ABOUT SOLAR ENERGY
The sun, an energy available for
free which can be used in many ways.
Energy from the sun can be used in three main
ways, and when talking about solar energy, it is important to
distinguish between these three types:
- Passive heat: This is heat which we receive
from the sun naturally. This can be taken into account in the
design of buildings so that less additional heating is
required
- Solar thermal: Uses the sun's heat to provide
hot water for homes or swimming pools (also heating systems)
- Photovoltaic energy (PV): Uses energy from the
sun to create electricity to run appliances and lighting. A
photovoltaic system requires only daylight - not direct sunlight -
to generate electricity.
Solar Thermal Applications and Technology
The basic principle common to all solar thermal systems is
simple: solar radiation is collected and the resulting heat
conveyed to a heat transfer medium - usually a fluid but also air
in the case of air collectors. The heated medium is used either
directly - for example to heat swimming pools - or indirectly, by
means of a heat exchanger which transfers the heat to its final
destination - for instance: space heating.
Solar thermal can be successfully applied to a broad range of
heat requirements including domestic water heating, space heating,
and drying. New exciting areas of applications are being developed
in particular solar assisted cooling. System design, costs and
solar yield are being constantly improved.
The process of turning sunlight into
electricity
Photovoltaic systems use cells to convert solar radiation into
electricity. The cell consists of one or two layers of a
semi-conducting material. When light shines on the cell it creates
an electric field across the layers, causing electricity to flow.
The greater the intensity of the light, the greater the flow
of electricity is.
The most common semi conductor material used in photovoltaic cells
is silicon, an element most commonly found in sand. There is
no limitation to its availability as a raw material; silicon is the
second most abundant material in the earth's mass.
A photovoltaic system therefore does not need bright sunlight in
order to operate. It can also generate electricity on cloudy
days.
Overview of available photovoltaic
technologies:
- Crystalline silicon technology: Crystalline
silicon cells are made from thin slices cut from a single crystal
of silicon or from a block of silicon crystals (polycrystalline),
their efficiency ranges between 12% and 17%. This is the most
common technology representing about 90% of the market today.
- Thin Film technology: Thin film modules are
constructed by depositing extremely thin layers of photosensitive
materials onto a low-cost backing such as glass, stainless steel or
plastic. Thin film manufacturing processes result in lower
production costs compared to the more material intensive
crystalline technology, a price advantage which is currently
counterbalanced by substantially lower efficiency rates (from 5% to
13%).
- Concentrated photovoltaic: Some solar
cells are designed to operate with concentrated sunlight. These
cells are built into concentrating collectors that use a lens to
focus the sunlight onto the cells. The main idea is to use very
little of the expensive semiconducting PV material while collecting
as much sunlight as possible. Efficiencies are in the range of 20
to 30%.
Photovoltaic applications:
- Grid-connected domestic systems: This is the
most popular type of solar PV system for homes and businesses in
developed areas. Connection to the local electricity network allows
any excess power produced to feed the electricity grid and to sell
it to the utility. Electricity is then imported from the network
when there is no sun.
- Grid-connected power plants: These systems,
also grid-connected, produce a large quantity of photovoltaic
electricity in a single point. The size of these plants ranges from
several hundred kilowatts to several megawatts. Some of these
applications are located on large industrial buildings such as
airport terminals or railway stations. This type of large
application makes use of already available space and compensates a
part of the electricity required by these energy-intensive
consumers.
- Off-grid systems for rural electrification:
Where no mains electricity is available, the system is connected to
a battery via a charge controller. An inverter can be used to
provide AC power, enabling the use of normal electrical appliances.
Typical off-grid applications are used to bring access to
electricity to remote areas (mountain huts, developing countries).
Rural electrificationmeans either small solar home system
covering basic electricity needs in a single household, or larger
solar mini-grids, which provide enough power for several homes.
More information is available at www.ruralelec.org
- Hybrid systems: A solar system can be combined
with another source of power - a biomass generator, a wind turbine
or diesel generator - to ensure a consistent supply of electricity.
A hybrid system can be grid-connected, stand-alone or grid-support.
More information is available at www.ruralelec.org
- Consumer goods: Photovoltaic cells are used in
many daily electrical appliances, including watches, calculators,
toys, battery chargers, professional sun roofs for automobiles.
Other applications include power for services such as water
sprinklers, road signs, lighting and phone boxes.
- Off-grid industrial applications: Uses for
solar electricity for remote applications are very frequent in the
telecommunications field, especially to link remote rural areas to
the rest of the country. Repeater stations for mobile telephones
powered by PV or hybrid systems also have a large potential. Other
applications include traffic signals, marine navigation aids,
security phones, remote lighting, highway signs and waste water
treatment plants. These applications are cost competitive today as
they enable to bring power in areas far away from electric mains,
avoiding the high cost of installing cabled networks.
Sources:
European Photovoltaic Industry Association: www.epia.org
European Solar Thermal Industry federation: www.estif.org