Photovoltaics

Photovoltaic (PV or solar cells) is a method of converting direct solar radiation into electricity supply. Normally, it is made from semiconductors (such as Si and Silicon). The photovoltaic panel could be divided into three layers: Junction region, n-type (extra electron) and p-type (extra hole). The solar radiation would cause the electrons separated from the atoms in the junction region. Then the electrons would move to one side (n-type) when holes to the other side. Current would be generated when wires are connected with the PV panels (Figure 1).

Figure 1. Working principle of PV panels

At present, Si is widely used as the material of solar panels. And there are three main types of Si PV module: Monocrystalline Si, Polycrystalline Si and Amorphous Si thin-film. Among these types, Monocrystalline Si has the largest efficiency when it is expensive to produce electricity, while Amorphous Si thin-film is the efficient one with a lowest production price.
The main reasons of using PV system are:
1. It is reliable when there are no moving parts in the whole system.
2. It has a very low operation and maintenance costs as the origin fuel of PV system is solar radiation.
3. It has no noise and no pollution to the environment during operation.
4. The direct converting from solar energy into electricity makes the PV system more efficient without transmission losses.

Nowadays, solar PV generates electricity in well over 100 countries and continues to be the fastest growing power-generation technology in the world. Between 2004 and 2009, grid-connected PV capacity increased at an annual average rate of 60%. According to the globe status report from Renewable 2010, solar PV accounts for about 16 percent of all new electric power capacity additions in Europe in 2009 (Figure 2).

Figure2. Solar PV-Existing world capacity (2004-2009)

Reference

DTI: Photovoltaics in Buildings - A Design Guide, Report No. ETSUS/P2/00282/REP, 1999
CIBSE TM25: Understanding Building Integrated Photovoltaics, 2000

G. Boyle: Renewable Energy: Power for a Sustainable Future, Oxford University Press, Oxford, 2003
T. Markvart: Solar Electricity, John Wiley & Sons, Chichester, 2000