DIFFERENCE BETWEEN IRRADIANCE AND ISOLATION

1. SESE 6222
PASSIVE SOLAR ENERGY
TECHNOLOGY
DIFFERENCE BETWEEN IRRADIANCE AND INSOLATION.
SOLAR ANGLES AND THEIR APPLICATION IN PASSIVE HEATING AND
COOLING.

2. SOLAR INSOLATION
• This refers to the amount of solar energy that is available at a given
location, per unit of area and time. Typically, solar insolation is
measured in kilowatt-hours per square meter per day (kWh/ m2
/day) and it is a very important factor to consider before installing a
PV system, since it is the main variable that affects output:
• System output (kWh/day) = PV Array Area (m2
) x Efficiency (%) x Solar
Insolation (kWh/ m2
/day)
• The array area and system efficiency are constant values, which
means that the only variable factor is solar insolation. Two identical
PV systems will have a different output if installed on locations with
different solar insolation rates.

3. Solar Insolation Map around the World

4. SOLAR IRRADIANCE
• Solar irradiance, on the other hand, is the instantaneous solar power
per unit area, and it is variable throughout the day. Solar irradiance is
measured in kilowatts per square meter, and it directly affects the
power generated by a solar PV system at a given moment.
• Solar PV system instant power (kW) = PV array area (m2
) x Efficiency
(%) x Solar Irradiance (kW/m2
)

5. Solar Irradiance and its components

6. Classification of Irradiance
• Irradiance can be classified into three forms:
• Direct Irradiance; radiation which comes directly from the sun
• Diffused Irradiance; radiation which is diffused by the sky, layers of
atmosphere and other surroundings
• Reflected Irradiance; radiation which is reflected back by the lake,
seas and other water bodies

7. Solar Angles Introduction
• The Earth is an obligated sphere, meaning that it is a sphere that is flattened at
the poles and bulges around the equator. For solar power calculations it is
sufficient to treat the Earth as a simple sphere with a diameter of approximately
12 800 km. Points on the Earth’s surface are defined in terms of longitude and
latitude.
• The latitude of a point (P) is the angle between a radius drawn from the point to
the centre of the Earth and a radius drawn from the centre of the Earth to the
equator
• The longitude of a point is the angle between the Greenwich (or prime) meridian
and the meridian that passes through the point

8. Longitude and Latitude of point P

9. Solar Angles Introduction Cont…
• All latitudes above 66.55° north are inside the Arctic Circle (Figure
below) and all points below 66.55° south are inside the Antarctic
Circle. All points between the latitudes of 23.45° north and 23.45°
south are inside the tropics with the Tropic of Cancer being at a
latitude of 23.45° north and the Tropic of Capricorn being at a latitude
of 23.45° south. Latitudes can be written as positive values indicating
north and negative values indicating south; so that the tropics span
from +23.45° to –23.45°.

10. Earth during the Solstices showing
Latitude (φ) and Declination Angle (δ)

11. Earth’s Revolution Cycle

12. Solar Angles
• The position of the Sun in the sky as viewed from any point on the Earth’s surface
can be defined using a variety of angles. The declination angle (δ) and the hour
angle (ω) most easily defined from a view looking back at the Earth in the figure
below
• The hour angle at a point P on the Earth’s surface is the angle between the
meridian containing point P and the meridian that is parallel to the Sun’s rays
(Figure below).
• More angles are defined by considering the path of the Sun across the sky when
viewed from point P on the surface of the Earth. The figure below shows the
solar zenith angle (θZ), the solar altitude angle (α) and the solar azimuth angle
(AZ). The height of the Sun in the sky at any time can be descried as either α° from
the horizon or θZ° from a normal running though point P from the centre of the
Earth (so that α + θZ = 90°).

13. Celestial Sphere showing Declination Angle (δ)

14. Solar Angles Cont…
• Declination's angle is measured north or south of the
celestial equator, along the hour circle passing through the point in
question
• There are several conventions for the solar azimuth; however, it is
traditionally defined as the angle between a line due south and the
shadow cast by a vertical rod on Earth. This convention states the
angle is positive if the line is east of south and negative if it is west of
south.For example, due east would be 90° and due west would be
-90°
• Solar altitude (Zenith) refers to the angle of the sun relative to the
Earth's horizon. The value of the solar altitude varies based on the
time of day, the time of year and the latitude on Earth.

15. Zenith Angle (θz), Altitude Angle (α) and
Azimuth Angle (Az)

16. Passive Solar Heating and Cooling
• Passive solar heating design aims to keep out summer sun and let in
winter sun while ensuring the building’s overall thermal performance
retains that heat in winter but excludes it and allows it to escape in
summer. It uses free heating direct from the sun to dramatically
reduce energy consumed for space heating and cooling
• Passive cooling is a building design approach that focuses on heat
gain control and heat dissipation in a building in order to improve the
indoor thermal comfort with low or no energy consumption.This
approach works either by preventing heat from entering the interior
(heat gain prevention) or by removing heat from the building (natural
cooling).

17. Passive Solar Design
• Passive solar design takes advantage of a building’s site, climate, and
materials to minimize energy use. A well-designed passive solar home
first reduces heating and cooling loads through energy-efficiency
strategies and then meets those reduced loads in whole or part with
solar energy
• Because of the small heating loads of modern homes it is very
important to avoid oversizing south-facing glass and ensure that
south-facing glass is properly shaded to prevent overheating and
increased cooling loads in the spring and fall (for location in the
Northern Hemisphere)

18. Passive Solar Design Cont…
• Two basic aspects are considered in Passive solar design;
• Energy Efficiency; Before you add solar features to your new home
design or existing house, remember that energy efficiency is the most
cost-effective strategy for reducing heating and cooling bills
• Site Selection; If you’re planning a new passive solar home, a portion
of the south side of your house must have an unobstructed “view” of
the sun. Consider possible future uses of the land to the south of your
site—small trees become tall trees, and a future multi-story building
can block your home’s access to the sun.

19. Example of passive design

20. Aspects of Passive Solar Design
• For location in the northern hemisphere;
• Properly oriented windows. Typically, windows or other devices that
collect solar energy should face within 30 degrees of true south and
should not be shaded during the heating season by other buildings or
trees from 9 a.m. to 3 p.m. each day.
• Thermal mass. Thermal mass in a passive solar home -- commonly
concrete, brick, stone, and tile -- absorbs heat from sunlight during
the heating season and absorbs heat from warm air in the house
during the cooling season. Other materials include water and phase
changing products.

21. Aspects of Passive Solar Design
Cont…
• Distribution mechanisms. Solar heat is transferred from where it is
collected and stored to different areas of the house by conduction,
convection, and radiation
• Control strategies. Properly sized roof overhangs can provide shade
to vertical south windows during summer months. Other control
approaches include electronic sensing devices, such as a differential
thermostat that signals a fan to turn on; operable vents and dampers
that allow or restrict heat flow; low-emissivity blinds; operable
insulating shutters; and awnings.

22. Aspects of Passive Solar Design
Cont…
• The passive solar design takes into consideration;
• Insulation and air sealing
• Window location, glazing type, and window shading
• Thermal mass location and type.
• Auxiliary heating and cooling systems.
• Above considerations are dependent on the circumstances,
conditions and orientation of the location.

23. Techniques in Passive Solar Design
• Passive solar design applies said aspects using techniques that include
• Direct Gain; In a direct gain design, sunlight enters the house through
south-facing windows and strikes masonry floors and/or walls, which
absorb and store the solar heat. As the room cools during the night,
the thermal mass releases heat into the house.
• Some builders and homeowners use water-filled containers located
inside the living space to absorb and store solar heat. Although water
stores twice as much heat as masonry materials per cubic foot of
volume, water thermal storage requires carefully designed structural
support. An advantage of water thermal storage is that it can be
installed in an existing home if the structure can support the weight.

24. Direct Gain Applied in Passive Design

25. Techniques in Passive Solar Design
Cont…
• Indirect Gain; An indirect-gain passive solar home has its thermal
storage between the south-facing windows and the living spaces. The
most common indirect-gain approach is a Trombe wall.
• The wall consists of an 8-inch to 16-inch thick masonry wall on the
south side of a house. A single or double layer of glass mounted
about one inch or less in front of the dark-colored wall absorbs solar
heat, which is stored in the wall's mass.
• The heat migrates through the wall and radiates into the living space.
Usally at an average rate of about one inch per hour, so the heat
absorbed on the outside of an 8-inch thick concrete wall at noon will
enter the interior living space around 8 p.m.

26. Trombe Wall (Indirect Gain)

27. Aspects of Passive Solar Design
Cont…
• Isolated Gain ; The most common isolated-gain passive solar home
design is a sunspace that can be closed off from the house with
doors, windows, and other operable openings. Also known as a
sunroom, solar room, or solarium, a sunspace can be included in a
new home design or added to an existing home.
• Sunspaces should not be confused with greenhouses, which are
designed to grow plants. Sunspaces serve three main functions; they
provide auxiliary heat, a sunny space to grow plants, and a pleasant
living area. The design considerations for these three functions are
very different, and accommodating all three functions requires
compromises

28. Sunspaces Applied in Passive Design
(Isolated Gain)

29. “You cannot teach a man anything; you
can only help him discover it in himself.”
Galileo Galilei (1564 - 1642)
Thank You