３．Mini Grid- Off Grid
Jun HAGIHARA
Tokyo Electric Power Company – e8 Member
Solar PV Design Implementation O&M
March 31- April 11, 2008
Marshall Islands
Marshall Islands March 31-April 11, 2008
3. Mini Grid – Off Grid
• Contents
3-1. Content
3-2. DC and AC supply
3-3. Off Grid:PV Mini Grid
3-3-1. Features of PV system
3-3-2. PV output and demand
e8 / PPA Solar PV Design Implementation O&M
3-3-3. System configuration
3-3-4. Examples
3-3-5. Design procedure
3-3-6. Planning & design
3-3-7. Design of operation pattern
3-3-8. Calculation of PV array output
3-3-9. Array configuration
3-3-10. Necessary components
3-3-11. Battery capacity
3-3-12. Various battery
3-3-13. Operation & Maintenance
3-3-14. Battery charging station (optional)
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Marshall Islands March 31-April 11, 2008
3. Mini Grid – Off Grid
• Contents
3-4. PV hybrid systems within mini-grid
3-4-1. System configuration
3-4-2. Examples
3-4-3. Other power source: Genset
3-4-4. Other power source: Micro hydro
3-4-5. Other power source: Biomass energy
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3-4-6. Other power source: Wind power
3-4-7. Planning & design
3-4-8. Operation & maintenance
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3-1. Content (1)
Date
Title
Sub-title
Grid
connection
Supplied
power
Size
Genset
Other
RNE
Battery
system
Note
April 1
(Tue)
SHS
DC SHS
Off
DC
< 1kW
No
No
Yes
By Mr. Wade
AC SHS
Off
AC
< 1kW
No
No
Yes
By Mr. Wade
April 2
(Wed)
Mini grid
PV Mini
grid
Off
AC
1 - 50kW
No
No
Yes
50 to 600
Households
Battery charge
station
PV hybrid
systems
within
mini-grid
Off
AC
10 – 500kW
Optional
(a few
hours
per day)
Wind
biomass
micro-hydro
etc.
Optional
New
components
Grid
connected
large PV
system
On
AC
> 40kW
No
No
Optional
With reliable
grid
(24H supply)
Grid
connected
hybrid
system
On
AC
> 100kW
Basically
No.
Optional
(a few
hours
per day)
Wind
biomass
micro-hydro
etc.
Optional
With reliable
grid
(24H supply)
April 3
(Thu)
Grid
connected
Large PV
system &
Hybrid
system
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e8 / PPA Solar PV Design Implementation O&M
3-1. Content (2)
Date
Title
Sub-title
April 4
(Fri)
Auxiliary
System Inverter &
Wiring
Inverter
Wiring
Topics to be covered
Note
Theory & circuit
Function
Selection, O&M
Exercise
By Mr. Wade
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3-2. DC and AC supply
Supplied power
Characteristics
Disadvantages
DC
Connection of
sources and
loads via DC
distribution
line
• Main energy sources connected
on DC bus
• Charger are needed for different
energy sources
• For illumination and DC loads
• Short distance between
components
• Expensive DC installation
• Poorly expandable
• Not easy to find standard
products
AC
Connection of
sources and
loads via AC
distribution
line
• Free selection of energy sources
(standard grid components)
• Long distances between
components
• Simple extendibility, future-proof
• Necessity of Inverters
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3-3. Off Grid: PV mini grid
Date
Title
Sub-title
Grid
connection
Supplied
power
Size
Genset
Other
RNE
Battery
system
Note
April 1
(Tue)
SHS
DC SHS
Off
DC
< 1kW
No
No
Yes
By Mr. Wade
AC SHS
Off
AC
< 1kW
No
No
Yes
By Mr. Wade
April 2
(Wed)
Mini grid
PV Mini
grid
Off
AC
1 - 50kW
No
No
Yes
50 to 600
Households
Battery
charge
station
PV hybrid
systems
within
mini-grid
Off
AC
10 – 500kW
Optional
(a few
hours
per day)
Wind
biomass
micro-hydro
etc.
Optional
New
components
Grid
connected
large PV
system
On
AC
> 40kW
No
No
Optional
With reliable
grid
(24H supply)
Grid
connected
hybrid
system
On
AC
> 100kW
Basically
No.
Optional
(a few
hours
per day)
Wind
biomass
micro-hydro
etc.
Optional
With reliable
grid
(24H supply)
April 3
(Thu)
Grid
connected
Large PV
system &
Hybrid
system
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3-3-1. Features of PV system
Advantage
Disadvantage
1.Clean generation system
1. Generation depends on sunshine
duration.
2.No moving and high temp/pressure
parts, possible automatic/unattended
operation and easy maintenance
2. Need wide footprint for large output
because of low energy density
3. Non-depletion energy
3. Still high cost under the present
situation
4. Possible mass production because of
modular structure
4. DC output (can be advantage in
some case)
5. Free and easy design from small to
large scale in accordance as needed,
and small limitation on installing
Source: ANRE, NEDO
8
3kW PV output and household demand (in Japan)
2
150
1.5
100
1
50
0.5
0
1
3 5 7 9 11 13 15 17 19 21 23
Countrywide demand (GWh)
Household demand (kWh)
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3-3-2. PV output and demand
0
Source: METI
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Marshall Islands March 31-April 11, 2008
3-3-3. System configuration(1)
PV panel (@ 50 kWp)
For a community that
is not too scattered.
Usually 50 to 600
households.
e8 / PPA Solar PV Design Implementation O&M
Inverter
Isolated, AC supply,
no genset
PCS
Battery
Delivers the power to
the households and
common equipments
through a grid
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3-3-3. System configuration(2)
Peripheral equipments
• Junction box
• Distribution
board
• PV array
• Inverter
•Insulation transformer
•Protection system
• Power
receiving panel
• kWh meter
• PV mounting
structure
• Battery system
•Battery
•Charger
• Load
• Others
•Measuring instrument
•Display unit
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3-3-4. Examples(1)
Source: GTZ-ZSW
• Installed in 2003 at Suohourima, Qinghai, China by GTZ
• 70 km [43 miles] from the next electricity line
• Between 300 and 400 households
• Old Diesel generator set is no longer in operation.
• Electricity is delivered according to energy availability (not for 24/24 hours)
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3-3-4. Examples(2)
PVgenerator
40 kW, 26 parallel strings with 18 modules, 85 W per module,
manufacturer Qinghai Gaofai, cells from Astropower, US
Charge
controller
13 channels, μC-controlled, sub arrays are switched off at the end of
charge voltage of the battery, manufacturer Hefei Sunlight Power
Battery
Sealed (AGM) lead acid battery, cells 2 V/1300 Ah, 3 parallel strings with
110 cells, 858 kWh, manufacturer Enersys Huada Solar
Inverters
PWM with transformer and μC-control, 220 VDC/220 VAC, 1 inverter with
16 kW, 1 inverter with 24 kW, manufacturer Hefei Sunlight Power
AC
Distribution
2 isolated and not grounded single phase grids supply different parts of
the township. The single households have electronic energy Meters
Households All electrified households have electric light (fluorescent lamps (9W) or
incandescent lamps (40W)), 90 % of the households have colour TV +
satellite receiver + DVD player, and chest freezer to store meat, more
and more households have electric heating blankets and pillows, some
have washing machines (for external hot water supply)
Source: GTZ-ZSW
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Marshall Islands March 31-April 11, 2008
3-3-4. Examples(3)
Source: GTZ-ZSW
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3-3-5. Design procedure
•
•
•
•
•
Significance
Concept
Feasibility study
– Generation
– Distribution
– Demand forecast and dispatching
– Environmental assessment
– Economical evaluation
Design
– System configuration
– Design
– Regulation
– Specification of components
– How to select
– Installation
O&M
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3-3-6. Planning & design
System, equip. spec., supplier, capacity, supply
characteristics, reliability, cost and so on.
Survey of various REN
Concept design of the system
Demand characteristics, energy cost, electricity tariff
Investigation of target site
REN main unit, inverter, grid connection, battery, env.
measure
Determination of equipment spec.
Estimate supplied power and energy
Estimate project cost
Generation cost,
distribution cost,
cash flow
Determine operation pattern
Estimate maintenance cost
Estimate total running cost
Analyze cost/benefit
Effect on environmental protection
Effect on energy conservation
Implementation
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3-3-6. Check list on planning (1)
• Concept and purpose
– For what?
 Purposed should be shared among concerned
parties.
– Where?
 In existing facility or not? Exact location.
– What load?
 Characteristics and size of load. Enough space
for installed equipment?
– Which system?
 Isolated or grid-connected? With battery or not?
– When and how much?
 Construction schedule and cost. Can it be
available?
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3-3-6. Check list on planning (2)
• Project team
–
–
–
–
Establish team and assign project manager
How to select the designer?
What is bidding strategy of construction work?
How can we maintain and manage the system?
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3-3-6. Check list on planning (3)
• Site survey
– Ambient environment
 Any obstacles to receive sunlight?
 Shadow of building, tree, mountain, stack, utility pole, steel
tower, sign board and so on.
 Effect of fallen leaves and sand dust, snow cover (depth and
frequency)
 Salt and/or lightning damage, wind condition – collect all
the possible obstacles
– Installed site
 Shape, width, direction, drainage, condition of foundation,
volume of construction work, carry-in route, Waterproof of
the building, effect on landscape
– Electrical facility
 Existing diagram and plot plan, space availability, wiring
route and space carry-in route
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3-3-6. Check list on planning (4)
• Preliminary consultation
– Local authority – Construction work, fire department,
necessity of permission
– Available subsidy
– Information collection from expert/consultants
• Concept check
– Is it firm concept? Site, load, system size and
configuration
– Is schedule fixed?
– Is budget made based on expected generation
output and its cost?
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3-3-6. Check list on design (5)
•
•
•
•
Reconfirmation of design condition
– Firm policy? – For what? Where? How big? How is the system?
When? How much?
– Constraints – Ambient environment, Site condition, existing
electrical equipment, regulation, necessary procedure
Design
– Direction and angle of PV panel – maximize output under the given
condition
– Array configuration and its installation
– Foundation, mounting frame, waterproof, intensity calculation
– Material, antirust and anti-corrosion of mounting frame material
– Compliance with regulation
– In accordance with the project purpose
– Established schedule, expected result and project cost.
Application
– Subsidy
– Application for local authority
Design check
– Fixed detail design, budget, construction schedule?
– Finish all the necessary application?
– Completed adequate bidding?
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3-3-7. Design of operation pattern
•
•
•
•
•
Estimate daily load curve
Daytime: PV for load and battery charge
Nighttime: Battery discharge for load
Investigate charge/discharge time
Calculate required PV and battery capacity
Wee hours
Daytime
AM
Supply from PV
Nighttime
PM
Charge to battery
Supply from battery
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3-3-8. Calculation of PV array output
•
•
First, estimated the total size of load EL
Array output PAS:
EL * D * R
(HA / GS) * K






EL : Average load size (consumed energy kWh / duration)
D : Load’s dependency rate on solar energy
HA: Amount of solar radiation during a given interval [kWh/sqft * day]
GS: Intensity of solar radiation at normal condition [kW/sqft]
R : Design margin ratio
K : of integrated design factor(0.65 – 0.8, loss and equipment
variation)
Array
Glass
Packing
Module
Cell
Backside film
Bracket
Cell
Filling
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3-3-9. Array configuration(1)
•
String: Series of PV modules.
– Number of series
(Rated DC voltage of inverter) * 1.1
Optimal operating voltage of PV module: Vpm
•
Array: Large panel consists of parallel strings.
– Number of parallel
Expected output of PV system
(Max output of PV module Pmax) * (Number of series)
•
In actual design, it is necessary to determine array configuration
in accordance with size of mounting frame and installation space.
Avoid the configuration in which a part of string is shadowed.
– Re-consider the series/parallel configuration again.
•
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3-3-9. Array configuration(2)
1 string consists of 8
modules in series
Shadow
Parallel connection in
junction box
Source: NEDO
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3-3-10. Necessary components(1)
•
Bypass device (diode) for each module
PV
module
PV
module
To junction
box or load
Bypass
Device
(diode)
PV
module
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3-3-10. Necessary components(2)
•
•
•
•
Junction box
– MCCB for PV array
– Back-flow prevention device for each string
– Main CB
– Lightning protection/Arrester
– Terminal block
– Box
PV array Junction box
Distribution board
Wh meter
Battery
From PV
array
Lightning
protection
Reverse flow protection
P1
N1
P
N
Main CB
To
inverter
P2
N2
Pn
Nn
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3-3-11. Battery capacity
•
•
•
•
Lifetime of battery heavily depends on Depth Of Discharge (DOD),
number of discharge and ambient temperature.
In application with PV, set the average DOD because of fluctuating
charging/discharging energy by weather.
Key point
– Estimate accurate load size
– Optimize PV capacity, battery capacity and operational
parameter of PCS
Procedure
–
–
–
–
Decide DC input power necessary for load
Understand inverter input power
Acquire amount of solar radiation at the site
Set number of days without sunshine based on solar radiation
condition and importance of load
– Set DOD from expected lifetime of battery
– Even in month with min solar radiation, determine capacity and angle
of PV array to make charging energy cover discharge for load.
– Calculate battery capacity
Daily power consumption * number of days without sunshine
Maintenance factor * DOD * Final voltage in discharge
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3-3-12. Various battery(1)
Battery
Seal
type
Clad
type
Other
Type
Expected
lifetime
[years]
Expected
cycle
Capacity
[Ah]
Water
refilling
MSE
7–9
1000
(DOD50%)
50 - 3000
Long life
12 –15
---
150 - 3000
Std
3–5
500
(DOD50%)
0.7 - 144
Long life
5–6
700
(DOD50%)
50 - 130
Std
---
1800
(DOD75%)
50 - 3000
Necessary
4-5
300
(DOD50%)
21 – 160 (5
hours)
Necessary
Maintenance
free
Source: NEDO
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At 25 degree celcius
1 cycle/day
10,000
# of Charge/discharge (cycles)
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3-3-12. Various battery(2)
5,000
Clad type
1,000
500
Seal type (MSE)
Small seal type)
0
10
20
30
40
50
60
Depth of discharge (DOD, %)
70
Source: NEDO
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3-3-13. Operation & maintenance
•
•
•
•
Load forecasting is most important.
Aim to full utilize PV power.
Reserve battery energy for emergency case.
Adjust charge/discharge energy in accordance with varying load.
Wee hours
Daytime
AM
Supply from PV
Nighttime
PM
Charge to battery
Supply from battery
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3-3-14. Battery charging station
(optional)(1)
BCS at suburb of Phnom Penh, Cambodia
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3-3-14. Battery charging station
(optional)(2)
Kanchanaburi Province, Thailand: 1992-1997
Budget: 316 million yen
The Sunlight made
Nighttime Pleasant!
Battery-Charging Station
A fully charged
battery provides
lighting for a week
Source: NEDO
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3-3-14. Battery charging station
(optional)(3)
Battery-Charging Station
Source: NEDO
Using a charged battery at home
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