Efficiency monitoring of solar hot water systems in the Fiji ...

EFFICIENCY MONITORING OF SOLAR HOT WATER SYSTEMS IN THE FIJI ISLANDS AND THE

KINGDOM OF TONGA

Rupeni Mario, Energy Project Officer South Pacific Applied Geoscience Commission

June 2000 SOPAC Technical Report 318

SOPAC Technical Report 318

Efficiency Monitoring of Solar Hot Water Systems in the Fiji Islands & the Kingdom of Tonga

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TABLE OF CONTENTS

page

Acknowledgements … .… … … … … … … … … … … … … … … … … . 4

List of Acronyms, Figures & Tables … … … … … … … … … … … .. 5

Executive Summary ...................................................… … … … 6

Project Objectives .......................................................… … … ... 7

Introduction and Background … … .........................… … … … … . 7

Monitoring Sites … … … … … … … … … ..… … ..… … … … … … … ... 8

System Description … … … … … … … … … … … … … … … … … … .. 9

Equipment and Instrumentation … … … … … … ................… … ... 12

Monitoring and Data Retrieval … … … … … … … … … … … … … … 13

The Data … … … … … … … … … … … … … … … … … … … … … … … 14

Data Analysis … … … … … … … … … … … … … … … … … … … … … 15

Results and Discussions… … … … … … … … … … … … .… … … … .. 16

Conclusion … … … … … … … … … ....… … … … … … … … … … … .. 19

References … ..… … … … … … … … … … … … … … … … … … … … . 21

Annex 1 Equipment & Instrument Characteristics … … … … … 22

Annex 2 Map of the Fiji Islands … … … … … … … … … … … … … 25

Annex 3 Map of the Kingdom of Tonga … … … … … … … … … .. 26



ACKNOWLEDGEMENTS

Assistance provided by the Fiji Department of Energy and the Tonga Energy Planning Unit,

particularly that of Messrs Ravindra Prassad and Talanoa Aholahi is gratefully acknowledged.

Comments and guidance by Mr Paul Fairbairn, Energy Manager, SOPAC, were invaluable in the

management of the project and preparation of this technical report.

System owners’ support and cooperation during the monitoring period were much appreciated.

Acknowledgement is also due to the Australia and New Zealand Governments for their financial

assistance through the SOPAC Energy Unit’s Small Energy Projects Programme.



List of Acronyms/Symbols 0C degree celcius CO2 carbon dioxide DOE Fiji Department of Energy EPU Tonga Energy Planning Unit kJ kilojoules kg kilograms LPG liquid petroleum gas m2 square metres MJ megajoules mm millimeters s seconds SOPAC South Pacific Applied Geoscience Commission SWH solar water heater TSS Tonga Solar Systems W watts

Figures

Figure Description Page

1 The Triangular Arrangement of the Monitoring Sites 8

2 The Beasley Solar Water Heater 9

3 A Remote Thermosyphon Solar Water Heater 10

4 A 300L Solahart (imported) Water Heater 10

5 A Tonga Solar System (locally constructed) Water Heater

11

6 Closed-coupled Thermosyphon Solar Water Heater 11

7 Set-up of Monitoring Equipment 12

8 Instantaneous Efficiency Curves of Selected Collectors

16

9 Energy Balance 17

10 Overall System Efficiencies & Instantaneous Collector Efficiencies

18

11 Accumulated End of Year Costs of Solar, Electric and LPG Water Heaters

19

12 Cost per m3 of Hot Water, Tonnes of Oil Equivalent & Tonnes of CO2 Emitted

20

Tables

Table Content Page

I Data Downloaded by the respective Energy Offices as at June 2000

13

II Data as Recorded by the Data Loggers 14

III Details of Systems Monitored 17

IV Selection Guide for Solar Water Heaters 18



EXECUTIVE SUMMARY

Solar water-heating systems are used in the region and are considered competitive on an

economic and financial basis with gas and electric water heaters.

However, due to the variable nature of solar radiation and seasonal temperatures their efficiency

can vary accordingly.

The project involved the Fiji Department of Energy and the Tonga Energy Planning Unit in

implementation and efficiency monitoring of selected solar water heaters installed in domestic

premises.

The sites selected were on the basis of a triangular arrangement so as to give as wide as

possible coverage of the region. In the Fiji Islands, there were four monitoring sites, two in Nadi,

located at latitudes 170 46? and longitude 1770 27?, and two in Suva, located at latitude 180 8? and

logitude1780 26?. The two monitoring sites in Tonga were in Nuku`alofa, located at latitude 210

20? and longitude 1740 55?. The selected solar water heaters were a Solahart water heater,

imported from Australia, Beasley solar water heater (locally constructed in the Fiji Islands) and a

Tonga Solar System (locally constructed in Tonga). The selection of the solar hot water systems

was based on a set of predetermined parameters taking into account the relative newness of the

systems and that installation was optimum in accordance with the manufacturer’s specifications.

The project was established following the preparation of an economic template where the cost of

providing hot water from solar water heaters is compared with other alternative supplies such as

electricity and liquid petroleum gas (LPG). As the installed solar water heater efficiency is one of

the key input into the template, it was deemed necessary to have more realistic efficiency figures

for the region.

As efficiency values stated by the manufacturers are usually for ideal conditions, then these are

generally not supported in practice. In addition, simple factors such as the orientation of

collector(s), insulation of the hot water storage tank and condition of the solar water heater all

contribute to the systems installed efficiency. General installation and the natural environment

also affect system performance.



The selected solar water heaters were monitored over a twelve-month period with the automatic

data loggers programmed to record quantity of hot water used per household, temperature of

water flowing into the system, temperature of the hot water flowing out of the system and

irradiance on the collectors.

Project results indicate that the installed efficiency of the solar water heaters was in the order of

10 – 15% less than its instantaneous collector efficiency. The comparison of locally-constructed

solar water heaters to imported solar water heaters reveals that the imported solar water heaters

have a slightly higher efficiency value. The paper also compares and discusses the various

models and their manufacture.

PROJECT OBJECTIVES

To measure, compare and substantiate efficiencies of selected solar water heaters installed in

domestic premises in the Fiji Islands and the Kingdom of Tonga.

INTRODUCTION AND BACKGROUND

Solar energy is free and available in abundance. The development in solar water heater

technology to harness this free energy has not only reduced the energy bill of the household but

has also improved living conditions hygienically. Interest in solar technology has developed to a

remarkable stage in the past years due to the increase in electricity tariffs and prices for other

commonly-used energy sources, although LPG for certain applications is a preferable option

especially in larger commercial locations.

Solar water-heating is perhaps one of the most common uses of solar energy. A well-designed

solar water heater should be able to deliver all the hot water required over the summer. At

present, research work with solar water heaters aim to improve system designs thus improving

their efficiencies.

Solar water heater technology is widely accepted in the Pacific island countries, however, due to

the high initial capital investment requirement, the Pacific Islands have not fully exploited this

source but have opted to use other means of water heating.

The project was established following the preparation of an economic template where the

economics of solar water heaters were compared with other alternative sources, namely,

electricity and liquid petroleum gas (LPG). The unavailable installed-efficiency values of



imported and locally-constructed solar water heaters lead the SOPAC Energy Unit to carry out

the efficiency monitoring project under its Small Energy Projects Program.

Testing of solar water heaters is not new. Suebroke and McCormick (1987) carried out tests on

Solar Edwards Hot Water System at the University of Western Australia. According to their

findings the overall system efficiency was 26%. An outdoor test carried out by Mario (1998) on

the Solco Solar Water Heater at the University of the South Pacific showed that the newly-

designed system had an average technical efficiency of approximately 38%.

Most manufacturers claim that their solar water heaters are between 50-65% efficienta, by which

they mean instantaneous collector efficiencies at best ambient conditions.

The data collated over the monitoring period has been analysed to provide efficiencies of

selected locally-constructed and imported solar water heaters installed at domestic premises.

These efficiency values will not only provide a better understanding of solar water heater

operation characteristics but will enable a more realistic comparison with electric and LPG water

heaters.

MONITORING SITES

The sites selected were on the basis of a triangular arrangement, see Figure 1, so as to give as

wide as possible coverage of the variable weather conditions in the region.

aFairbairn & Kaupp; Economic Analysis of SHW Systems

Figure 1 The Triangular Arrangement of the Monitoring Sites



Fiji Islands

The Fiji Islands is located between longitudes 1750 east and 1780 west and latitudes 150 and 220

south. There are over 300 islands in the Fiji archipelago of which about ninety-seven are

inhabited.

The chosen sites were Nadi, located at latitudes 170 46? and longitude 1770 27? with an average

insolation rate of 18.6 MJ/m2day and an annual average rainfall of 1900 mm, and two in Suva,

located at latitude 180 8? and logitude1780 26? with an average insolation rate of 16 MJ/m2day

and annual average rainfall of 3500 mm.

Kingdom of Tonga

The Kingdom of Tonga is a small Pacific island country with a land area of about 750 km2 and a

population of 98 000 dispersed over 36 islands.

The monitoring sites are both in Nuku`alofa located at latitude 210 20? and longitude 1740 55? with an average insolation rate of 16.5 MJ/m2day and an annual average rainfall of 2300 mm.

SYSTEM DESCRIPTION

In the Fiji islands, the four systems monitored

were two Beasley water heaters as in Figure 2

and two Solahart water heaters, Figure 4.

A Tonga Solar System (TSS) water heater,

Figure 5, and a Solahart water heater were the

two systems monitored in Nuku`alofa, Tonga.

The Beasley water heater is a remote

thermosyphon system as in Figures 2 and 3. It

has a hot water storage tank capacity of 180

litres and a collector area of 2.28 m2. The

collector is constructed using copper with black

paint coating.

Figure 2 The Beasley (locally constructed in the Fiji islands) Solar Water Heater



The Tonga Solar System water heater is a close-coupled thermosyphon system. Materials used

in its construction are similar to that of the Beasley system in the Fiji islands.

The solar water heaters are fitted with electric boosters, which are manually controlled to

maintain the water at a preset temperature when there is insufficient sunshine. The use of the

booster is optional, and it usually depends on the hot water demand of the household. Booster

hours in the monitoring are insignificant, as the respective households do not use the electric

boosters.

Figure 3 A Remote Thermosyphon Solar Water Heater

Figure 4 A 300L Solahart (imported) Water Heater

The Solahart water heater, Figure 4, is a

close-coupled thermosyphon system as in

Figure 6. It has a hot water storage tank

capacity of 300 litres (180 litres for the

system in Tonga) and is insulated with

polyurethane foam. The effective collector

area of 3.98 m2 (2.0 m2 for the system in

Tonga) is constructed of high conductive

aluminium with black polyester coating. The

collector(s) is covered with low iron solar

glass and insulated with fiberglass.



1Figure 6 Close-coupled Thermosyphon Solar Water Heater

Figure 5 A Tonga Solar System (locally constructed) Water Heater



EQUIPMENT AND INSTRUMENTATION

Based on technical specifications prepared by SOPAC, Scott Technical Instruments Ltd of New

Zealand supplied the monitoring equipment and instrument needs. These include: CR500 model

dataloggers, temperature probes (Model 108), silicon cell pyranometers (Model SP437), Model

PC1% T-O-P pulse flowmeters, SC32A Optically Isolated RS232 Interface with cable, a

PC208W WINDOWS support software, spare HV7-12 Hitachi 12 volt, 7 amp/hr capacity sealed-

cell lead acid batteries, and LAC-1203 lead acid battery chargers. Refer to the Annex at the end

of this report for detailed characteristics and specifications of these equipment and instruments.

SOPAC through consultation with Scott Technical Instruments set up the monitoring equipment

as illustrated in Figure 7.

Figure 7 Set-up of Monitoring Equipment

cold watertemperature probe

Flow meter

hot watertemperature probe

pyranometer

CR500datalogger



MONITORING AND DATA RETRIEVAL

The Fiji Department of Energy (DOE) and the Tonga Energy Planning Unit (EPU) were

responsible for the identification of suitable systems to monitor, arranging the monitoring

equipment installation, downloading the data on a monthly basis for the duration of the

monitoring period, and forwarding the downloaded data to SOPAC, reference Section 3 of the

Memorandum of Understanding, as follows.

3. Implementation Arrangement 3.1 The Fiji Department of Energy and the Tonga Energy Planning Unit will be

the Executing Agencies for the activities in Fiji and Tonga respectively, and will be responsible for the Project. In particular, they will undertake the following:

? ? Co-ordinate the in-country component of the project including: ? ? identification of suitable solar hot water systems to monitor; ? ? liase with the owners of the individual systems to be monitored and

supervise installation and removal of the monitoring equipment; ? ? identify and appoint a contractor / consultant for installation / removal of the

monitoring equipment; and downloading the data ? ? Ensure that the integrity of the monitoring equipment is maintained; ? ? Ensure that the contractor / consultant downloads the recorded data; ? ? Forward the downloaded data to the Secretariat; ? ? Ensure that following the removal of the monitoring equipment that the

individual system owners are totally satisfied with the reinstatement; and ? ? On completion of the project return all loggers, sensors, and ancillary

equipment purchased for the Project to the Secretariat.

Installation commenced in October 1998 with the final commissioning of all systems in March

1999. The initial four months were spent on ensuring the proper/correct operation of the logger

programs including training on the data collection and downloading. The logger programs were

modified accordingly as advised by Scott Technical Instruments Ltd. of New Zealand so as to

ensure the quality of the data.

The quantity of data downloaded by the respective energy offices is as follows.

Table I Data Downloaded by the Respective Energy Offices as at June 2000.



The difference in the number of months of data downloaded by the Fiji Department of Energy as

shown in Table I are mainly due to technical faults. As for the loggers 5 and 6 in Tonga, the

limited data provided by the Energy Planning Unit has been due to technical faults and the very

irregular sequence in the downloading process, which resulted to data been over-written.

THE DATA

The automatic data loggers were programmed to record the time interval, the year, Julian day,

the time, quantity of hot water used by the household, the temperatures of water flowing into and

flowing out of the hot water system, and irradiance. The following table illustrates a typical set of

data recorded by the loggers. Line 6 of Table II shows the recordings at midnight indicating the

logger number (1), the battery voltage (12.67 V) and ambient temperature (24.71 0C).

The data loggers record at different time intervals: every ten minutes between 0530 and 2130

hours and for every sixty minutes between 2200 and 0500 hours. The temperature readings

(columns 5 & 6) are in degree Celsius (0C), irradiance (column 7) in Watts per square metres

(W/m2) and flow (column 8) in litres (l).

Table II Data as recorded by the Data Loggers



DATA ANALYSIS

Generally, the approach taken was to consider the solar water heater system as “one”; thus,

calculations are based on the total energy collected by the collector(s) and the energy output as

hot water available at the tap.

Efficiency refers to the ratio of solar energy needed to heat a required volume of water to solar

energy available on the collector(s) over the same time period.

Energy needed to heat a volume V of water from temperature T1 to temperature T2 is calculated

by:

where c = specific heat capacity of water (0.004184 MJ/kg0C)

(T2 – T1) = ? T, change in water temperature (0C)

V = volume of hot water required per day (litresb/day)

The energy available on the collector(s) over the same time period is calculated as the product

of solar radiation and the effective collector area, equation (ii).

where G = solar radiation (MJ/day)

A = effective collector area (m2)

Efficiency (? ) is therefore defined as “volume of hot water used per day ? 0.004184 ? ? T

divided by daily solar radiation received by the collector(s)”, as in equation (iii).

b note that density (? ) = mass divided by volume. Assuming ? of water ? 1.0, this implies that mass ? volume (kg ? litres).

V ? c ? (T2 – T1) [MJ] (i)

G ? A [MJ] (ii)

(iii) %100?

?????AG

TcV?



RESULTS AND DISCUSSION

This section sets out the findings of the project and also attempts to verify that installed

efficiencies of solar water heaters are less than their respective instantaneous collector

efficiencies.

Instantaneous Collector Efficiencies

Figure 8 is a graphical representation of instantaneous collector efficiencies. The profiles are

generated from results of long term tests of typical collectors that are commercially available.

One of the factors clearly shown in Figure 8 is that at higher temperatures the effectiveness of

heat transfer is reduced by losses due to radiation and convection.

Consider Suva as an example. With an average solar radiation (G) of approximately 1000 W/m2

and change in water temperature (? T) of 36 0C, ? T / G equals 0.036. Figure 8 shows

instantaneous collector efficiency within the range of 39 – 67%, depending on the type of

collector being used.

The solar water heaters monitored in this project have their collectors coated with black paint

(Beasley & TSS) and black polyester (Solahart), see Figure 8 for their respective curves. Their

instantaneous collector efficiencies are therefore 39 - 46% and 61% respectively.

Figure 8 Instantaneous Efficiency Curves of Selected Collectors

black paint black polyester



Efficiencies of the Solar Water Heaters (domestic installed efficiency)

The downloaded data was collated, analyzed and summarized into Table III.

With system efficiency values ranging from 20 - 25%, the 75 - 80% (that is, 100% – 25% &

100% – 20%) losses are attributed to losses from the collector(s), pipes and the hot water tank,

Figure 9, through radiation and convection.

Comparison of Solar Water Heaters

Figure 10 illustrates the difference in the solar water heater system efficiency and their

corresponding instantaneous collector efficiency. The imported solar water heaters, when

compared with the locally-constructed solar water heaters, have a slightly higher system

efficiency. This is perhaps due to the technology and materials used in the manufacturing

process.

Incident SolarRadiation

Collector Losses

Pipe Losses

Tank Losses

Energy to load

Table III Details of the Systems Monitored

Figure 9 Energy Balance

The percentage loss at each stage

largely depends on the insulation

type and the thermal conductivity of

material used in the construction of

the system.



If we consider the collectors, Solahart uses high conductive aluminium for the plate material with

black polyester as the surface finish, while the Beasley and the Tonga Solar System uses

copper and black paint.

One of the major factors in determining system efficiency is the hot water usage within the

household (note that efficiency is directly proportional to volume of hot water used). It is

important that a selection guide as in Table IV is used when selecting solar water heaters for

domestic purposes.

Daily hot water usage

allow 38 litres / person

Tank with booster

(litres)

Tank without booster

(litres)

Number of collectors

(collector area = 2.38m2)

2 people 110 150 2

3 people 150 230 3

4 people 230 300 4

5 people 300 400 5

6 people 400 450 6

7 people 400 530 7 Please note that the above table is for the Beasley solar water heater, however this could be used as a guide for anyone selecting a

solar water heater; source: Western Electric Co. Ltd & Hussain Solar Industries Ltd, Lautoka, Fiji Islands.

Figure 10 Overall System Efficiencies and Instantaneous Collector Efficiencies

Table IV Selection Guide for Solar Water Heaters



CONCLUSION

Project results indicate that installed efficiency of selected solar water heaters range from 20 –

25%. These values are 10 – 15% less than their respective instantaneous collector efficiencies.

The comparison of locally-constructed solar water heaters to imported solar water heaters

reveals that the imported solar water heaters have a slightly higher efficiency which could be

attributed to the materials used in the manufacturing of the solar water heaters.

Given a more realistic efficiency of solar water heaters installed at domestic premises, it is of

further interest to explore the economics of solar water heaters. An extract from the Economic

Analysis of Solar Hot Water Systems – A Comparison with Electrical and LPG Systems

template, Figure 11 & Figure 12, reveals that in the long term the solar option is more

economical.

Another area in which the same template focuses on is the saving on carbon dioxide (CO2)

emissions. Figure 12 gives a comparison of “tonnes of oil equivalent” (TOE) used and the

corresponding CO2 emissions when considering the LPG and the electric option.

Figure 11 Accumulated End of Year Costs of Solar, Electric and LPG Water Heaters

Note: The project results (solar water heater system efficiency) were used in the Economic Analysis of Solar Hot Water Systems – A Comparison with Electrical and LPG Systems template to produce the above graph.



With the substantiation of the solar water heater efficiencies, their economical advantages over

electric and LPG water heaters, and environmental friendliness it is important that the Pacific

island countries continue to work towards minimizing the initial investment costs associated with

solar water heaters.

Figure 12 Cost per cubic metre of Hot Water, Tonnes of Oil Equivalent (TOE) and

tonnes of Carbon Dioxide (CO2) Emitted

Note: The project results (solar water heater system efficiency) were used in the Economic Analysis of Solar Hot Water Systems – A Comparison with Electrical and LPG Systems template to produce the above figures.



REFERENCES

? ? Fairbairn, P. and Kaupp, A.; Economic Analysis of Solar Water Systems – A Comparison

with Electrical and LPG Systems; Energy Division, Forum Secretariat, Suva, Fiji Islands;

October 1997.

? ? Fairbairn, P. and Mario, R.; Solar Water Heaters – SOPAC Technical Report 297; Energy

Unit, South Pacific Applied Geoscience Commission, Suva, Fiji Islands; July 1999.

? ? Standards Association of Australia; Solar Water Heaters – Method of Test for Thermal

Performance – Outdoor Test Method; Australian Standards 2984 – 1987.

? ? Suebroke and McCormick; Tests on Solar Edwards Hot Water System; University of

Western Australia; 1987.

? ? Twidell, J. and Weir, A.; Renewable Energy Resources; E & F. N. Spon Ltd, 11 New Fetter

Lane, London EC4P4EE; 1986.



ANNEX 1 Equipment & Instrument Characteristics

CR500 Datalogger

Features

? ? Easy, point and click programming;

? ? 2 differential or 4 single-ended analog

inputs;

? ? 3 pulse counting channels: 2 full function, 1

switch closure only;

? ? SDI-12 compatible;

? ? Non-volatile Flash memory to store up to

24000 data points;

? ? Digital output port for on/off control;

? ? 12V power source; alkaline or

rechargeable batteries; low power drain;

? ? Supports all CSI telecommunication and

data retrieval options;

? ? Reduced cost; and

? ? 3-year warranty.

Specifications

? ? Program execution rate *Hz;

? ? Analog inputs: accuracy of voltage

measurements ? 0.1%;

? ? Excitation outputs: range ? 2.5 V; resolution

0.67 mV; accuracy ? 2.5 mV (00 to 40 0C),

? 5 mV (-250 to +50 0C); output current ? 25

mA;

? ? System power requirements: voltage 9.6 to

16 Volts; batteries – any 12V battery can

be connected as a primary power source;

? ? Physical specifications: size 8.4”? 1.5”? 3.9”;

weight 15 oz; and

? ? CPU and Interface: memory 128 K Flash

and 32 K SRAM standard; display 8 digits.

Temperature Probe (Model 108)

Specifications

? ? Temperature Measurement Range: -50 to +95 0C

? ? Thermistor Interchangeability Error: typically <? 0.2 0C

over 0 0C to 70 0C ? 0.3 @950C.

? ? Polynomial Linearization Error: <? 0.5 over –7 0C to +900C

Silicon Cell Pyranometer

Specifications

? ? Spectral response peaks at 700 nm, 70% response points at 500 & 900 nm;

? ? Linearity of output current is better than 1%;

? ? Current temperature coefficient is 0.1%/0C;

? ? Calibration is within 5% of a grade 1 pyranometer;

? ? Cosine response errors related to angle to vertical are:

0-60 degrees less than 1%



Model 108

Pyranometer



Flowmeters (Model PC1% T-O-P pulse)

Specifications

? ? Meter thread size G ? B inch;

? ? Starting flow rate 5.7 litres/hr;

? ? Minimum indicating digit value 0.1 litre;

? ? Output pulse 0.5 litres;

? ? Weight 1.08kg;

? ? Meter resets to zero at 10000 m 3; and

? ? Meter diameter 86 mm; meter length 115 mm.

Optically Isolated Interface (RS-232)

Specifications

? ? Power drawn from the serial ports of the computer

and datalogger;

? ? Connections: 25-pin RS-232 female port configured

as DCE, 9-pin male port connects to datalogger via the SC12 cable;

? ? Operating temperature range –25 0C to +50 0C

? ? Size: 2.25”? 1.0”? 3.5”

? ? Weight 0.25 lb; and

? ? SC32A shipped with SC12 cable.

Support Software (PC208W)

Model PC1% T-O-P pulse

The RS-232



Battery (High Power HV Type Sealed Lead -Acid)

Specifications

? ? Model HV7-12;

? ? Nominal voltage 12 V;

? ? Rated capacity 7 Ah / 20 hrs;

? ? Weight 2.7 kg;

? ? Internal resistance Approx 22 m? ; and

? ? Maximum discharge current 105 A; maximum charging current 2.1 A.

High Power HV Type Sealed Lead-Acid



ANNEX 2 Map of the Fiji Islands



ANNEX 3 Map of the Kingdom of Tonga

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