Environmental Engineering Reference
In-Depth Information
Chapter 4
Photovoltaics
I
NTRODUCTION
The word 'photovoltaic' consists of the two words, photo and Volta. Photo
stands for light (Greek phõs, photós: light) and Volta (Count Volta,
1745-1827, Italian physicist) is the unit of the electrical voltage. In other
words, photovoltaic means the direct conversion of sunlight to electricity. The
common abbreviation for photovoltaic is PV.
The history of photovoltaics
goes back to the year 1839, when Becquerel
discovered the photo effect, but in that century the technology was not
available to exploit this discovery. The semiconductor age began about 100
years later. After Shockley had developed a model for the p-n junction, Bell
Laboratories produced the first solar cell in 1954. The efficiency of this cell
was about 5 per cent. Initially, cost was not a major issue, because the first
cells were designed for space applications.
In the following years, solar cell efficiency increased continuously;
laboratory silicon solar cells have reached efficiencies of around 25 per cent
today. The main material used in the construction of solar cells is still silicon,
but other materials have been developed, either for their potential for cost
reduction or their potential for high efficiency. Costs have decreased
significantly in recent decades; nevertheless, photovoltaic electricity generating
costs are still higher than the costs of conventional power plants (see Chapter
6). Due to high growth rates in the photovoltaic sector, cost reduction will
continue.
Photovoltaics offer the highest versatility among renewable energy
technologies. One advantage is the
modularity
. All desired generator sizes can
be realized, from the milliwatt range for the supply of wristwatches or pocket
calculators to the megawatt range for the public electricity supply.
Many photovoltaic applications are built into consumer appliances or
relate to leisure activities or off-grid site supply, for example,
telecommunications or solar home systems. In several countries, particularly
in Japan and Germany, large governmental programmes were initiated,
advancing grid-connected installations. Tens of thousands of grid-connected
systems that have been installed since the early 1990s have proven the
suitability of the technology. The potential for photovoltaic installations is
enormous. Theoretically, PV systems could cover the whole electricity demand
of most countries in the world.
