Water Power and Dam Construction. Issue March 2010
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Let IWP&DC’s readers know about your forthcoming conferences and events.
For publication in a future issue, send your diary dates to: Carrieann Stocks, IWP&DC, Global Trade Media Ltd, Progressive House, 2 Maidstone Road,
Foots Cray, Sidcup, Kent, DA14 5HZ, UK. Alternatively, email: carrieannstocks@globaltrademedia.com, or fax:+44 208 269 7804
DIARY OF EVENTS
WWW.WATERPOWERMAGAZINE.COM MARCH 2010 11
DIARY
June
23-26 June
16th British Dam Society Conference
Glasgow, Scotland
CONTACT: Barbara Sharp,
British Dam Society, C/O Atkins
Water, UK.
Tel: +44 1372 756 838.
barbara.sharp@atkinsglobal.com
http://www.britishdams.org
July
27-30 July
Hydrovision International
North Carolina, US
CON T A CT: L ibby Sm i t h,
PennWell.
Tel: +1 (918) 831-9560.
Email: LibbyS@PennWell.com.
September
12-16 September
21st World Energy Congress
Quebec, Canada
CONTACT: Organsing Committee,
740 Notre-Dame Street West, 8th
Floor, Montréal, Québec, Canada
H3C 3X6.
Tel: + 1 (514) 397-1474.
Fax: +1 (514) 397-9114.
www.wecmontreal2010.ca.
22-23 September
8 t h I CO L D E uo p ea n C lu b
S y m p os iu m: Da m S af et y -
Sustainability in a Changing
Environment
Innsbruck, Austria
CONTACT: IECS2010 Organizing
Committee, Stremayrgasse 10/II,
A-8010 Graz, Austria.
Fax: +43 316 873 8357.
IECS2010@TUGraz.at.
www.iecs2010.tugraz.at.
27-29 September
Hydro 2010
Lisbon, Portugal
CONTACT: Hydropower & Dams,
Aqua~Media International Ltd, PO
Box 285, Wallington, Surrey
SM6 6AN, UK.
Tel: +44 (0)20 8773 7244.
edit@hydropower-dams.com.
www.hydropower-dams.com.
October
25-29 October
Risk Management in Hydropower
Development
Trondheim, Norway
CONTACT: International Centre
for Hydropower (ICH), Klaebuveien
153, N-7465 Trondheim, Norway.
Tel: +47 73 59 0780.
Fax: +47 73 59 0781.
Email: mail@ich.no.
www.ich.no.
November
24-26 November
16th International Conference on
Hydropower Plants
Vienna, Austria
CONTACT: Dr. Eduard DOUJAK,
Vienna University of Technology.
Tel.:+43-1-58801-30515.
eduard.doujak@tuwien.ac.at.
www.viennahydro.com.
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12 MARCH 2010 INTERNATIONAL WATER POWER & DAM CONSTRUCTION
NEW TECHNOLOGY
W
HEN it comes to discussions on green energy it is all
too easy to overlook tidal stream power when set
against the high profile rollout of other renewable
sources of energy such as wind, wave and solar. The
reality, however, is that tidal stream, on a cost benefit analysis,
stacks up extremely well against the alternatives and is increas-
ingly being looked upon as a serious contender in the renewable
energy field.
The fact that, to date, tidal stream has been largely untapped can
be attributed to a number of factors, particularly the need for proof-
of-concept devices to be developed and trialled, something which is
now happening on the ground. A major advantage with tidal streams
is their predictability, which means we can forecast output to a high
degree of accuracy and for many years into the future. The capacity
factor is therefore fully determinant. The utilisation of sheltered estu-
arine sites, which nevertheless evidence strong tidal streams, provides
ease of maintenance compared to wind or wave with a significant
reduction in O&M costs.
COMMERC IALLY SUSTAINABLE
Thankfully, things are changing and, after considerable time and
effort, tidal stream energy has now reached the stage where it
can be offered at a commercially sustainable level. For our own
part, at Neptune Renewable Energy Ltd (NREL), we have been
developing a tidal stream power capability for the past five years.
Building on an intensive research and development process, we
have reached a major landmark with the announcement that we
are in a position to deploy the first full-scale demonstrator of our
vertical-axis Proteus tidal stream power plant in the Humber
Estuary at Hull, England.
The Proteus, to be moored in the Humber for an initial three
month trial, features a lightweight exoskeletal structure. It has
been specifically designed for estuarine sites where there are not
the problems, and stresses, associated with wave activity but
which nonetheless exhibit powerful currents and have the advan-
tage of lower access, cabling and maintenance costs compared
with offshore environments. Looking at the potential to roll-out
Proteus, we consider that there are at least 10 estuarine sites in
Britain with peak spring currents of more than 2.5m/s-1 which
could quite comfortably support this technology. There are, liter-
ally, hundreds of suitable sites worldwide.
As highlighted, the major benefit offered by tidal stream power is
the delivery of a predictable source of renewable energy compared to
more variable, less consistent, options such as wind. Certainly this
reliability has to be seen as a key benefit when it comes to the supply
of energy to individual sites and also to the national grid. Crucially,
once moored in the free stream, the state-of-the-art Proteus is able to
A powerful proposition
Jack Hardisty is the technical director of Neptune Renewable Energy in the UK. Here he
explains why tidal stream power is a serious contender in the renewable energy field
The Proteus demonstrator
The Proteus generator under construction
WWW.WATERPOWERMAGAZINE.COM MARCH 2010 13
NEW TECHNOLOGY
work equally well in ebb and flow currents.
Work on the £2M (US$3M) full-scale Proteus NP1000 demon-
strator was undertaken over six-months from May 2009, with 25
shipyard workers involved in the construction phase. The completed
unit is in the process of being transferred to Hull with commissioning
anticipated shortly thereafter.
The patented NP1000 device, which once in place is scheduled to
go through in-situ tests on the Humber, is the culmination of five
years of intensive effort by the team at Neptune and our partners.
Key landmarks in the development process over this time include:
the design, construction and testing of 1/10 and 1/40 scale tank
models. During the first-half of 2007, computational fluid dynamics
(CFD), mathematical and physical modelling resulted in a number
of design modifications. By 2008 we were ready to seek investment
for the full-scale demonstrator. With sufficient funding in place,
March 2009 saw us obtain Lloyds approval for the completed
structural designs and the electronic and electrical designs were also
finalised. The construction of the Proteus demonstrator itself began
in the middle of last year with the finished device currently being
moved to the Humber (February 2010).
AN ATOMY OF A TIDAL POWER GENERATOR
Weighing more than 150 tonnes and stretching to around 20m
long, with a beam of 14m, the full-scale demonstrator of the
Proteus NP1000 consists of a steel hull, vertically mounted turbine,
and buoyancy chambers. The vertical shaft within the Neptune
Proteus connects to a 1:200 gearbox and generator in the deck
housing. Associated valves and electrical and electronic processing
and control for the Proteus are mounted onshore, connected by a
floating cable-bridge.
Looking at the Proteus’ turbine in more detail, this is a 6mx6m
vertical axis cross-flow design which is mounted within a patented
symmetrical Venturi diffuser duct below the steel deck. A cross-flow
turbine – such as that adopted in the Proteus – is a radial free stream
turbine and due to its specific speed is classified as a slow-speed tur-
bine. Practically, guide vanes impart a rectangular cross-section to the
water jet which then flows through the blade ring of the cylindrical
rotor, first from the outside inward and then – after passing through
the inside of the rotor – from the inside outward.
CONTROLLING THE FLOW
The device’s rotor is maintained at optimal power outputs by sets
of computer-controlled shutters within the duct and by the variable
electrical load.
Focusing on the patented flow control shutters on the Proteus, these
maximise the area of water hitting the turbines to increase torque and
power output.
Crucially, the efficiency of all turbines depends upon the tip speed
ratio (TSR), specifically the ratio of the tip speed to the fluid speed.
In the case of the vertical axis, cross-flow rotors on Proteus, maxi-
mum efficiencies are achieved at TSR =0.35. The computer controlled
shutters direct the flow at variable angles onto the blades in order to
maintain this optimum TSR regardless of flow speed and thus max-
imise the electrical output.
Within the Proteus, the axle torque is taken by a right angle gear-
ing to 2 x 250kW permanent magnet DC generators and then, via
industrial regenerative drives and control systems, cabled ashore and
grid connected.
Theoretical work and laboratory experiments, suggest that we will
be able to realise an overall efficiency for the Proteus in situ of greater
than 25% and, potentially, generate 30% more electricity compared
to traditional hydro designs.
TESTING TIMES
Extensive model tests at the University of Hull’s Total Environmental
Simulator Research Facility have allowed the design to be continu-
ously refined and optimised in a number of crucial ways to reach the
stage of the Mark III design of the Proteus NP1000. The Mark I ver-
sion was constructed at 1/10 scale and tested in the tidal River Hull.
Detailed CFD analysis was then conducted to refine the rotor and
duct design with the result that, for a Mark II version, the rotor was
redesigned and duct angle reduced by seven degrees. Also, a single
deflector plate was replaced by two sets of three vertical shutters to
direct the flow close to the optimum angle of 16 degrees onto the
rotor. Further enhancements introduced for the Mark III (patented)
design of the Proteus NP1000 focused on the rotor, ducts and buoy-
ancy chambers.
ENERGY PRODUCTION
Cost engineered for estuarine energy production the Proteus offers
considerable practical benefits including:
The demonstrator will be deployed in the Humber Estuary
14 MARCH 2010 INTERNATIONAL WATER POWER & DAM CONSTRUCTION
NEW TECHNOLOGY
U Generating electricity at both capital and operating costs that are
significantly less than other tidal stream power devices and compa-
rable to onshore wind.
U Greater proximity of the generating capacity to the grid or distribu-
tion supply points.
U Ability to be moored in relatively sheltered locations meaning that waves
are not impacting on the structure, with the potential for damage.
U Being close to land means simpler installation (including cabling)
and maintenance.
WHY THE HUMBER?
The Humber Estuary for the first deployment of Proteus as its depth
and tidal flow is considered one of the best locations in the British
Isles for tidal stream power, whilst also being relatively close to our
base in North Ferriby, East Yorkshire. The Humber has also been
identified consistently as one of the key areas of concentrated tidal
stream power potential in British waters, a case in point being the UK
Atlas of Offshore Renewable Energy Resources (2004) published on
behalf of the DTI (Department of Trade and Industry).
Another benefit of the Humber area was that we were able to
call upon the expertise of local naval architects IMT Marine, engi-
neers Water Hydraulics, Ormston Technology in Beverley and Dane
Electrical Engineering in Scarborough.
Once deployed we anticipate that the advanced Neptune Proteus
NP1000 will generate at least 1000MWh/yr - this is based on a peak
spring tidal stream site of about 3m s-1.
MUNICIPAL SUPPORT
Throughout the process, at a municipal level, Hull City Council
has been extremely supportive of our efforts and this type of back-
ing is a key consideration for any project of this type. The Council
can clearly see the economic and practical benefits of Proteus and
have already agreed that the output from the demonstrator will
help to power The Deep Submarium (an aquarium tourist attrac-
tion in Hull).
Upon the completion of the demonstrator trials, the aim is to have
the world’s first tidal stream power array, consisting of advanced
Proteus designs, up and running close to The Deep in the Humber
during 2011-12. When it comes to the environment, as the Proteus
is a moored system, so the demonstrator will have a minimal impact
when located in the Humber. Also, the bulk of its steel and composite
construction can be recycled in the future.
OPERATIONAL AND COST BENEFITS
At this stage we are not aware of any similar device which is designed
to capture the shallow water resource at significantly lower capital
and O&M costs. Certainly, a major innovation is the cross-sectional
shape that has been adopted by our patented design. In the Proteus’
square turbine cross-section 30% more electricity per unit channel
width is generated compared to circular turbines. Additionally the
CFD tested and patented flow control shutters adopted, with their
computer control, are able to increase the impacted length of the
flow on the turbine to almost half of the circumference, thus increas-
ing shaft torque and power outputs.
When it comes to operation and maintenance, all Neptune turbine
components have been designed to be serviceable on site except for
the lower bearing which can be serviced and replaced with local dry-
docking. Crucially, the device can be towed to site using a small tug.
Overall, we believe that our Proteus device delivers reduced capital
and operation and maintenance costs and, as a moored system, its
environmental footprint is low – making it an attractive option in
particularly sensitive locations.
FACING THE FUTURE
The future for Neptune Renewable Energy and Proteus is extremely
bright, especially in light of the growing focus on renewable power
generation in the wake of the Copenhagen summit. This technol-
ogy can be successfully expanded and applied to other sites in the
UK. It can also be looked at as a practical power proposition for
locations worldwide.
For more information on Neptune Renewable Energy Ltd
(NREL) please visit www.neptunerenewableenergy.com
IWP& DC
View inside the tidal power generator
16 MARCH 2010 INTERNATIONAL WATER POWER & DAM CONSTRUCTION
NEW TECHNOLOGY
F
OR Jim Fiske, who has been working with a variety of
energy storage technologies for more than 10 years, hydro
power was a new challenge. He was looking for an entre-
preneurial opportunity to deliver yet another grid support
system, and with some concepts to examine, a focus on basic
physical principles plus reviewing swathes of publicly-available
information on hydro power, out came an unusual result – a shaft-
and-weight piston system that is a fresh take on closed, modular
technology for pumped storage operations.
His idea is called the Gravity Power Module (GPM) and, in con-
cept, it is like a sealed water-filled piston and so employs familiar,
classic mechanical engineering. But the GPM system is enormous,
the piston being an extremely large weight stack within a vertical
‘storage’ pipe that also holds water, and that column is housed in
a shaft that has been excavated hundreds of metres into deep rock.
The bored shaft also holds a second, thinner ‘return’ pipe. The pipes
link at their bottoms and at their tops for the inlet and outlet of a
pump-turbine.
When operating at peak demand times or for other grid reasons,
the pressurised unit will generate electricity by allowing, through fine
hydraulic control, water to be disgorged from the bottom of the stor-
age pipe under the force of the weight stack drifting down under
gravity in a plunger-type action. The water flows up the return pipe to
drive the pump-turbine and is discharged continuously back into the
top of the storage pipe, above the stack, in the closed system.
During off-peak times, the pump-turbine reverses the flow to inject
water at the bottom of the storage pipe and push the stack back up,
locking-in the desired potential, or gravitational, energy until the next
call from the grid. The pipes always remain full of water, including
above and below the stack, whether it is stationary or moving.
Armed with the core idea, for which patent application has been
made (US Patent Application – US20090193808), and keenly aware
of its business potential as a fast-response grid support system, Fiske
raised initial capital, recruited a team and is adapting the concept,
refining designs. As work continues with strategic partners and inves-
tors, this year could see construction begin for a commercial proto-
type, likely in Texas.
CONC EPT
GPM might be a fresh look at hydro power but the driving force
behind its development is traditional pumped storage – charge your
system with cheap energy, sell it back when the market needs it and
is paying more.
Electricity is generated when the weight stack descends, and is
stored when it rises in the storage pipe. The former sees the stack
eject water to drive a generator, the latter sees the pump-turbine inject
the flow to raise the weight. There is no buoyancy involved in the
GPM system.
With buoyancy not a factor to either maintain or change the posi-
tion, or elevation, of a weight stack within a pipe, holding that posi-
tion will depend on integrity of equipment as well as seals. Research
is also underway into the fit of the stack against the pipe wall to limit
leakage and drift, or loss of stored energy, in effect, but the system is
said to be able to tolerate some peripheral seepage.
Beyond the focus on single shafts there is the significant possibility
of clusters of such installations being constructed from the modular
GPM system, and they could be charged individually with stacks set
to different elevations. The variety could provide varying responsive-
ness to grid demands.
Elevation of a stack does not, however, determine the head, or driv-
ing pressure, in the system. The position within the pipe only serves
to set the maximum time a stack could drift down, and hence the
duration of the power output. For example, a unit could be designed
to give power output of, say, 15MW with half an hour of storage
– meaning the GPM system would deliver constant power of that
amount as the stack was in a controlled drift down the column for
30 minutes. Typical drift rates are anticipated to range from 0.2m/
sec-0.4m/sec, depending on the service to be provided to the grid.
Fiske comments that it can sometimes elude some hydro power
people that the operating head is not influenced by the elevation of
the stack. Instead, the head is determined by the size of the weight, or
more precisely given the constants of cross section and material den-
sity, its vertical dimension – height. As such, it is unchanged over the
cycle, he says. As a gravity-based operating system, weight equates to
force. Then, multiply by velocity, or drift rate, and the power of the
system can be calculated and established, he adds.
The weight stacks are to be assembled from locked concrete blocks,
and their underside will have shaped docking plates, or boxes, to fit
the base of the shafts.
GPM is a different take from regular hydro power systems although
both are driven by gravity: the more common, water pushes on water;
and, in the GPM concept, a concrete weight pressing on water.
R&D
Rights to GPM are held by Gravity Power LLC, which was founded
by Fiske, and he is chief executive and a co-owner. The firm was
launched late last year as a spin-out from LaunchPoint Technologies
Inc, a California-based venture engineering and hi-tech incubator
company in which Fiske is also VP of the Advanced Systems divi-
sion. Before its launch, Gravity Power LLC was previously called
LaunchPoint Innovations LLC.
The genesis of the GPM concept extended over several years, and
the focus of the venture was always to develop intellectual property
(IP) for a business to offer profitable energy services to the grid. A
variety of concepts were examined before GPM, as an underground
system, was selected as the most viable to initially pursue.
While the excavated shaft system is the main focus for the present
R&D effort, which is supported by strategic partners in a develop-
ment team, the firm’s patent application also covers both more gen-
eral, and other, versions the GPM concept – i.e., gravitational storage
of cheap energy using weights. Those variations are mostly based
on water recirculation for pumped storage and include constructing
offshore steel towers, either floating or placed on the seabed. But,
separately, the concept also extends to a wind power-driven system
of gears to move a weight.
For the underground GPM system for pumped storage, excava-
tion is a challenge but geology is not viewed as presenting an overly
restrictive barrier. The system’s small footprint would offer a marked
degree of flexibility in choosing site locations and help to reduce con-
struction risk. Favoured rock, though, includes limestone, chalk and
A weighting game
A fresh step in closed, modular hydro power concepts comes in US firm Gravity Power
LLC’s shaft-and-weight piston system. Report by Patrick Reynolds
WWW.WATERPOWERMAGAZINE.COM MARCH 2010 17
NEW TECHNOLOGY
gypsum – ‘great media’, says Chris Grieco, executive vice president.
The main GPM shaft in a commercial-scale operation could be
between 500m-2000m deep, the firm says. However, this range is
not fixed at this stage, and the depths that will be achievable will be
determined as processes and methods are proven.
Energy storage capacity in a GPM shaft and pipes-system increas-
es with the square of the depth. However, the merits of deeper shafts
versus, instead, opting for cluster farms of shallower units would
be analysed case-by-case with clients, such as utilities or independ-
ent power producers (IPPs), or possibly even considered by Gravity
Power LLC when taking investment views with partners on poten-
tial markets and sites.
The company is examining potential business models to help
exploit the core IP of the GPM system. But R&D effort surrounding
the concept has also given rise to opportunities for an in-house project
on pump-turbines. There is potential for serial production of smaller-
than-usual units in hydro power through a standardised approach,
the firm notes. It adds that there could also be bonus opportunities
beyond their use in GPM installation.
FUNDING PARTNERS
An initial funding round to help the R&D work raised US$2M in
January 2009. The equity stakes in Gravity Power LLC were taken
by 21 Ventures and Quercus Trust, and are confidential. The fund-
ing support helped with concept development, patent work and also
detailed engineering, siting and permitting studies. The funds also
helped towards business development and operational costs.
Employees and LaunchPoint Technologies are also shareholders in
the firm, and funding rounds continue with presentations being made
to potential equity investors.
“We are making strong progress on attracting venture and strategic
investment for our Series B Round, which will fund the commercial
prototype Phase I in Texas, plus allow for R&D on improving shaft
boring technologies and some corporate branding, marketing and
more,” says Grieco.
The firm is also pursuing grant funding, such as under the US
Department of Energy’s (DoE) push for Smart Grid technologies.
Pumped storage hadn’t been listed as an application category in the
recent awards, and so the non-conventional approach of GPM, while
interesting, didn’t clear the hurdle that time. However, other opportu-
nities with DoE are anticipated, such as the forthcoming solicitation for
grid-scale energy storage via the ARPA-E initiative, and again matching
funds could come from investors and strategic collaborators.
Future opportunities exist on federal and also state levels in the US
and other countries, Grieco adds.
While the business case for investment does not count on tax
credits, the bolster from achieving them is a recognised as a poten-
tial bonus. The system works well in the wind power sector, which
Grieco has had some entrepreneurial experience in through his pre-
vious business development work while engineering director with
Dehlsen Associates LLC, which develops renewable energy systems.
He joined Gravity Power LLC a year ago.
In addition to securing and pursuing funding support, the firm has
also been developing relationships with a series of strategic partners,
and this is an ongoing process, notes Grieco. He says that partners
may be active in underground construction, equipment, technology,
or have market or regional experience, or might be interested in tech-
nology licences or potentially be users of GPM installations, such as
utilities or renewable power producers.
DEVELOPMENT TEAM
Members of the development team recruited by Gravity Power LLC
have included key engineers with LaunchPoint Technologies, of
course, as well as a selection from a number of other US companies:
tunnel boring machine manufacturer The Robbins Co; hydro power
consultant HDR/DTA; contractor Atkinson Construction; financial
modelling and portfolio development consultant Competitive Energy
Insight; and, contractor Granite Construction.
Their contributions to the R&D process have been varied since
work began in earnest in early 2009, and range from design and siting
studies to financial modelling and analyses of component capabilities.
However, the nature of the formal relationships during the develop-
ment phase is confidential, and there is no comment on such for the
commercial roll-out and scale-up of the GPM system.
But Grieco says: ‘We have spent many months looking for proactive,
Left, from top to bottom: Artists Perspective of the GPM concept
GPM headworks, top view;
Surface view of the array assembly
18 MARCH 2010 INTERNATIONAL WATER POWER & DAM CONSTRUCTION
NEW TECHNOLOGY
capable development partners for this business. Many aspects of this
business are not commonplace, i.e., multiple shafts in one location,
serial production of hydro power equipment and more. Those that
have or will someday step up and view this as a business and partner-
ship are more likely to participate in our longer-term endeavours.”
Involvement of ‘many other’ collaborators is anticipated, such
as in construction, component manufacturing, project develop-
ment and operation.
PROTOTYPES, PRODUCTION
Prototype testing for GPM is to be done in two phases – a field dem-
onstration and then a full-scale test. The proposed location for the
tests is Texas, at a site yet to be finalised but the company hopes to
start construction by mid-year. The state was chosen for a combina-
tion of its favourable business climate, good geology and wind farms
– a producer of fluctuating output, presenting challenges for the grid.
Talks with potential customers are underway.
Phase 1 is expected to take about 18 months and involves construc-
tion of a relatively short shaft (approx. 100m) with a production-scale
diameter (approx. 6m), piston stack of concrete blocks, and seals. The
production head for tests is to be approx 300m. The minimum weight
of a production-scale piston stack is more than 6000 tonnes.
Design work for Phase 1 is underway with assistance from a global
expert in underground construction. The co-operation began recently
as Gravity Power LLC changed its plan for the location of the proto-
type tests, switching from its planned new offices on the West coast
to Texas as part of a move to reduce construction and business risk.
While the assisting expert is undisclosed it is not Robbins.
Full-scale tests in Phase 2 would require the shaft to be extended to
a commercial depth (at least 500m) and testing would then move to
using production-scale power equipment, such as its inhouse pump-
turbine. Phase 2 is expected to start at the end of Phase 1, possibly
sooner, and last possibly only 20 months, depending on power equip-
ment sourcing.
The shaft is to be capable of providing more than 15MW in Phase
2 but only a fraction of that power in Phase 1.
Production roll-out for commercial applications could start before
the end of Phase 2, depending on market demand and also how risks
have been eliminated through the tests in Phase I and some of Phase
2. The firm expects the largest of the single shafts to be capable of
providing more than 50MW for four hours or more, which is at least
200MWh of storage.
Separately, late last year the merits of constructing an offshore
GPM unit in Hawaii were being explored at an early stage but refine-
ment of the firm’s plans has since deferred that option.
MARKET OPPORTUNITIES
Charging up cheaply and discharging when electricity prices are
higher, or time-shifting, is the ‘holy grail’ of the business model, espe-
cially in a diurnal cycle, says Grieco.
But additional, fast response services will include grid frequency
regulation – which is the initial target market using 500m deep shafts
– and black starts. The weights don’t need to be already drifting to
provide a fast response; there’s no need for an equivalent to ‘spin-
ning reserve’ motion. The units are being designed to ramp from zero
activity to full power in well under a minute.
For such ancillary services it is possible to also have multiple pump-
turbines at a shaft, such as a three-unit design.
However, the GPM installations that focus on time-shifting market
opportunities will probably be the basic design, using a shaft with a
pair of pipes linked at the top to a single pump-turbine. That unit
would be operated at the best efficiency point (BEF) suited to obtain-
ing maximum return on investment (RoI), says Fiske.
Given the variety and scale of different needs in grids, and the IP
combinations being developed as standard, core technology to scale
and adapt to sites, Gravity Power LLC is open to a range of potential
business opportunities, including: being an owner-operator; selling
energy services to utilities; licensing the GPM system; and, providing
services as specific elements from the supply chain. Consequently, it
sees many potential ways to engage with partners.
“We are not looking to tie ourselves,” Grieco says, and adds that
the key is not to give up control on any aspect.
Beyond the US, the firm is looking at areas such as Europe, China
and South Africa – anywhere there are grid-scale opportunities.
The modular system would allow installations to be expanded with
time. But, as with any localised, repeatable, modular process, the
opportunity to construct a number of GPM shafts in clusters would
help amortise equipment and optimise costs and methods. In addi-
tion, there can be programme benefits.
Also, in the wider economic sense, many grid-scale energy storage
markets would require hundreds of megawatts at nodes or a site,
and again clusters would be the most likely approach. Besides, like
conventional pumped storage systems, seeking small installations can
be uneconomic, even if GPM’s footprint is small and would seem
relatively unobtrusive, like an oil wellhead on the sea floor.
In general, for economic reasons as well as operational flexibility,
it is more likely that higher power and larger storage capacities are
obtained by exploiting GPM’s modular concept to develop the instal-
lation in varieties of clusters.
IWP& DC
Below: Runner and hub CFD surface mesh
Above: GPM Headworks, side view
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20 MARCH 2010 INTERNATIONAL WATER POWER & DAM CONSTRUCTION
NEW TECHNOLOGY
I
N the context of climate and environmental challenges, R&D
has a key role to play in finding new solutions. From a com-
pany’s perspective, R&D is also about safeguarding business
outlook and shaping growth ambitions. This means that we
need to improve existing technologies as well as work on building
new renewable energy solutions.
Statkraft has been engaged in developing new renewable energy
technologies since the early 1990s. Based on the company’s history
as a major Norwegian power generator, our focus has been on har-
vesting the energy that is available along the far-reaching Norwegian
coastline. For more than a decade we have been working interna-
tionally, in close collaboration with R&D parties, as well as with
universities in order to find ways to produce renewable energy from
the natural forces of the ocean.
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 freshwa-
ter 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 1600TWh/yr – equivalent to half
the annual power generation in the European Union.
OSMO TIC PO WER
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 1970s,
when he designed the world’s first semi-permeable membrane for
desalination of saline water for production of drinking water based
on reverse osmosis. Osmotic power is based on naturally occurring
osmosis, triggered by nature’s drive to establish equilibrium between
different concentrations in liquids. Osmosis is a process by which
solvent molecules pass through a semi-permeable membrane from a
dilute solution into a more concentrated solution (Figure 1).
The difference in concentration of salt between seawater and
freshwater creates a strong force towards mixing. The effects
of this strong force to mix can be intensified through a special
membrane which separates salt and freshwater in a finite space
and which only lets the water pass through the membrane, while
the salt ions are rejected. In this way, an osmotic pressure can be
achieved by the amount of freshwater moving to the seawater side.
This pressure can be in the range of 24 to 26 bars depending on
the salt concentration of seawater.
More precisely, in a PRO system, filtered freshwater and seawater
Pressure
Membrane
Pressure retarded osmosis
Saltwater Freshwater
Below: Figure 1 – The principle of pressure retarded osmosis
The power of osmosis
With more than a hundred years of experience in developing and operating
hydro power, Norwegian utility Statkraft is now on course to strengthen its
position in the quest for new forms of renewable energy generation, including
the development of osmotic power. Stein Erik Skilhagen reveals all
Example of the river outlet where energy is
released when freshwater meets seawater