While solar power plants have been coming on line all over the nation, some of them are using traditional fuel sources to ensure that a steady supply of electricity is available at all times.

This is often the case with natural gas plants that use photovoltaic panels to meet peak electricity demand during the day, and with solar thermal plants that can heat turbines for only so many hours after the sun goes down.

With that in mind, Xcel Energy announced the first-of-its-kind demonstration of a hybrid coal/solar plant located at the company's Cameo Generating Station near Grand Junction, Colorado.

The project is expected to help Xcel burn less coal at the facility while also making more efficient use of its resources. This is particularly important when factoring in a carbon-intensive energy source like coal.

Other solar technologies are being developed that can help store energy for increasingly long periods of time. For example, Swiss researchers are working on a solar-powered plane that they plan to test on an overnight flight in the coming months.