World Energy Challenge
The world population is still rapidly growing, and several studies have predicted a world population of 9billion around 2040 in contrast to the 7 billion people Currently living on the planet today.
All these people will need energy, which increases the global energy demand. Furthermore, in many countries the living standard is rapidly increasing like China and India, where approximately 2.5 billion people are living, which represents more than a third of the World’s population.
The increasing living standards lead to an increased energy demand. Unfortunately, fossil fuels are not a sustainable energy source and may not be able to meet the increased demand for energy. Even with more oil and gas being produced through unconventional methods today, such as extracting oil from tar sands in Alberta, Canada and producing oil and gas with fracturing such as in large parts of the United States, the energy demand still remains a challenge. These unconventional methods use more energy for production and introduces several risks and environmental challenges like oil spill.
A further challenge is that by burning fossil fuels we produce the so-called greenhouse gases like Carbon dioxide (CO2) which contributes to worsening our climate change dilemma. Thus, we have a dual energy challenge of increasing demand and increasing CO2 emissions from conventional energy sources like fossil fuels.
To solve this energy challenge, we are increasingly turning to renewable energy sources like wind, heat and solar energy to reduce CO2 emissions. With improvement in technology for the manufacture of photovoltaic cells, Solar energy is proving to be the energy of the future. Solar energy installations using solar PV panels have increased exponentially over the last few years with Europe, Asia Pacific and North America leading the way.
Advantages of Solar Electricity
Some key advantages of solar power are:
• Energy Independence
• Environmentally friendly technology
• The fuel (sunlight) is abundant everywhere
• It requires minimal maintenance
• Maximum reliability
• Reduce vulnerability to power loss
• Due to its modularity, system can easily be expanded.
Photovoltaic Cells or Solar Cells
Photovoltaic cells are the main building block for solar PV panels. A Solar cell consist of a thin wafer of Silicon just like a computer chip, but it is much larger and much cheaper. The sun light energy that falls on the cells is converted into electric current however, they do not store the electric energy generated. The fuel for solar cells is sun light which is abundant all over the earth.
How Does Solar Cells Change Sun Light Energy into Electricity?
The working principle of solar cells is based on the photovoltaic effect, i.e. the generation of a potential difference at the junction of two different materials in response to electromagnetic radiation in this case sun light radiation. Most solar cells consist of a P-type and N-type semiconductor material. A simple model of a typical solar cell is shown below:
As shown above, Light penetrates the cell. Particles of light called photons bounce into negatively charged electrons around the silicon atoms of the cell and knock these electrons free from their silicon atoms. The energy of the photon is transferred to the electron in the process. There are billions of billions of photons falling on the cells every second, so there are lots of electrons knocked loose. Each electron is pushed by an internal electric field that has been created in the factory in each cell. The flow of electrons pushed out of the cell by this internal field is what we call the electric current which can be used to drive an electric circuit.
As long as there is light flowing into the cells, there are electrons flowing out of the cells. The cells do not use up its electrons and loose power, like a battery. It is just a converter, changing one kind of energy (sunlight) into another (flowing electrons). For every electron that flows out of the wire connected to the front of a cell, there is another electron flowing into the back from the other return wire.
Difference between Solar PV Systems and Solar Thermal Energy Systems.
Photovoltaic (photo = light; voltaic = produces voltage) or PV systems convert light directly into electricity using semiconductor technology, while solar thermal systems, convert sunlight energy into heat which is then further used to produce electricity.
Solar PV Terminology
PV Cells
The photovoltaic cell or PV cell is the basic building block for PV modules. Some PV cells are round while others are square. A typical solar cell or PV cell produces 0.5V or 0.6V. PV cells can be connected in series or parallel. When the cells are connected in series, the voltage = the number of cells in series x open circuit voltage of one cell, while the current remains the same. If the PV cells are connected in parallel, the current = the number of cells in parallel x current per cell. A PV cell is shown below:
Most Solar cells in a Solar PV panel are connected in series to achieve larger voltage levels.
PV Modules
A group of PV cells connected in series and/or parallel and encapsulated in an environmentally protective laminate make up a PV module. The names PV module and solar module are often used interchangeably. Modern PV modules often contain 60 (10 × 6), 72 (9 × 8) or 96 (12 × 8) solar cells that are usually all connected in Series in order to maximize voltage and minimize resistive losses. A typical PV module is shown below:
A solar Panel
A solar panel consists of several PV modules that are electrically connected and mounted on a supporting structure. However these days, reference to a solar panel refers to a single PV module which is kind of a misnomer but it has stuck.
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| A solar Panel |
PV Arrays
A PV array consists of several solar panels. An example of such an array is shown below:
This PV array above consists of two strings of two solar panels each, where string means that these panels are connected in series.
Typical Specifications of Solar PV Panels
Most solar PV modules in the market today have the following technical electrical specifications at standard Test Conditions (STC) at irradiance of 1000W/m2 , temperature of 25 degree C, AM1.5:
(1) Rated Power (Pmpp) – This is the maximum rated power of the solar module
(2) Rated Current (Impp) – This is the rated current in Amps of the PV module at peak power.
(3) Rated Voltage (Vmpp) – This is the rated voltage (volts) of the PV module at peak power.
(4) Short Circuit current (Isc) of the PV module.
(5) Open Circuit Voltage (Voc) – This is the voltage of the PV module without load at the terminals
(6) Dimensions – Every Solar PV module has its stated dimensions and it different from manufacturer to manufacturer.
(7) Maximum Warranty on Pmpp – This is the warranty on the maximum power provided by the
solar module, and it is typically 25 years for most solar panels.
There are other specifications such as mechanical properties, certifications and warranty and temperature coefficients that manufacturers of solar panels usually produce in addition to the electrical specifications.