Solar Collection and Energy Transport.

Solar Collection and Energy Transport. Fixing of atmospheric Carbon into the biomass photosynthesis is a form of solar collection and energy storage.

The Key to efficient use of solar energy lies in efficient modes of heat transfer. There are three possible modes:

Conduction

Transfer of energy via the vibration of atoms in some medium. The best conductors are silver and copper.

Convection

Transfer of energy via the bulk motion of a medium (e.g. air, water)

Thermal
Radiation

Cooling of a material to thermal equilibrium via radiation losses. Stored energy re-emitted (Power per unit Area) goes as T4

Thermal Conduction:

So Clearly metals are required for efficient heat transfer.

Heat flow through a wall:

Convection: liquids and gases transfer heat this way motion of the medium between regions of different temperatures.

Fireplaces produce natural convection warm air rises and is replaced by cold air

Most space heating systems operate via convective heat transfer (forced air)

Thermal Radiation:

Water is the clear winner followed by concrete. So thermal mass is most effectively used in the form of large tanks of water or several tons of concrete in an insulated container.

Solar Energy: Collector Systems

Variation of Incident Sunshine with location in the US

Flat Plate Collector Systems:

Heat transfer to a circulating liquid (antifreeze) to be used as supplemental space heating source in the Winter

Basic System Design

On average, a house loses 1 BTU per cubic foot per degree day

A degree day = 65 - average 24 hour temperature

Energy losses in a flat plate collector system:

Orientation of collector with respect to sun is crucial part of overall efficiency

Focusing Collectors:

Not practical for the homeowner somewhat dangerous due to high temperatures.

Parabolic reflectors (heliostats) are pretty expensive

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