| Q. |
What
are the different methods to convert solar energy into electricity? |
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| A. |
Solar
energy can be converted into electricity primarily in two ways:
| 1. |
Photovoltaics
(PV), where sunlight is converted directly into electricity,
and |
| 2. |
Concentrating
Solar Power (CSP) (also synonymous to Solar Thermal), heat is
extracted from sunlight and converted into other forms of energy
like electricity. |
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| Q. |
What
is Photovoltaics (PV)? |
| |
|
| A. |
Photovoltaics
is the direct method of converting sunlight into electricity using
a device known as a solar cell. |
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|
| Q. |
How
does a solar cell work? |
| |
|
| A. |
When
semiconductors such as silicon are exposed to sunlight, they produce
small amounts of electric charge (electrons and holes). A well-designed
solar cell separates this charge to form a positive and negative terminal.
Hence, these terminals produce a voltage, and when connected to an
external circuit, cause a current flow. In this way, a solar cell
in the Sun works just like a battery. |
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| Semiconductor
structure... |
|
...looks like... |
|
...works like... |
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| Q. |
How
much energy does sunlight carry? |
| |
|
| A. |
1018 kilowatt-hours of sunlight reaches the earth’s surface every
year, which is 6,000 times greater than the world’s annual energy
demand. This means that the Sun provides world’s annual energy
to the earth in one hour! In another metric, on a clear day, sunlight
measures a power density of 1 kilowatt per square-meter or area. |
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| Q. |
How
much power can a solar cell generate? |
| |
|
| A. |
The power
generated by a solar cell depends on the amount of sunlight it receives,
area of the solar cell and its efficiency. For example, on a clear
day, a 15% efficient solar cell of area 15 x 15 cm2 will
produce 3.4 watts of power. |
| |
|
| Q. |
What
is the difference between a solar cell and a photovoltaic panel? |
| |
|
| A. |
A solar
cell is a single semiconductor device, while a photovoltaic module
consists of multiple solar cells connected together into a single
unit to protect the solar cells and increase the voltage and power
above that of a single solar cell. “Photovoltaic panels”
and “Photovoltaic arrays” are sometimes used interchangeably,
but they refer to the collective system of photovoltaic modules connected
together in the system. |
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|
|
|
| Solar or PV
cell. |
|
PV module. |
|
PV array. |
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|
| Q. |
How
much power does a solar module generate? |
| |
|
| A. |
Just
as individual batteries can be interconnected, solar cells too can
be connected in series and parallel connections and encapsulated into
a module to output desired power. |
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|
|
|
| PV module
circuit. |
|
Equivalent
battery circuit. |
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|
| Q. |
What
type of electricity does a solar module generate? |
| |
|
| A. |
PV panels
produce DC power, which is the same type of power produced by batteries.
An inverter is used to convert this DC into AC power in order to run
typical household appliances. |
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|
| Q. |
What
are the potential uses of photovoltaics? |
| |
|
| A. |
Due to
its versatility, photovoltaic energy can be used in a wide range of
applications requiring power from a couple of milliwatts for small
electronics to a couple of megawatts to support entire communities.
Traditionally, the most common application of photovoltaics has been
for electrical loads that cannot be easily plugged into the electricity
grid, either because they should be transportable – such as
solar calculators, watches, etc. – or because the electricity
grid does not exist at a particular location. Where the grid is located
far away from a particular application, photovoltaics is being used
to provide “remote power”. Examples of these applications
are houses not connected to grid power, telecommunications, remote
villages, water pumping and space applications. However, a recent
and rapidly growing application for photovoltaics is for residential
or building-integrated which are connected to the electricity grid.
During the day, power is used from photovoltaics, and at night power
is used from the electricity grid. A final application is utility-scale
photovoltaics, in which a utility company installs a large amount
of photovoltaic power. These larger systems, which are far less common
than other applications, are typically installed to achieve a specific
technical goal. |
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|
| Q. |
How
does a photovoltaic system work? OR what are the components of a photovoltaic
system? |
| |
|
| A. |
A photovoltaic
system mainly consists of:
| 1. |
Solar
panels, which directly convert sunlight into DC electricity, |
| 2. |
Charge
controller, which interfaces the solar panels to the rest of
the photovoltaic system and ensures maximum power extraction
from the solar panels, |
| 3. |
Batteries,
if the system is designed to store energy, |
| 4. |
Inverter,
to convert DC electricity into AC if required, |
| 5. |
Net-metering
equipment, if the generated power is fed back into the electricity
grid, and |
| 6. |
Monitoring
equipment, if it is intended to monitor the photovoltaic system. |
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|
|
|
| Typical grid-connected
home PV system. |
|
Typical stand-alone
PV water pump system. |
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|
| Q. |
How
does a photovoltaic system provide power at night? |
| |
|
| A. |
Solar
cells do not directly work at night; however, typical solar systems
are designed to store power generated during the day into batteries,
and power can be extracted from batteries at night. |
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| Q. |
How
long does a photovoltaic system last? |
| |
|
| A. |
Photovoltaic
systems are very robust and reliable, since there are no moving parts.
A photovoltaic system would be expected to last in excess of 20 years.
Many manufacturers have 20-year warranties on the photovoltaic modules.
The electronic components can also be made reliable, since again there
are no moving parts, but the warranties on these systems tend to be
lower, about 5 years. If the photovoltaic system contains batteries
(most stand-alone systems do and residential grid-connected do not),
then the batteries will need to be replaced every 5 to 10 years.
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