CEC332

2.  Energy produced
by the sun
 Clean, renewable
source of energy
 Harnessed by
solar collection
methods such as
solar cells
 Converted into
usable energy
such as electricity
Photovoltaic
(solar) panel
Set of solar panels
Sun and electrical
power lines

3. The surface receives about 47% of the total
solar energy that reaches the Earth. Only
this amount is usable.

6.  Eliminates work
◦ No daily search for
firewood
 2 Billion people rely on
wood for cooking fuel!
◦ No risks to women
and children
◦ Frees time for other
activities
◦ No need to stir food
◦ Helps to liberate
women

7.  Cooks foods slowly
and thoroughly
 Preserves nutrients
 Foods will not burn
 Pots are easy to
clean; less clean
water is needed
 Use for canning
vegetables
 Use for dried fruit
 Kill insects in dry
grains

8. Solar Thermal
Water heating and cooking
 Systems can be passive or
active
 Passive systems only
found in warmer climates,
as they are prone to
freezing
 Active: Roof-top
collectors heat glycol
which then passes
through a heat exchanger
in the storage tank to heat
water
 Electric pump can be run
on solar PV

9. Cooking Water Heating

10. Using the sun
to heat water
The simplest
solar
technology

11. This includes heating water for use in our
homes for cooking, bathing and cleaning,
or for heating swimming pool water, or
even providing space heating in winter.
These systems have been refined and
improved and widely used over the years to
the point where they pay for themselves in
energy savings while making people’s lives
more comfortable and lowering their energy
bills.

12. The rooftop solar
collectors on this
office building
provide hot water.
Solar water
heating is one of
the oldest and
most reliable
renewable energy
technologies.

14. Silicon-based
solar cell
Dye-
sensitized
solar cell
 Generate electricity
directly from sunlight
 2 Main types:
◦ Single-crystal silicon
(traditional)
 Widespread
 Expensive to manufacture
◦ Dye-sensitized (“nano”)
 Newer, less proven
 Inexpensive to manufacture
 Flexible

15.  Solar cells are devices
that take light energy
as input and convert it
into electrical energy
Light energy
Solar cell -
converts light
energy to
electricity
Electrical energy
(carried through
wires)

16. • Like chloroplasts in plants, solar cells can only
absorb specific wavelengths of light.
• In both, light that isn’t absorbed is either transmitted
through or reflected back.
• Whether a certain wavelength of lights gets
absorbed depends on its energy.
Chlorophyll molecules
absorb blue and red
light, but reflect green
light

17. Single electron
transition in an
isolated atom
• Absorption occurs only when the energy of
the light equals the energy of transition of
an electron
Light

18.  Electrons can
jump between
“bands”
 Incident light
with energy ≥
than the “band
gap” energy can
be used to
excite the
electrons

20.  Photovoltaic (PV) systems convert light
energy directly into electricity.
 Commonly known as “solar cells.”
 The simplest systems power the small
calculators we use every day. More
complicated systems will provide a
large portion of the electricity in the
near future.
 PV represents one of the most
promising means of maintaining our
energy intensive standard of living
while not contributing to global
warming and pollution.

21.  Sunlight is composed of photons, or bundles of
radiant energy. When photons strike a PV cell,
they may be reflected or absorbed (transmitted
through the cell). Only the absorbed photons
generate electricity. When the photons are
absorbed, the energy of the photons is
transferred to electrons in the atoms of the solar
cell.

23. • Solar cells are usually made of two thin pieces of
silicon, the substance that makes up sand and the
second most common substance on earth.
• One piece of silicon has a small amount of boron
added to it, which gives it a tendency to attract
electrons. It is called the p-layer because of its
positive tendency.
• The other piece of silicon has a small amount of
phosphorous added to it, giving it an excess of free
electrons. This is called the n-layer because it has a
tendency to give up negatively charged electrons.

24.  Large companies like
Google, Walmart, and
Microsoft use solar
energy to partially power
some of their facilities
Solar panels on Microsoft building
Solar panels being tested
on Walmart store

25.  These 20-kW Solar
Systems dishes dwarf
visitors in Alice Springs,
Australia.
 The concentrators use
an array of mirrors to
focus sunlight onto
high-efficiency solar
cells.
 Four supports hold the
cells in front of the
mirrors
 The supports also
supply cooling water
and electrical
connections

26.  General idea is to collect the light from many reflectors
spread over a large area at one central point to achieve
high temperature.
 Example is the 10-MW solar power plant in Barstow, CA.
 1900 heliostats, each 20 ft by 20 ft
 a central 295 ft tower
 An energy storage system allows it to generate 7 MW of
electric power without sunlight.
 Capital cost is greater than coal fired power plant,
despite the no cost for fuel, ash disposal, and stack
emissions.
 Capital costs are expected to decline as more and more
power towers are built with greater technological
advances.
 One way to reduce cost is to use the waste steam from
the turbine for space heating or other industrial
processes.

27. Power tower in Barstow, California.

28.  Focus sunlight on a smaller receiver for each device; the
heated liquid drives a steam engine to generate
electricity.
 The first of these Solar Electric Generating Stations
(SEGS) was installed in CA by an Israeli company, Luz
International.
 Output was 13.8 MW; cost was $6,000/peak kW and
overall efficiency was 25%.
 Through federal and state tax credits, Luz was able to
build more SEGS, and improved reduced costs to
$3,000/peak kW and the cost of electricity from 25
cents to 8 cents per kWh, barely more than the cost of
nuclear or coal-fired facilities.
 The more recent facilities converted a remarkable 22%
of sunlight into electricity.

29. Because they work best under direct sunlight,
parabolic dishes and troughs must be steered
throughout the day in the direction of the sun.
Collectors in southern CA.

30.  Photovoltaic cells are capable
of directly converting sunlight
into electricity.
 A simple wafer of silicon with
wires attached to the layers.
Current is produced based on
types of silicon (n- and p-
types) used for the layers.
Each cell=0.5 volts.
 Battery needed as storage
 No moving partsdo no wear
out, but because they are
exposed to the weather, their
lifespan is about 20 years.

31.  Efficiency is far lass than the
77% of solar spectrum with
usable wavelengths.
 43% of photon energy is used
to warm the crystal.
 Efficiency drops as
temperature increases (from
24% at 0°C to 14% at
100°C.)
 Light is reflected off the front
face and internal electrical
resistance are other factors.
 Overall, the efficiency is about
10-14%.
 Cost of electricity from coal-
burning plants is anywhere
b/w 8-20 cents/kWh,
while photovoltaic power
generation is anywhere b/w
$0.50-1/kWh.
 Does not reflect the true
costs of burning coal and its
emissions to the
nonpolluting method of the
latter.
 Underlying problem is
weighing efficiency against
cost.
◦ Crystalline silicon-more
efficient, more expensive
to manufacture
◦ Amorphous silicon-half as
efficient, less expensive to
produce.