［ A Case Study of the Installed System ］

Construction of Komekurayama
Solar Farm
Keywords

Mega Solar Farm, PV inverter, Monitoring system for solar farm, Substation facilities

Abstract

For the joint business project by Yamanashi Prefecture and Tokyo ElectricPower Company, a 10 MW solar farm (Komekurayama Solar Farm) was constructed in Komekurayama located in Shimo-mukoyama-cho, Kofu City, Yamanashi
Prefecture Japan.
About 80,000 solar modules are spread all over the site area of approximately
12.5ha. The estimated annual power yield amounts to approximately 12GWh whichcorresponds to the power usage level of about 3400 households. The estimatedreduction of CO2 emission is about 5100 tons annually that compares with theamount of emission from about 1000 households.
We received an order on an EPC (Engineering, Procurement and Construction)basis. Construction work was started in October 2010 and completed in January
2012.

1 Preface
In order to reduce the emissions of greenhousegases with respect to global warming, there is ahigh expectation for the increased use of renewableenergy resources. As such, Photovoltaic (PV) generation systems are rapidly spreading from smallscale residential power to large-scale solar farms.
The large-scale solar projects are mostly promoted
by electric power utilities. The Act on SpecialMeasures Concerning Procurement of Renewable
Electric Energy by Operators of Electric Utilities
came into effect in August 2011 and the Feed-in
Tariff System was put into operation in July 2012. Asan energy resource which will contribute in realizing
a low-carbon society, it is expected that solar power
will be actively developed and promoted in Japan.
This paper introduces the construction workfor the Komekurayama Mega Solar Farm for whichwe are an EPC (Engineering, Procurement andConstruction) contractor. This project is partly undertaken by a power utility company.

2 Introduction of the Construction Site
2.1 Climate
Kofu City, Yamanashi Prefecture is known formany hours of sunlight, ranked as top class in02

Satoshi Suzuki,
Takamitsu Ito,
Koji Taniguchi,
Hiroaki Miyazawa

MEIDEN REVIEW Series No.162 2014 No.3

Japan. The lowest temperatures reported are thenext lowest to those of northern area (Hokkaido andTohoku) in Japan.
The longer the duration of sunlight, the morepower is generated. It is noted that the PV module
performance is better when the temperature is low
as the lower temperature yields more power. Thisparticular site is ideal for a solar farm.

2.2 Geographical Site Conditions
Komekurayama is located on the south side of
the Kofu Basin Valley and the site is located on thesouthern slope of a small mountain. The site wasalready developed by Yamanashi Prefecture andthere are twelve small and large ﬂat zones which
are distributed in different tiers.

2.3 Design Notes
Since the solar modules installation zone islocated at the top of the mountain, such a place issubject to wind. We therefore analyzed the rate ofincreased wind speeds by considering the projectsite terrain and cell modules installation layout plan.
According to the analytical results, the basic designof the supporting structures for solar modules at thewind load base accommodates for the speciﬁc site
conditions.

3.2 Solar Modules

3 Outline of Electrical Facility
Conﬁguration

The solar modules employ a Copper Indium
Selenide (CIS) type polycrystalline thin-ﬁlm for 87.5Wand 155W per module, respectively. The adequate
number of modules is distributed in proportion to thearea of each zone. The total number of modules is32,202 (87.5W) and 46,340 (155W). The features ofthe CIS type cell module are as follows:( 1) Outstanding spectrum-response characteristics help to absorb a wider range of wavelengthcomponents compared with crystal silicon typesolar cell module.
( 2 ) In the case of the CIS type, shadows are lesslikely to impact all over the modules because of
unique characteristic of cell connection comparedwith that of the crystal silicon type.

3.1 Overall System Conﬁguration
Fig. 1 shows a conﬁguration outline of theKomekurayama Solar Farm. In most solar farms,
solar modules are concentrated in a vast area however, on this solar farm, the installation zone is separated into 12 zones and the solar modules are laidout according to each zone. Each zone comes witha sub-substation and the generated power is transmitted through overhead distribution lines on thepremises and gathered at the main substation. The
power is then fed into the grid.

Remote monitoring andcontrol system, master station

PV monitoring system

66kV power transmission lineMain substation

I/O panel
Remote monitoring
and control system,
follower station

VCT

Protective
relay panel

Monitoring andcontrol panel

10,000kVA
66kV/6.6kV

HubAux.
machineSub-substation (1)Sub-substation (2)Sub-substation (4)Sub-substation (6)Sub-substation (8)Aux.
equipment
1500kVA
6.6kV/410V

Aux.
equipment
1500kVA
6.6kV/410V

Aux.
equipment
1000kVA
6.6kV/410V

Aux.
equipment
1000kVA
6.6kV/410V

Aux.
equipment
1000kVA
6.6kV/410V

Data terminal

Data terminal

Data terminal

Data terminal

PCS 250kW
6 units

PCS 250kW
3 units

PCS 250kW
3 unitsPCS 250kW
4 units

Sub-substation (9)Sub-substation (3)Sub-substation (5)Sub-substation (7)Aux.
equipment
1000kVA
6.6kV/410V

Aux.
equipment
1500kVA
6.6kV/410V

Aux.
equipment
1000kVA
6.6kV/410V

Aux.
equipment
1500kVA
6.6kV/410V

Data terminal
PCS 250kW
5 units

Meteorologicalinstruments

Data terminal

Data terminal

Data terminal

Data terminal

PCS 250kW
4 units

PCS 250kW
3 units

PCS 250kW
2 units

PCS 250kW
5 units

Data terminal

Data terminal

Data terminal

PCS 250kW
2 units

PCS 250kW
2 units

PCS 250kW
1 unit
PCS: Power Conditioning SubsystemFig. 1

Outlined Facility Configuration

Conﬁguration of facilities installed on the premises of the power station is shown.

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3.3 PV Inverters
Forty units of Meiden PV inverters (SP300250) are employed. As shown in Fig. 2, each inverter
is accommodated in an enclosed casing. Since thearea of the each zone is different from one other,each package is designed to accommodate therequired number of inverters according to the output
capacity of the solar modules. Table 1 shows theoutline of the inverterʼs speciﬁcations. For systeminterconnection within the solar farm, a transformerless system is adopted in order to avoid the use of
any insulation transformer inside the inverter casing. We are then able to realize a very high conversion efﬁciency of 96.4%.
According to commands from a PV monitoring
system, it is possible to restrict power output and togenerate reactive power for power network stabilization.

3.4 Substation Facilities

Fig. 2

PV Inverters

Inverters are accommodated in the enclosed casing speciﬁed foroutdoor use. According to the project site area of each divisionzone, there are multiple types of casings where 1 to 6 inverters
are accommodated.

Table 1 Outline of Specifications for SP300-250
Outline of speciﬁcations of SP300-250 type PV inverters areshown below.
Item

Rating andperformance

Remarks

TypeSP300-250/410/50 Transformerless

Circuiting system

Self-excited voltage
type PWM inverter

Type of rating

100% continuous

Rated capacity

250kW

No. of phases

3-phase 3-wire

DCinput

Rated voltage

400V

Max. permissible
voltage

600V

Rated operating
voltage

250〜550V

Figs. 3 and 4 show the sub-substation and themain substation, respectively. The inverter outputs
are collected at the sub-substation and then thevoltage is stepped up to 6.6kV. The generated electric power is transmitted through overhead lines
inside the solar farm and collected at the main substation. The system voltage is increased to 66kV by
the main transformer and the power is fed to the66kV power network system of the Tokyo ElectricPower Company, Incorporated.
( 1) Sub-substation
The sub-substation is composed of a step-up
transformer (oil-immersed, natural air-cooled type)to raise the voltage up to the distribution voltage.
The other is an outdoor cubicle casing enclosing acircuit-breaker, a local transformer, and protective

Max. power
follow-up
operation

Reduced-rating
225〜250V,
operating voltage 550〜600V
ACRated voltage
410V
outputPermissible volt- Rated voltage
age deviation range ±10%
Rated frequency

50Hz

Permissible
frequency deviation range

Rated frequency±3%

Continuous
operation

Output power
factor

0.99 lagging orabove

For rated operation

Output current
distortion

Total 5% Max.,
each order 3% Max.

Power conditioning
efficiency

04

Continuous
operation

96.4% or above

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JIS C 8961

Fig. 3Sub-Substation

For local power distribution in the substation, the PV inverter output voltage is increased from 410V to 6.6kV. The substationtransformer has two types of capacities, 1500kVA and 1000kVA,
to be chosen according to the site area.

Fig. 4Main Substation

At the main substation, output voltage from the solar farm is increased from 6.6kV to 66kV for interconnection with the grid.
The photo shows the 66kV power receiving facilities and the66kV/6.6kV main transformer, the feeder panels for local power
distribution, and the monitoring casing containing incoming powerprotective relay units, monitoring and control panels, and remotemonitoring and control system.

relays. According to the area size, two sizes of transformers (1500kVA and 1000kVA) are used.
( 2 ) Main Substation
The 66kV main substation facilities are equippedwith the super-clad, conduit-coupling type gas-insulated switchgear, a 10,000kVA step-up main transformer (oil-immersed, natural air-cooled type), anda gas-insulated VCT and EVT.

3.5 Monitoring and Control System
The monitoring and control system for the solar
farm comes with the following two units:( 1) Remote monitoring and control system( 2 ) PV monitoring system

3.5.1 Remote Monitoring and Control System
The remote monitoring and control system performs the monitoring of the ON-OFF operation of
the circuit-breaker and the assessing of the statusof equipment in the main substation. This system
also monitors (in batch mode) the status of equipment in the downstream side form the intermediate
substation, as well as various telemetry data values
at the grid-connection point with the power station.
It is managed from the monitoring system of theTokyo Electric Power Company, Incorporated

3.5.2 PV Monitoring System
The PV monitoring system performs the monitoring of the ON-OFF operation of the circuit-breakerin each sub-substation and the assessing of the status of equipment in each sub-substation. It also
controls run and stop of each PV inverter and monitors the status of the PV inverter. It displays variousFig. 5

Screenshot of the PV Monitoring System

At the PV monitoring system, it is possible to monitor the overall
operating conditions in the solar farm. It is also possible to startand stop inverters and set up the scheduled operation.

telemetry values. Fig. 5 shows an example of thescreen of the PV monitoring system.
For the automatic control functions of the solar
farm, the following two functions are available:( 1) Output limiter function
According to the demand and supply conditions in the grid, power output from PV generation
may be restricted in some cases. In such a case, byusing the output limiter function, it is possible torestrict the inverter output below the speciﬁed level.
When a calendar feature is used, the output limit
values can be registered for the predetermined days
such as the Golden Week (a series of holidays inMay), New Yearʼs Holiday, and other national holidays.
( 2 ) Grid stabilization function
While the status of grid system voltage andfrequency is monitored, this function is used tocompute the active and reactive power required tomaintain the power quality in a favorable state andtransmit commands to each inverter. In regard to
the PV monitoring system of this solar farm, the gridstabilization function offers the features as described
below.
( a ) Voltage stabilization function
If the voltage at the grid connecting point of
the solar farm is found to be beyond the preset deadband, this function is used to compute the necessary reactive power to control such variation.
( b ) Constant power factor operation
A voltage rise is caused when electric powerfrom PV generation ﬂows into the grid. In order toMEIDEN REVIEW Series No.162 2014 No.305

restrain this voltage rise, this function is used tocompute the necessary reactive power in proportion to the amount of active power output.
( c ) Frequency control function
If the monitored grid frequency is found to be
beyond the preset dead band, the output limit
value described in (1) above is controlled in thedirection for controlling the frequency variation.

4 Postscript
This paper described the features of theKomekurayama Solar Farm that started its commercial operation in January 2012.
According to the Act on Special Measures
Concerning Procurement of Renewable Electric06

MEIDEN REVIEW Series No.162 2014 No.3

Energy by Operators of Electric Utilities which iscoming into effect, many solar farm constructions
are under planning stages throughout Japan. We
are conﬁdent that our experiences and expertise
we acquired through the construction of theKomekurayama Solar Farm will help us in other solarfarm constructions and will contribute to realizing a
low-carbon society.
We would like to express our sincere thanks
and gratitude to all of those who offered invaluablesuggestions and provided steadfast cooperation
during the construction of this solar farm.
・All product and company names mentioned in this paper are
the trademarks and/or service marks of their respective owners.