I just read about a remarkable development in solar energy technology. At least I think it is remarkable. A unit of United Technologies called Hamilton Sundstrand has developed a solar power plant that will use molten salt to store the energy and generate electricity when the sun isn't shining. They will be trying to commercialize this technology with US Renewables which is a private equity fund. Read the press release as I couldn't find a news article long enough to provide good detail.
The success of this technology will make or break renewable energy in my opinion. If the intermittent nature of the supply is removed from the equation then it can compete with current sources like coal. I'm not sure about the cost or other safety issues but it sounds exciting from what I have found.