A solar panel converts light from the sun into electricity.
A solar panel consists of many solar cells which each contain silicon crystals. When sunlight hits the silicon atoms in the crystals it knocks electrons off them, which can then move around in the crystal lattice. Other material is added to the silicon crystal to create an atomic structure that only allows the electrons to move in one direction through the silicon.
As the electrons move around, this structure creates a directional flow of electrons through the silicon. The electron flow is picked-up and returned by electrical connections at the ends of the solar cell.
Types of Solar Cell
There are three construction methods used to make solar cells.
The most efficient solar cells are made from a single, continuous, silicon crystal. The continuous crystalline structure means that the
energy conversion process works most efficiently. These solar cells are called monocrystalline cells.
The next most efficient solar cells are made from cast silicon. As the silicon slowly cools and solidifies during the casting process many separate crystals form. The discontinuous crystal structure slightly reduces the effectiveness of the energy conversion process.
These solar cells are called polycrystalline cells.
The least efficient solar cells are made by spraying silicon vapour onto a base to produce a very thin layer of silicon. The thinness of
the silicon layer limits the effectiveness of the energy conversion process. These solar cells are called thin-film cells.
Thin–film cells are considerably less efficient than either polycrystalline or monocrystalline cells, which means that they take up more space to collect the same amount of energy; however, they are cheaper to make.
Polycrystalline cells are a little less efficient than monocrystalline cells; however, other factors that affect the energy-collecting ability of these cells can overcome the small efficiency difference between them.
Solar Panel Performance
The performance of solar panels is measured and rated so that different brands and types can be directly compared. Solar panels are always tested under the same, standardised, conditions of light and temperature. The amount of power that a solar panel produces under these conditions is the panel’s nominal power rating.
When we use a solar panel we are interested in the amount of energy that it can collect for us over the course of the whole day and over the whole year. A solar panel’s power rating is only one of the factors that affect its ability to collect energy for us.
A solar panel mostly doesn’t operate under ideal conditions. A solar panel’s ability to operate when the light is low in the morning
and afternoon, or when it is cloudy, is very important to its overall ability to collect energy.
A solar panel’s performance is affected by its temperature. A hot climate or poor ventilation will increase the panel’s temperature and reduce its ability to collect energy.
A solar panel is mounted so that, as much as possible, sunlight falls squarely onto it. However, most of the time sunlight will not fall
squarely onto the panel because the sun moves across the sky and is only ideally positioned for an instant.
Sunlight from the sun is scattered by the air that it passes through; we see this scattered light as the blue of the sky; it’s why we mostly can’t see the stars during the day. Sunlight also reflects off clouds. The scattered light from the sky and the clouds falls onto to a solar panel from all directions, so a solar panel’s ability to use light that falls on it obliquely is very important to its overall ability to collect energy.
Solar Panel Installation
The sun crosses the sky from east to west, and rises higher into the sky in the summer than in the winter. A solar panel must be orientated | correctly to get the most energy possible from the sun as it traverses the sky.
In the southern hemisphere, the sun is to the north of straight overhead during most of the day in the summer, and during all of the day in the winter. Rather than facing straight up, a solar panel must be inclined towards the north to catch the most sun light. To be most effective, the angle that it is inclined at must be slightly greater than the latitude of the place where it is installed.
Solar panels are commonly installed on a building roof. There are limitations to doing this.
Panels mounted on a roof may have limited air flow around them, causing them to get hot, reducing their performance. The orientation of the panels is unlikely to be ideal unless expensive custom-made frames are used.