A Brief History of Solar PV

All the energy stored in the Earth’s reserves of coal, oil, and natural gas is matched by the energy from just 20 days of sunshine. How we capture this energy is by the use of photovoltaics (PV). Of course, the challenge is capturing this energy. Outside Earth’s atmosphere, the sun’s energy contains about 1,300 watts per square meter. About one-third of this light is reflected back into space, and some is absorbed by the atmosphere (in part causing winds to blow).

The term “photovoltaic” comes from the Greek φῶς (phōs) meaning “light”, and “voltaic”, meaning electric, from the name of the Italian physicist Volta, after whom a unit of electro-motive force, the volt, is named.

The photovoltaic effect was first recognized in 1839 by French physicist A. E. Becquerel, who discovered that certain materials would give off a spark of electricity when struck with sunlight. This photoelectric effect was used by Charles Fritts in 1883, who coated the semiconductor selenium with an extremely thin layer of gold to form the junctions, creating the world’s first solar cells. The device was around 1% efficient, meaning that it transformed approximately 1% of the sunlight that engaged the cell into electricity.

Albert Einstein explained the photoelectric effect in 1905, for which he received the Nobel prize in Physics in 1921. The basic explanation of the photovoltaic effect is this: When sunlight enters the PV cell, it’s energy knocks electrons loose in the two layers. Because of the opposite charges of the layers, the electrons want to flow from the N-type (-) layer to the P-type (+) layer, but the electric field at the P-N junction prevents this from happening.

The presence of an external circuit, however, provides the necessary path for electrons in the N-type layer to travel to the P-type layer. Extremely thin wires running along the top of the N-type layer provide this external circuit, and the electrons flowing through this circuit provide the cell’s owner with a supply of electricity.

Twenty-five years later, in 1946, Russell Ohl patented the modern junction semiconductor solar cell, which was discovered while working on the series of advances that would lead to the transistor. In the 1950s, scientists at Bell Laboratories revisited this technology and, using silicon, produced solar cells that could convert four percent of the energy in sunlight directly to electricity. Due to the extremely high cost of production, the only useful application of the technology at the time was in space exploration.  The US satellite Vanguard 1, launched in March 1958, was the first to be powered by solar PV cells.

50 years later, the manufacturing price for PV modules has decreased from $40,000 per watt to under $5 per watt, and cell efficiency has surpassed 18%, making the dream of harnessing the virtually unlimited power of the sun a reality, with groups as wide-ranging as off-grid survivalists, local school districts, world governments, militaries, families, and international corporations discovering and re-discovering the value of solar energy for sustainability and profit.