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Report on Renewable Energy Sources and Climate Change Mitigation

Special Report on Renewable Energy Sources and Climate Change Mitigation
The Special Report on Renewable Energy Sources and Climate Change Mitigation (SRREN), agreed and released by the Intergovernmental Panel on Climate Change (IPCC) on May 9th in Abu Dhabi, assesses existing literature on the future potential of renewable energy for the mitigation of climate change. It covers the six most important renewable energy technologies, as well as their integration into present and future energy systems. It also takes into consideration the environmental and social consequences associated with these technologies, the cost and strategies to overcome technical as well as non-technical obstacles to their application and diffusion.

Summary for Policy Makers (SPM): Summary of the report, released on May 9th 2011:

Number of interesting facts and charts, including comparison chart of energy sources by price


Renewable energy sources and technologies considered in this report

Bioenergy can be produced from a variety of biomass feedstocks, including forest, agricultural and
livestock residues; short-rotation forest plantations; energy crops; the organic component of
municipal solid waste; and other organic waste streams. Through a variety of processes, these
feedstocks can be directly used to produce electricity or heat, or can be used to create gaseous,
liquid, or solid fuels. The range of bioenergy technologies is broad and the technical maturity varies
substantially. Some examples of commercially available technologies include small- and large-scale
boilers, domestic pellet-based heating systems, and ethanol production from sugar and starch.
Advanced biomass integrated gasification combined-cycle power plants and lignocellulose-based
transport fuels are examples of technologies that are at a pre-commercial stage, while liquid biofuel
production from algae and some other biological conversion approaches are at the research and
development (R&D) phase. Bioenergy technologies have applications in centralized and
decentralized settings, with the traditional use of biomass in developing countries being the most
widespread current application.4 Bioenergy typically offers constant or controllable output.
Bioenergy projects usually depend on local and regional fuel supply availability, but recent
developments show that solid biomass and liquid biofuels are increasingly traded internationally.
[1.2, 2.1, 2.3, 2.6, 8.2, 8.3]

Direct solar energy technologies harness the energy of solar irradiance to produce electricity using
photovoltaics (PV) and concentrating solar power (CSP), to produce thermal energy (heating or
cooling, either through passive or active means), to meet direct lighting needs and, potentially, to
produce fuels that might be used for transport and other purposes. The technology maturity of solar
applications ranges from R&D (e.g., fuels produced from solar energy), to relatively mature (e.g.,
CSP), to mature (e.g. passive and active solar heating, and wafer-based silicon PV). Many but not
all of the technologies are modular in nature, allowing their use in both centralized and
decentralized energy systems. Solar energy is variable and, to some degree, unpredictable, though
the temporal profile of solar energy output in some circumstances correlates relatively well with
energy demands. Thermal energy storage offers the option to improve output control for some
technologies such as CSP and direct solar heating. [1.2, 3.1, 3.3, 3.5, 3.7, 8.2, 8.3]

Geothermal energy utilizes the accessible thermal energy from the Earth’s interior. Heat is
extracted from geothermal reservoirs using wells or other means. Reservoirs that are naturally
sufficiently hot and permeable are called hydrothermal reservoirs, whereas reservoirs that are
sufficiently hot but that are improved with hydraulic stimulation are called enhanced geothermal
systems (EGS). Once at the surface, fluids of various temperatures can be used to generate
electricity or can be used more directly for applications that require thermal energy, including
district heating or the use of lower-temperature heat from shallow wells for geothermal heat pumps
used in heating or cooling applications. Hydrothermal power plants and thermal applications of
geothermal energy are mature technologies, whereas EGS projects are in the demonstration and
pilot phase while also undergoing R&D. When used to generate electricity, geothermal power
plants typically offer constant output. [1.2, 4.1, 4.3, 8.2, 8.3]

Hydropower harnesses the energy of water moving from higher to lower elevations, primarily to
generate electricity. Hydropower projects encompass dam projects with reservoirs, run-of-river and
in-stream projects and cover a continuum in project scale. This variety gives hydropower the ability
to meet large centralized urban needs as well as decentralized rural needs. Hydropower technologies
are mature. Hydropower projects exploit a resource that varies temporally. However, the
controllable output provided by hydropower facilities that have reservoirs can be used to meet peak
electricity demands and help to balance electricity systems that have large amounts of variable RE
generation. The operation of hydropower reservoirs often reflects their multiple uses, for example,
drinking water, irrigation, flood and drought control, and navigation, as well as energy supply. [1.2,
5.1, 5.3, 5.5, 5.10, 8.2]

Ocean energy derives from the potential, kinetic, thermal and chemical energy of seawater, which
can be transformed to provide electricity, thermal energy, or potable water. A wide range of
technologies are possible, such as barrages for tidal range, submarine turbines for tidal and ocean
currents, heat exchangers for ocean thermal energy conversion, and a variety of devices to harness
the energy of waves and salinity gradients. Ocean technologies, with the exception of tidal barrages,
are at the demonstration and pilot project phases and many require additional R&D. Some of the
technologies have variable energy output profiles with differing levels of predictability (e.g., wave,
tidal range and current), while others may be capable of near-constant or even controllable
operation (e.g., ocean thermal and salinity gradient). [1.2, 6.1, 6.2, 6.3, 6.4, 6.6, 8.2]

Wind energy harnesses the kinetic energy of moving air. The primary application of relevance to
climate change mitigation is to produce electricity from large wind turbines located on land
(onshore) or in sea- or freshwater (offshore). Onshore wind energy technologies are already being
manufactured and deployed on a large scale. Offshore wind energy technologies have greater
potential for continued technical advancement. Wind electricity is both variable and, to some
degree, unpredictable, but experience and detailed studies from many regions have shown that the
integration of wind energy generally poses no insurmountable technical barriers. [1.2, 7.1, 7.3, 7.5,
7.7, 8.2]