Solar Energy Fundamentals
Solar Energy Fundamentals
Solar Energy Fundamentals
Energy reaching the earth is incredible. By one calculation, 30 days of sunshine striking the Earth
have the energy equivalent of the total of all the planet’s fossil fuels, both used and unused!
The heat energy produced by sun, if ever captured completely, can satisfy entire mankind’s energy
requirement for hundreds of years
Disadvantages
Sun does not shine consistently throughout the season and varies across geographical locations –
Also the 23 ½ degree tilt of earth axis ensures non-uniform distribution of solar energy
Solar energy is a diffuse type of heat source. To harness, it must be concentrated into an amount
and form that we can use such as heat and electricity. The diffusion occurs due to various
environmental factors like clouds, moisture, dust, pollutant and altitude of the location
The intensity of solar radiation after diffusion can vary from 10% to 100%
Methods of concentration –
1) Collection 2) Conversion 3) Storage
How much solar energy?
O n a t y p i c a l d r y d a y, t h e s u r f a c e r e c e i v e s a b o u t 4 7 %
of the total solar energy that reaches the Earth
which is usable
Units of Solar Energy
Photo-Voltaic (PV) cells are used for generating electricity from solar radiation –
It is often represented using kilowatt-hour per square meter (KWh/m2) or Watt per
square meter(W/m2) – The energy collected by photo voltaic is generally in DC mode.
Using an INVERTER, it is converted to AC mode for domestic applications. A single
PV module can generate between 10 to 300 watts.
Solar energy used for water and space heating application is generally represented
in British thermal units per square feet (BTU/ft2) – Based on type of collector used,
the quantity of water (or space) to be heated varies – As a thumb rule 20 square feet
(2 square meters) of solar panel is necessary for heating around 50 to 60 US gallons (
190 to 230 liters) of water. For every additional family member, add 8 to 10 square feet
(0.73 to 1 square meter) of solar panel. The tank size should be accordingly increased
– For every square feet of panel area, consider 1.5 gallons ( 5.7 liters) to 2 gallons
(7.7 liters)
Solar Energy for heating Water
Two methods of heating water: Passive
(no moving parts) and Active (utilizing
pumps).
In both, a flat-plate collector is used to
absorb the sun energy to heat the
water.
The water circulates throughout the
closed system due to convection
currents.
Insulated tanks can be used for storing
hot water throughout the day
Heating Water—Last Thoughts
Efficiency of solar heating system is always less than 100% because:
Percentage of heat transmitted depends on angle of incidence
Number of glass sheets (single glass sheet transmits 90-
95%), and
Composition of the glass
Solar water heating saves approximately 1000 megawatts of energy
annually equivalent to eliminating the emissions from two medium
sized coal burning power plants
By using solar water heating over gas water heater, more than 30%
energy conservation can be achieved
Although the initial installation is a complex process, the heating
system saves “conventional energy” in long run
Heating Living Spaces
Best design of a building is for it to act as a solar collector and storage
unit. This is achieved through three elements: insulation, collection,
and storage
Efficient heating starts with proper insulation on external walls, roof,
and the floors. The doors, windows, and vents must be designed to
minimize heat loss
Collection: south-facing windows and appropriate landscaping
Storage: Thermal mass – amount of heat holding capacity
• Water= 62 BTU per cubic foot per degree F
• Iron=54, Wood (oak) =29, Brick=25, concrete=22 and loose stone=20
Heating the living spaces
Passive Solar
With minimum maintenance, the solar heating systems can last longer
– almost close to 25 years !
Solar-Thermal Electricity:
Power Towers
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, California having 1900
heliostats, each measuring 400 square feet with a 295 feet central tower
An energy storage system allows it to generate 7 MW of electric power
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.
Power Towers
Assembly of collectors
Because they work best under direct sunlight, parabolic dishes and
troughs must be steered throughout the day in the direction of the
sun.
Direct Conversion into Electricity
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 – Higher the
power, higher will be the battery
capacity
No moving parts means they do o no
wear out. But because they are exposed
to the weather, their lifespan is about
20 years.
Efficiency and Disadvantages
Does not reflect the true costs of
Efficiency is far lass than the burning coal and its emissions to
77% of solar spectrum with the nonpolluting method of the
usable wavelengths. latter.
Efficiency drops as temperature Underlying problem is weighing
increases (from 24% at 0°C to efficiency against cost.
14% at 100°C.) Crystalline silicon-more efficient
but expensive to manufacture
With proper designing, the
electricity generated from solar Amorphous silicon- Half as
energy can light up entire house efficient but expensive to produce
The cost of power generation will
The solar energy is noise free,
be three to four times conventional
pollution free, and maintenance
method with present day
free
technologies
At present, solar heating system
components are expensive
Final Thought
Argument that sun provides power only during the day is countered by
the fact that 70% of energy demand is during daytime hours. At night,
traditional methods can be used to generate the electricity
Goal is to decrease dependence on fossil fuels
Currently, 75% of electrical power is generated by coal-burning and
nuclear power plants
Solar energy reduces the effects of acid rain, carbon dioxide, and other
impacts of burning coal and counters risks associated with nuclear
energy
Pollution free, indefinitely sustainable
The primary source – SUNLIGHT – is available, free, throughout life!
The End, only for now….