Solar Thermal
By:
Alicia Turner
Alejandro Delgado
Nick Laskovski
Tim Ferdinand
Pumped Solar Water heater
Collector panel
• Panel is tilted
perpendicular to the
suns rays
• A steel plate is bonded
to copper tubing acts
as the main absorber
of solar energy
Storage Tank
• Insulated with
fiberglass or
polyurethane foam
• Heat Exchanger
circulated the water
from the panel to the
bottom of the tank
Pump circulation system
• Transfers heat from
the panel to the tank
• Sensors turn on the
pump when the
collector becomes hot
• The water contains
antifreeze to prevent
pipe bursting
Thermosyphon solar water heater
• Used in frost-free
climates
• Relies on the natural
convection of hot
water to circulate the
water
• On cloudy days, when
little solar energy is
available, an electric
heater heats the water
Low vs. High Temperature
Solar Energy Collection
Low temperature
• Involves glass and other surfaces and their
ability to trap reradiated energy
High temperature
• Involves concentrating solar energy using
complex mirrors
Radiation
Diffuse radiation
• Light in a scattered form
after encountering clouds
Direct radiation
• Sunshine direct to the
earth
• Can provide up to 1
kilowatt per meter squared
Tilt and Orientation
• The earth’s tilt and the seasons determine the
degrees at which the solar collector will recieve
the most energy
• Summer—a small angle is needed because the sun
is higher in the sky
• Spring/fall– the angle equals the latitude of your
position
• Winter– panel must be almost upright because the
sun is low in the sky
Heat loss depends on…
• The temperature difference between the two
areas
• The total area measured
• The insulating properties of the material
Convection vs. Conduction
• Occurs between two
mediums where a warmed
substance expands,
becoming less dense….it
then rises
• Reduced by utilizing less
mobile gases or reducing
the space available for gas
movement
• Energy flow from from
hotter to colder regions
• Measured by its thermal
conductivity or is ability
to exchange heat at a
certain rate
• Reduced by using
insulators that do not have
good thermal conductivity
and do not lose heat easily
Varieties of Solar Heating Systems
Free-Standing Thermosyphon Solar Hot Water
Heater
Swimming Pool Heating
Conservatory (or Sunspace)
Trombe Wall
Direct Gain
Free-Standing Thermosyphon
Solar Hot Water Heater
http://reslab.com.au/resfiles/lowtemp/text.html
Swimming Pool Heating
Conservatory (or Sunspace)
Trombe Wall
Direct Gain
Active Solar Heating
• Invented in 1909 by William J Bailey in California
• His system had an insulated tank which could keep water hot
over night
• He was put out of business by the discovery of natural gas in
the 1920s
• 80% of homes in Miami between 1935 and 1941 had solar systems
• By 1950, the US solar industry completely succumbed to fossil fuel
o The Oil crisis in 1973 led to the reappearance of many solar
systems
Solar Collectors
•
•
•
•
•
•
Unglazed Panels, 0-10 °C Rise
Flat Plate Water Collector, 0-50 °C Rise
Flat Plate Air Collector, 0-50 °C Rise
Evacuated Tube Collector, 10-150 °C Rise
Line Focus Collector 50-150 °C Rise
Point Focus >100 °C Rise
Passive Solar Heating
“ Passive solar design refers to the use of the sun's
energy for the heating and cooling of living spaces. In
this approach, the building itself or some element of it
takes advantage of natural energy characteristics in
materials and air created by exposure to the sun.
Passive systems are simple, have few moving parts,
and require minimal maintenance and require no
mechanical systems.”
Sustainable building sourcebook
Passive Solar Heating
Direct gain:
• Solar energy enters a
building through
windows, is absorbed by
thermal mass of building,
and redistributed. Can
utilize 60-75% of sun’s
energy
Passive Solar Heating
Indirect gain:
• Solar energy is absorbed
by thermal mass located
in-between sun and
building and heat energy
is transferred to building
through conduction. Can
utilize 30 - 45% of the
sun's energy.
Passive Solar Heating
Isolated gain:
• Solar energy is absorbed
by a structure that is
attached but separate from
main building. Heat
energy is partially
transferred through
conduction and partially
remains in separate
structure. Can utilize 15 30% of sun’s energy
Passive Solar Heating
• The use of passive solar heating
dates back to the Roman
empire.
• Romans built windows into
their bath houses to allow the
sun to shine through.
• When empire collapsed the use
of glass disappeared until 17th
century.
• In late 19th century building
designers started incorporating
windows into their designs to
increase the quality of living
and working conditions.
Passive Solar Heating
• Want to think about what gross heat demands of
building are and where they are coming from
– Free heat gains- body heat, cooking, washing,
appliances, lights
– Passive Solar gains- windows
– Fossil Fuel
• A ordinary house in the UK has 14% passive solar
gains
Passive Solar Heating
To optimize solar heating gains:
1) Buildings should have longest walls running east to west
with windows facing south and to wall ratio of 2535%
2) Building should have a relatively large thermal mass which
can store thermal energy
3) Buildings should be well insulated to prevent the heat from
escaping.
4) building should have efficient back up heating system
5) buildings should be located so as to avoid overshading by
other buildings
Passive Solar Heating
To determine the necessary balance window to insulation
balance you can ask the following questions:
1) what is the buildings average internal temperature
2) what is the average external temperature during the months
that the building requires heat
3) how much sun do you get on average
4) where are the windows in the house located and in which
direction are they orientated
5) calculate the U-value of the windows in your house
Passive Solar Heating
Conservatories, greenhouse, and atria (Isolated gain)
• can be added to existing buildings, provides thermal
buffering and insulation, preheats air that enters the house,
conducts heat through walls of house, tend to be
expensive, must not be heated like the rest of the house or
savings will be non-existent
Trombe walls (Indirect gain)
• Instead of building a conservatory or greenhouse 8-16 inch
masonry wall is built and coated with dark heat absorbing
material, then this is covered by glass located ¾ to 6 inches
away. The wall absorbs heat and it slowly passes into
house.
High-Temperature Applications for
Solar Energy
• If
the sun’s rays are concentrated using mirrors, high enough
temperatures can be generated to boil water to drive steam engines.
• These as a result, can be used to produce mechanical work for
water pumping or driving electric generators.
•Today the most common device used to concentrate solar energy is
called.
A Parabolic Mirror
– All rays of light entering parallel to the axis of a u-shape
mirror are reflected to one point, the focus.
– Rays that enter off-axis will miss the focus.
– In order to keep the sun in focus, the collectors must face
south and track the suns elevation and azimuth.
–Parabolic collectors can produce temperatures that range from
200C – 1500C.
Solar Engines
The process of converting the concentrated powers of the sun in to useful
mechanical work started in the 19th century.
– 1860’s France lacked the supply of cheap coal
– Augustin Mouchot, mathematician creates a solar-powered steam
engine
– Towards the end of the century Mouchot and his colleague Abel Pifre
had created a series of machines like: Solar cooker, solar engines
driving refrigerators, solar printing press, solar wine stills
– Early French steam engines were not capable of producing steam at
high temperatures, and as a result their thermal efficiencies were poor
– In 1890 investments in mines and railways brought back the coal
– At the beginning of the 20th century, ideas continued to improve the
eficiency of solar power steam engines
– But little after the first world war came the cheap oil era, and interest in
solar steam engines collapsed
The New Solar Age
It was not until the early 1980’s that serious large experimental electricity generating
schemes were built to make use of high temperatures.
Power Towers (Central Receiving Systems)
– This used a field of tracking heliostats, which reflect the sun’s rays onto a
boiler at the top of a central tower
Solar Electricity Generating systems ( Parabolic trough concentrator systems)
– Way in which most of the world’s solar generated electricity is produced
– SEGS are essentially large fields of parabolic trough collectors, that heat
synthetic oil to 319 degrees Celsius, which can then produce high temperature
steam through the use of heat exchangers
– Luz international, has nine solar electricity generating systems located at the
Mojave Dessert in California
Parabolic Dish Concentrator System
– An alternative approach, where an engine is placed at the focus of a parabolic
mirror
– Created to avoid conveying solar heat from the collector down to a separate
engine
Solar Ponds
– Different approach to solar thermal heating production
– It uses a large salty lake, as a flat plate collector, where the proper gradient of
salt concentrations and water clarity allow for solar energy to be absorbed from
the bottom of the pond. (Initially developed in Israel, nowadays experiments
are carried out in the U.S and Saudi Arabia)
Ocean Thermal Energy Conversion (OTEC)
– It uses the ocean as a solar collector
– It exploits the temperature difference between the warm surface of the sea, and
the cold water at the bottom
– Not very efficient
Solar Chimneys
– Exploits the warm air produced at large greenhouses
– As hot air rises through tall chimneys, it turns an air turbine at the base of the
chimney, driving a generator to produce electricity
– It requires considerable amounts of land
Economics and Environmental Impacts
Active Solar Water Heating
– At present solar water heaters have high prices and low sales
– The life expectancy of solar water heaters is about 25 years, producing between 1000 to
1500 kwh of heat per year
– Their payback periods range from 10 to 20 years
– Countries like Austria, Greece, Germany, Spain and Netherlands happen to be major
contributors in the
– Production keeps increasing
– China Represents the biggest solar market world wide
– Promoting solar water heating is way to reduce CO2 emissions, and environmental
impacts all over the world
– The systems may turn out to be visually intrusive
Active Solar Space Heating
– Is technically feasible, but it is much more cost effective to invest in insulation to cut
back space heating demand
– Collectors used for space heating are said to have a 30 years
– Have performance collection of about 384kwh per m^2 per year
– Prices for these collectors are still high
Passive Solar Heating
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Highly economic, possibly free
Potentials are limited
Through adequate passive solar design, electricity consumption can be reduced
Environmentally beneficial
Solar Thermal Engines
– Dependent on the incidence of direct solar radiation
– Currently in sunny dessert locations, solar thermal electricity is cheaper than
photovoltaic power at current prices
– Low fossil fuel prices, have dampened interests in solar thermal electricity
generation
– Low thermodynamic efficiencies of some of these systems (solar pond, and solar
chimney) are so low that they require very large areas of flat land
– OTEC systems may release dissolved carbon dioxide from deep sea waters