21-01-2013, 03:26 PM
Solar Energy: Resources and Technologies
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Solar Energy
• Solar energy is, and has always been, the Earth’s
primary energy resource
– Drives our climate
– Responsible for plant photosynthesis
• Solar energy has been “alternative energy” only for a few
decades in the industrialized parts of the world
• Fossil fuels (coal, oil, natural gas) are the stored,
concentrated, products of photosynthesis
• Wind, biomass and hydro are the result of solar energy
input
Solar Resource
• The Earth receives 1,366 Watts per square
meter (W/m2) from the sun continuously
• This is equivalent to over 43,000 times the entire
planet’s electric generating capacity
• But…
– Solar energy is not “concentrated” in the same way as
fossil fuels
– It needs to be “collected” before it can be used
– It sometimes must be stored since it’s not always
available when needed
• Solar energy is really electromagnetic radiation across a
broad spectrum of wavelengths
• The radiation generated by the sun travels through
space to the Earth, and through the atmosphere
• Not all of the sun’s radiation gets to the surface of the
Earth
• The amount of energy available at the surface depends
on:
– Atmospheric conditions including clouds, humidity, atmospheric
density, and dust
– Time of day (rotation of the Earth)
– Season (location of the Earth in its orbit around the sun)
– Latitude (distance from the equator)
– Orientation of the collector’s surface
Solar Energy Conversion
• To use solar energy means that we must
converting parts of the electromagnetic
energy spectrum to two other forms:
– Heat (thermal energy)
– Electricity
• The amount of heat or electricity produced
depends on the technology used and its
efficiency
Photovoltaic Technology - Background
• Photovoltaics (PV) converts sunlight to DC electricity
using a semiconductor cell
• The PV effect was discovered in the 19th century by
Alexander Becquerel
• Bell Labs pioneered early applications, especially for
satellites, in the 1960s
• Very small, remote applications emerged in the 1970s
and early 1980s
• As costs declined PV became more common for larger
applications in the late 1980s and early 1990s
PV Cell Materials
• The most common PV cells are made from
crystalline silicon wafers
• Other types of materials include thin films like
Cadmium Telluride (CdTe), Copper-Indium-
Gallium-Diselenide (CIGS), amorphous silicon (a-
Si)
• The main goals for manufacturers are to
minimize the amount of materials and maximize
efficiency
• Today, the best crystalline silicon cells are about
15% efficient; the best thin films are about 8%
efficient
How Are PV Systems Rated?
• PV modules are rated based on the
maximum power produced in Watts when
the amount of sunlight is 1,000 Watts/m2
• PV systems are rated based on the
maximum combined power output of the
PV modules
• Since the amount of sunlight changes, the
power output of the system will vary
Solar Thermal Technologies - Background
• Solar thermal is the oldest solar energy
technology – has been used for centuries
• Solar thermal technologies can be divided
into three types
– Passive solar building design
– Thermal collectors for hot water, space
heating, and other uses
– Solar thermal power plants
Passive Solar Design
• Passive solar design is a set of practices that
accommodate the local climate by:
– Letting the sun into the building in the winter
– Keeping the sun out in the summer
• The most important aspects of passive solar
design are:
– Building and window orientation
– Insulation and building materials
– Shading
Solar Thermal Collectors
• Thermal collectors convert solar radiation
into heat
• Main uses are water heating and space
heating for homes and businesses
• Many different types, but they can be
categorized as:
– Flat plate collectors
– Concentrating collectors
Solar Energy Benefits
• About 70% of all air pollution (sulfur dioxide, nitrogen oxides,
particulates) comes from our use of fossil fuels for generating
electricity, transportation, space and hot water heating
• Solar energy emits no air or water pollutants, and virtually no solid
waste
• Solar energy produces no greenhouse gases, which are linked to
global warming and climate change
• “Fuel” doesn’t require mining, drilling or transportation, and costs
nothing
• Does not require energy supplies to be imported from insecure
regions
• Systems can be installed exactly where the energy is needed
Solar Energy Issues and Barriers
• “Fuel” is free but the systems are not. Can be
costly to install compared to grid-supplied
electricity and fossil fuels
• Certain technologies, like PV, can require large
areas
• Some PV technologies use toxic materials,
although in very small amounts
• Energy storage must be used in some cases
Future of Solar Energy
• Solar thermal energy is already very cost-effective for
providing low temperature heat almost anywhere
• PV is very cost-effective for providing electricity in
remote areas and in niche applications
• As the costs of fossil fuels and electricity increase, PV is
becoming more cost-effective compared to electricity
from conventional sources
• The costs of all solar technologies are declining
• Federal and state incentives are increasing the use of
solar energy, which helps to increase awareness and
promote solar technologies