Sun is 99.85% of mass of the Solar System Suns magnetic polarity flips regularly with 22-year cycle. Magnetic field is concentrated by 1000x in center of sunspots. Suns luminosity has increased by 30% since its birth --- now grows by 1% every 100 Myr. May cause a runaway Greenhouse on Earth in 500 Myr that will extinguish multicellular life. Process of nuclear fusion within stars (fusing hydrogen into helium) A full-disk multiwavelength extreme ultraviolet image of the sun taken by Solar Dynamics Observatory on March 30, False colors trace different gas temperatures. Reds are relatively cool (about 60,000 K); blues and greens are hotter (greater than 1 million K). Fig. 6-3, p. 165 What is the main problem with solar power? What are the time scales over which sunlight reaching a location varies? Day (day-night) Minutes to weeks (weather) What are the time scales over which sunlight reaching a location varies? Day (day-night) Minutes to weeks (weather) Year (seasonal rotation of tilt of axis) Annual variation in the output of solar panels at the AT&T Baseball Park in San Francisco Solar panels in Antarctica Solar panels in Madagascar Archimedes: 214 BCE, defending Syracuse from the attacking Romans Native American Anasazi built cliff dwellings into south- facing cliffs 1774: Antoine Lavoisier builds a solar furnace that can reach 1700C 1878: August Mouchot uses a solar furnace to run a small printing press Why a parabola? Solar energy can be used for cooking: CooKit solar cooker, Ghana (used for boiling water, killing, parasites, pasteurization, etc.) Parabolic mirror slow cooker (Spain) SOLAR WATER HEATING: 95% for heating swimming pools (< 110F) SOLAR WATER HEATING: 95% for heating swimming pools (< 110F) 5% for Domestic Hot Water (DHW) (140F - 180F) Solar domestic hot water system with heat exchanger Passive solar house can reduce heating costs by up to 50%, but has to be built into the design of the house What is the purpose of the awning? A thermal mass is needed to store the energy, like a concrete or tile floor. Solar energy can be used for desalination