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 25-

35%

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

– 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