October 25, 2002 ENO Presentation 1

Frederick M. IshengomaDept. of Electrical Power Eng.

NTNU

Stand-alone PV power supply for developing countries

October 25, 2002 ENO Presentation 2

Access to Grid electricity

Estimated 2 billion people across the world don't have access to electricity

Majority of these are in the developing countries especially in rural remote areas

October 25, 2002 ENO Presentation 3

Access to Grid electricity Southern Africa: About 21.74% of population have access to electricity in their homes particularly in urban areas (40million/184 million)

In rural remote areas, population is dispersed, has low incomes and the grid power supply is not fully extended to these areas due to viability and financial constraints fuelwood, candles, kerosine, dry-cell batteries,

diesel generators, etc. are used to meet energy needs

October 25, 2002 ENO Presentation 4

Push for Renewable energy

Potential threat of global climate change

Increasing energy demand world-wide

Uncertainty of non-renewable energy (price and availability)

World energy policy on using clean (non-polluting source of energy)

October 25, 2002 ENO Presentation 5

Photovoltaic (PV)

Photovoltaic – Generation of electricity from the sun using solar cells

Reliable and economical power source in rural remote areas

October 25, 2002 ENO Presentation 6

Advantages of PV Non-polluting: No fuel burning Availability Reliability: Service time of at least 20 years Low operating costs: The fuel is free. With

no moving parts, the cells require little upkeep.

Modularity: Portability and sizebility Low Construction Costs: PV systems are

placed close to where the electricity is used, hence shorter and few wires, shorter construction time

October 25, 2002 ENO Presentation 7

Disadvantages of PV High initial capital cost

Very low PV cell conversion efficiency (efficiency of solar modules differs depending on the materials used)

R&D ->development of low-cost PV materials (less $/Wp) and cost reduction in BOS components production of modules with higher efficiencies (about 30%).

October 25, 2002 ENO Presentation 8

PV costs and production trend

October 25, 2002 ENO Presentation 9

Solar energy

Most of dev. Countries have abundance of the solar energy resource all year round

PV for RAPS, telecommunication, water pumping, etc.

Solar water heating (SWH): hot water supply (domestic, commercial and industrial use)

October 25, 2002 ENO Presentation 10

October 25, 2002 ENO Presentation 11

Barriers to PV Usage Slow pace of power sector liberalisation and

privatisation =>Independent Power Producers

Low levels of industrial development (delivery time and expensive due to transport, maintenance, labour costs).

Hardware from Europe, SA, Germany, USA

Lack of renewable energy policies Lack of training and capacity building

initiatives Courses which provide exposure to energy

technology ->renewable energy engineers and technicians

October 25, 2002 ENO Presentation 12

Types of PV systems

Grid connected PV power system Fastest growing applications in

developed countries Stand-alone PV power supply

(SAPS) or Remote Area PV Power Supply (RAPS)

October 25, 2002 ENO Presentation 13

Grid connected PV system

+ -

PV generator

Battery

Bi-directionalinverter

~=

DC load

AC load

DC bus

AC bus

Grid

October 25, 2002 ENO Presentation 14

Hybrid system

+ -

PV generator Charge Controller Battery

Inverter

~=

DC load

AC load

G~

=RectifierGenset

or Wind turbine

October 25, 2002 ENO Presentation 15

Stand-alone PV system

PV generator ChargeController

Battery

Inverter

~=

DC load

AC load

+ -

Sun

October 25, 2002 ENO Presentation 16

Main areas of PV research Optimization of solar cells Optimization of solar power

conversion Power electronics and control

algorithms in the PV conversion process (efficiency of DC-DC converters, efficiency of inverters, improvement in battery charging mechanism, etc.)

October 25, 2002 ENO Presentation 17

Model of PV cell (module)

D Rsh

Rs

RLoad

Iph

I D

I sh

Ipv

Vpv

October 25, 2002 ENO Presentation 18

I-V and P-V characteristics

October 25, 2002 ENO Presentation 19

I-V and P-V characteristics - constant solar cell temperat.

October 25, 2002 ENO Presentation 20

I-V and P-V characteristics - constant Irradiance

October 25, 2002 ENO Presentation 21

Maximum Power Point Tracker (MPPT)

0 5 10 15 200

10

20

30

40

50

60

70

80

Voltage [V]

Sol

ar c

urre

nt [

A]

MPP

October 25, 2002 ENO Presentation 22

Control

DC

DC

PV ArrayL0

Transformer

Co

Inverter

Ba

ttery

Interface board

DSP

AnalogSignals to beconditioned

Conditionedsignals (0-5V)

Switch(relay)

Cd

PW

M f

or

DC

/DC

co

nve

rte

r

PW

Ms f

or

inve

rte

r

Relay control signal

Buck converter

Invert

er

sta

tus s

ignals L

oa

d

PersonalComputer

Sun

October 25, 2002 ENO Presentation 23

Advantages of digital Control Flexibility due to programmability

Modification of control algorithms and performing complex tasks which are impossible using analog circuitry

Modifications to the design are made through code changes, not component changes

Reduces components of the system (cost and weight)

October 25, 2002 ENO Presentation 24

Main tasks Mathematical Models for a PV module to be used

in Matlab/simulink for MPPT and battery charging Interface board for signals required for control MPPT algorithm Four states battery charging algorithm (trickle,

bulk, overcharge and float states) with temperature compensation)

Control algorithm for inverter for linear and non-linear loads and dimensioning of LC filter for inverter

Extra: PECCTerm development and logging function

October 25, 2002 ENO Presentation 25

Conclusion The cost of PV energy technologies is on a

falling trend and is expected to fall further as demand and production increases

PV technology will serve rural areas population in developing countries from costs incurred in using costly energy sources and will improve their social and economical life

Locally produced hardware and local experts will ensure availability of service and maintenance and increase confidence in PV usage