Lecture # 7 Solar Thermal Energy 1. Low Potential Heat

1. Solar Thermal Energy 1 Low Potential Heat

IE350

2. Solar Thermal 1 Low Potential Heat

Solar Thermal 1
Low Potential Heat
Greenhouses
Trombe walls
solar cookers
solar water heating systems
CPC collectors, troughs, vacuum pipes
implementation of solar ponds
Solar desiccant cooling
Integration with PV
Acquaintance with AUA solar hot water and
desiccant cooling system

3. Solar thermal energy

Visible
IR
With all objects on
Earth, solar heating
reaches a state of
temperature
Convection
homeostasis as the
Infrared (IR) heat imparted by
the sun is offset by
Visible
the heat given off
through reflection,
IR radiation, and
convection.
Contact heat transfer

4. Greenhouse

5. Greenhouse

6. Greenhouse – controllable temperature

7. Solar thermal energy

White objects
stay dramatically
cooler than other
objects because
the most
important
variables are
characteristics of Slowly but surely an
extinct glacier in a
the surface:
remote corner of the
- reflectance, Peruvian Andes is being
returned to its former
- emissivity,
colour, not by falling
- convection, snow or regenerated ice
- surface area. sheets, but by
whitewash. RESULT
Real snow on Chalon
Sombrero - not paint

8. Albedo = whiteness

• The albedo of an object is a measure of
how strongly it reflects light from light
sources such as the Sun. It is therefore a
more specific form of the reflectivity term.
• Albedo is defined as the ratio of totalreflected to incident electromagnetic
radiation. It is a unitless measure indicative
of a surface's or body's diffuse
reflectivity.

9. Various Albedo remember that relative value is important

Surface
Typical
albedo
Fresh asphalt
0.04
Worn asphalt
0.12
Conifer (evergreen)
forest (Summer)
0.08, 0.09 to
0.15
Deciduous trees
0.15 to 0.18
Bare soil
0.17
Green grass
0.25
Desert sand
0.40
New concrete
0.55
Ocean Ice
0.5–0.7
Fresh snow
0.80–0.90

10. Solar thermal energy

• Silvery objects get hot even though
they are excellent reflectors because
they are very poor in heat emission.
Human skin, and many other living
surfaces, like tree leaves, have near
perfect emissivity (~1.0), and so stay
pretty cool.
• Black people in Africa emit more IR
than white people.
• A perfect sunscreen is a dye that
perfectly absorbs, with high
emissivity, or perfectly reflects,
ultraviolet and infrared while being
transparent in visible light.

11. Foil Survival Blanket reflective thermal first aid

Made from metalized
polyester film, this ultrainsulating material is coated
on both sides with a heatreflective metallic surface.
It is ideal for treating or
preventing hypothermia
after first aid has been
administered. The
emergency foil blanket
retains most radiated body
heat while protecting
against wind and rain.

12.

13. Solar thermal energy

• Solar water heaters have solar collectors that are installed
outside dwellings, typically on the roof or nearby.
• Many models are the direct-gain type, consisting of flat panels
in which water circulates.
• Other types may use dish or trough mirrors to concentrate
sunlight on a collector tube filled with water, brine or other
heat transfer fluid. A storage tank is placed indoors or out.
• Circulation is caused by natural convection or by a small
electric pump. At night, or when insufficient sunlight is present,
circulation through the panel can be stopped by closing a
valve and/or stopping the circulating pump, to keep hot water
in the storage tank from cooling.
• Depending on the local climate, freeze protection, as well as
prevention of overheating, must be addressed in their design,
installation, and operation.

14. Passive Solar - Solar Cookers

• A solar cooker is a way of using the sun's power
to cook. There are mainly two types of solar
cookers: concentrating and solar box cookers
(usually known as solar ovens because of the
way they are used).
• Since they use no fuel they are free to run,
humanitarian organizations are promoting their
use worldwide to help slow deforestation and
desertification caused by the need for firewood
with which to cook.

15. Passive Solar: Solar Cookers

16.

17. Passive Solar - Solar Cookers

Passive Solar Solar Cookers

18. Lusine Machyan, IESM 2009 – in Altoetting, Germany, learning solar cooker production technology.

19. Gegham Sargsyan, IESM 2009 – in Altoetting, Germany, learning solar cooker production technology.

20. Passive Solar - Trombe walls

A Trombe wall is a sun-facing wall built from
material that can act as a thermal mass
(such as stone, concrete, adobe or water
tanks), combined with an air space,
insulated glazing and vents to form a large
solar thermal
collector.
Adobe wall
(not a Trombe wall)

21. Trombe Walls

• During the day, sunlight would shine through the
insulated glazing and warm the surface of the
thermal mass. At night, heat would escape from
the thermal mass, primarily to the outside.
Because of the insulating glazing, the average
temperature of the thermal mass can be
significantly above the average outdoor
temperature. If the glazing insulates well
enough, and outdoor temperatures are not too
low, the average temperature of the thermal
mass will be significantly higher than room
temperature, and heat will flow into the house
interior.

22. Trombe Walls

• Modern Trombe walls have vents added to the
top and bottom of the air gap between the
glazing and the thermal mass. Heated air flows
via convection into the building interior. The
vents have one-way flaps which prevent
convection at night, thereby making heat flow
strongly directional. This kind of design is an
isolated passive thermal collector. By moving the
heat away from the collection surface, it greatly
reduces thermal losses at night and improves
overall heat gain. Generally, the vents to the
interior are closed in summer months when heat
gain is not wanted.

23.

24. Solar Architecture

25. Solar Architecture

26. Solar Architecture

Look at south (in northern hemisphere)
Use the sun ecliptics
Use Trombe walls
Use controllable windows
Use integrated PV
Provide Aesthetics

27. Solar water heating panels

• A bucket of water can use solar energy
too.
• Need to prevent losses
• Provide comfort of use through
engineering
• Provide best price per peak watt.

28. Tel Aviv Picture by Eric Arevshatyan, IESM’07

29. Tel Aviv

30. Tel Aviv

31. Solar Water Heating Panel:

1) flat-plate absorber, - intercepts and
absorbs the solar energy,
2) transparent cover(s) - allows solar
energy to pass through but reduces heat
loss from the absorber,
3) heat-transport body - air, water or
antifreeze, flowing through tubes to
remove heat from the absorber
4) heat insulating backing

32.

33. Solar thermal energy

Visible
IR
With all objects on
Earth, solar heating
reaches a state of
temperature
Convection
homeostasis as the
Infrared (IR) heat imparted by
the sun is offset by
Visible
the heat given off
through reflection,
IR radiation, and
convection.
Contact heat transfer

34. Solar Water Heating Panel

Low Iron Tempered Glass
Piping,
liquid
Selective coating
Rear Screen (metal)
AIR
Absorber
Rear insulation

35. Selective Coatings

One of these tricks is "selective coating". In selective coating a
thin layer of either finely divided nickel (black nickel) or
chromium (black chrome) is formed on the surface usually by
electrolysis.
Such a layer has the property that it absorbs solar energy almost
as well as a matt black surface but it is a poor emitter of energy
at the temperature of the base metal. The net result is that,
other things being equal, a selectively coated absorber
exposed to sunlight will get hotter than a simple matt black one.
This in turn means that the lower conductivity of an aluminum
sheet can be compensated by having it run hotter so that the
copper water tubes do not have to be put closer together and
the sheet does not have to be made thicker.
A second advantage of selective coatings is that they enable the
collector to work better in poor conditions (weak sunshine.

36. Efficiency: vacuum pipe vs. flat panel

37. Efficiency

• Conversion Factor: 0 = 0.717
Loss Coefficient: a1 = 1.52 W/(m2K)
Loss Coefficient: a2 = 0.0085 W/(m2K2)
G - insolation level in
Watts/m2,
Ta - ambient
temperatures
Tm - average manifold
temperature (average
panel temperature).
Tm = (Tinlet+Texit)/2

38. Main factors that influence SHW panel efficiency

1. Temperature difference between the inlet
and outlet liquid, T, depending on your
working cycle.
2. Ability to isolate the convection through
air.
3. Ability to block the infrared (IR) radiation.

39. Greenhouse

40. Vacuum almost totally prevent convection losses.

41. Evacuated pipe collector in CPC (curved parabolic) design

42. Vacuum collector

43. Solar Water Heating Systems

1.Passive – based on fluid
convection
2.Active – based on
forced circulation via
pumps

44. Solar Water Heating Systems

1. Single Contour – no freezing
environment, no need in
antifreeze
2. Double or triple contour freezing temperatures in the
environment, need in antifreeze,
certain hygiene norms.

45.

46. SHW Systems

47. SHW Systems

48. SHW Systems

49. SHW Systems

50.

51. Solar cooling

• Photovoltaic + conventional
air conditionaire.
• Desiccant cooling.

52. AUA SOLAR SYSTEM

53. Desiccant Cooling

• We have constant flow of inlet air, exhaust
is dumped to the atmosphere.
• Solar energy is used to regenerate the
media that absorbs humidity.
• Pre-desiccated room inlet air is humidified,
low temperatures and acceptable humidity
levels are attained.
• The system is usually coupled with a heatrecovery system, that returns energy back
to the room from the exhaust channel.

54. Desiccant Cooling

55. Desiccant Cooling

56. Desiccant Cooling

57. Energy factor and Solar Fraction

• The solar energy factor is defined as the energy
delivered by the system divided by the electrical or gas
energy put into the system. The higher the number, the
more energy efficient. Solar energy factors range from
1.0 to 11. Systems with solar energy factors of 2 or 3 are
the most common.
• Another solar water heater performance metric is the
solar fraction. The solar fraction is the solar portion of the
total conventional hot water heating load (delivered
energy and tank standby losses). The higher the solar
fraction, the greater the solar contribution to water
heating, which reduces the energy required by the
backup water heater. The solar fraction varies from 0 to
1.0. Typical solar factors are 0.5–0.75.

58. Heat pumps

A final development in water heating, which is not strictly solar
but is sometimes set up in a "solar assisted" manner, is the
heat-pump.
A heat pump is essentially a refrigeration system working in
reverse. Instead of pumping heat from an evaporator inside
the refrigerator to a condenser in the room the heat pump
pumps heat from an evaporator in the atmosphere to a
condenser attached to the hot water cylinder.
For convenience the evaporator is sometimes mounted on the
roof of the house where the sun helps to provide input to the
evaporator.
Despite the appearance of roof mounted heat pump
evaporators, the heat pumps are really electrical heating
systems which use electricity in a much more energy efficient
way than simple conventional resistance heaters.
There is not a lot to distinguish between a good solar system
and a heatpump in terms of overall net consumer savings
over a year.

59. Windcatchers - Iran

60. Homework

• Find from internet the total worldwide
amount of solar water heating capacity
installed. Copy paste the reference link.
• Imagine your home has a south looking
wall of a specific size (e.g. 3 x 6 m). Now
you plan to build a Trombe wall on it.
Roughly estimate the budget based on the
bill of materials to construct it.

61. Second half of NEXT Lecture

A trip to the
rooftop