This document discusses various types of renewable energy sources including solar energy (photovoltaics and solar thermal), wind energy, hydropower, biomass/biofuels, and geothermal energy. It provides details on how each type of renewable energy works, examples of technologies used, and which countries are world leaders in different renewable energy uses. The overall message is that renewable energy sources can provide clean, sustainable alternatives to fossil fuels and help address issues like climate change if developed and utilized more widely.

2. What renewables are
• These are resources found in nature that are self-
regenerating:
• These sources are normally used to produce clean (or green)
energy. This production does not lead to climate change and does
not involve emission of pollutants.
• A related term is sustainable energy: this concept refers to
generating energy with an awareness of the future, i.e. in a way that
would enable future generations to meet their energy needs too. The
concept is related not only to renewables, but also to energy
efficiency.

3. Renewable energy is growing in
importance and popularity:
• because of the desire and necessity to avert irreversible
climate damage;
• because of increasing oil prices;
• because of the unreliability of non-renewable resources
(e.g. the depletion of oil wells).
• In view of all these and other factors, governments
worldwide support renewables with various incentives.
• This, in turn, encourages entrepreneurs to make large-scale
investments in renewable energy.

4. Main types of renewable energy
• Solar energy
• Wind energy
• Hydropower (water power)
• Biofuels
• Geothermal energy
There are many sources of renewable energy, but all of them,
except geothermal energy, are more or less directly related to
the sun: the main source of clean and sustainable energy for
the earth.

5. Solar energy
Apart from the everyday applications of solar energy, such as room lighting, it is
harnessed by two quite different methods: photovoltaics and solar thermal.
Photovoltaics (PV): the
Solar thermal energy (STE): a
application of solar cells
technology that uses solar
to convert sunlight directly
energy to produce thermal
into electricity. When PV
energy, i.e. heat. There are low-,
cells are assembled, they
medium-, and high-temperature
form a PV module (or
solar thermal collectors. The first
panel). An installation of
two types are flat plates
panels is called a PV
generally used to heat water.
array.
High-temperature collectors
Solar cells are often made concentrate sunlight with mirrors
from wafers: slices of or lenses and are mostly used to
semiconductor material, produce electricity. This
such as silicon crystal. technique is known as
World leaders in PV use: concentrated solar power
Germany, USA, Spain (CSP).

6. Solar energy (2)
CSP systems are also able
to track the movement of
the sun. The radiation There are various concentrating
they concentrate is used technologies, the most prominent
as a heat source for a being the solar trough, the
conventional plant to parabolic dish and the solar power
produce heat or electricity tower.
[concentrating solar
thermal (CST) systems] or
is directed to PV surfaces A notable and ambitious project is
to generate electrical the solar power satellite: a system
power [concentrating PV of solar collectors in space that
(CPV) technology]. would be directly exposed to the
sun’s radiation and would transmit
CSP allows solar the generated power to a large
installations to increase antenna on the earth. The costs for
their productivity. CSP the satellite’s construction,
plants take up smaller however, would be very high.
areas, which helps to
reduce costs.

7. Wind energy
The energy of wind is
Wind energy currently
harnessed with wind turbines.
generates only 1% of all
They are usually grouped in
electricity on a global scale,
wind farms (sometimes called
but its share is growing
wind parks).
There are onshore rapidly. In Denmark, for
farms (which, example, wind already
however, are often accounts for 19% of the total
near water); electricity production.
nearshore farms
(on land or on sea
within several km Since wind is intermittent,
turbines can’t constantly
of a coast); and
work at their full
offshore parks capacities. The ratio of
(ten km or more actual annual productivity
from land). to the theoretical
maximum capacity is
World leaders in wind energy use: called capacity factor. It
Germany, USA, Spain, India typically reaches 20% to
40%.

8. Another
technology that
Hydropower utilizes a dam
but no reservoir
is the run-of-
Hydropower (also
Hydropower was harnessed with the-river
called hydraulic or
waterwheels to operate hydroelectric
water power) is generation. Here,
watermills, sawmills, textile
derived from the the dam cuts
machines and others long before
force of moving electric power came into use. across the river,
water. Since water ensuring water
is much denser will fall from its
than air, its Hydropower supplies some 19% of upper edge, pass
movement all electricity in the world. It is through turbines
generally far cheaper than fossil
generates more and flow back
fuels or nuclear energy.
energy than wind into the lower
does. level of the river.
Hydroelectricity is mostly In some run-of-
Electricity generated in dams. Water is the-river
generated with first collected in dams, then let installations,
hydropower is flow through turbines. A great water is directed
called advantage of this technology is into a pipe, from
hydroelectricity. that the amount of energy where it passes
produced can be easily adjusted through turbines
to the level of demand by and returns into
controlling the outflow of water. the river.

9. Hydropower (2)
The lack of a reservoir reduces the negative environmental impact of the power
installations. However, there are certain problems related to dams, such as high
construction and maintenance costs, the risk of dam breakage, and perils for water
fauna. To avoid these complications, damless hydroelectricity has been created.
Another up-and-coming electric source is
Tidal power technologies convert wave power. One wave power technology
the energy of tides into electricity. employs buoyant objects that the waves
Their biggest advantage is the fact move, creating electricity. With wind
that tides are much more turbines, the air fluctuations caused by the
predictable than wind or solar moving water can also be used to produce
energy. However, tidal power is power. A project that uses the movement
not very common yet. of the water below its surface has also been
Tidal energy is captured with tidal developed.
stream systems which use the
kinetic energy of moving water to The first wave farm (a World
drive turbines. A less popular collection of wave power leaders in
technology to capture tidal energy generators) in the world
was opened in 2008 in
hydropower
are barrages (similar to dams),
which use the water’s potential Portugal. Its capacity is use: China,
energy. Barrages are not preferred 2.25 MW. Scotland plans to Brazil,
because of higher costs and bad build an even larger facility Canada,
environmental effects. with a 3 MW capacity. USA, India

10. Biomass and biofuel
Biomass consists of living or recently dead organisms or other biological
material, i.e. carbon. Biomass is used to produce biofuel. The most common
material for biofuels are photosynthetic plants. A plant especially grown to be
used for biofuel manufacturing is known as an energy crop.
Biodiesel is a very Biogas is produced by the Bioalcohol (or
common biofuel. It is biological breakdown of organic alcohol fuel) is
made from oils matter in the absence of produced with the
(extracted from oxygen. The biodegradable help of fermentation-
maize, soy, rapeseed, materials in question can be inducing
sunflower, palm fruit manure, sewage, green waste microorganisms. The
and sometimes from (plant parts), household and most common is
animal products) that industrial waste. Biogases are ethanol fuel (or
undergo chemical rich in methane. They can be bioethanol) that is
processing. Used used to generate heat, electric widely used instead of
edible vegetable oil is or mechanical energy, or as fuel petrol to power cars in
sometimes for vehicles. some countries,
transformed into predominantly Brazil.
Biogas is produced in facilities
biodiesel too.
for biological treatment of
Biodiesel is mixed with waste. It is also formed World leaders in
mineral diesel to be naturally in landfills where it biomass use: USA,
used in diesel engines. contributes to the greenhouse Germany, Brazil,
effect. UK

11. Geothermal energy
This type of energy is obtained by tapping the heat of the earth, which is
mostly in the form of hot water and steam. Various technologies are used to
get to the heat under the earth’s surface at different depths.
In some areas of the planet
Several metres under geothermal energy is closer to the
the earth’s surface the surface and therefore easier to
temperature is between Geothermal power harness. One of the most favourable
10° and 16°C. In winter stations are areas is Iceland with its high
this heat can be expensive to build concentration of volcanoes.
brought to buildings but their operating Geothermal sources account for 19%
with pipes. costs are low. A of Iceland’s electricity production,
significant and geothermal heating is used in
Another technology advantage is that
uses deep wells in hot 87% of homes in the country.
geothermal energy Iceland also plans to go fully fossil-
rock in which fluid is is not dependent on
heated to produce fuel free in the near future.
weather conditions.
steam, which then A major The country with the greatest
drives turbines to disadvantage is the geothermal energy production,
generate electricity. risk for land however, is the USA. There is the
The facilities that stability in the biggest dry steam field, The Geysers,
enable this process are region where such with an annual capacity of 750 MW.
called dry steam, flash a plant is
steam and binary-cycle Another country with significant
constructed.
plants. geothermal energy resources and
production is the Philippines.

12. Pros and cons
We can’t run out of renewables Biomass and geothermal
because nature replenishes them energy need wise
faster than we consume them. management to avoid their
depletion.
The use of domestic power
If clean energy becomes
generators (e.g. solar
prevalent, the electricity
panels on the roof) reduces
transmission and distribution
the strain on power
systems must be
distribution systems.
transformed and managed
more actively (why: see next
slide).
Green electricity is
becoming increasingly
accessible to the
average consumer. Renewable heat is still
expensive and hard to
access.
Renewables are
generally not hazardous Some green energy installations
to the environment. take up large pieces of land that
can be used to grow crops.

13. Distributed generation
Traditional energy generation is mostly done in centralized
facilities from where energy must travel a lot to reach the
end consumer:
large plant power power
substation consumer
transmission distribution
This is done to achieve economies of scale, or to bring energy generation
closer to the resource (e.g. mines) and away from populated areas (for
health reasons). However, some of the energy, especially heat, is lost
during the transportation.
By contrast, renewables are often associated with distributed
generation (also called dispersed generation or decentralized
energy). This is producing energy in many small facilities and
transporting it over short distances. Roof solar panels and wind
turbines are examples of distributed energy resources (DERs).
In order for renewable energy to become massively used, energy
systems must be adjusted to reflect the shift from centralized to
dispersed generation.

14. What energy qualifies as renewable
Some scientists and politicians argue that nuclear
energy is renewable since the resources from which it
is derived (such as uranium) would not be exhausted
in millions of years.
These claims, however, have
not been proven;
furthermore, nuclear energy
has an extremely dangerous
byproduct: nuclear waste.
For this reason, governments
Fossil fuels could be regarded as biomass
don’t recognize nuclear
since their have biological origin; however
energy as renewable and it is
they are neither sustainable nor green
not eligible for state
because:
subsidies.
•this is organic material that has undergone
millennium-long geological transformation;
•thus, the regeneration rates of fossil fuels
are extremely slower than the rate at which
they are consumed;
•fossil fuels emit CO2 when burnt.

15. Feed-in tariffs
Feed-in tariffs were
introduced as early as
1978 in the USA. Now,
they are implemented in
Since renewables are still around 50 countries
innovative and in active development, around the world.
they are often not competitive with
traditional energy sources. Therefore, In Germany, for example,
green-minded governments provide feed-in tariffs are
various incentives that encourage regulated by the
investments in the sector and promote renewables law
its faster development. Among the most (Erneubare-Energien-
common is the feed-in tariff. This is an Gesetz). The programme
adds around EUR 1 to
obligation imposed on utilities by the
each monthly residential
government to buy a certain amount of electricity bill, which
renewable electricity at prices higher translates into billions of
than the markets rates. The higher euro of subsidies for the
expenditure for the utility is passed on to clean energy sector each
its customers. The increase of prices that year. The country aims at
customers have to bear is usually small, generating 12.5% of its
electricity from
but these small contributions are a
renewable sources by
powerful and effective way to support 2010. The percentage
green energy. should rise to 20 by
2020.

16. So, in a word…
A plethora of renewable energy is all around us, with even more ways
to make use of it.