Solar Energy Technology
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Transcript of Solar Energy Technology
Solar Energy Technology
Free energy, but expensive technology.
Outline
Solar Energy on the earth.– Insolation
Solar Heating Technology– Direct incidence– Flat plates and concentrating mirrors.– Storage– Applications
The atmospheric filter
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.
Solar Energy incident on flat surfaces during December
Solar Energy received by tilted surfaces during December
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.
Direct collection system
Direct collection system at night
Indirect Solar Collectors
Flat Plates– Glazing– Absorbing surface– Storage and distribution– Insulation.
Concentrating Mirrors– Focused light through flat or cylindrical
mirrors.
A flat plate energy collection system
Collector Efficiency
Efficiency: ratio of heat stored to the amount of solar energy reaching the surface.
Typically 50%.Losses:
T– Emissivity and
absorptance
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 gallonsT
Other applications
Space HeatingWater HeatingAbsorption cooling!CookingElectricity – using large collection towers
or rows of cylindrical mirrors.Next time -- Photovoltaics