I've been a huge proponent of "green" energy for years, and after watching it for those years, it's becoming more and more obvious the technology just isn't there yet. The best we can do is pump more money into research and ignore these poorly planned start ups that are only profitable due to subsidies. Every major type of renewable energy has some aspect which makes it at least a decade and several breakthroughs away from viability.

Cellulosic/Algae Ethanol: About an order of magnitude off on cost, many orders away on capacity. They are still immature technologies but seem to have a lot of promise.

Photovoltaic Solar: Cost is almost there, but no one has a plan for what to do when the sun isn't shining. Solar systems can only produce energy for about 6 hours a day, which presents a problem when we need energy for 24 hours. It doesn't produce energy during peak demand (~5-9pm) to even help with load balancing. People can currently make a small profit selling back to the grid, but there's virtually no chance of it providing more than about 5% of demand.

Solar Thermal Collectors: Better than photovoltaic as they can generally produce power for about 8 hours, then molten salt batteries can provide energy for another couple; but still not a viable large scale solution.

Wind: Geographically limited, very high maintenance costs.

Hydrogen: Only an energy storage medium, not a means to produce energy. In most cases there are more efficient ways to use the energy directly without the additional loss of producing hydrogen.

Corn Ethanol: Energy storage medium, and a bad one. The most optimistic numbers I've found indicate it requires about .84 gallons of gasoline to produce 1 gallon of ethanol. Most numbers are significantly worse, in the 1.2-1.4 range. It sounds great if the lower numbers are accurate, but 1 gallon of ethanol contains ~2/3 the energy of 1 gallon of gasoline so it's still a net loss. (note: I haven't done any serious research on sugarcane ethanol, which at first glance appears somewhat better)

Hydroelectic: Great technology that is proven, cost effective, and viable; but is severely limited geographically and the dams can cause major environmental concerns.

After years of following the news, studying it, and taking classes in renewable energy; it always comes back to nuclear. If it wasn't for legislative bungling, lawsuits preventing new plants, and the occasional (comparatively) minor failure of 40 year old technology we wouldn't even be talking about a clean energy problem. I'd love for one of these technologies to prove me wrong but there is little indication they will in the near future.