Speaking of sun-powered planes, the Solar Impulse just made its final test flight around the San Francisco Bay Area before embarking on a cross-country voyage next week.
The reason astronomers want to observe reflected sunlight during the transit of Venus is to test whether they can detect the faint imprint of passage of the sun's light through the atmosphere of Venus.
Pyron Solar's 20-kilowatt test installation in San DiegoMost concentrating solar installations also swivel to track the sun during the day, which is far more effective than a fixed array.