３．３． Mini Grid- Off GridMini Grid- Off GridJun HAGIHARA

Tokyo Electric Power Company – e8 Member

Solar PV Design Implementation O&MMarch 31- April 11, 2008

Marshall Islands

e8 /

PPA

Sola

r PV

Desi

gn Im

plem

enta

tion

O&M

2

Mar

shal

l Isl

ands

Mar

ch 3

1-Ap

ril 1

1, 2

008

3. Mini Grid – Off Grid 3. Mini Grid – Off Grid

3-1. Content3-2. DC and AC supply3-3. Off Grid:PV Mini Grid

3-3-1. Features of PV system3-3-2. PV output and demand3-3-3. System configuration3-3-4. Examples3-3-5. Design procedure

3-3-6. Planning & design3-3-7. Design of operation pattern3-3-8. Calculation of PV array output3-3-9. Array configuration

3-3-10. Necessary components3-3-11. Battery capacity3-3-12. Various battery3-3-13. Operation & Maintenance

3-3-14. Battery charging station (optional)

• Contents

e8 /

PPA

Sola

r PV

Desi

gn Im

plem

enta

tion

O&M

3

Mar

shal

l Isl

ands

Mar

ch 3

1-Ap

ril 1

1, 2

008

3. Mini Grid – Off Grid 3. Mini Grid – Off Grid

3-4. PV hybrid systems within mini-grid3-4-1. System configuration

3-4-2. Examples3-4-3. Other power source: Genset3-4-4. Other power source: Micro hydro

3-4-5. Other power source: Biomass energy3-4-6. Other power source: Wind power3-4-7. Planning & design3-4-8. Operation & maintenance

• Contents

e8 /

PPA

Sola

r PV

Desi

gn Im

plem

enta

tion

O&M

4

Mar

shal

l Isl

ands

Mar

ch 3

1-Ap

ril 1

1, 2

008 3-1. Content (1)3-1. Content (1)

Date Title Sub-title Grid connection

Supplied power

Size Genset Other RNE

Batterysystem

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 600HouseholdsBattery charge station

PV hybrid systems within mini-grid

Off AC 10 – 500kW Optional (a few hours per day)

Windbiomassmicro-hydroetc.

Optional New components

April 3 (Thu)

Grid connected Large PV system & Hybrid system

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)

Windbiomassmicro-hydroetc.

Optional With reliable grid (24H supply)

e8 /

PPA

Sola

r PV

Desi

gn Im

plem

enta

tion

O&M

5

Mar

shal

l Isl

ands

Mar

ch 3

1-Ap

ril 1

1, 2

008 3-1. Content (2)3-1. Content (2)

Date Title Sub-title Topics to be covered Note

April 4 (Fri)

Auxiliary System - Inverter & Wiring

Inverter Theory & circuitFunctionSelection, O&MExercise

Wiring By Mr. Wade

e8 /

PPA

Sola

r PV

Desi

gn Im

plem

enta

tion

O&M

6

Mar

shal

l Isl

ands

Mar

ch 3

1-Ap

ril 1

1, 2

008 3-2. DC and AC supply3-2. 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

e8 /

PPA

Sola

r PV

Desi

gn Im

plem

enta

tion

O&M

7

Mar

shal

l Isl

ands

Mar

ch 3

1-Ap

ril 1

1, 2

008

Date Title Sub-title Grid connection

Supplied power

Size Genset Other RNE

Batterysystem

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 600HouseholdsBattery charge station

PV hybrid systems within mini-grid

Off AC 10 – 500kW Optional (a few hours per day)

Windbiomassmicro-hydroetc.

Optional New components

April 3 (Thu)

Grid connected Large PV system & Hybrid system

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)

Windbiomassmicro-hydroetc.

Optional With reliable grid (24H supply)

3-3. Off Grid: PV mini grid 3-3. Off Grid: PV mini grid

e8 /

PPA

Sola

r PV

Desi

gn Im

plem

enta

tion

O&M

8

Mar

shal

l Isl

ands

Mar

ch 3

1-Ap

ril 1

1, 2

008

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

3-3-1. Features of PV system3-3-1. Features of PV system

e8 /

PPA

Sola

r PV

Desi

gn Im

plem

enta

tion

O&M

9

Mar

shal

l Isl

ands

Mar

ch 3

1-Ap

ril 1

1, 2

008 3-3-2. PV output and demand 3-3-2. PV output and demand

1 3 5 7 9 11 13 15 17 19 21 23Source: METI

2

1.5

1

0.5

0

150

100

50

0

Hou

seho

ld d

eman

d (k

Wh)

Cou

ntry

wid

e de

man

d (G

Wh)

3kW PV output and household demand (in Japan)

e8 /

PPA

Sola

r PV

Desi

gn Im

plem

enta

tion

O&M

10

Mar

shal

l Isl

ands

Mar

ch 3

1-Ap

ril 1

1, 2

008

PV panel (50 kWp)

3-3-3. System configuration(1)3-3-3. System configuration(1)

Inverter

Battery

PCS

For a community that is not too scattered. Usually 50 to 600 households.

Delivers the power to the households and common equipments through a grid

Isolated, AC supply, no genset

e8 /

PPA

Sola

r PV

Desi

gn Im

plem

enta

tion

O&M

11

Mar

shal

l Isl

ands

Mar

ch 3

1-Ap

ril 1

1, 2

008 3-3-3. System configuration(2)3-3-3. System configuration(2)

• PV array

• PV mounting structure

• Junction box

• Inverter•Insulation transformer•Protection system

• Battery system•Battery•Charger

• Others•Measuring instrument•Display unit

• Distribution board

• Power receiving panel

• kWh meter

• Load

Peripheral equipments

e8 /

PPA

Sola

r PV

Desi

gn Im

plem

enta

tion

O&M

12

Mar

shal

l Isl

ands

Mar

ch 3

1-Ap

ril 1

1, 2

008 3-3-4. Examples(1)3-3-4. Examples(1)

• 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)

Source: GTZ-ZSW

e8 /

PPA

Sola

r PV

Desi

gn Im

plem

enta

tion

O&M

13

Mar

shal

l Isl

ands

Mar

ch 3

1-Ap

ril 1

1, 2

008 3-3-4. Examples(2)3-3-4. Examples(2)

PV-generator

40 kW, 26 parallel strings with 18 modules, 85 W per module, manufacturer Qinghai Gaofai, cells from Astropower, US

Chargecontroller

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

ACDistribution

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

e8 /

PPA

Sola

r PV

Desi

gn Im

plem

enta

tion

O&M

14

Mar

shal

l Isl

ands

Mar

ch 3

1-Ap

ril 1

1, 2

008 3-3-4. Examples(3)3-3-4. Examples(3)

Source: GTZ-ZSW

e8 /

PPA

Sola

r PV

Desi

gn Im

plem

enta

tion

O&M

15

Mar

shal

l Isl

ands

Mar

ch 3

1-Ap

ril 1

1, 2

008 3-3-5. Design procedure3-3-5. 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

e8 /

PPA

Sola

r PV

Desi

gn Im

plem

enta

tion

O&M

16

Mar

shal

l Isl

ands

Mar

ch 3

1-Ap

ril 1

1, 2

008 3-3-6. Planning & design3-3-6. Planning & design

Survey of various REN

Concept design of the system

Investigation of target site

Determination of equipment spec.

Estimate project cost

Determine operation patternEstimate maintenance cost

Estimate total running cost

Analyze cost/benefit

Effect on environmental protection

Effect on energy conservation

Implementation

System, equip. spec., supplier, capacity, supply characteristics, reliability, cost and so on.

Demand characteristics, energy cost, electricity tariffREN main unit, inverter, grid connection, battery, env. measure

Generation cost, distribution cost, cash flow

Estimate supplied power and energy

e8 /

PPA

Sola

r PV

Desi

gn Im

plem

enta

tion

O&M

17

Mar

shal

l Isl

ands

Mar

ch 3

1-Ap

ril 1

1, 2

008 3-3-6. Check list on planning (1)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?

e8 /

PPA

Sola

r PV

Desi

gn Im

plem

enta

tion

O&M

18

Mar

shal

l Isl

ands

Mar

ch 3

1-Ap

ril 1

1, 2

008 3-3-6. Check list on planning (2)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?

e8 /

PPA

Sola

r PV

Desi

gn Im

plem

enta

tion

O&M

19

Mar

shal

l Isl

ands

Mar

ch 3

1-Ap

ril 1

1, 2

008 3-3-6. Check list on planning (3)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

e8 /

PPA

Sola

r PV

Desi

gn Im

plem

enta

tion

O&M

20

Mar

shal

l Isl

ands

Mar

ch 3

1-Ap

ril 1

1, 2

008 3-3-6. Check list on planning (4)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?

e8 /

PPA

Sola

r PV

Desi

gn Im

plem

enta

tion

O&M

21

Mar

shal

l Isl

ands

Mar

ch 3

1-Ap

ril 1

1, 2

008 3-3-6. Check list on design (5)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?

e8 /

PPA

Sola

r PV

Desi

gn Im

plem

enta

tion

O&M

22

Mar

shal

l Isl

ands

Mar

ch 3

1-Ap

ril 1

1, 2

008 3-3-7. Design of operation pattern3-3-7. 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 Nighttime

PMAM

Supply from PV Charge to battery Supply from battery

e8 /

PPA

Sola

r PV

Desi

gn Im

plem

enta

tion

O&M

23

Mar

shal

l Isl

ands

Mar

ch 3

1-Ap

ril 1

1, 2

008

• 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)

3-3-8. Calculation of PV array output3-3-8. Calculation of PV array output

Cell

Module

Array

Backside film Cell

Packing

Filling

Glass

Bracket

e8 /

PPA

Sola

r PV

Desi

gn Im

plem

enta

tion

O&M

24

Mar

shal

l Isl

ands

Mar

ch 3

1-Ap

ril 1

1, 2

008 3-3-9. Array configuration(1)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.

e8 /

PPA

Sola

r PV

Desi

gn Im

plem

enta

tion

O&M

25

Mar

shal

l Isl

ands

Mar

ch 3

1-Ap

ril 1

1, 2

008 3-3-9. Array configuration(2)3-3-9. Array configuration(2)

1 string consists of 8 modules in series

Shadow

Parallel connection in junction box

Source: NEDO

e8 /

PPA

Sola

r PV

Desi

gn Im

plem

enta

tion

O&M

26

Mar

shal

l Isl

ands

Mar

ch 3

1-Ap

ril 1

1, 2

008 3-3-10. Necessary components(1)3-3-10. Necessary components(1)

• Bypass device (diode) for each module

PV module

PV module

PV module

To junction box or load

BypassDevice (diode)

e8 /

PPA

Sola

r PV

Desi

gn Im

plem

enta

tion

O&M

27

Mar

shal

l Isl

ands

Mar

ch 3

1-Ap

ril 1

1, 2

008 3-3-10. Necessary components(2)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

• Distribution board• Wh meter• Battery

From PV array

PV array Junction boxP1

N1

P2N2

PnNn

NP To

inverter

Reverse flow protection

Main CB

Lightning protectio

n

e8 /

PPA

Sola

r PV

Desi

gn Im

plem

enta

tion

O&M

28

Mar

shal

l Isl

ands

Mar

ch 3

1-Ap

ril 1

1, 2

008 3-3-11. Battery capacity3-3-11. 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

e8 /

PPA

Sola

r PV

Desi

gn Im

plem

enta

tion

O&M

29

Mar

shal

l Isl

ands

Mar

ch 3

1-Ap

ril 1

1, 2

008 3-3-12. Various battery(1)3-3-12. Various battery(1)

Battery Type Expected lifetime[years]

Expected cycle

Capacity [Ah]

Water refilling

Seal type

MSE 7 – 9 1000 (DOD50%)

50 - 3000 Maintenance free

Long life 12 –15 --- 150 - 3000

Std 3 – 5 500 (DOD50%)

0.7 - 144

Long life 5 – 6 700 (DOD50%)

50 - 130

Clad type

Std --- 1800 (DOD75%)

50 - 3000 Necessary

Other 4 - 5 300 (DOD50%)

21 – 160 (5 hours)

Necessary

Source: NEDO

e8 /

PPA

Sola

r PV

Desi

gn Im

plem

enta

tion

O&M

30

Mar

shal

l Isl

ands

Mar

ch 3

1-Ap

ril 1

1, 2

008 3-3-12. Various battery(2)3-3-12. Various battery(2)

0 10 20 30 40 50 60 70 Depth of discharge (DOD, %)

10,000

5,000

1,000

500

# of

Cha

rge/

disc

harg

e (c

ycle

s)

Small seal type)

Seal type (MSE)

Clad type

At 25 degree celcius1 cycle/day

Source: NEDO

e8 /

PPA

Sola

r PV

Desi

gn Im

plem

enta

tion

O&M

31

Mar

shal

l Isl

ands

Mar

ch 3

1-Ap

ril 1

1, 2

008

3-3-13. Operation & maintenance3-3-13. 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 Nighttime

PMAM

Supply from PV Charge to battery Supply from battery

e8 /

PPA

Sola

r PV

Desi

gn Im

plem

enta

tion

O&M

32

Mar

shal

l Isl

ands

Mar

ch 3

1-Ap

ril 1

1, 2

008 3-3-14. Battery charging station 3-3-14. Battery charging station

(optional)(1) (optional)(1)

BCS at suburb of Phnom Penh, Cambodia

e8 /

PPA

Sola

r PV

Desi

gn Im

plem

enta

tion

O&M

33

Mar

shal

l Isl

ands

Mar

ch 3

1-Ap

ril 1

1, 2

008

A fully charged battery provides lighting for a week

Kanchanaburi Province, Thailand: 1992-1997

Budget: 316 million yen

The Sunlight made Nighttime Pleasant!

Battery-Charging Station

11

Source: NEDO

3-3-14. Battery charging station 3-3-14. Battery charging station (optional)(2) (optional)(2)

e8 /

PPA

Sola

r PV

Desi

gn Im

plem

enta

tion

O&M

34

Mar

shal

l Isl

ands

Mar

ch 3

1-Ap

ril 1

1, 2

008

Battery-Charging Station

Using a charged battery at home

12

Source: NEDO

3-3-14. Battery charging station 3-3-14. Battery charging station (optional)(3) (optional)(3)