What is photovoltaic energy?

What is photovoltaic energy?

The word ‘photovoltaic’ carries its own meaning:  ‘photo’ mean light, and ‘voltaic’ comes from the word voltage—which is one of the units used to measure electricity.

Often written in short form as PV, a solar or PV panel is made up of many small solar cells all connected together.  Each solar cell, when exposed to sunlight, produces a small electrical charge.  This is the photovoltaic effect.

Compared to the other sources of renewable energy, photovoltaic electricity was a late starter. The  photovoltaic effect was finally brought to life when Daryl Chapin, Calvin Fuller, and Gerald Pearson developed the silicon photovoltaic (PV) cell at Bell Labs in the USA—the first solar cell capable of converting enough of the sun’s energy into power to run everyday electrical equipment. Bell Labs produced a silicon solar cell with 4% efficiency and later achieved 11% efficiency.

Silicon is the most common material used in solar cells, representing approximately 90% of the modules sold today. Crystalline silicon cells are made of silicon atoms connected to one another to form a crystal lattice. This lattice provides an organized structure that makes conversion of light into electricity more efficient.

Solar cells made out of silicon currently provide a combination of high efficiency, low cost, and long lifetime. Modules are expected to last for 25 years or more, still producing more than 80% of their original power after this time.

More sophisticated are the thin-film solar cells.

CdTe is the second-most common PV material after silicon, and enables low-cost manufacturing processes. While this makes them a cost-effective alternative, their efficiencies still aren’t quite as high.

CIGS cells have favorable electronic and optical properties, though the complexity involved in combining four elements makes the transition from lab to manufacturing challenging and more expensive. Both CdTe and CIGS require more protection than silicon to enable long-lasting operation outdoors.

A thin-film solar cell is made by depositing one or more thin layers of PV material on a supporting material such as glass, plastic, or metal. There are two main types of thin-film PV semiconductors on the market today: cadmium telluride (CdTe) and copper indium gallium diselenide (CIGS). Both materials can be deposited directly onto either the front or back of the module surface.

The efficiency of the cells has also improved.  The first solar cells only converted about 10 % of the sun’s energy to electricity. The efficiency of commercially-available solar cells now is closer to 20%.  In the lab, efficiencies can reach closer to 50%.

The technology, at first very expensive, started to become commercialized in the 1960s–mainly for satellites that needed low levels of power for long periods of time. In 1958, Vanguard I & II, Explorer III, and Sputnik-3 satellites were launched–each powered by solar PV arrays. In 1959, Explorer VI was launched with an array of 9600 cells.

Terrestrial applications were few and far between because the PV cells were expensive. Communication systems in isolated areas were an early niche market.

PV powers up

In 1978 a 3.5 kW solar array was installed on the Papago Indian Reserve in southern Arizona—the world’s first village PV system.  A few years later, in 1982, the first megawatt-scale solar photovoltaic power plant started up in Hesperia, California.  The PV panels with a peak output of 1 MW, were installed on 108 tracking structures that kept the panels facing the sun over the course of the day.

But what has shaken up the energy world over the last 20 years is the way that the cost of generating electricity from this reliable, clean, and renewable source of energy has dropped so far and so fast. Photovoltaic power is now one of the least cost options—cheaper than all the fossil fuels.

Not surpringly, the development of huge megawatt-scale PV power plants is now underway.

In early 2018 it was reported that Saudi Arabia and SoftBank Group Corp. had signed a memorandum of understanding to build a $200 billion photovoltaic power plant that would be exponentially larger than any other project worldwide.

The deal is the latest in a number of record-breaking announcements from Saudi Arabia—a country that is promising to massively scale up its access to renewable energy.

At 200 Gigawatts, the photovoltaic power plant planned for the Saudi desert would be about 100 times larger than the next largest proposed utility-scale PV development, and more than double the level of power that the global photovoltaic industry installed in 2017.

Two hundred billion dollars for two hundred billion Watts—that’s one dollar USD per Watt.  No fossil fuel alternative can match that price.

There’s also a key point to bear in mind.  As solar cells and PV panels become cheaper, they start to become the most cost-effective option even in regions with lower levels of sunlight.  An installation will require more panels to get the same output as an installation in a sunnier region. But if the panels are cheap—it’s not necessarily a serious problem. And the ‘balance of system’ costs–which represent the major component of the capital cost, don’t change, because even though the array is larger the power output is the same.

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