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Solar power is radiant light from the sun that can be converted into thermal and/or electrical energy. The conversion directly into electrical energy is by way of photovoltaic (PV) cells.

Such a PV system is active and will be the focus of this primer. Solar is one of the cleanest sources of energy and is renewable. Solar energy is measured in watt-hour (the amount of solar energy in the world is estimated at 173,000 terawatts that strikes the Earth continuously).

That is more than 10,000 times the world’s total energy consumption.

Photosynthesis in which solar energy is converted by green plants into chemical energy which creates the biomass that makes fossil fuels. Expanding solar power is key to meeting the climate and weather goals.

According to the International Energy Agency solar energy is the fastest growing energy sector, will projections of “more than 10% of the global electricity market by 2050”.

Photovoltaics cells commonly called solar cells were first invented at Bell Laboratories in 1954.

The New York Times April 26, 1954, proclaimed, “The beginning of a new era, leading eventually to the realization of one of mankind’s most cherished dreams — the harnessing of the almost limitless energy of the sun for the uses of civilization.”

The Space industry has been employing this technology since the 1960s to power spacecraft and terrestrial satellites. The oldest such satellites have just logged over 6 billion miles around the earth.

The Sun produces a spectrum of light on Earth commonly referred to as the Solar irradiance spectrum.

This radiation is close to that of a black body (thermal electromagnetic radiation surrounding a body) at a temperature 5800 ºK. The sun emits radiation over the most of the electromagnetic spectrum from X-rays to ultraviolet to radio waves. The Earth atmosphere filters out so of the light and protected us from some of the harmful radiation. I have enclosed the spectrum solar radiation on the Earth to understand the spectrum completely.

How do Photovoltaics Cells Work?

Photovoltaics is the only way of converting the suns energy directly to light. A number of materials absorb light particles (photon) and release negative charge particles (electrons). These types of materials exhibit the photoelectric effect. During the energy crisis in the 1970s, photovoltaic technology gained recognition as an important source of power for earth applications and several solar cell goals cost goals were outlined, mainly, least than a dollar/watt.

Shown below is a map of the mean total sunshine hours provided by the National Oceanic and Atmosphere Administration (NOAA). Presently, according to the Department of Energy, there is enough capacity to power the equivalent of 5.7 million average American homes.

Solar (PV) cells are made from semiconductor materials, such as silicon used in the nanotechnology/microelectronic industry. Thin film solar cells use layers of semiconductor materials only a few micrometers thick.

Thin film technology has made it possible for PV cells to now double as rooftop shingles or roof tiles. When light stokes this material, electrons are released from the semiconductor material and these electrons can be captured and used to power a lot, such as a light or a tool. This is illustrated in the diagram shown above.

A number of the PV cells are electrically connected to each other and mounted to a support structure or fame commonly called a photovoltaic module. The modules are designed to provide a known voltage typically 12 or 24 volts.

The modules are wired together to form an array. This array produces direct current (dc) electricity.  The cells can be single junction or multi-junction. The multi-junction cells are more efficient in converting sunlight into energy and convert more of the energy spectrum of light into electricity.

The PV system comes in two flavors; flat plate and/or concentrator. Both can be utilized to generate electricity. The flat-plate flavor just covers the Earth with PV cells.

The concentrator approach focuses the light to a spot, uses smaller PV cells and a tracking system. (Remember the magnifying glass you got as a toy in Cracker Jacks and focused it down to a spot and burned ants, that similar to the concentrator approach.)

A comparative manufacturing cost analysis of the two types of systems is always considered. But for most application, the flat plate approach is more cost effective.

Much of today research focuses on advanced multi-junction cells made from materials like gallium arsenide and gallium indium phosphide tunnel junction cells (also called tandem cells). Such multi-junction cells have reached efficiencies of around 35% under concentrated sunlight. There is also a cheap PV cell approach using multi-junction devices employing amorphous silicon and copper indium diselenide.

Total global solar energy generation capacity averaged 40 percent annual growth from 2000 (1.5 GW) to (208 GW and 343 GW) by 2016 Solar is the fastest growing source of renewable electricity in the world and in the United States.

Recommended Articles

The Silicon Solar Cell Turns 50, by John Berlin, https://www.nrel.gov/docs/fy04osti/33947.pdf
Solar Cells: Operating Principles, Technology, and System Applications, Martin A Green, ISBN-13: 978-0138222703, Prentice-Hall, 1982
Third Generation Photovoltaics: Advanced Solar Energy Conversion, Martin A. Green, ISBN-13: 978-3540265627, Springer Series in Photonics, 2005
Journal: Progress in Photovoltaics: Research and Applications

Dr. Gary L. Harris is a professor of electrical and computer engineering at Howard University in Washington D.C. He is also academic dean of the university’s Graduate School, associate provost for research and graduate studies, and director of the Nanoscale Science and Engineering Facility. He is a co-principal investigator of a new science and technology center. The Center for Integrated Quantum Materials, which is funded by the National Science Foundation (NSF), supports multi-institution programs that explore the unique electronic behavior of quantum materials. 

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