currently the largest subsidies go to nonrenewable fossil fuels. If for example all energies had to pay for their environmental impact (say co2 output) rather than being subsidized by public governments renewable energies would become much more economically practical.
One nonrenewable energy source that is relatively friendly environmentally is nuclear. I see this as one of the few technologies that we can switch too quickly that has the potential to meet our energy needs. It won't last for ever especially if we try to do everything with it but there is also a lot of room for research. If we ever figure out how to gain energy from fission to there is a huge potential for energy there.
Well thats the way I see it at least part of it. It might be in shells short term interest to ditch wind, solar, hydro but they may be limiting their lifespan.