[Dr. Scott W. Tinker] You may remember that I said we don't have a working nuclear fusion reactor. Well, that's not true. There is one, and it's been powering the Earth for over four billion years. It's the sun. This square meter will receive over a thousand watts of sunlight today. In fact, the surface of the earth receives enough sunlight in a single day to meet the energy demand of the world for over a year if it can be captured, and that is the challenge. Our solar array at the bureau can turn about 15% of that sunlight into electricity. That's pretty typical for solar panels and it's been that way for years. Why is that? A solar panel is essentially two layers of silicon, like the material found in sand. One layer is positively charged and one is negatively charged, like the batteries we made earlier. Sun strikes the layers, excites electrons between them, which flow onto this wire mesh and off the panel. You remember the light comes in different wavelengths along the spectrum from infrared to ultraviolet. Most bounces off or passes through the panel. Only a narrow band excites the electrons in between. We can make panels nearly three times as efficient at capturing energy by adding more layers sensitive to different bands of light, but this makes the panels many times more expensive and high price is already the greatest challenge of solar. So some think the solution is to go the other way. Make panels that are three times less expensive even if they are three times less efficient. That way, they're easier to install everywhere. Of course, there are other types of solar electricity. These plants capture the sun's heat rather than the light. They concentrate it with mirrors, heat water to make steam which turns a generator like in any other steam electric plant. But these two are only about 15% efficient. Part of that is due to clouds and night. As we've said, these make solar's output intermittent which can be a challenge to handle in an electricity system. If we could figure out more affordable storage to smooth out this curve and more affordable panels to make them broadly appealing, we'd see a lot more of it.