SERIS is a research institute at the National University of Singapore (NUS). SERIS is sponsored by the National University of

Singapore (NUS) and Singapore’s National Research Foundation (NRF) through the Singapore Economic Development Board (EDB). 1

Solar DC nano-grids: A technology perspective on village electrification Timothy WALSH

Solar Energy Research Institute of Singapore (SERIS)

National University of Singapore (NUS)

Smart Villages Workshop

Kuching, Sarawak, Malaysia

27-29 January 2015

2 SERIS is a research institute at the National University of Singapore (NUS). SERIS is sponsored by the National University of

Singapore (NUS) and Singapore’s National Research Foundation (NRF) through the Singapore Economic Development Board (EDB).

Founded in 2008; focuses on applied

solar energy research

Part of the National University of

Singapore (NUS)

Rapid growth (now ~160 people and

> 6000 m2 of space)

> USD 30 million investments for labs

R&D focus is on PV (cells, modules,

systems) and solar buildings

Specialised in professional services

for the PV industry

ISO 9001 & ISO 17025* certified

(* PV Module Testing Lab)

Introduction to SERIS Solar Energy Research Institute of Singapore

SERIS is a research institute at the National University of Singapore (NUS). SERIS is sponsored by the National University of

Singapore (NUS) and Singapore’s National Research Foundation (NRF) through the Singapore Economic Development Board (EDB). 3

Off-grid PV systems group at SERIS

Obviously Singapore is not a big market for off-grid PV systems

Thus the group focuses on the wider South East Asian region

Research topics include;

Innovative applications of off-grid PV for “productive use”,

particularly where the storage is provided by the load

Solar refrigeration and solar ice making

Solar air-conditioning using peltier devices

Solar-powered boats

Solar DC nano-grids

PhD candidates are welcome to apply

SERIS is a research institute at the National University of Singapore (NUS). SERIS is sponsored by the National University of

Singapore (NUS) and Singapore’s National Research Foundation (NRF) through the Singapore Economic Development Board (EDB). 4

Access to electricity worldwide

17% of the world’s population have no access to electricity

85% of these people live in (often remote) rural areas

Sustainable Energy for All, Global Tracking Framework,

http://www.worldbank.org/en/topic/energy/publication/Global-Tracking-Framework-Report

Numbers in millions of people

SSA = Sub-Saharan Africa

SA = South Asia

SERIS is a research institute at the National University of Singapore (NUS). SERIS is sponsored by the National University of

Singapore (NUS) and Singapore’s National Research Foundation (NRF) through the Singapore Economic Development Board (EDB). 5

Defining “electrification”

The UN Sustainable Energy for All (SE4All) global initiative

defines five tiers for access to electricity supply

Attribute Tier 0 Tier 1 Tier 2 Tier 3 Tier 4 Tier 5

Types of

loads

- Task

lighting

AND

phone

charging

(OR radio)

General

lighting

AND

television

AND

fan

(if needed)

Tier 2

AND

any

low-power

appliances

Tier 3

AND

any

medium

power

appliances

Tier 4

AND

any

high-power

appliances

Duration

(hours per

day)

- >4 >4 >8 >16 >22

Evening

supply

(hours)

- >2 >2 >2 >4 >4

Sustainable Energy for All, Global Tracking Framework,

http://www.worldbank.org/en/topic/energy/publication/Global-Tracking-Framework-Report

SERIS is a research institute at the National University of Singapore (NUS). SERIS is sponsored by the National University of

Singapore (NUS) and Singapore’s National Research Foundation (NRF) through the Singapore Economic Development Board (EDB). 6

Options for village electrification

Grid extension

AC mini-grids

Solar home systems

Solar DC nano-grids

SERIS is a research institute at the National University of Singapore (NUS). SERIS is sponsored by the National University of

Singapore (NUS) and Singapore’s National Research Foundation (NRF) through the Singapore Economic Development Board (EDB). 7

Grid extension

Most expensive option in many cases

Viable only under certain circumstances

Villages are not too remote

Village populations are of a certain size

Government is willing to invest in infrastructure

Not viable for many villages

Villages are too remote

Populations are too small

Governments (of some countries) may be unwilling

to make the investment

SERIS is a research institute at the National University of Singapore (NUS). SERIS is sponsored by the National University of

Singapore (NUS) and Singapore’s National Research Foundation (NRF) through the Singapore Economic Development Board (EDB). 8

AC mini-grids

230 V alternating current (mains equivalent)

Variety of generation sources possible

Micro-hydro (excellent if it is available)

Wind

PV

Diesel

Or combinations of the above

Problems;

Still a fairly expensive option

No control over the loads which users can buy

e.g. rice cookers use more energy per day than

refrigerators!

This makes sizing difficult

Load-side demand may quickly overload design

generation capacity

http://www.top10.cn/news/32/36/Really-Rice-cookers-consume-more-energy-than-refrigerators.html

SERIS is a research institute at the National University of Singapore (NUS). SERIS is sponsored by the National University of

Singapore (NUS) and Singapore’s National Research Foundation (NRF) through the Singapore Economic Development Board (EDB). 9

Solar home systems

Provide a reasonable level of energy services

Cheaper than AC mini-grids, but still fairly expensive

Require either “donation” by governments or NGOs (not

recommended)

Or individual households must borrow capital to pay for them

Enormous micro-credit infrastructure is required

Individual households pose a credit risk

SERIS is a research institute at the National University of Singapore (NUS). SERIS is sponsored by the National University of

Singapore (NUS) and Singapore’s National Research Foundation (NRF) through the Singapore Economic Development Board (EDB). 10

Solar DC nano-grids

Least expensive option

Electricity from PV is very cheap

< USD $0.10/kWh (DC) when the sun is shining

If energy needs to be stored in batteries, then price goes

up by a factor of 3 or 4

One set of PV panels and batteries serve a cluster of

households (i.e. a village)

Each house is connected via a cable and energy meter

Each household gets a fixed number of Watt-hours per day

The users are charged a flat fee for service, depending on

their tier

A daily energy quota is provided on a “use it or lose it” basis

SERIS is a research institute at the National University of Singapore (NUS). SERIS is sponsored by the National University of

Singapore (NUS) and Singapore’s National Research Foundation (NRF) through the Singapore Economic Development Board (EDB). 11

The solar DC nano-grid concept

SERIS is a research institute at the National University of Singapore (NUS). SERIS is sponsored by the National University of

Singapore (NUS) and Singapore’s National Research Foundation (NRF) through the Singapore Economic Development Board (EDB). 12

Business aspects of solar DC nano-grids

Infrastructure is (at least partially) owned and managed locally

Either as a private enterprise owned by an entrepreneur

Or as a cooperative owned by all the users

Fees are collected locally, door-to-door

No complex centralized payment infrastructure is required

Maximum of one loan per village is required

Risk of default is spread over all users

Amortization period of < 2 years at kerosene prices

Future profits can be used for maintenance or expansion

The profitability of a mini-grid enterprise makes it “bankable”

SERIS is a research institute at the National University of Singapore (NUS). SERIS is sponsored by the National University of

Singapore (NUS) and Singapore’s National Research Foundation (NRF) through the Singapore Economic Development Board (EDB). 13

AC DC Alternating Current or Direct Current

Rotating generators naturally produce AC

Certain loads (such as induction motors) require AC

However…

Most modern loads and appliances either require DC, or are

available in a DC version

LED lighting

Mobile phone charging

Computers, tablets

Televisions

Fans

Photovoltaics produce DC electricity

Batteries store energy as DC

There’s no point to convert from DC to AC back to DC

Keep everything DC and avoid the conversion losses

SERIS is a research institute at the National University of Singapore (NUS). SERIS is sponsored by the National University of

Singapore (NUS) and Singapore’s National Research Foundation (NRF) through the Singapore Economic Development Board (EDB). 14

Loads – provided with the nano-grid

With modern technology, basic energy services can be

provided for very little energy consumption Tier 1

Load Peak power

(W)

Usage time

(hours/day)

Energy consumption

(Wh/day)

LED light 100 lm 1 6 6

LED light 100 lm 1 6 6

USB charger 3 2 6

Radio 0.2 3 0.6

5.2 18.6

Tier 2

Load Peak power

(W)

Usage time

(hours/day)

Energy consumption

(Wh/day)

LED light 100 lm 1 6 6

LED light 100 lm 1 6 6

LED light 200 lm 2 6 12

LED light 200 lm 2 6 12

USB charger 3 2 6

Radio 0.2 3 0.6

TV 6 4 24

15.2 66.6

SERIS is a research institute at the National University of Singapore (NUS). SERIS is sponsored by the National University of

Singapore (NUS) and Singapore’s National Research Foundation (NRF) through the Singapore Economic Development Board (EDB). 15

Some technical details

Our solar DC nano-grids are a bit “smart”

Central system status monitoring and communication to

energy meters allowing variable “tariffs” depending on

conditions

Nighttime (high), daytime (medium), battery full (low)

Loads operate at 12 V DC

Electricity is distributed at 12 V (for now)

Resistive losses in cables are still acceptable

e.g. 10% cable loss for tier 1 load at a distance of 100 m

We will go to 48 V for distribution later with DC-DC converters

This will allow greater distances with lower cable losses

DC voltages are still “touch safe”

Productive use can be included cheaply, provided;

The productive use is located near to the PV system

The productive use operates in the daytime only (no

storage required)

SERIS is a research institute at the National University of Singapore (NUS). SERIS is sponsored by the National University of

Singapore (NUS) and Singapore’s National Research Foundation (NRF) through the Singapore Economic Development Board (EDB). 16

Components required and their availability

Component Availability

PV modules Available

Batteries Available

Charge controllers Available

Loads Available

Cables Available

Signal transmitter Under development

Energy meters Under development

SERIS is a research institute at the National University of Singapore (NUS). SERIS is sponsored by the National University of

Singapore (NUS) and Singapore’s National Research Foundation (NRF) through the Singapore Economic Development Board (EDB). 17

Conclusion

Solar DC nano-grids are the least expensive way to bring

modern energy services to rural villages

They provide a business model along with the technology

which makes them feasible without subsidies or donations

We are implementing several such nano-grids under a pilot

project in Bangladesh sponsored by GIZ

Partnerships and collaborations with interested parties in

South East Asia are most welcome

SERIS is a research institute at the National University of Singapore (NUS). SERIS is sponsored by the National University of

Singapore (NUS) and Singapore’s National Research Foundation (NRF) through the Singapore Economic Development Board (EDB). 18

Thank you for your attention!

For more information, contact me

tim.walsh@nus.edu.sg