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Coastal power plant: a hybrid solar-hydro renewable energy technology

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This article offers a demonstration of a novel technology that uses hydro and solar power combined with battery storage to generate electricity for deployment off coastal regions. Called the coastal power plant (CPP), such an installation has a multistorey water reservoir that draws in seawater that is then pumped up in vertical stages by geyser pumps into an overhead tank, from which it is released into a hydropower plant to generate electricity. The ocean surface is utilized to install a floating solar plant for photovoltaic energy generation. The intermittent renewable source is combined with a battery energy storage system to meet peak demands. Offshore oil industry technologies are utilized in fabricating the structures on shore and towing them to the site. The potential and cost effectiveness of a 201-MW CPP are also analyzed. Results demonstrate the effectiveness of the new design in terms of investment and operation/maintenance costs. These compare favorably with other renewable energy technologies.
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© The Author(s) 2018. Published by Oxford University Press on behalf of National Institute of Clean-and-Low-Carbon Energy.
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Received 25 January, 2018; Accepted 14 April, 2018
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R A
Coastal power plant: a hybrid solar-hydro renewable
energy technology
Cawas PhirozeNazir*
Panchsheel Apartment, Flat No. 3D, 3rd Floor, 41/1B Jhowtala Road, Kolkata 700019, India
*Corresponding author. E-mail: cpnazir@gmail.com
Abstract
This article offers a demonstration of a novel technology that uses hydro and solar power combined with battery
storage to generate electricity for deployment off coastal regions. Called the coastal power plant (CPP), such an
installation has a multistorey water reservoir that draws in seawater that is then pumped up in vertical stages
by geyser pumps into an overhead tank, from which it is released into a hydropower plant to generate electricity.
The ocean surface is utilized to install a oating solar plant for photovoltaic energy generation. The intermittent
renewable source is combined with a battery energy storage system to meet peak demands. Offshore oil industry
technologies are utilized in fabricating the structures on shore and towing them to the site. The potential and cost
effectiveness of a 201-MW CPP are alsoanalyzed. Results demonstrate the effectiveness of the new design in terms of
investment and operation/maintenance costs. These compare favorably with other renewable energy technologies.
Key words: renewable energy; hydro power; solar energy; concrete gravity structure; coastal plant; hybrid solar-
hydro energy
Introduction
Coastal regions in many developing countries are only
partially connected to continental electrical grids and
lack of major power has left them less developed. Most
coastal regions have a good renewable energy potential.
In this context, one of these sources is ocean energy.
Most ocean energy technologies fall under two categories
[1], thermal energy from the sun’s heat and mechanical
energy from the tides and waves. However, these plants
have high costs, work under a variable load and have a
variable output. Amore recent technology, the offshore
hydroelectric plant [2], was developed whereby steady
electric power was generated from a recharging ow of
water from the ocean. Co-locating solar with hydro to
maximize the generation potential of the coastal site has
motivated the development of a new technology called
the coastal power plant (CPP). The hybrid solar-hydro
station dedicates a signicant portion of its solar power
resources to operate geyser pumps [3] that pump water
into an overhead tank, from where it is released into a
hydropower plant to generate electricity. The ocean sur-
face is utilized to install a oating solar plant. The inter-
mittent nature of the renewable source is combined with
a battery energy storage system to meet peak demands.
The coastal ocean is a shallow (<200 m) area covering 7%
of the global ocean. About 40% of the world’s population
lives within 100 km of the coastline and the proportion
is increasing [4]. This article shows how the new design
could access the full potential of ocean energy and the
innitely renewable source of sunlight. Salient features of
design, construction and costs are discussed.
Clean Energy, 2018, 1–10
doi: 10.1093/ce/zky010
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1 Overall concept
The aim of this research was to prove the viability of a
coast-based hybrid solar-hydro power plant that could pro-
vide power during peak periods, thereby improving overall
utilization and economics of the electric grid. We used the
concept of tapping energy potential created by head differ-
ences to generate electricity. In the present study, pumping
is used to articially maintain the head required for ow.
Locating the plant in shallower waters, nearer to centers
of demand, would reduce transmission costs and larger
capacity factors could offset, to some degree, the greater
capital costs. Solar panels mounted on oating pontoons
would harvest energy from the sun and provide the energy
required to operate the pumps. Hybridizing the solar and
hydropower sources with storage batteries would cover
the periods of time without sun to provide a realistic form
of power generation. Atypical layout of the new design,
called the coastal power plant, is shown in Fig.1. It has the
following salient features:
Multistorey water reservoir (MWR) having tanks stacked
vertically in a staggered conguration. Geyser pumps
installed in these tanks raise water to the topmost tank
(Figs1–3). Roof and vertical sides of tank walls are cov-
ered with photovoltaic (PV) arrays.
A large oating solar PV plant to provide the bulk of
solar power is being built in Chiba, Japan [5].
A battery energy storage system installed on the MWR.
A powerhouse (PH) (Fig. 4) at sea level with turbines
driven by water owing from the MWR through pen-
stocks. An offshore substation is integrated with the PH.
A concrete gravity substructure (CGS) (Fig.5), such as those
used in oil and gas projects [6], to support the PH caisson.
Submarine cable to carry power to the shore-based grid.
The stages of operation for the working of the plant, with
reference to the diagrams shown in Fig. 1, are outlined
briey here:
1. Water is allowed to ow from the sea through the
intakes into the sumps of the MWR. Water from the
sumps ows into the rst tank located at sea level.
2. Simultaneously, solar energy is collected during day-
light hours from the PV arrays atop the MWR and one
segment of the oating solar PV plant. This is then con-
verted into electrical energy to power the blowers that
operate the pumps. Energy from the second segment
of the oating PV plant charges the battery bank dur-
ing daylight hours, which can then supply power to the
pumps during periods without sun.
3. Geyser pumps then raise the water into the tank located
at the next higher level. These steps are repeated till
the nal set of geyser pumps discharge the water into
the topmost tank.
4. Water from the topmost tank of the MWR is led by a
penstock to a set of turbines installed in the PH located
at sea level to produce electricity, which is then trans-
ported to the grid.
Floating PV modules
MSL
MWR
MWR
PH
A
Scale: 1:1000
ASection A–A
Fig.1 Schematic plan and section of CPP
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2 Preliminarydesign
It is impossible to record here all the detailed steps lead-
ing to the nal design. The more important steps may be
divided into the following stages:
Given the basic parameters such as availability of head
and depth of sea adjacent to coastlines and places of
power shortage, the rst need is to show the estimated
power to be generated and the number of units.
Collecting eld information in the areas of climatology;
seismic, hydrological and geotechnical surveys; wave
modelling, tidal and current circulation, nautical and
environmental studies; amount of insolation; site of
sources of construction material; and location of con-
struction facilities preferably with marine experience.
Selection of key electromechanical equipment, includ-
ing hydraulic turbines, generators, cranes, gates, valves,
geyser pumps, blowers, PV panels, pontoons, battery
banks, inverters, control room equipment, cables, trans-
formers, etc.
Determining size of geyser pumps, their submergence
depth, lift, air ow requirement and their numbers
based on discharge required from turbines and head to
be maintained.
Design and sizing of key buildings such as the MWR, PH
and CGS.
Determining type and array of PV panels and their
method of installation on the MWR and oating solar
PV plant.
Designing the battery bank.
Determining thickness of bed protection for marine
gravity foundations [7].
Design of electrical collection and transmission system.
Design of towing and installation systems.
3 Detailed plant design
3.1 MWR
The multistorey water reservoir building is developed
using a special concrete gravity base structure (CGS). The
advantages of the CGS [8] lie in the economy of materials
used; it is easy to make the structure buoyant in the con-
struction and towing phases and it can act as a foundation
structure in the operation phase. The prestressed concrete
structure consists of a watertight monolithic oor, a num-
ber of tanks stacked vertically one above the other in a cas-
cading conguration and side compartments for buoyancy
as shown in Figs1–3. Awell-ventilated building is provided
over the roof of the tanks for storage of batteries. On the
roof and sides (south, east and west) of this structure are
installed an array of solar panels to generate solar energy.
The in-place foundation stability is ensured by enough
weight and friction. In areas with low-bearing-capacity
soils it may be necessary to use soil improvement tech-
niques and their costs must be considered in the decision-
making process. Part of the building (~2 m above mean
sea level (MSL)) is built in dry dock, oated out to site and
installed on a prepared seabed. It is ballasted against ota-
tion. Balance concreting and installation of equipment is
done at site. Geyser pumps are installed within the tanks
to lift water from the sump to the upper reach of the top-
most tank. The pumps are operated by blowers. Control
panels, blowers, inverters, etc., are located on a cantilever
platform built above the respective tanks.
3.1.1 Geyserpump
The geyser pump works on the principle of buoyancy.
Ageyser inertia pump (GIP) was used for this design. It
has a long suction pipe through which water ows by
inertia after each pulse cycle. As inertia ow volume is
7–10 times the ejected liquid, the energy required for
pumping becomes less because the power consumed is
only to eject the volume of liquid that was suctioned into
the discharge riser. Fig. 6 shows diagrammatically the
working of aGIP.
3.1.2 Solarplant
The MWR building provides a large surface area on which
arrays of PV modules are mounted to generate electricity
from sunlight (Fig.3). Additional panels are mounted on
a oating solar PV plant (Fig.1). The electrical charge is in
direct current (DC) form and is inverted from DC to alter-
nating current (AC) for grid connection.
3.2 PH
The powerhouse (PH) is a reinforced concrete caisson
fabricated onshore, oated out to the site and placed on
supporting shafts of the CGS. The turbine caisson houses
the turbine/generator sets including transformers, switch
gear, control and protection systems and cabling (Fig.4).
Integrated with the PH structure is an offshore substation
that houses the transformers, control panels and switch
gear.
3.3 CGS
The main functional requirement of the CGS is to support
the PH. The design solution for the CGS consists of a cellu-
lar concrete caisson; the structure has a base slab, perim-
eter walls, number of cells and multiple cylindrical shafts
for supporting the PH (Fig.5). The base slab of the PH is
cast along with the supporting shafts of the CGS. The CGS
is built in dry dock, oated out to the site and installed on
a prepared seabed. It is ballasted against otation. Balance
concreting of PH is done on site.
3.4 Grid connection
The electrical system integrates AC power from each tur-
bine and transforms voltage via a step-up transformer
for export via submarine cable to onshore substations.
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Submarine cables constitute a major portion of con-
struction costs, so a high voltage AC is suggested as it is
the most economical option for distances shorter than
50 km [9].
4 Example
Made as a practical design application, is a conceptual
design and cost estimates for a CPP based near Mishap,
Gujarat in India. The plant is located 7 km from shore
where the water depth is ~11 m. The mean tidal range
between successive high and low tides is taken as 1.0
m.Atypical layout for one module would be as shown in
Fig.1, and comprises a hydro plant (31 MW) and two PV
plants (7.08 MW each), one of which will have a 22-MW
battery energy storage system. This example proposes
three such modules, with a total plant capacity of ~201
MW. This power will be fed to the grid during peak period
over a 10-hr period.
4.1 MWR
Each MWR is composed of tanks built at nine levels.
Installed in tanks at each level are 435 geyser pumps to
pump water vertically from the lower reach of the sump
into the topmost tank at a rate of 44 cumecs. The total
height difference is 84.6 m. The supporting structure of
the MWR is made of prestressed concrete and is 167.4 m
long, 125.6 m wide and ~85 m high. Its base is 11 m below
MSL. Atypical cross section is shown in Fig.3. The outer
perimeter of the structure is divided into compartments
by longitudinal and transverse cross walls. Each compart-
ment is 9.3×11.5×11.3 m deep. There are 18 tanks (com-
partments) along the intake side. Alongside are built 14
additional tanks as shown in Fig.2. In each of these are
installed 24 GIPs with their suction pipes extending into
the intake sump. Tanks along the balance perimeter of the
building serve as buoyancy chambers. Similar tank struc-
tures are built in nine stages at vertical intervals of 9.4
m, with the tank above being stepped back as shown in
Fig.3. The elevated tanks are supported on a framework of
beams and columns. Ashaft 18.6×11.5×66 m high with
800-mm-thick walls is built at one end and functions as a
shear wall. An intake chamber 46×10×11.3 m high is pro-
vided at one end of the building with provision for trash
screens and vertical gates. A well-ventilated structure is
built on the roof of the rst tank to house the batteries,
inverters and other electrical equipment. A 1.5-m-wide
platform located at the top of each tank supports the blow-
ers, control panels, etc., for the geyser pumps and the solar
system.
4.1.1 Geyserpumps
GIPs 12 inches (or 300 mm) in diameter were used [10]
to pump water from the lower tank to the one above.
The pumps are submerged to a depth of 8.1 m and lift
water to a height of 9.4 m above water level. Asuction
pipe (300-mm dia, ~20 m long) is tted to the pump;
this provides an increased ow due to the inertia effect.
Based on these parameters, the rated ow is 364 m3/hr,
Floating PV panels
Detail X
Bottom cluster
Geyser
pump
Top cluster
PV panels
Part top plan
MWR
Geyser
pumps
X
Settling
tank
Intake
sump
Part bottom plan
Scale: 1:300
Bottom cluster
Fig.2 Sectional plan at top and bottom of MWR
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the air ow required is 25 cfm (0.065 cum/min) and the
operating pressure is 14 psi (96.46 kPa). At each stage,
the water ow required is 44 cumecs (158 400 m3/hr).
Thus the number of pumps required/stage = 158 400/
364=435.
At each level of the MWR there are 18 compartments,
with 24 pumps located in each, as shown in Fig.2.
4.1.2 Blowers
To supply air to the GIPs, positive displacement air
blowers [11] were considered, and blower model ZS 55
VSD was selected. From the specifications of this model,
against a pressure of 14.7 psi (101.28 kPa), the air flow
is 1688 m3/hr (994 cfm) and the motor capacity is 55 kW.
Blowers operate on electricity generated by the solar
plant.
The total air requirement for one stageis:25×435=10 875
cfm (307.6 cum/min).
Thus the number of blowers requiredis: 10 875/994=10.9
(round to 11).
One blower was used for a cluster of 40 pumps.
Power required for 11 blowers: 11×55=605 kW.
Thus for nine stations: 9×605=5445 kW.
4.1.3 Solar PV powerplant
The PV panels are supported on MWR and two oating
platforms. It is assumed that the solar plant and the blow-
ers will operate for 10hr/day. For 5daylight hours, one-half
of the solar plant will supply power directly to the blowers
via inverters and transformers. The second half of the plant
also operates for 5hr/day, the power being used to charge
a battery bank through a charge controller. Inverters and
transformers carry the converted AC power to the blowers
(see Fig.7). To collect as much sunlight as possible, the roof
and walls on the south, east and west sides of the MWR
are covered with an array of PV modules (see Figs2 and 3).
However, the bulk of PV panels are supported on a oat-
ing platform such as the Heliofort [12] (see Figs1 and 3).
Solar power generates in DC and is converted to AC; then,
using power transformers, the generated and modied AC
power is fed to power the blowers. Standard solar panels
from Titan Energy Systems Ltd. (Secunderabad, Telangana,
India) were employed in this study. The PV module speci-
cation is TITAN M6-72 Polycrystalline [13]. The key speci-
cations of the PV panels provided by the manufacturer are
shown in Table1.
Other parameters assumed:
Max solar insolation at site near Mishap, Gujarat is
~6.18 kWh/m2/day as indicated in India Solar Resources
[14]. Average daily sun hours assumed to be 5 hr. Total
sunny days=330.
Setup:
Total number of PV panels required to operate blowers
is calculated using Wholesale Solar’s panel calculator [15]
Data provided for calculating the number of PV panels
is as follows:
No. of blowers=99
Watts consumed by each blower=55 000
Floating solar
panels
MSL
Intake
Battery
enclosure
Solar
panels
Blower
MW
R
Geyser
pumps
Scale: 1:250
Fig.3 Part longitudinal section of MWR
Table1 Parameters of PV module
Model TITAN M6-72 Polycrystalline
1 Open circuit voltage, 36.72 V
2 Output current 8.17 analog to digital
conversion
3 Maximum power 300 watts peak
4 Dimensions, 1975×988×58mm
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Hours on/day=5
Then, total watt hours per day=27 225 000 W
Hours per day, assuming inherent efciency
loss=35 392 500.
After calculation,
Energy=1 061 775 kWh/month
Maximum system size for 5 peak sunny hours/
day=7 078 500 W
For 300-W solar panel, number of solar panels
required = 23 595. As the second PV plant also operates
for 5hr/day, the number of panels required are the same.
Power is used to charge the batteries to run the blowers of
the hydroplant.
PV panels accommodated on MWR assuming a xed tilt
system.
Total area of roof available=16 600 m2.
Area of wall surface on south side=13 745 m2.
Area of wall surface on east and west side=10 246 m2.
As per [16], only ~58% of this area is effective. Thus
0.58×10 246=5943 m2.
Then, total area available on surface of MWR=36 288 m2.
Less 15% buffer for mounting frames=5443 m2.
Net total=30 845 m2.
No. of panels that can be accom modated = 30 845/
1.975 × 0.988=15 818.
No. of oating panels distributed on two oating plants=
(2×23 595)−15 818=31 372.
Approximate area required is based on the Kyocera
plant in Japan [5], where 51 000 panels were installed on
an area of 180 000 m2 or ~3.5 m2/panel. Therefore area
required for 31 372 panels=31 372×3.5=109 802 m2. These
panels are installed on pontoons in two areas of 234×234
m as shown in Fig.1. Research [17] has shown that a oat-
ing PV system yields 11% greater output than a terrestrial
counterpart, primarily because the module temperature of
a oating system is lower than that of a land-based sys-
tem. However, this has not been considered in the present
design.
Battery bank sizing. The total number of batteries required
to operate blowers for a period of 5hr is calculated using
Wholesale Solar’s battery bank calculator [18]. Adeep-cycle
solar battery bank was selected, a Crown 1290AH, 12VCD,
15 480Wh (6), Model No. 1898720 [19]. The key parameters
used for battery selection are shown in Table2.
Results of calculation:
1) Total battery capacity needed, 2 300 513 AH
2) No. of strings wired in parallel, 1784
3) No. of batteries wired in series, 4
4) Total no of batteries required, 7136
Inverters. Total wattage required by blowers=99×55=5445
kW, capacity provided is 25–30% larger than actually
required for the total wattage of the applicances [20].
Thus 1.25×5445=6806 kW.
A SatCon PowerGate Plus 500 kW 480/3 inverter [20] , which
has an in-built power point tracking (MPPT) system, was
considered for the PV power plant.
No. of inverters=6806/500=13.6 (rounded to 14).
Costs are approximate and based on prevailing rates. Costs
for the solar plant are taken from the U.S. Department of
Energy [21].
4.1.4 MWR civil and equipment cost, $ million
Concrete 92 816 m3 @ $600/m3=55.69.
Crushed rock for bed laying & scour @ 3%=1.67.
Steel platform, etc., 44 t @ $1500/t=0.66.
Geyser pumps, 3915 @ $5000=19.57.
Blowers, 99 @ $2000=0.19.
Solar panels 14.16×106 W @ $0.65/W=9.2.
Additional PV panels due to degradation @ 1.63%=0.55.
Racking 14.16×106 W @ $0.16/W=2.26.
Balance of system 14.16×106 W @ $0.16/W=2.26.
Inverters 14.16×106 W @ $0.14/W=1.98.
Batteries, 7136 @ $1900=13.55.
Battery replacement @ 180%=24.4.
Miscellaneous items for MWR such as lighting, etc.
LS=0.25.
Subtotal=132.23.
Transportation & erection @ 8%=10.57.
Total cost of MWR (Cmwr)=142.8.
4.2 PH
The PH caisson has two turbines. Taking the mean high-
water level (MHWL) as 707.5 m, MSL as 707 m and full-
supply level (FSL) of the topmost tank as 791.2 m gives
a maximum head of 84.2 m.The rated head is taken as
81.42 m and the quantity of water available at this head
is 22 cumecs per unit. Based on this input, and using
HydroHelp’s Excel-based program to select a turbine gen-
erator [22], the type recommended is a vertical axis Francis
turbine with steel casing and a throat diameter of 1.43
m.The power generated by each turbine is 15.5MW.
The PH building, consisting of the turbine hall and
auxiliary bay (serving as offshore substation), is built of a
module housing two turbines. Two steel penstocks, 1.3 m
in diameter, lead the water from the topmost tank of the
MWR to the turbines. The two turbines are spaced 10 m
apart. Atypical arrangement is shown in Fig.4. The con-
crete caisson for the turbine hall is 17× 22 ×4.6 m high.
Table2 Parameters for battery selection
Crown Model No. 1898720
1 AH rating for battery 1290
2 Voltage rating for battery 12 V
3 Battery depth of discharge 0.5
4 Average winter time ambient temperature 70°F
5 System voltage 48 V
6 Daily watt-hr requirement 35 392 500
7 Max number of consecutive cloudy days 2
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The superstructure for the turbine hall is 16.5×21.5×10 m
high. The crane girder is designed for a 64-t crane. Aconi-
cal draft tube having inner dimensions of 2.5 m and outlet
diameter of 3.5 m discharges the ow from the turbine to
the sea. The sill level of the draft tube is 5.7 m below MSL.
The plants will be operated from onshore control stations
as is the practice for offshore wind farms [23].
4.2.1 PH civil and equipment cost, $ million
Concrete: 1320 m3 @ $600/m3=0.79.
Steel (penstocks, etc.): 248 t @ $1500/t=0.37.
Turbines: 31×103 kW @ $700/kW=21.7.
Subtotal=22.86.
Transportation and erection @ 8%=1.82.
Total cost of PH (Cph)=24.68.
4.3 CGS
The CGS is designed to support the PH. It is a reinforced
concrete structure having a base slab with dimensions of
20 m × 25 m and ~0.8 m thick with a 12-m-high perim-
eter wall. It has 30 compartments formed by internal walls
spaced at 5-m intervals. Four cylindrical shafts with 4-m
external diameter and a height of 5.4 m provide support
for the PH. Atypical plan and section is shown in Fig.5. The
raft of the PH is built over the shafts, and the CGS is oated
out to sea and placed on a prepared seabed. It is ballasted
against otation. Balance concreting of the PH and instal-
lation of equipment is done at the site.
4.3.1 CGS civil cost, $ million
Concrete: 1320 m3 @ $600/m3=0.79.
Crushed rock for bed laying and scour @ 3%=0.02.
Subtotal=0.81.
Transportation and erection @ 8%=0.06.
Total cost of CGS (Ccgs)=0.87.
Turbine
penstock
MSL
CGS
Turbines Sec. A–A
Powerhouse
Offshore
substation
AA
Transformer
Plan Cable to grid
Scale: 1:250
Fig.4 Part plan and section of PH
B
AA
B
CGS
CGS
PH
MSL
Sec. A-A
Sec. B-B Scale: 1:125
Fig.5 Plan and section of CGS
Suction pipe
Sump
Outer air chamber
Large air bubble
Riser
Water line
Air
Inner air chamber
Fig.6 Diagram of geyser pump
Nazir | 7
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4.4 Grid connection
Power from the generators in the PH is collected by a local 11-kV
system that is then transformed up to 90 kV, using conven-
tional AC transformers, and transmitted to the mainland via a
7-km-long submarine cable (see Fig.8). The cost is based on [9].
4.4.1 Grid connection cost, $ million
Cost of 7-km-long, 90-kV AC submarine cable @ $ 755 000/
km=5.28.
Cost of 3700-m-long 11-kV cables @ $ 381/m=1.41.
Cost of 11-kV switchgear: 6 @ $50 000=0.3.
Cost of transformer: one 11/90kV @ $2.6×106=2.6.
Fixed mobilization=2.85.
Total cost of grid connection (Cgr) =12.44.
4.5 Othercosts
For other costs (Co), an estimated lump sum gure of $3 mil-
lion has been included for design and advance planning.
5 CPP economics
Besides the technical feasibility of CPP generation, the eco-
nomic aspects also must be considered. These will depend
on the overnight construction costs of the project ($/kW), the
levelized electricity costs (¢/kWh) and the capacity factor.
5.1 Overnight constructioncosts
These are the capital costs of the project if it could be con-
structed overnight (and do not include interest), as deter-
mined by dividing the total construction costs (Cc) by the
plant capacity (Pcap). The total construction costs for three
plants can be determined by adding the separate costs as
obtained from Equation(1).
CCCC
CC
cmwr ph cgsg
ro
3=++
()
++
(1)
Cc=[3(142.8+24.68+0.87) + 12.44+3] 106=$520.49×106
Power from three hydro plants=3×31=93.0 MW.
Power from three solar plants=3×14.16=42.48MW.
Power from three battery banks=3×22=66.0MW.
Pcap=93+42.48+66=201.48 MW.
Then overnight construction costs are given in
Equation (2).
C
P
MW
c
cap
=×
520 49 10
201 48 25810
6
6
.
.$. / (2)
5.2 Capacityfactor
The hydro plant runs for 10hr/day for a total of 330days.
Thus the plant runs for 3300hr/yr out of a total of 8760hr/
yr, giving a capacity factor of 0.38.
5.3 Annual generation
Using a capacity factor of 0.38, the yearly energy output (Ea)
per kilowatt of plant capacity would be with a generator
efciency of 0.95 [24].
Ea124365 38 95 3162 kWh
00..
Power available from three hydro plants=3×31 ×103=9
3×103kW.
The overall energy conversion of the plant is the net
energy produced by the hydro, solar and battery plants less
the energy consumed by the blowers.
Energy from three hydro plants=93×103×3162=294 0
99×103 kWh/yr.
Energy from three solar plants=3×2×1061×103×11=
70 026×103 kWh/yr.
Energy from three battery banks=3(1290×12×7136×
0.5×330)/1000=54 678×103 kWh/yr.
Energy used by blowers in three hydro plants=3×99×
55×10×330=53 905×103 kWh/yr.
Net energy from plant, Enet=(294 099+70 026+ 54 678−
53 905)103=364 898×103 kWh/yr.
11 kV cable
6 × 15.5 MW
(93 MW)
11 kV
11/90 kV
transformer
90 kV cable
Onshore grid
Fig.8 Single-line diagram of transmission system
Solar
array
Charge
controller
Battery bank Inverter
Blowers
(AC)
Hydro
plant
Sub
Station
Grid
Fig.7 Block diagram of a PV/hydro hybrid power plant
8 | Clean Energy, 2018, Vol. XX, No. XX
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5.4 Levelized electricitycosts
The levelized electricity costs represent the generating
costs after initial investment. They are given by divid-
ing the total construction costs in a lifetime (Ccl), by the
total net energy produced during this lifetime (Enl). For this
example, the simplied lifetime cost of energy (COE) is cal-
culated based on the formula [25] in Equation(3).
Net COE
initial capital cost capital recovery factornet
e
=
×/
nnergy production
fixed OM costlevelized replaceme
++
&n
nt cost
misc operating expensesnet energy production+
./
(3)
where CRF is the ratio of constant annuity to the present
value of receiving the annuity for a given length of time.
The following data has been used:
Capital cost= 520.49× 106 $. As MWR is a concrete struc-
ture, plant life assumed=40years; CRF =0.058; discount
rate=5%; xed operation and maintenance (O&M) costs
taken as 2.5% of investment cost/kW/yr [26].
Net energy from plant=364 898×103 kWh/yr.
Then, based on Equation (3), COE=0.082+0.035=0.117¢/
kWh.
Note that these gures should be treated with caution,
and are not a substitute for detailed system analysis. They
do, however, give an idea of the order of magnitude to be
expected.
6 Results and discussion
6.1 Constructioncosts
Based on the estimated costs from the previous section it
can be concluded that CPP has high-investment construc-
tion costs. However, with increased installed capacity, this
price will continuously drop over the years as a result of
technological improvements, economies of scale and vol-
ume production. The levelized electricity costs, on the
other hand, are on the low side. Renewable energy gener-
ated at this cost would be commercially attractive.
6.2 Cost comparison
Table3 presents typical average total installed costs and
the levelized cost of electricity of utility-scale renew-
able power generation [21]. It can be seen that CPP is now
within the same cost range of other renewable power tech-
nologies and even lower than for offshorewind.
In another comparison, estimates from The Carbon
Trust’s Accelerating Marine Energy” [27] put the levelized
cost of energy for offshore waves at 38–48p/kWh (61–77¢/
kWh), and for tidal at 29–33p/kWh (46–53¢/kWh).
6.3 Scale-up
An array of such modules, electrically coupled, would allow
for expansion to power plants with capacities in excess of
1000 MW. These would give high-value power in a reliable,
non-polluting and cost-effective way.
6.4 Cleanenergy
Renewable energy technologies provide an excellent oppor-
tunity to mitigate greenhouse gas emissions and reduce
global warming [28]. It is estimated that 300kg of CO2 could
be avoided for each MWh generated by ocean energy [29].
Thus, clean energy from the present plant could effectively
prevent annually~58 417 t of CO2 entering the atmosphere.
7 Conclusions
This article supports the technical feasibility of a com-
mercially viable, hybrid solar-hydro coastal power plant
that taps the oceans’ enormous energy resource and the
innitely renewable source of sunlight. The approach
taken in this concept study was driven by the need to
use a constantly recharging ow of water that provides
the energy that the plant exploits to make electricity. It
provides essentially unlimited quantities of renewable
energy for coastal regions that are only partially con-
nected to the continental electrical networks and lack
major power, leaving them less developed. Co-locating
solar with hydro has helped in maximizing the genera-
tion potential of the coastal site. The intermittent nature
of the renewable source is combined with a battery
energy storage system to meet peak demands. As more
countries adopt CPP as an element of their generation
capacity, the price will decrease making it more attrac-
tive. The next stage requiring signicant investment will
help greatly in demonstrating design concepts and reli-
ability of new design.
Acknowledgement
Grateful acknowledgement is made to the late Dr Sam Kondo and
to Mr Fadi Kassir of Geyser Pump Tech, LLC (USA) for their help
with data provided for the geyser pump.
Conict of interest statement. None declared.
Table3 Typical average installed costs and LCOE of utility-scale
renewable powera generation
Plant
characteristic
Average installed
cost USD/kW
Average LCOE
USD/kWh
Solar PV 2330 0.08
Biomass power station 4300 0.04–0.14
Onshore wind 2000 0.06–0.08
Offshore wind 4500 0.10–0.17
Concentrated solar
power
6740 0.17
Hydropower 1000 to 3500 0.02–0.15
Geothermal power 1850 to 5100 0.05–0.10
CPP generation 2580 0.12
aSource: [21].
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Mallampaya: the first CGS built in Asia
  • Collier
Collier D. Mallampaya: the first CGS built in Asia. Ove Arup Journal U.K.
Patent US 8047808 B2, Geyser Pump
  • M Kondo
Kondo M. Patent US 8047808 B2, Geyser Pump. 2011. http:// www.google.co.in/patents/ US 8047808 B2 (January 2015, date last accessed).
Japan building world's largest floating solar power plant
  • J Boyd
Boyd J. Japan building world's largest floating solar power plant. IEEE Spectrum. https://spectrum.ieee.org/energywise/ energy/renewables/japan-building-worlds-largest-floatingsolar-power-plant (January 2017, date last accessed).
Collection and Transmission System for Offshore Wind Power
  • J Green
  • A Bowen
  • J F Lee
Green J, Bowen A, Lee JF, et al. Collection and Transmission System for Offshore Wind Power. Presented at: Offshore Technology Conference, Houston, Texas, 2007.