Lecture 3 Review
Moving
on from Solar Thermal energy, Lecture 3 covered Solar Photovoltaic.
Using this technology we can convert solar energy directly to
electricity. Many of us have this available on calculators, however
solar cells have far higher capabilities, and the Photovoltaic energy
represents one of the most promising means of generating electricity
without contributing to global warming. The technology has only been
seriously considered since the mid 1970's, and large advances have been
made since then, to the point where an efficiency of 36% has been
achieved (Spectrolab).
To
understand how a solar cell works, you need a some background
information on semi-conductors. Solar cells are made from silicon
mainly, but by adding small amounts of group 3/5 elements (doping) the
electrical properties of the silicon are changed so that they become
able to conduct electricity. This is due to the shrinking of
the forbidden gap which brings the conduction and valence bands
closer
together. Energy given to electrons in the valence band then allows
them to jump to the conduction band. If this is combined with the use
of a junction, the electrons will flow, generating a current.
There
are two types of silicon used in solar cells, crystalline and
amorphous. The more expensive crystalline silicon has higher
efficiencies and is stable, where as the amorphous silicon is cheaper,
but has lower efficiencies and degrades to some extent over the first two years of
use. Cells are arranged in systems called arrays, which are made up of
separate solar panels. These systems are connected to other equipments
to make the solar electricity usable. This involves converting it from
DC to AC, and sometimes storing it, for use during overcast times, or
at night.
There
are 3 types of solar system. The stand alone kind is for use in remote
locations, and generally is used for simple tasks such as water
pumping, where it would be difficult to get power from an electrical
grid. The hybrid system involved combining solar panels another form of
power generation (e.g. wind or diesel generator) so that the maximum
solar energy can be extracted depending on the conditions. The load
receives a constant supply from the combination of generators. The
final option is a grid tied system, which allows any electricity not
used at the generation site to be sold back to the grid, thereby
reducing the owners electricity bill.
Finally
the economics of solar power were covered. Currently it is a very
expensive means of energy production (40 cents/kiloWatt hour). So it
only makes economic sense in certain locations. The best locations are
the remote ones, i.e. more than 0.5 miles from the grid. At these
locations it would save you money to use solar energy, as a pose to
installing a connection to the grid, provided that the site received
enough solar energy.
To
understand how a solar cell works, you need a some background
information on semi-conductors. Solar cells are made from silicon
mainly, but by adding small amounts of group 3/5 elements (doping) the
electrical properties of the silicon are changed so that they become
able to conduct electricity. This is due to the shrinking of
the forbidden gap which brings the conduction and valence bands
closer
together. Energy given to electrons in the valence band then allows
them to jump to the conduction band. If this is combined with the use
of a junction, the electrons will flow, generating a current.There
are two types of silicon used in solar cells, crystalline and
amorphous. The more expensive crystalline silicon has higher
efficiencies and is stable, where as the amorphous silicon is cheaper,
but has lower efficiencies and degrades to some extent over the first two years of
use. Cells are arranged in systems called arrays, which are made up of
separate solar panels. These systems are connected to other equipments
to make the solar electricity usable. This involves converting it from
DC to AC, and sometimes storing it, for use during overcast times, or
at night.There
are 3 types of solar system. The stand alone kind is for use in remote
locations, and generally is used for simple tasks such as water
pumping, where it would be difficult to get power from an electrical
grid. The hybrid system involved combining solar panels another form of
power generation (e.g. wind or diesel generator) so that the maximum
solar energy can be extracted depending on the conditions. The load
receives a constant supply from the combination of generators. The
final option is a grid tied system, which allows any electricity not
used at the generation site to be sold back to the grid, thereby
reducing the owners electricity bill.Finally
the economics of solar power were covered. Currently it is a very
expensive means of energy production (40 cents/kiloWatt hour). So it
only makes economic sense in certain locations. The best locations are
the remote ones, i.e. more than 0.5 miles from the grid. At these
locations it would save you money to use solar energy, as a pose to
installing a connection to the grid, provided that the site received
enough solar energy.
