Solar Water Heating Systems: Improvement and
Potential Applications
Abstract
The present study involved the thermal evaluation of the locally-manufactured solar water
collector in Jordan using an absorber painted with modified black paint which was prepared by
National Energy Research Center (NERC) at El Hassan Science City and in cooperation with
Industrial Chemistry Center (ICC) at the Royal Scientific Society. Selected materials of nanoparticles were prepared and grinded to smaller size and added to black paint formulas with
varying material type and material-to-black paint ratio. The surface emissivity of each absorber
is measured using AE1 emissometer instrument. The purpose of adding the nano-particles to the
black paint is to reduce the thermal emittance while conserving the thermal absorptance as high
as possible. The thermal emittance of about 0.95 of the conventional collector absorber was
reduced to about 0.70 using the above mentioned modified paint. The thermal losses by the solar
collector were reduced and collector performance was considerably increased. The test results by
the the solar simulator lab at Royal Scientific Society showed that thermal performance of the
modified-absorber collector was increased by about 11% as compared with the conventional
collector.
The study revealed that improving the thermal performance of the locally
manufactured solar collectors by adopting this type of modified paint will be positively reflected
on the solar systems distribution. While the solar water heater distribution for year 2008 shows
that the total area of exiting installed solar water system in Jordan is about 890,000 square
meters, which reduces the CO2 emitting by about 133,000 ton per year.
Introduction
To improve the thermal efficiency of the solar collector, collector surface is deposited coated by
electrical or chemical processes. Collector surface can also be painted with certain modified
paint to improve the collector efficiency. Coatings are characterized by two optical properties:
solar absorptance (), which represents the most fraction of incident solar radiation absorbed by
the surface; and thermal emittance (), which is the magnitude of energy lost from the collector
surface due to the emission of thermal Infra Red (IR) radiation. Since more than 20 years, many
international and experiments were devoted in reducing the emittance of the collector while
maintain the absorptance as high as possible by modifying the absorber coating characteristics.
There are two types of solar coatings or paints known as selective and non-selective coatings.
Non-selective coatings have high  as well as high  (e.g., ordinary black paints with  = 0.900.95 and  = 0.85-0.9). Selective coatings have a high  and low  (e.g., black chrome with  ≈
0.90 and  < 0.5) so they are more attractive for use in solar collectors.
There are several solar systems manufacturing companies established in Jordan. The total
number of the registered solar water heaters manufacturing company, as mentioned by Amman
Chamber of the Industry, is 20 companies located in Amman. Another two registered
manufacturing companies located in Zarqa. Only three of these companies are considered as big
companies regarding to there annual mass productions and manufacturing Flat Plate Collectors
according to the RSS specifications. While other small companies and work shops
manufacturing the solar heaters with less quality. [1]
Jordanian flat plate collectors industry relies on ordinary non-selective dull black paints as solar
absorber painting that causes high thermal loss.
The performance benefit of selective coatings is greatest in evacuated collectors to lowering the
emissivity losses. In flat plate collector and for absorber temperature lower than 100 C,
convection heat transfer begins to dominate if the  is reduced below about 0.5. The collector
heat loss is reduced dramatically if  is reduced from 0.95 to 0.3, but a further reduction in 
from 0.3 to 0.1 brings only a small benefit. Therefore the selective paints with their low cost look
more attractive for flat plates. Generally, paints are cheaper and easier to apply than the coatings
deposited by chemical or electrical processes [2].
The aim of this study is to investigating the thermal impact of the modified paints on the
collector performance by adding certain nano-materials to the dull carbon black paint.
Procedure:
1) Nano-Material Paint Preparation
Dull black carbon paint was first prepared by mixing the carbon black, particle sizes ranging
between 20 t0 44 µm with short alkyd resin. Nano particles of some metal oxides were
prepared and added to the carbon black paint formulas. Preparing the nano-particles was
carried out by Industrial Chemistry Center (ICC) at Royal Scientific Society in El Hassan
Science City. The nano particles selected for this work as additives are Chromium (Cr),
Copper (Cu), Iron (Fe), Zinc (Zn), Titanium (Ti), Phillipsite mineral , Offretite mineral and
Clinoptilolite mineral .
Nano-materials-combination or single material was added to the black paint, respectively.
Nano- materials paint was added to the above carbon paint formulas with varying the
material type.
Different panel surfaces were painted by the following processes:

The panels were cleaned with chemical cleaner to ensure a good paint-panel
adhesion.

A panel were pained with dull black carbon and considered as a base reference panel.

Several panels with different nano-material (modified paints) were painted.

All panels were quick dried by using oven at 200 C.
2) Lab scale spectral measurements.
Seven lab scale absorber panels were painted and dried by electrical oven for a period of
about 24 hours at 200 C. The material-to-black paint ratio was kept 5% during preparing the
mixing paints. The surface emissivity of each panel was measured using emissometer model
AE1 supplied by Service and Device company, consisting of sensing surface of stainless steal
plate and black paint plate insuring constant response to thermal wave (3-30 µm) and
linearity within ± 0.01 emittance units.
Panels Test Results:
The lab scale panels were prepared and tested by using the above instruments. Measurement
results of the lab scale absorber panels can be summarized in Table (1) as follows:
Table (1): Measurement Results
No.
Surface ID
Thickness
Emissivity (ε)
(Micron)
1
Carbon black paint
100
0.90
(Reference)
2
Iron oxide (Fe2O3 )
100
0.91
3
Copper oxide (CuO )
100
0.85
4
Zinc oxide (Zn O)
100
0.89
5
Chromiumoxide
100
0.79
(Cr2O3)
6
Titanium oxide (TiO2)
100
0.81
7
Cr2O3-TiO2
100
0.86
combination
It can be shown from the above table that the emissivity of most of the mixed paints is
high and almost close to the carbon black paint, except panel number 5. The best result
was found when Chromium oxide, was added to the black paint. The emissivity of lab
scale panel which painted with Cr2O3 is 0.79. Therefore, the heat loss for chromiumpainted surfaces was reduced by about 9%, as compared with the standard black paints.
Collector Performance Lab Test
Two flat plate collectors were prepared in order to be tested by the solar simulator lab test
at RSS. One collector was painted with carbon black paint while the second one was
painted with the chromium- carbon black combination. These collectors were
manufactured at local manufacturing company (NUR Company).
Solar collector with geometrical and physical properties is shown in Table 1.
Table 1 Design parameters for solar flat-plate collector
Property
Value
Width × length
0.75 × 1.75 m
Riser pipe diameter
12 mm (½ “)
Absorber material
steel
Number of Riser
7
Number of glaze
1
Insulation thickness
Slope
Azimuth
50 mm
45°
Tracking the sun
Results and Discussion
Thermal performance of collectors was evaluated by using solar lab at RSS and
efficiency.
Efficiency curves for solar collectors shown in Figure 1 are appended with stagnation
temperatures. Stagnation temperatures are the absorber temperatures achieved in the state
of no heat removal from collector given for reference extreme climatic conditions
(irradiation 1000 W/m2, ambient temperature 30 °C) [3] and represent the requirements
for temperature resistance of materials used in solar collectors.
Figure 1 shows that the stagnation temperature for the modified (selective) collector was
increased by about 19 °C. Therefore the opportunity of using these collectors for wide
applications such as space heating, and industrial processes will be increased.
It is obvious that the collector with low-emissive absorber painting will achieve lower
heat loss and first derivation (slope) of efficiency curve will show lower values compared
to the non-selective alternative. It was also found from the above figure that the optical
collector efficiency was increased by about 4.5%. Moreover, the efficiency slope was
also improved by about 15%.
Figure (1): Efficiency curves for solar collectors with different absorber paints
The actual improvement can be found by estimating the annual useful heat that can be
gained using each of the collectors as applied for domestic hot water system. Of shortcut
method program available, F-Chart [4] is one of the most desirable packages since it is
based on monthly average weather data. Monthly weather data used for Amman city were
provided by the Jordanian Meteorological Department [5].
The results shows annual difference heating delivered about 277 kWh per square meter of
collector, and the annual thermal performance for the modified collector was improved
around 11% over the existing local manufactured collector.
This modification on solar flat plate collector will increase the market penetration of the
local manufactured so that it will competes the exported solar collector and therefore, will
considerably reduce the CO2 emission in Jordan.
A survey was made by Department Of Statistics (DOS) in Jordan in 2009 for the Housing
Units in 2008 and by referring to the information provided by National Energy Research
Center regarding to the distribution of the solar heater system in the commercial and
industrial building, it was shown that the total area of exiting installed solar water system
for year 2008 in Jordan is about 890,000 square meters, which reduces the CO2 emitting
by about 133,000 ton per year [6].
Conclusions
According to the results for modified solar collector by adding nano-chromium particles to
the carbon black paint, the following conclusion can be derived:
1. The optical collector efficiency was increased by about 4.5%.
2. The efficiency slope was also improved by about 15%.
3. The annual thermal performance for the modified collector was
improved around 11% over the existing local manufactured collector.
References
1 S. Jaber, 2010, “Survey of companies manufacturing solar water heaters in Jordan”, GTZ.
2 Ari Rabl, 1980, Active Solar Collectors and Their Applications.
3 Tomas Matuska, “DETAILED MODELING OF SOLAR FLAT-PLATE COLLECTORS WITH DESIGN
TOOL KOLEKTOR ”, 2009, Eleventh International IBPSA Conference.
4 F-CHART User’s Manual, micro computer version 6.58, F-CHART software.
5 Jordan Climatologically Data Handbook, Season 1922 – 1998, Meteorological Department, Jordan.
6 Jordan in Figures, Department Of Statistic, 2008, Amman, Jordan.