Transcript Solar panels 011211b

SOLAR PANELS
A solar panel is made up of photovoltaic cells.
A photovoltaic cell converts light energy into electricity.
Photovoltaic
cell
Photovoltaic
cell
Photovoltaic
A conductor is something that electricity can travel through. Conductors
vary in their ability to allow electricity to flow.
Semiconductors are made from materials such as silicon. Other
chemicals are then added to change the behaviour of the electricity.
P type Boron
N type Phosphorus
The silicon is treated with an antireflective coating to absorb more
energy.
Solar cells are usually quite small so many cells are combined to make
a solar panel.
Solar panels are made up of photovoltaic cells.
A photovoltaic cell converts light energy into electricity.
At the heart of a photovoltaic cell is an NP junction where negative and positive plates made of silicon and other
materials are placed close together. Electrons want to jump across from the Negative to the Positive side. This
force is known as voltage but energy is still needed to make electrons jump across.
Energy in the form of photons from sunlight enables electrons to jump across which creates the flow of electricity which
is known as current.
Even the best solar cells only achieve around 40% efficiency.
There are several things than can improve the efficiency of solar cells:
Silicon is very shiny so most of the sunlight is reflected which is a waste of energy. This is why solar panels have a
dark non-reflective coating so that more light flows into the cell.
Light can have different amounts of energy just like it can have different colours.
Most solar cells are designed to create electricity with only a small amount of light but this means that only a low
voltage is produced.
The strength of the voltage known as “Band gap energy” depends on how much energy is required for electrons to jump
across the NP junction.
In strong sunlight you get extra current but the voltage doesn’t really increase. New research involves multi-junction
cells which have more than one electric field. This allows the panel to operate in low light and also take advantage
of stronger light with increased current and voltage.
Another issue is that the electricity generated by a photovoltaic cell needs to travel through a semiconductor and
semiconductors aren‘t great at conducting electricity. Wires are good conductors but they block out light so new
transparent conductors are being developed to improve solar cell efficiency.
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Dumping ground
Another strategy for increasing efficiency is to use two or more layers of
different materials with different band gaps. Remember that depending on
the substance, photons of varying energies are absorbed. So by stacking
higher band gap material on the surface to absorb high-energy photons
(while allowing lower-energy photons to be absorbed by the lower band gap
material beneath), much higher efficiencies can result. Such cells, called
multi-junction cells, can have more than one electric field.
Concentrating photovoltaic technology is another promising field of
development. Instead of simply collecting and converting a portion of
whatever sunlight just happens to shine down and be converted into
electricity, concentrating PV systems use the addition of optical equipment
like lenses and mirrors to focus greater amounts of solar energy onto highly
efficient solar cells. Although these systems are generally pricier to
manufacture, they have a number of advantages over conventional solar
panel setups and encourage further research and development efforts.