Construction of a Small Scale Laboratory for Solar Collectors and Solar Cells in a Developing Country

doi:10.4236/eng.2013.51B014

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Engineering, 2013, 5, 75-80

doi:10.4236/eng.2013.51b014 Published Online January 2013 (http://www.SciRP.org/journal/eng)

Construction of a small scale laboratory for solar collectors

and solar cells in a developing country

Gentile Niko1*, Davidsson Henrik1, Bernardo Ricardo1, Gomes Joao2, Gruffman Christian3, Chea

Luis4, Mumba Chabu5, Karlsson Björn6

1 Energy and Building Design, Lund University, Lund, Sweden

*Corresponding Author email: [email protected]

2 Solarus Sunpower Sweden AB, Stockholm, Sweden

3 Finsun AB, Älvkarleby, Sweden

4 Universidade Eduardo Mondlane, Maputo, Mozambique

5 University of Zambia, Lusaka, Zambia

6 Division of Energy Engineering, Mälardalen University, Västerås, Sweden

Received 2013

Abstract

In the field of renewable energy, self-provided research in developing countries is barely present, but most welcomed.

The creation of know-how and self-development of technologies should reduce the dependence on industrialized coun-

tries for both materials and knowledge. This work presents technological and social issues related to the construction of

a low budget solar laboratory in Mozambique. The goal is to demonstrate that scientific level research can be carried

out in developing countries by using affordable solutions without sacrificing quality of the results. For this investiga-

tion, a solar laboratory was built in 2011 at Universidade Eduardo Mondlane of Maputo. The laboratory enables meas-

urements to evaluate solar thermal and photovoltaic-thermal hybrid collectors. Thanks to the flexibility of the sys-

tem, students and teaching staff can add/remove equipment and develop customised local research programs. In addi-

tion, a course on the principles of solar energy and collector simulation for local students was taught. The needed data

acquisition devices usually used in Europe were compared with cheaper and easy-maintenance ones. Calibration and

estimation of the uncertainty were successfully performed. Approximately 9% of inaccuracy in the measurement was

introduced by the cheaper equipment, but the investment cost was reduced by more than 90%. Other issues, results and

future recommendations are shown.

Keywords: solar thermal; solar hybrid; small-scale laboratory; scientific research; developing country; Mozambique.

1. Introduction

The flow of foreign aid to developing countries during

the year 2006 was 103.6 billion USD, while the global

amount disbursed in the past 50 years is over 2.3 trillion

USD [1]. The resulting benefits are often negligible,

even if not detrimental, as revealed by different studies

[2, 3]. Nevertheless foreign aid is still an essential condi-

tion to stimulate investments and to reduce the gap be-

tween industrialized and developing countries [4].

Moreover, the consequences of a drastic reduction in

foreign aid can be dramatic for the population (e.g.,

about half of the Government budget in Mozambique is

underpinned by foreign aid [5]). The discussion nowa-

days is consequently oriented toward improvements in

the efficacy of aid. Williamson argues that the possibility

that both donors and recipients do not have adequate

knowledge to achieve development goals must be ad-

dressed [6]. In this view, long term collaboration be-

tween Universidade Eduardo Mondlane (UEM) in Ma-

puto (Mozambique), University of Zambia and Lund

University (LU) permitted characterization of Mozambi-

can primary needs in terms of technology, as well as the

weaknesses of previous aid projects. By means of re-

sources mostly provided by the Swedish International

Development and cooperation Agency (SIDA), a low

budget solar laboratory for scientific research was thus

built. Several reasons oriented both donor and recipients

to this new approach to foreign aid.

Firstly, according to the 2012 appraisal, about 1.6 billion

people worldwide have no access to electricity, of whom

more than a third are living in the African continent [7].

N. GENTILE ET AL.

Particularly in Sub-Saharan Africa less than a quarter of

the population can use electricity [8]. In Mozambique the

percentage is as low as 6% [9]). Lack of access to af-

fordable electricity is a major determinant of poverty

[10], confirmed by barely $500 of GDP/pp in Mozam-

bique [11]. In view of the availability of solar radiation

in the country [12], recent projects are largely based on

the installation by donors of stand-alone photovoltaic

systems in remote areas. The effectiveness of interven-

tion is strongly related to both local expertise and the

availability of material and spare parts, which are often

disregarded [13]. Furthermore, the systems themselves

are directly produced and imported from industrialized

countries, which is the cause of the continued depend-

ence status of the developing countries for further rural

electrification projects.

The absence of domestic production of photovoltaic and

solar thermal systems can be related, not only to lack of

economic resources but also to the lack of local scientific

research. Issues for African Universities concerns the

availability of funds and difficulties in receiving instru-

ments from industrialized countries because of bureau-

cracy, shipping costs and risks, and a very long waiting

time. The proposed solution is to replace expensive in-

struments with cheap, locally available and

easy-maintenance ones; precision and accuracy should

be only sacrificed inside a range of acceptability. By

offering knowledge and a basic set of tools, this work is

a contribution to the start-up for local scientific research.

The installed equipment allows general training for en-

gineers even outside the field of solar energy, e.g. data

logger programming for developers or improvement of

the solar tracking system for mechanical engineers. Na-

tional testing agencies for instruments can arise and ex-

ploit the laboratory as reference. As a direct conse-

quence, an increase in local patents could occur, with

general improvement of domestic production. In a virtu-

ous circle, economic growth should allow higher invest-

ment in research, which is an essential condition for the

transition from basic to high level scientific research.

Data-loggers, solar radiation, temperature and angle

sensors are part of the laboratory equipment. The system

was set up in the furtherance of easy customizations for

increased local researches in the future. At the present

time a prototype of concentrating Photovoltaic/Thermal

(PV/T) hybrid collector is being tested [14]. UEM can

perform reliable testing and get acquainted with the

tools, while LU can afford tests in very different climatic

conditions.

In the first section of this paper the methodology fol-

lowed in choosing instruments and solutions is explained

in detail. The second section shows discussions and the

results of a comparison of the sensors, including a calcu-

lation example and related accuracy. The conclusions

highlight the results achieved and underline improvable

aspects for further similar projects.

2. Methods

2.1. Project schedule

The preliminary schedule of work was drawn up in LU

during the beginning of year 2010. The early design

phase of the project concerned the definition of several

key-words:

 “Involving”. Recipients must be completely involved

in the job achievement. Courses to local students

were given, an MSc student participated in the meas-

urement phase and the presence of personnel from

UEM was always requested during the building and

testing process. A local member was also assigned as

responsible for the facilities after the end of the pro-

ject.

 “Customizable”. Recipients must be allowed to run

their own researches, also in other fields. Easy

adaptability of the lab to different acquisition devices

is fundamental. Adaptable data logger and sensor

were chosen.

 “Cheap”, “Simple” and “Efficient”. The choice of

devices stressed the importance of affordable prices,

easy understanding and installation, without exces-

sively sacrificing the quality of measurements.

 “Low maintenance” and “Locally available”. Sensors

and devices are not always available in Africa. Long

life and easy obtainable replacements are the distin-

guishing characteristics of a project with a long term

perspective.

 “Low water usage”. Water is a precious, rare and

expensive resource in Africa. Grid water supply is not

always guaranteed. A closed water circuit with a 250

l boiler was studied for the solar thermal part. Rather

than using fresh water from the grid, water can flow

through the system during the night to cool down the

storage.

During the second part of year 2010, the project passed

from the early design stage to a more detailed level. Dif-

ferent sensors and devices were tested in Lund and the

definitive adopted equipment was eventually chosen.

The team from LU reached Maputo in January 2011 and

worked for three months. The combination of both de-

lays in material delivery and the low availability of spare

parts in Mozambique, caused changes to the initial

schedule. Though the solar laboratory was successfully

built by the end of the visit, some planned works could

not be carried out (e.g. tracking system). Sensors were

installed to check ageing during the subsequent visit.

During the 12 weeks basic courses on solar energy were

given to UEM and University of Zambia students. They

covered topics such as: solar radiation basics and solar

conditions in Mozambique, basics on different collector

N. GENTILE ET AL.

types and systems, optimization of solar collector sys-

tems and cost analysis for local conditions.

An additional visit by a Lund University team to Maputo

was made in November 2011. The main activities con-

cerned finalization of the laboratory construction, a

check on the ageing effect on the products and perfor-

mance of further tests. No additional courses were of-

fered, but an MSc student from University of Zambia,

Mr. Chabu Mumba, was fully engaged in the activities as

an exchange researcher. Works concerned the imple-

mentation of the HSAT and other minor improvements

to the piping system.

Further tests had the aim to assess ageing effects on both

the panels and sensors. Cheap devices were compared

with the scientific ones.

2.2. Choice of data acquisition devices

The tests performed during 2010 made it possible to find

devices with a satisfactory quality/price ratio. Manufac-

turers of the chosen products were subsequently involved

in the project. In the following list, “a)” indicate the ref-

erence device, “b)” the tested option.

1) Data Logger.

a) Campbell CR1000 DataLogger. Analog, digital and

pulse inputs are suitable for the adopted scientific data

logger. For the mean voltage input range ±2.5V, maxi-

mum resolution is 0.67 mV and measurable through up

to 16 single-ended ports. High accuracy, versatility and

reliability allowed this product to be spread worldwide

for scientific application. The price is approximately

1500 USD.

b) MELACS®. It enables stand alone data logging and

remote collection through the built in web server. Con-

nection of multiple loggers (e.g. to increase the number

of ports) is possible through the Ethernet port. Voltage

input range is fixed to ±3.3V, corresponding to 0.8 mV

of resolution and measurable through 8 channels. Pulse

and digital channels are also available. It works with

open source GPL software. Current price is about 260

USD.

2) Water temperature.

a) PT100 Class A. High precision temperature meas-

urements were carried out through a PT100 sensor with

immersed insert. The Class A definition guarantees the

accuracy of ∆T=±(0.15+0.002·|T|), where |T| is the ab-

solute temperature in °C. Pentronic AB was the chosen

manufacturer, which supplied and tested 30 sensors ac-

cording to EN10204. In order to have similar offset in

measurements, the two PT100 with closer response dur-

ing the test were chosen for the ∆T measurements. De-

spite the benefit of fluid immersed measurement, appro-

priate plumbing adaptation is required (Fig. 1). Adaptors

are rather expensive, approximately 60 USD, and hardly

available in Mozambique. The price of the RTD itself is

approximately 56 USD.

b) LM35CZ. LM35CZ are precision integrated-circuit

temperature sensors produced by National Semiconduc-

tor Corporation. Voltage output is linearly proportional

to Celsius temperature with 0 mV as set point for 0°C

and +10.0 mV/°C scale factor; nonlinearity typically

below ±1.4°C is guaranteed over the full range of

55-150°C. Accuracy is ±0.4°C, hence ±4 mV, at 25°C,

up to a typical value of ±0.8°C in extreme conditions.

The price is of approximately 5 USD each. Copper paste

on the surface and good insulation around the pipe must

be carefully provided to have good thermal contact and

low heat losses. Indeed, the sensor could record the air

temperature in the proximity of the pipe instead of the

pipe surface temperature (Fig. 1). Since the device is not

specifically designed for water temperature measure-

ments, it can be successfully used for other applications.

Figure 1. PT100 (left) and LM35 (right) positioning

3) Solar radiation

a) Kipp&Zonen CMP 11. Scientific pyranometer cali-

brated after purchase according to the technical regula-

tions of World Meteorological Institute. Estimated com-

bined expanded uncertainty for the used device is ±1.4%,

corresponding to 8.67 µV/W/m2 of sensitivity at normal

incidence on horizontal pyranometer. Commercial price

is about 4,000 USD.

b) Finsun SRS1000. Basic pyranometer with sensing

element made of single crystal Si-cell. The output volt-

age is 100 mV when exposed to 1000 W/m2 solar radia-

tion. Sensitivity, offset and ageing tests were performed.

Commercial price is approximately 115 USD.

4) Flow meter. Kamstrup 10EVL-MP110 energy and

flow meter was adopted. No cheaper flow meter was

tested.

5) Concentrating thermal and PV/T-hybrid collectors.

Two prototypes of asymmetrical CPC-collectors, one

PV/T and the one thermal, were installed.

6) Solar tracker. A horizontal single axis tracker

(HSAT) was installed. The tracker is based on an engine

driven by Melacs® logger. The software controls the po-

sition of solar panels using time and location as input.

This solution allows a correct positioning without the use

of additional photodiodes-based trackers, thus cutting

costs and maintenance.

3. Results and discussion

N. GENTILE ET AL.

3.1. Data logger

Acquisition devices were connected to both the data

loggers. The resolution of CR1000 is higher than that of

Melacs® and mismatching was expected especially for

the solar irradiance measurement. On the contrary, no

significant difference in recorded voltage was observed

during the tests. At this level of approximation the two

loggers can be considered equivalent. Campbell CR1000

values were used for the following calibrations for pre-

cautionary reasons.

3.2. Pyranometer

Solar irradiation must be properly measured. Three dif-

ferent pyranometers were installed:

 Kipp&Zonen CMP11 LU, the reference pyranometer,

is the property of Lund University, provided with a

recent calibration certificate;

 Finsun SRS1000 new, is the proposed economic

pyranometer, installed in November 2011 (test peri-

od);

 Finsun SRS1000 old, is the proposed economic

pyranometer, installed in January 2011 to test the

ageing effects after about one year;

The pyranometers were mounted on the same flat sur-

face, built-in to the solar collectors (Fig. 2). Hence, sen-

sors follow the panels in the solar tracking.

Figure 2. Two of the installed pyranometers: a) CMP11 LU

and b) new SRS1000

The ageing effect on the SRS1000 is negligible in terms

of differentials, but not in terms of absolute values. In-

deed, a fairly constant overestimation of approximately

5% of solar irradiation was observed in the aged

pyranometer. The same parameter for CMP11 is guaran-

teed by the producer to be lower than 0,5% per year

from. Further investigations have to be carried out to

fully understand the behavior of SRS1000.

The calibration was performed on the aged SRS1000

(Gsrs) through data collected during a sunny day (9th,

November 2011). The photosensitive surface of SR1000

lies slightly below the external edge. This causes reading

errors due to shadows when the solar incidence angle is

close to 90°, i.e. typically sunrise and sunset; random

deviations up to 50% from the reference values of

CMP11 (Gref) are registered in this situation. Calibration

attempts did not take in consideration or weighted less

low those solar irradiance values.

The least squares method was applied to the ratio be-

tween global solar irradiance from the reference sensor

and the tested SRS1000 calculated over the whole day.

The aim was to find a correction curve for which Gref/Gsrs

was as close as possible to 1. Records where Gref<400

W/m2 were excluded for best curve fitting at higher solar

irradiance levels. Linear and logarithmic least squares

were applied, but the results were not satisfactory. In-

stead a slightly more complex polynomial interpolation

was chosen and equation (1) found:

 

. (1)

Fig. 3 shows calibrated values of SRS1000 (Gcal) during

the observed day. Change in the tilt of panels caused the

step around half past ten. Equation (1) was applied to the

series of data recorded on site during November 2011.

The standard deviation of Gcal from Gref was σ=±6,1%.

The provided value is intended along the whole radiation

range, though it is strongly recommended not to rely on

Gcal<200 W/m2.

Figure 3. Calibration of pyranometer SRS1000

3.3. Water temperature sensors

Immersed resistance thermometers based on PT100 are

used as reference. They should guarantee more accurate

measurements than LM35 for three reasons: 1) according

to the product data sheets, the thermal resolution differs

by an order of magnitude, 2) the sensor is immersed in

the fluid, and 3) the devices used are tested and certified

by an accredited laboratory.

Calibration was performed to investigate contingent

measurement error and time shift due to the disadvanta-

geous position of LM35. Sensors were previously tested

and calibrated at LU solar laboratory in controlled condi-

tions. Various LM35 were tested against the same PT100

to check random and/or systematic errors. Negligible

variations between them were registered and a general

behaviour was spotted.

N. GENTILE ET AL.

The collected data were treated in a single elaboration in

order to find a general law of LM35 behaviour against

PT100 reference. Different mean trends were isolated. In

particular, the comparison between LM35s and PT100

showed.

Figure 4. Calibration of LM35

1) Low temperature (up to 30°C). In both steady and

dynamic condition no significant variations of the

registered temperature were found (Fig. 4.a). LM35

temperature can be assumed correct and does not

need any additional calibration.

2) Fast temperature reversal. Slight time shift for LM35

is observed (Fig. 4.b), most probably due to the sen-

sor position (Fig. 1). Subsequently to deepened inves-

tigations on a significant number of fast temperature

reversals, the delay was settled to 1 minute.

3) Warming up to 90°C. Non-linear increasing of tem-

perature underestimation is shown by LM35. The gap

is constant when the rate of warming/cooling is in-

creased/decreased (Fig. 4.c). Thus, an unequivocal

empirical logarithmic relation between the tempera-

tures of LM35 (Tlm35) and the new calibrated temper-

ature (Tcal) was proposed.

  (2)

 

 .

By defining Tpt the temperature recorded by the ref-

erence PT100, equation (2) represents a least squares

interpolation for which the Tpt/Tcal ratio should be as

close as possible to 1. Conditional setting δ=1 at

Tlm35≤30°C avoid an increase in the mean deviation

when the system is running at low temperature for a

long time.

4) High temperature (>30°C) and steady conditions.

Temperature is underestimated, but the LM35 profile

is quite stable (Fig. 4.d). Equation (2) is still valid.

The quality of calibration equation (2) was evaluated

through on site measurement in Mozambique. Measure-

ments were performed continuously for 30 hours. During

this time the system was heated and cooled several times.

Though the boundary conditions, as well as the used

sensors, were slightly different, the standard deviation

was σ=±1.7%. Longer time series are needed in order to

be able to estimate the annual effects for using this type

of correction.

3.4. Calculation example

The energy gain rate q of a solar collector [15] can be

defined by the simplified equation (3):

, (3)

in which the optical efficiency (τα) and the heat loss co-

efficient U are features of the considered collector. In

this example, the related uncertainty of these constants is

neglected. G is the solar irradiance and ∆T=Tmean-Tamb is

the difference between the mean temperature of the col-

lector and the ambient temperature, with

Tmean=(Tin+Tout)/2. Tin and Tout represent respectively the

inlet and outlet water temperature in the collector. By

introduction of the standard deviations, the equation (3)

becomes:

, (4)

Derived standard deviations are calculated according to

the propagation of error law for independent and sto-

chastic variables [16]:







 . (5)

In (5) the standard deviation of Tmean is the result of Tin

and Tout standard deviations combination. For a generic

flat plate solar collector with (τα)=0,87, U=3,83 W/m2K

and when G=1000W/m2, Tin=50°C and Tout=100°C, the

rate of energy gain calculated with the installed cheap

sensors will be q=679±61,45 W/m2. Deviation is ap-

proximately 9% of the measurement. The effect of G in

(4) is predominant. If the equations used were mostly

influenced by T values, the results would be more accu-

rate. Hence, the example is precautionary.

Table 1. Cost and accuracy reduction for the example.

EQUIPMENT

PRICE

(USD)

TOTAL

PRICE

(USD)

COST

REDUCTION

HEAT GAIN

Q [W/M2]

ACCURACY

REDUCTION

SCIENTIFIC

CR1000

1500

5788

93,3%

679±0

9,05%

PT100 (X3)

288

CMP11

4000

TESTED

MELACS

260

390

679±61,45

LM35 (X3)

SRS1000

115

N. GENTILE ET AL.

Presuming that the reference sensors give correct values

without uncertainty, the proposed calculation can be

combined with the equipment cost (tab. 1).

4. Conclusion

Scientific research requires investments in materials and

resources. Universities of developing countries interested

in starting research cannot usually rely on adequate

funding. In the majority of the cases they are obliged to

give up and the knowledge gap constantly increases. This

study concludes that:

 Scientific research in solar energy can be initialized

with fairly low costs. The equipment cost can be cut

by up to 95% through using alternative sensors with a

drop in accuracy of measurement of about 9%. Ap-

proximations in the results obtained with the pro-

posed instruments should be always estimated and

underlined in report and publications;

 A large part of the approximation is due to uncertain-

ty in solar irradiance measurement. Even if the man-

ufacturer could improve the design of only the sensor,

its performance could be easily improved. For future

solar laboratory, the choice should consider the aims

and the needs of the research. Thus, the decision

could consist in finding the best fitting invest-

ment/accuracy ratio for each case. For the example

discussed in this article a pyranometer more accurate

than the SRS1000 is recommended.

 It is strongly recommended to involve local members

from the early stages. It is very important to instill a

sense of belonging and to state clearly the hoped-for

long term aim. By investing in local research, the

weak points of the previous form of foreign aid, e.g.

pre-packed stand alone photovoltaic systems in rural

areas, could be overcome;

 The executed program in Mozambique is intended to

be a suggestion for future similar projects. Different

sensors and building solutions have to be tested in

order to find the best cost-efficient solution. At the

present time, the results and experiences gained are

working as inputs for the design of modular solar la-

boratories to be built in universities and research in-

stitutes of several developing countries;

 In order to make the information available and reduce

the knowledge gap, donors and recipients are en-

couraged to publish their work and results in open

access journals.

5. Acknowledgements

The authors are grateful to the Swedish International

Development Cooperation Agency for sponsoring the

project.

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