Quick! Think of solar power! The image you probably came up in your mind is a roof covered in shiny black panels. Right? Those are photovoltaic cells. They make power when the sun shines. When it's cloudy or the sun is inconveniently on the other side of the planet, though, they don't.
Enter concentrating solar power, or CSP -- if you want to sound all cool about alternative energy. These things concentrate the sun's energy like a sophisticated magnifying glass hovering over a poor, defenseless ant on the sidewalk. But instead of burning innocent ants, the energy is so intense it becomes hot enough to heat a fluid, often molten salts, to somewhere in the neighborhood of 1,000 degrees Fahrenheit (537.8 degrees Celsius). This fluid can be stored, with energy inside it, until it's needed. Then it can power a turbine or engine to create electricity.
This already sounds fancy, and it is, but it's going to get fancier. And hotter. If researchers have their way, the energy from the sun will heat the fluid, which will be something like molten glass (which sounds super cool), to over 2,000 degrees Fahrenheit (1,093.3 degrees Celsius). This will, in theory, be far more efficient and far cheaper than the CSP systems in use already. And MOLTEN GLASS!