Bioenergy
Solid Biomass: Covers organic, non-fossil
material of biological origin which may be used
as fuel for heat production or electricity generation.
Wood, Wood Waste, Other Solid Waste: Covers
purpose-grown energy crops (poplar, willow etc.),
a multitude of woody materials generated by an industrial
process (wood/paper industry in particular) or provided
directly by forestry and agriculture as well as
wastes such as straw, rice husks, crushed grape
dregs etc.
Charcoal: Covers the solid residue of the
destructive distillation and pyrolysis of wood and
other vegetal material.
Biogas: Gases composed principally of methane
and carbon dioxide produced by anaerobic digestion
of biomass and combusted to produce heat and/or
power.
Liquid Biofuels: Bio-based liquid fuel from
biomass transformation, mainly used in transportation
applications.
Municipal Waste: Municipal waste energy comprises
wastes produced by the residential, commercial and
public services sectors and incinerated in specific
installations to produce heat and/or power. The
renewable energy portion is defined by the energy
value of combusted biodegradable
material. (1)
The most successful forms of biomass are sugar
cane bagasse in agriculture, pulp and paper residues
in forestry and manure in livestock residues. It
is argued that biomass can directly substitute fossil
fuels, as more effective in decreasing atmospheric
CO2 than carbon sequestration in trees. The Kyoto
Protocol encourages further use of biomass energy.
The Intergovernmental Panel on Climate Change (IPCC)
has concluded that although the longer-term maximum
technical energy potential of biomass could be large
(around 2 600 EJ), this potential is constrained
by competing agricultural demands for food production,
low productivity in biomass production, and other
factors. (2)
Geothermal Energy
Available as heat emitted from within the earth's
crust, usually in the form of hot water or steam.
It is exploited at suitable sites for electricity
generation after transformation or directly as heat
for district heating, agriculture, etc. (1)
Geothermal plant capacity and utilization, for
both power generation and direct heat supply, is
increasing, although the pace of growth in power
generation has slowed compared to the past, while
that of direct heat uses has accelerated. Over-exploitation
of the giant Geysers steam field has caused a decline
in geothermal capacity in the USA in recent years,
which has been partly offset by important capacity
additions in other countries. A large increase in
the number of geothermal (ground-source) heat pumps
has contributed to the increase in direct heat application.
Although the short- to medium-term future of geothermal
energy looks encouraging, its long-range prospects
depend on the technological and economic viability
of rock heat (HDR). (2)
Hydropower
Potential and kinetic energy of water converted
into electricity in hydroelectric plants. It includes
large as well as small hydro, regardless of the
size of the plants. (1)
Hydropower accounts for 17% of the world electricity
supply, utilizing one third of its economically
exploitable potential. Hydro projects have the advantage
of avoiding emissions of greenhouse gases, SO2 and
particulates.
Their social impacts, such as land transformation,
displacement of people, and impacts on fauna, flora,
sedimentation and water quality can be mitigated
by taking appropriate steps early in the planning
process. Whilst a question remains over the advantages
of smaller hydro schemes over larger ones, generally
hydropower is the most developed and well established
technology. (2)
Ocean Energy
Mechanical energy derived from tidal movement,
wave motion or ocean current and exploited for electricity
generation. (1)
Despite the high predictability of tidal energy's
resource and timing, long construction times, high
capital intensity and low load factors will most
likely rule out significant cost reductions in tidal
technologies in the near term.
Recent favorable developments in wave energy
due to the increased focus on climate change include,
technological developments in Scotland, Australia,
Denmark and the USA, and a high potential for energy
supply - wave energy could provide 10% of the current
world electricity supply (if appropriately harnessed)
- and the potential synergies with the offshore
oil and gas industry could be significant. However,
there are still a number of unresolved technological
issues. The possibility of wave energy unit costs
falling to 2-3 pence/kWh within 3 to 5 years mentioned
in the commentary is derived from experience of
onshore wind energy costs, not from experience in
wave energy. Nevertheless, the full utilization
of wave energy potential appears to be some way
off.
The many benefits of ocean thermal energy conversion
(OTEC) include: small seasonal and daily variations
in availability, benign environmental performance
and by-products in a family of deep ocean water
applications, for example food (aquaculture and
agriculture) and potable water, and improving economics
as a result of higher oil prices. However, a number
of key component technologies and further R&D are
still needed, in order to be able to build a representative
pilot plant to demonstrate OTEC's advantages to
prospective investors.
It is acknowledged that there has been little research
into utilizing marine current energy for
power generation and today no commercial turbines
are in operation (thus making the assessment of
production costs difficult). There is, however,
a large global marine current resource potential
which possesses a number of advantages over other
renewables, such as its higher energy density, highly
predictable power outputs, independence from extreme
atmospheric fluctuations and a zero or minimal visual
impact. (2)
Solar Energy
Solar radiation exploited for hot water production
and electricity generation. Does not account for
passive solar energy for the direct heating, cooling
and lighting of dwellings or other. (1)
Raising the contribution of solar and other renewable
resources to 50% of total primary energy supply
by 2050, as indicated in one of the Shell scenarios,
would require sweeping changes in the energy infrastructure,
a new approach to the environment and the way that
energy is generated and used.
Despite the progress in the development of modern
solar energy over the past forty or fifty years,
the technology still needs a higher profile and
more involvement from scientists, engineers, environmentalists,
entrepreneurs, financial experts, publishers, architects,
politicians and civil servants. (2)
Wind Energy