The Sun: Active Solar Heating

1
The Sun Active Solar Heating

• Bringing the Sun Inside

2
Concentrating Sunlight

• The suns radiation can be concentrated using
  curved mirrors
• In this design, light is focused on a
  fluid-filled pipe
• Solar concentrators must always point toward the
  sun

3
Solar Cookers

• Solar cookers concentrate sunlight enough to cook
  a meal
• The suns heat is trapped in a glass-covered box
  by the greenhouse effect
• Requires good insulation

4
Active Solar Heating

• In active solar heating, a fluid or air is first
  heated by the sun
• Pumps or fans are used to distribute heat to
  storage or direct use

5
Solar Collectors

• Flat Plate Collectors are the most common type of
  domestic solar collectors
• Solar radiation is absorbed by a metal plate
• Glass covers prevent heat from escaping

6
Flat Plate Collectors

• Heat from a flat plate collector is exchanged
  with fluid in metal tubes
• Water can also trickle down corrugated metal
  sheets

7
Orientation of the Collector Plates

• Since more heat is required in winter, collector
  plates should face more towards the winter sun
• A good rule is to angle the plate halfway between
  the noon height of the sun in fall and winter

8
Calculating the Tilt of a Collector

• Ignore the calculation in the previous slide (it
  is incorrect)
• The optimum angle in spring or fall is
• anglefall your latitude
• The optimum angle in winter is
• anglewinter your latitude 23.5
• Thus optimum angle (anglefall anglewinter)/2

9
Example

• What is the optimum angle for a solar collector
  in Stevens Point (44.5 N)?
• anglefall 44.5
• anglewinter 44.5 23.5 68.0
• optimum angle (44.5 68.0)/2 56.3

56.3
10
Domestic Hot Water Systems

• Some active systems are used only to heat water
• Antifreeze solution is pumped through the
  collectors (to prevent freezing in winter)
• Heat from the antifreeze is exchanged with water

11
Domestic Heating Systems

• Active systems can be used to heat the house as
  well
• Some heated water is circulated through pipes in
  the floor, which heats the house

12
Hot Air Heating

• Air is heated in a flat plate collector and
  circulated with fans
• Some heat from the air is stored in a bin full of
  rocks, the rest is used to heat the house
• Cold water is heated by circulating through the
  heated rocks

13
Example

• How large a collector is required to heat a home
  that requires 100,000 Btu/hr? Assume the
  insolation is 1300 Btu/hr/ft2 and the collector
  is 50 efficient.
• Answer Q I x ? x A
• I insolation, ? efficiency, A area of
  collector
• Rearrange equation to obtain A Q/(I x ?)
• 100,000/(1300 x 0.5) 154 ft2

14
Solar Cooling

• The sun can be used to passively cool a house
  using solar convection currents (breezes)
• Active solar cooling is also possible (i.e. using
  the suns heat to run an air conditioner)

15
Using the Sun to Generate Electricity

• Solar cells can convert sunlight directly into
  electricity
• We will discuss these in more detail later in the
  course