13-05-2013, 04:03 PM
OSMOTIC POWER – a new, renewable energy source
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INTRODUCTION
During the past decade, global climate change challenges and the world’s steadily growing
demand for energy have brought the need for more renewable energy to the top of the
international community’s agenda. Therefore, the United Nations decided at the first World
Summit on Sustainable Development (2002, Johannesburg) to create a specific forum
dedicated to further advance the deployment of renewable energy sources: the International
Conference for Renewable Energies. At the forum’s first meeting, all countries reaffirmed
their commitment “to substantially increase with a sense of urgency the global share of
renewable energy in the total energy supply.” During a follow-up meeting in 2008, it was
clearly stated that in order to reach this goal, it is imperative to use both existing and new
renewable energy sources.
Based on more than a hundred years of experience in developing and operating
hydropower, the Norwegian utility company Statkraft1) has set the course for corroborating
its leading role in renewable energy generation by investing in the quest of new renewable
energy sources in strategic areas. As a result the company is today the world leader in
development of Osmotic Power, and has made state of the art achievements during the last
years.
BACKGROUND
The pressure on the environment caused by human activities and especially the climate
change challenges related to continuously increasing greenhouse gas emissions, calls for a
thorough research of alternatives. Since the Kyoto Protocol in 1997, efforts to reduce
carbon emissions have been intensified. Among others, the EU adopted an integrated
energy and climate change policy in December 2008, including ambitious targets for 2020.
It aims at bringing Europe onto a more sustainable energy track – towards a low-carbon
future with an energy-efficient economy, which will cut greenhouse gases emissions by
20%, reduce energy consumption by 20% through increased energy efficiency, and meet
20% of Europe’s energy needs from renewable sources.
The power of osmosis
It has been known for centuries that mixing
freshwater and seawater releases energy. For
example, a river flowing into the salty ocean
is releasing large amounts of energy. The
challenge is to utilise this energy, since the
energy which is released from the mixing of
salt and freshwater leads only to a very small
increase of the local water temperature.
During the last few decades at least two
concepts for converting this energy into
electricity instead of heat have been identified.
One of these is Pressure Retarded Osmosis (PRO). Thanks to this technology it may be
possible to utilise the enormous potential of a new, renewable energy source. This potential
represents a worldwide electricity production of more than 1600 TWh per year – equivalent
to half the annual power generation in the European Union.
For Pressure Retarded Osmosis, also known as Osmotic Power, the released chemical
energy is transferred into pressure instead of heat. This was first pointed out by Professor
Sidney Loeb in the early 1970’s, when he designed the world’s first semi-permeable
membrane for desalination of saline water for production of drinking water based on
reverse osmosis.
Statkraft has been engaged in the research and development of Osmotic Power and related
enabling technologies since 1997. Together with its international R&D partners, Statkraft is
the main active and most progressive technology developer globally and therefore an
Osmotic Power knowledge hub. The team has made state-of-the-art achievements in terms
of developing a new energy efficient membrane technology during the past years.
Environmental issues
The mixing of seawater and freshwater is a process that occurs naturally all over the world.
Osmotic Power plants will extract the energy from this process without polluting
discharges to the atmosphere or water. Moreover, this process produces no other emissions
that could have an impact on the global climate. Osmotic Power’s excellent environmental
performance and CO2-free power production will most likely qualify for green certificates
and other supportive policy measures to increase the share of renewable energy.
One area where there has been some discussion is whether there will be an negative effect
on the marine environment due to the discharge of brackish water by the Osmotic Power
plant. This may alter the local marine environment and result in changes for animals and
plants living in the discharge area. However, the osmotic plant will only displace the
formation of brackish water in space without modifying the water quality so this will not be
a significant environmental impact.
Since most rivers run into the ocean at a place where people have already built cities or
industrial areas such as harbours, most of the potential sites for Osmotic Power generation
can be utilized without affecting pristine areas. Moreover, the plants can be constructed
partly or completely underground (e.g. in the basement of an industrial building or under a
park) which will make them very discreet. In these areas the environmental impacts on
shore are estimated to be of minor importance. These impacts will mainly be related to the
building of access roads, channels and connections to the electricity grid. A power plant the
size of a football stadium could supply around 30 000 European households with
electricity.
The market potential
To establish an understanding of the potential addition of power generation capacity
Osmotic Power might represent, surveys of the sites where freshwater meets seawater has
been made. To evaluate the potential power production from a river detailed information
about water quality, seasonal variations, sea water salinity and quality, and also of course
the amount of freshwater available is required. Based on this information it is obvious that
there are several regions in both the northern and southern hemisphere that has a significant
potential. North-America, South-America, Europe, North Asia and Africa all has a
substantial resources that can contribute to their renewable energy mix.
OSMOTIC POWER DEVELOPMENT STATUS
The efforts by Statkraft in the field of Osmotic Power was initiated already in 1997 when
the Norwegian research organization SINTEF was engaged to perform feasibility studies of
the concept on behalf of the company. The result of the study was that Osmotic Power
could have a significant, global potential and also involved similar activity to hydropower
regarding the use of water to produce renewable energy. But the studies also revealed that
in particular one component would require significant improvement, and this was the semipermeable
membrane.
THE OSMOTIC POWER PROTOTYPE
The world’s first osmosis driven prototype for power generation has now been put into
operation. In the southern part of Norway, approximately 1 hour drive from Oslo, a
complete prototype of an Osmotic Power plant has been built. The prototype represents a
major milestone towards the commercialization of Osmotic Power and creates a unique test
site for future technology development of Osmotic Power. The plant did generate the first
small kWh of electricity from osmosis in November 2009, and the first proof of the concept
of producing power by osmosis has been recorded.
Design of the prototype
The prototype is designed with all necessary systems and components for continues PRO
operation. Based on the assumption that a membrane with an efficiency of 5 W/m2 will be
developed during the lifetime of the plant, 10 kW installed power capacity was set as the
overall design criteria. This gave the lead for water supply for both water qualities, as well
as sizing of the individual components.
The sea water feed to the plant is supplied trough water pipes from approximately 30
meters below sea level, just outside the harbour. The water is filtered through a mesh before
it enters the plant.
THE ROAD TOWARDS COMMERCIAL OSMOTIC POWER GENERATION
Based on the information provided in this paper one can clearly understand that there are
several technical and system-related tasks to be addressed. And there are today several
groups of companies and research institutes working to solve the challenges discussed
earlier. So, what is then necessary for establishing Osmotic Power as one of the contributor
to the generation of renewable energy in the future? We believe that to succeed in the
development of Osmotic Power, one need to understand the most important value drivers.
Statkraft has spent significant time and effort on the development of Osmotic Power, and
will continue to do so. The solution is very attractive due to the environmentally friendly
solution it represent, but to really make this a new and attractive solution in the renewable
energy market one will depend on the three major factors.
Supplier industry
It is well known that Osmotic Power was founded in the field for desalination. And there
are still significant resemblance looking into the individual components. It is crucial that
the future suppliers for Osmotic Power such as membrane manufacturers are willing to
spent time and resources on bringing the technology from where it is today and improve
and scale it up into an industrial size.