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