Renewable Energy in Small Island Grids

Design and Case study - Tuvalu

Overview

1. About ITP

2. Types of grid

3. Solar and storage integration

4. Case Study – Tuvalu northern islands

5. Long term operation

About ITP

•Specialist renewable energy consulting firm

•Over 30 years international experience and 1,500 projects

•Founded in the UK in 1981

•Major regional offices in UK, India, China and Australia

About ITP - Australia

• Head office in Canberra, offices in South Australia, NSW

and Auckland

• Active in Australia and the Pacific region for over 10

years

• Involved in RE projects of all scales (1 kW to 50+ MW)

• Services

• Engineering Consultancy

• Project Engineering

• Energy Markets and Advisory

• International Aid and Development

Types of island grid

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• Generally speaking, a micro-grid is self-contained and

limited by geography

• Loads can vary from being very small (e.g. a few houses)

to very large (e.g. a remote town with a large energy

user)

• Smallest form is individual home energy systems (1

house)

• Mini-grids (100 – 1,000 kWh/day) – eg remote islands

• Small grids (1,000 – 30,000 kWh/day) – eg larger rural

town centre or “main” island

• Medium grids (30,000 kWh/day – 100,000 kWh/day)

• Large grids (100,000 kWh/day +)

Mini-grids

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• Small, remote islands in the Pacific (pop. 200 – 2000)

• Typically one or two villages

• Mostly residential/rural energy use

• Small power station operated by trained staff

• In the past, typically diesel generators

Why renewable energy?

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• Reduce reliance on

imported diesel

• Reduce running costs

• Cleaner

• Quieter

• Improve reliability

• But:

• Upfront cost can be high

• Only works during day

• Storage required

• Can have integration

problems with generator

Integrating renewable energy

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Three broad diesel/PV hybrid design options:

• PV fuel-save (no battery storage, providing

~10% annual load contribution),

• PV fuel-save plus (sometimes utilising a small

amount of battery storage, providing up to 30%

annual load contribution), or

• PV primary (utilising a large amount battery

storage, providing >50% annual load

contribution).

PV fuel save

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•Sized to supply about 30% of the average midday load.

•Diesel generators run continuously. PV reduces their loading during

the day.

•No batteries or specialist integration equipment.

•Lowest initial capital cost.

•Reduce annual fuel bills by around 10%.

PV fuel save plus

10 of xx slides

• Intelligent control system that occasionally spills some PV output to ensure that the generators are kept sufficiently loaded.

• Diesel generators still run continuously, but over the year, the PV makes a much larger contribution (~30% total, 60% in the middle of the day).

• Sometimes include a small battery bank to optimise loadings.

PV primary

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• Large battery bank able to meet load with all generators off.

• Relatively high integration costs

• Highest annual contribution from renewable energy sources (can go to 100%)

• Economically viable for smaller loads or where diesel costs are unusually

high or supply is uncertain.

Economics of renewable energy in mini-grids

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Grid size Diesel Efficiency Cost of generation Economic level of RE

Mini 1-2 kWh/L $0.70 - $2.00 / kWh 90% +

Small 2-3 kWh/L $0.50- $0.70 / kWh 30% - 70%

Medium 3-4 kWh/L $0.20- $0.50 / kWh 20% - 50%

Large 4+ kWh/L $0.20- $0.30 / kWh 10% – 30%

Case study 1: Tuvalu Energy Sector

Development Program (TESDP)

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TESDP – Tuvalu

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TESDP – Tuvalu

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TESDP – Overview

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• Four-year program funded by the World Bank, started in

2015

• Provides assistance in energy efficiency, prepayment

metering, and renewable energy

• Will push renewable energy penetration on main island of

Funafuti well beyond 100% to increase RE contribution

TESDP – Generation on Funafuti

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• Population is around 7,000 people

• Midday load is 800 kW on weekdays, 500 kW on

Sundays

• 3 x 600 kW diesel generators

• 750 kWp PV capacity

• PV curtailment device installed on 410 kWp

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Sat

Sun

Weekdays

TESDP – Current PV generation

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TESDP – Increasing penetration

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• Project will add up to another 900 kWp of capacity

• Goal will be to turn generators off during the day grid-

forming inverter required

• ~1 MW inverter capacity, 1-2 MWh electricity storage

• Expect >40% RE contribution

TESDP – Challenges

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• Very little space for large amounts of PV

• Requires good communication between PV field and

controller at power station

• Retraining of staff necessary. Dispatching done manually,

but an inverter-based system will need to be

automatically controlled.

Case study 2: Tuvalu Renewable

Energy Program (TERP)

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Case study – Tuvalu northern islands

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• Nine small atoll islands

• Total population approx. 10,000

• 6,000 on the capital, Funafuti

• Other islands populations 100-1,500

• Outer islands only accessible by boat, typically 24hrs by

boat to each island

• Irregular shipping (every 3-6 weeks)

• Shipping often disrupted by weather or boat unavailability

Case study – Tuvalu northern islands

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• Existing low voltage AC

electricity grids (diesel)

since 2001

• Grids operated by

electricity utility (Tuvalu

Electricity Corporation)

• Local operators (TEC

employees) deal with day

to day running

• Technicians from the

capital visit periodically or

for repairs when required

Nanumea power station

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Generators

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Tuvalu northern islands- key issues

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• Reliability • Only 12-18 hours of power per day normally (down to 2-4 hrs

sometimes)

• Frequent diesel shortages due to shipping unreliability

• Generator breakdowns

• Long delays for repairs (can take weeks to send a technician from Funafuti)

• Cost • Estimated ~$1.20 to $1.50/kWh cost of supplying energy (possibly

more)

• Vulnerable to diesel price changes

• Vulnerable to utility cash flow issues

• Tariffs ~25c/kWh – outer islands subsidised by main island and by government

• Remote diesel grids were built as a service to the community, but are very expensive for the government

Transportation

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Transportation

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Vulnerability to weather

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Aims of outer islands solar project

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• Outer islands 100% renewable energy

• 24hr power

• System to last 20 years without need for major

modification

• Reduce operating costs of outer islands power systems

• Improve power reliability (and availability during

disasters)

• Grant-funded (NZ Govt)

• Eliminate need for aid fuel subsidies

Load curve – Nanumea island

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5.0

10.0

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35.0

00:00 03:00 06:00 09:00 12:00 15:00 18:00 21:00 00:00

Load

(kW

)

After load growth

Assumed loads

From data logger

Load estimate - Nanumea

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• Average 550 kWh per day

• Little seasonal variation, but some “busy” times of year.

• Highest demand around Christmas and special events

• 40% of demand during “solar” hours

• 60% evening/night time

• Allowance for extra days with poor sun – 2 days

• Use this to size battery bank

• Then size solar PV array to meet day time load plus

enough extra energy to fully charge the batteries.

System sizing overview

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• 33,000 Ah battery bank (sealed lead acid batteries)

• 200 kW solar PV array

• SMA modular inverter/charger units

• Diesel generator to be switched off normally.

Design schematic

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Design features

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• Modular

• if one unit fails, most of the system can be kept online

• Spares kept on island, easy to swap out

• Off-the-shelf inverter/controller, easy to order a new one

• Robust and corrosion resistant

• Cyclone proof structure

• No air conditioning required

• Because the air conditioner is often a failure point

• Low maintenance

Completed system

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Display

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Modular inverter/chargers

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Sealed batteries

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Passive cooling

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Performance so far

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• System is very large for current loads

• Batteries drop to 80% overnight, are fully charged before

midday if sunny

• Can go for 5 days of cloudy weather without generator

• 1 inverter failure – local operator successfully replaced it

and sent it back for warranty claim

• Effective cost of energy supply reduced to about

$0.55/kWh (from over $1)

• However this is still higher than the tariff ($0.25/kWh)

Training and operation

42 of xx slides

• Local operators involved from beginning of construction

• Training throughout construction and troubleshooting

• Other staff in Funafuti (capital) have been doing solar

training over a longer period

• Very challenging for the outer island operators to adapt to

the new technology

Community

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Lessons/challenges

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Less well-known challenges ITP has seen over the years:

• Systems becoming too reliable (operators stop maintaining

generators totally/ get lazy)

• Social problems with 24hr power (eg loud music at night)

• Logistics can be very complicated

• Getting accurate data and information is difficult (eg

powerhouse data, shipping schedules)

• Limited market for companies with experience in designing

and building renewable energy systems on island

environments

Southern Cross House,

6/9 McKay St, Turner, ACT

PO Box 6127 O’Connor, ACT 2602

info@itpau.com.au

p +61 (0) 2 6257 3511

f +61 (0) 2 6257 3611

itpau.com.au

IT Power Renewable Energy Consulting

Questions