1. Solar Energy Technology Free energy, but expensive technology.

2. Outline • Solar Energy on the earth. • Insolation • Solar Heating Technology • Direct incidence • Flat plates and concentrating mirrors. • Storage • Applications

3. The atmospheric filter

4. Solar Insolation • Insolation: The amount of energy that falls per area of the surface of the earth. • Measured in either • Btu/ft2-day OR W/m2-hr • Important factors: • Seasonal, daily, climactic variations • Direct or diffuse? • Horizontal surface vs. tilted surface.

5. Solar Energy incident on flat surfaces during December

6. Solar Energy received by tilted surfaces during December

7. Insolation in Macomb • About 600 Btu/ft^2-day for a horizontal surface in December. • About 1000 Btu/ft^2-day for a tilted surface. • Need about 500,000 Btu per day. • That’s 500,000 Btu/day  1000 Btu/ft^2-day = 500 ft2, or about half the size of a medium sized home, assuming we can collect all that energy! • Direct collection – south-facing windows.

8. Direct collection system

9. Direct collection system at night

10. Indirect Solar Collectors • Flat Plates • Glazing • Absorbing surface • Storage and distribution • Insulation. • Concentrating Mirrors • Focused light through flat or cylindrical mirrors.

11. A flat plate energy collection system

12. Collector Efficiency • Efficiency: ratio of heat stored to the amount of solar energy reaching the surface. • Typically 50%. • Losses: • T • Emissivity and absorptance

13. Heating storage • Storage and regulation systems: • Water tanks • Rocks • Concrete • Heat Capacity: • Example: to store 500,000 Btu by heating water from 60 to 150 degrees F. • Q = c m T • m = Q / (c ) = 500,000 Btu / (1 Btu /lb*F)/ (90 F) = 5,555 lbs = 2500 kg = 665 gallons T

14. Other applications • Space Heating • Water Heating • Absorption cooling! • Cooking • Electricity – using large collection towers or rows of cylindrical mirrors. • Next time -- Photovoltaics