2
CONSIDERATION OF
ALTERNATIVES
2.1
Background to the Project
Wind
energy has been the world’s fastest growing sector of the energy industry over the past two decades. Technological developments have made wind energy a promising renewable source
of power in the near term. The many benefits wind energy offers the world are compelling:
pollution-free, technological innovation, rapid development, diversity,
security of supply, etc. Globally,
this was about 40,000MW of installed capacity of wind energy at the end of 2003
and it is one of the faster
growing, reliable and competitive sources of renewable
energy.
As a
continual commitment to promoting environmental protection and sustainable
development, the Hongkong Electric Co Ltd (HEC) commenced a feasibility study
in April 1999 to collect wind data on Po Toi and Lamma Island to evaluate the
wind potential for utilization of wind energy on these two outlying islands. The colleted wind data revealed that Po Toi and
Lamma have similar wind potential and are both suitable for power generation.
After
careful consideration of the technical, economic and environmental factors
pertinent to the best choice for utilizing wind energy, HEC is proposing to
install a 600-850kW wind turbine at Tai Ling of Lamma Island as a demonstration
of the potential for wind utilization in generating power. The wind turbine will be built in a
grid connection scheme for supplying “green” electricity to HEC customers. The objectives of the project are as
follows:
·
Demonstration of
utilizing wind energy for power generation: The
proposed wind turbine will
be the first utility scale and grid-connected wind project in Hong Kong. Based on the wind potential on Lamma,
the proposed wind turbine will harvest about 700MWh of electricity per annum, helping to avoid the use
of up to 240 tonnes of coal and reduce
the associated emissions every year.
·
Education purpose: Visitors’
facilities such as display boards and guided tour will be provided at the wind turbine site to
explain the principle of power generation by wind and the benefits of renewable
energy. The wind turbine project
will serve as educational use for promotion of green awareness among the
public, in particular with students.
·
Wider application of
renewable energy: The project will provide invaluable local experience on the design, construction, operation
and maintenance of wind turbines. Future utilization of wind energy in Hong Kong can
be explored based on the information collected and experience gained, keeping pace with Government's
policy, and the publics expectation of the promotion of renewable energy and improvement in air quality.
2.2
The Future Plan
The proposed wind turbine project will be planned and implemented by
HEC’s in-house staff together with consultants and contractors. Site erection will commence in early
2005 and commissioning of the project is scheduled for early 2006. The design life of the wind turbine is
20 years. A project area of about 4,400 m2 is being applied
through short term tenancy (STT) for an initial term of 5 years and renewal of
the STT will be made subject to further evaluation of the situation at that
time.
The wind turbine project will serve as a pilot project for demonstration
of power generation by wind and grid-connection with renewable energy. The performance of the wind turbine
will be monitored and evaluated during the operational phase including:
·
Amount of electricity generated: The annual electricity harvested by
the wind turbine will be compared with design figures to verify the site
specific performance of the wind turbine at Lamma where the terrain is
complicated and air turbulences are hard to predict.
·
Quality of power: As wind is time and season dependent and fluctuating in
nature, the interaction between the wind turbine and the existing 11kV power
grid will be monitored to assess the effects of connecting the electricity
generated by the wind turbine to the grid.
·
Resistance to wind load: Hong Kong is situated in a
typhoon-affected zone and it is essential to ascertain that the wind turbine
can be designed to withstand strong winds.
Subject to the result of evaluation on various technical, environmental
and commercial aspects and data collected during operational phase of the
project, HEC will evaluate the potential for wider application of wind energy
in Hong Kong. Any further plan for
installation of additional wind turbine will be subject to approval by the
Government.
2.3
Justification for Choosing the Present Site
The EIAO
Study Brief issued for this Project requires the justification for choosing the
present site (Clause 3.3.3) with a
view to avoiding or minimising the potential environmental impacts of the
Project, specifically intrusion into Country Parks and other environmentally
sensitive areas.
As a demonstration project for
renewable energy, the study envelope was confined to locations away from
densely populated areas. Po Toi
and Lamma Islands were subsequently identified for assessment of wind
potential. Two wind monitoring stations, one on Po Toi and
another on Lamma, were set up in April and November 2001 respectively to record
one-year wind profile. The wind
monitoring was completed at the end of 2002 and the data were fed into computer
software for analysis.
Desktop screening and site surveys were
subsequently conducted after completion of wind data logging to identify
potential sites for a wind turbine of suitable size on Lamma and Po Toi Island
based on the criteria recommended in the guidelines for wind energy development
issued by reputable international organizations of wind energy. The site search was confined to Lamma
and Po Toi where reliable wind data are available.
2.3.1
Po Toi Island
Po Toi Island is an ecologically sensitive area
which has been identified as a potential Country Park. As there
is no vehicular access on Po Toi, a properly paved access road with a minimum
width of 5m and a maximum inclination of not greater than 15° has to be constructed to link up the pier and sites of favourable wind
potential for construction of a 600-850kW wind turbine. Access roads meeting the above criteria
on Po Toi would have a length of approximately 1,000m and cross the hill-
slopes on western part of the island (Figure 2.1). The new access road and the associated extensive
reinforcement works would inevitably change the natural landscape (mainly shrub
cover hillside) and disturb the habitat of resident species. Construction of new road in a hilly island
was therefore
not considered suitable due to the
potential adverse environmental impacts.
Alternatively the wind turbine equipment and construction tools will
have to be transported to the wind turbine site on Po Toi by helicopters. Considering the limited payload of
local helicopter services, the maximum capacity of a wind turbine on Po Toi
would be restricted to about 50 kW.
Moreover, electricity generated on Po Toi could only be transmitted to
the HEC grid through the use of submarine cables. The shortest possible route of the proposed submarine cable
extended from Hong Kong Island would have a length over 5km. It would not be cost effective without
a large capacity of output (e.g. a wind farm of less than 20MW). Given that the marine waters between Po
Toi, Hong Kong and Lamma Island are already quite congested with seabed
utilities, finding an acceptable route for a cable may prove technically
challenging. Although not expected
to be unacceptable, the installation of a submarine cable would introduce
additional environmental impacts.
At present, electricity
supply on Po Toi is by means of an independent and autonomous grid. Currently two 50 kW diesel generators
installed by EMSD are operated during the night-time and residential tee-off points
are connected to the nearest lampposts to take power from the grid. To cater for the mismatch of wind
profile and demand pattern on the island, a costly hybrid control system and
battery bank will be required for synchronization of the wind turbine with the
existing diesel generator.
Worldwide experience in the wind-diesel power generating system is
rather limited and there are very few suppliers that can offer a reliable
hybrid control system.
In view of the accessibility considerations and
absence of a power grid, Po Toi is considered neither technically feasible nor
environmentally and economically attractive for a demonstration project with
commercial scale wind turbine. The
aerial photograph of West Po Toi Island where the wind potential is sufficient
for wind turbine is presented in Figure 2.1.
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Figure 2.1 Aerial
Photo of West Po Toi Island |
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2.3.2
Lamma Island
Once the above considerations had been accounted
for, site selection was focussed on Lamma Island. The wind turbine site was then examined against engineering requirements and environmental concerns and further refined using the following site screening criteria.
Wind Potential
Following completion of a 12-month wind power monitoring at Lamma in
November 2002, a wind atlas was developed to assess the wind potential of Lamma
Island. Figure 2.1
shows the “isovent” map of equal power density in terms of energy per swept
area of wind turbine blades.
Areas of wind
power density over 150 W/m2, equivalent to the average wind speed of
about 5.5 m/s, are considered suitable for wind energy utilization and warrant
further evaluation ([1])
([2])
([3]). Modern wind turbines have the cut-in
wind speed of approximately 2.5 to 4 m/s and sites with annual wind speed below
5.5 m/s are in general not
considered economically viable due to low electricity output of wind
turbine. Areas of high wind
potential are in general found on hilltops and areas of high elevation. Most of the potential areas are
concentrated in South Lamma island.
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Figure 2.2 Wind
Source Map of Lamma Island |
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Site Access
For Lamma Island, the vehicular roads that allow passage of heavy vehicles
and mobile equipment are the 275kV Cable Routes built by HEC (Figure 2.2). Since building a new access road leading to a remote site is
not recommended from environmental and economical viewpoints, potential sites
on Lamma Island for the wind turbine are limited to areas along HEC’s cable
routes or closed to existing berthing facilities. South Lamma
Island, which consists of Site of Special Scientific Interest (SSSI) and potential Country Park and frequent records
of the Romer’s Tree Frog was therefore avoided.
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Figure 2.3 Vehicle
Access Road on Lamma Island |
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Height Restriction
The Civil Aviation Department
(CAD) has imposed height restriction for all permanent structures on Lamma
Island in accordance with the Hong Kong Airport Control of Obstructions
Ordinance. Most areas in North Lamma along the 275 kV Cable Routes fall between the restricted
heights of 160 to 165 m above the Hong Kong Principal Datum (PD) respectively (Figure 2.3). Taking consideration of the regulations as well as the
topography of North Lamma, the design and height of the wind turbine will be
restricted. In selection of suitable sites for a wind turbine of the appropriate
capacity, consideration should be given to the maximum tip height of about 68 m and 90 m for a 600kW and 1MW wind turbine
respectively.
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Figure 2.4 Height
Restriction Map for Lamma Island |
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Electrical Connection
Electricity generated from the wind turbine will
have to be transmitted to the load center or connected to the main power
grid. Lamma Island has presently a
network of the 11 kV network allowing connection by the wind turbine via new
power cables and transformer. The
distance and routing of the transmission cable connecting the potential sites
to the main power grid are evaluated from technical, environmental and cost
considerations.
Area and Land-use
South Lamma is of
high ecological value consisting of SSSI,
potential Country Park, Restricted Area and conservation area. However, Lamma Island is not an
identified/ reported important site for migratory birds. Lands along the 275 kV Cable Routes are located on North Lamma which are
well away from areas of ecological importance such as green turtle’s
nesting
site in Sham Wan, and have been zoned mainly as agricultural and green belt
areas and are therefore compatible.
A working platform of
about 30 m x 20 m including the 15 m x 15 m wind turbine foundation is required for erection
of a 600kW class wind turbine.
Areas meeting the above requirement along the 275 kV Cable Routes were further identified taking into account
the landownership, present and future land-use with reference to the latest
Lamma Island Outline Zoning Plan.
2.3.3
Preferred Sites on
Lamma Island
Taking into account the above criteria, six potential sites were
identified with the application of
constraint mapping techniques (Figure 2.4). The details are presented in the Site
Search Report (Annex A). The six long-listed
sites are:
Site 1 - Lamma Power
Station Extension
Site 2 - Tai Ling
Site 3 - Yung Shue Long
Site 4 - Tai Peng
Site 5 - Pak Kok Tsui
Site 6 - Lamma Quarry
All of the sites avoided ecologically sensitive areas, SSSI and the
potential Country Park at South Lamma.
The six identified sites are situated away from the ecological sensitive areas
and along the existing 275 kV Cable Routes which are the only vehicular
roads on Lamma island.
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Figure 2.5 Long-listed
Sites for Wind Turbine Installation |
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Having identified sites that meet the broad environmental
and engineering criteria, a site-specific appraisal has been conducted to
establish a short-list of feasible sites for further detailed investigation.
Qualitative approaches have been adopted to
identify potential conflicts with the development of the wind turbine. Each potential
site was scrutinized more closely
with engineering criteria on wind potential, geological considerations and
electrical connection; and environmental criteria concerning visual, noise and
ecological impacts. Of the 6
long-listed sites within the areas of least constraints, four sites have been
excluded due to principal conflicts identified (Annex A), leaving the following two sites for
the final comparative assessment:
Site 2 -
Tai Ling
Site 4 -
Tai Peng
The two sites have been evaluated
and compared according to the potential impacts likely to arise as a sequence
of construction and operation of the wind turbine system. Site 2 – Tai Ling is identified as the overall
preferred site due to its distinct merits in site access, ground conditions,
noise and visual impact compared with Site 4 – Tai Peng (Annex A). The site at Tai Ling is also the more
remote of the two in terms of proximity to village houses.
The preferred site at Tai
Ling is a relatively level platform to the east of joint bay of HEC's existing
cable route. Taking advantage of
the joint bay area as part of the works area for erection of the wind turbine,
the landtake requirement can be optimized. Moving the wind turbine site further north away from the
noise sensitive receivers are not preferred due to the need for extensive
excavation of the hill slope to form access road for the wind turbine, and the terrain
around Tai Ling site is indicated in Figure 2.6.
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Figure 2.6 The existing
terrain around Tai Ling site |
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2.4
Potential Capacity for the Wind Turbine
The planned capacity of the wind
turbine at Tai Ling is 600 to 850 kW depending on the model sizes
available from respective suppliers.
The wind turbine capacity is
selected based on the following considerations:
·
600 kW class wind turbine is of
proven design with a large number of installations worldwide.
·
600 kW class wind turbine is
now becoming the smallest size available from the majority of the suppliers due
to the worldwide trend for large capacity machines.
·
600 kW class wind turbine is
the maximum size of machine complying with the height restriction at Tai Ling
Site.
The wind turbine design, construction methods and Project programme are
further discussed in Section 3.