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A Review: Solar Water Heating Systems


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This paper reviews and encompasses the technological developments in the filed of solar thermal extraction and storage. A timeline of over a century of research efforts is prepared and a performance based comparison is presented. To conclude, characteristics of an ideal solar water heating system are furnished.
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NCEVT’14 Sachin Tadvi 1
A Review: Solar Water Heating Systems
Tadvi Sachin Vinubhai,
PG Student, Department of Mechanical Engineering,
Parul Institute of Engineering & Technology, Limda, Vadodara-391760(Gujarat-INDIA)
E-mail ID:
Jain Vishal R,
Assistant professor, Department of Mechanical Engineering,
Parul Institute of Engineering & Technology, Limda, Vadodara-391760(Gujarat-INDIA)
E-mail ID:
Dr. Keyur Thakkar,
Head of Department, Department of Mechanical Engineering,
Babaria Institute of Technology, Vadodara - Mumbai NH # 8, Varnama, Vadodara - 391240(Gujarat-INDIA)
E-mail ID:
In the present review paper, the existing solar water heating systems are studied with their applications. Nowadays, hot water is used
for domestic, commercial and industrial purposes. Various resources i.e. coal, diesel, gas etc, are used to heat water and for steam
production. Solar energy is the chief alternative to replace the conventional energy sources. The solar thermal water heating system
is the technology to harness the plenty amount of free available solar thermal energy. The solar thermal system is designed to meet
the energy demands. The size of the systems depends on availability of solar radiation, temperature requirement of customer,
geographical condition and arrangement of the solar system, etc. Therefore, it is necessary to design the solar water heating system
as per above parameters. The available literature is reviewed to understand the construction, arrangement, applications and sizing
of the solar thermal system.
Solar energy collector, Active & Passive system, Heat
transfer fluid.
The sun has been a powerful presence and force
throughout the history of human existence on earth. It
has been regarded by many cultures as a god of one
form or another, and understood by most to be the
ultimate source of life on this planet. It has also been
intentionally exploited by many clever means over the
centuries, in order to better utilize this life giving
energy. As far as renewable energy sources go, the sun
represents the best and most stable we have. It is
infinite with respect to all practical timescales,
immensely powerful, understood and predictable in its
overall trends and patterns, and for the foreseeable
future beyond anthropogenic effects. In short, the
perfect energy source; but it is not without difficulties.
Solar heater is a device which is used for heating the
water, for producing the steam for domestic and
industrial purposes by utilizing the solar energy.
Modern systems designed for capturing the suns energy
and transferring it to water, either for immediate use or
as a storage medium, have been studied and put to use
since the 1970’s, when they were first used for pool
heating in California. Continued research and
innovation has resulted in products feasible in much
colder and less sunny climates today (Bennet T, 2007).
The history of using the sun for energy goes way back
to the Ancient Greeks and Romans as their buildings
were constructed such that the rays of the sun provided
light and heat for indoor spaces. The Greek philosopher
Socrates wrote, “In houses that look toward the south,
the sun penetrates the entrance in winter.” Romans
advanced this art by covering the openings to south
facing building with glass, in order to retain the heat of
the winter sun.
NCEVT’14 Sachin - Keyur 2
The history of utilizing solar energy in recent times
dates from 1861 when Mouchout developed a steam
engine powered entirely by the sun and in 1883
American inventor Charles Fritts described the first
solar cells made of selenium wafers.
The Arab oil embargo in 1973 confirmed the degree to
which the western economy depended upon there,
being a cheap and reliable flow of oil. In the 1970s it
was thought that through massive investment in
funding and research, solar photovoltaic costs could
drastically reduced, such that eventually solar cells
could become competitive with fossil fuels.
In the mid 50’s Israeli engineer, Levi Yissar, suggested
the use of solar energy for heating up domestic water
with Israelis responding by the mass purchasing of
solar water heaters. By 1983, 60% of the population
heated their water from the sun. When the price of oil
dropped in the mid 1980s, the Israeli government
required its inhabitants to heat their water with the sun.
Today, more than 90% of Israeli households own solar
water heaters.
By the 1990s, the reality was that the costs of solar
energy had dropped as predicted and the huge PV
market growth in Germany and Japan from the 1990s
to the present has boosted the solar industry.
Furthermore, such large PV productions are creating
steadily lowering costs. Meanwhile, the heating of
water by solar energy is an increasingly cost effective
means of lowering gas and electricity demand (Ken
Butti, John Perlin, 1980).
In the 19th century, people used a stove to heat water
by burning pieces of wood or coal. In cities, the
wealthier heated their water with gas manufactured
from coal. In many areas, wood, coal or gas could not
be easily obtained and hence such fuels were often
expensive. To avoid these problems, a much easier and
safer way to heat water was created. This was achieved
by placing outside a black painted metal tank full of
water to absorb solar energy. The disadvantage was
that even on clear hot days it usually took from
morning to early afternoon for the water to get hot. As
the sun went down, the tank rapidly lost its heat
because it had no insulation (Charles Smith, 1995).
The history of Solar Water Collectors in Greece started
when the first collectors were imported from Israel in
the mid 70’s. The Greek Solar Industry Association
was established in 1978 and the promotion of solar
systems started around the same period. The
technology of the Solar Water Heaters was largely
accepted by the market and small units of 2m
installed in order to cover the needs of a household
(SHC annual report, 2001).
Solar technologies are commonly grouped into three
major categories, generally differing in the ways they
collect, store and use energy.
Passive solar systems involve direct utilization of the
sun’s radiation as light or possibly heat. Examples
include energy efficient windows, skylights,
greenhouses, and hybrid lighting fixtures, which use
fiber optic cable to transmit sunlight into interior
rooms. Next are solar thermal, which collect and use
the sun’s energy as heat. They are different from direct
heating in their ability to store thermal energy for later
use. Modern applications include domestic and
industrial water heating, air and space heating, radiant
slab heating, and even the operation of heat pumps and
sterling engines (Bennet T, 2007).
The energy and the temperature level required to be
supplied to carry out everyday tasks will vary.
Generally, a domestic hot water supply at temperatures
in the range of 50 to 60 degree Celsius is considered to
be acceptable (SOPAC Technical Report, 1999).
The performance of a solar water heating system
depends on the following factors.
Ambient conditions
The amount of incident radiation determines the
absorbed solar radiation by the collector while the
ambient temperature determines the thermal losses
from the collector. Cloudy conditions limit the beam
isolation levels and thus the radiation absorbed by the
collector especially the concentrating collectors (Duffie
J.A and Beckman W.A, 1991).
Collector orientation and tilt
Geographic orientation and collector tilt can affect the
amount of solar radiation the system receives.
Fig. 1 Solar Collector orientation
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Collector orientation is critical in achieving maximum
performance from a solar energy system. In general,
the optimum orientation for a solar collector in the
northern hemisphere is true south (azimuth of 180°) as
illustrated in Figure 1. However, recent studies have
shown that, depending on the location and collector tilt,
the collector can face up to 90° east or west of true
south without significantly decreasing its performance.
The optimum tilt angle for solar collector is an angle
equal to the latitude (Duffie J.A and Beckman W.A,
Collector array arrangement
The performance of the collector array depends on how
the collector modules are connected. In parallel
connection, module inlet and outlet ports are fed to the
common respective headers. Assuming identical
modules, fluid inlet temperature is the same to all
modules in the array.
This is also true to fluid outlet temperature. The
performance of the collector array is thus the same as
the performance of the individual collector. In series
connection, the performance of the second and
subsequent modules will not be the same as the first
because its inlet temperature is the outlet temperature
of the first (Duffie J.A and Beckman W.A, 1991).
The transport fluid flow rate
Low collector fluid flow rates of about 1 to 4 gallons
per minute increases the thermal performance of the
collector by increasing the degree of storage tank
thermal stratification. In a stratified tank, the
temperature of fluid at the bottom of the storage tank is
lower than at the top. Collector inlet temperature is
reduced because the collector inlet fluid is fed from the
bottom portion of the tank. Lower inlet collector
temperature reduces thermal losses. This results in
increased useful energy gain (Duffie J.A and Beckman
W.A, 1991).
Solar water heating systems are classified depending
on how the domestic water is heated or how the heat
transfer fluid (water or antifreeze fluid) flows through
the collector. Based on this, there are basically two
types of solar water heating systems, namely; Direct
(open loop) and Indirect (closed loop) water heating
systems which can either be passive or active (Roger
Taylor, 2006).
Direct systems heat up water as it flows directly in the
collector whiles indirect systems heat up water through
a heat exchanger employed between the collector and
the hot water storage tank. Active systems use
electrically driven pumps to circulate water or another
heat absorbing fluid, and sometimes use electrically
operated valves for freeze protection. Passive systems
have no electrical pumps. They rely upon convection to
circulate hot water through the collector and storage
tank (Duffie J.A and Beckman W.A, 1991).
Passive systems
In passive systems, hot water is either stored in the
collector itself or is transferred to a storage tank located
above the collectors by means of a thermosyphon.
Passive systems do not employ pumps to circulate
water or collector fluid. Two types of passive systems;
thermosyphon systems and integral collector storage
systems are briefly described below.
Thermosyphon systems
A typical thermosyphon system is indicated in Figure.2
As the sun shines on the collector, the water inside the
collector flow-tubes is heated. As it heats up, this water
expands slightly and becomes lighter than the cold
water in the solar storage tank mounted above the
collector. Gravity then pulls heavier, cold water down
from the tank and into the collector inlet. The cold
water pushes the heated water through the collector
outlet and into the top of the tank, thus heating the
water in the tank.
Fig. 2 Thermosyphon system
A thermosyphon system requires neither pump nor
controller. Cold water from the city water line flows
directly to the tank on the roof. Solar heated water
flows from the rooftop tank to the auxiliary tank
installed at ground level whenever water is used within
the residence. This system features a thermally
operated valve that protects the collector from freezing.
It also includes isolation valves, which allow the solar
system to be manually drained in case of freezing
NCEVT’14 Sachin - Keyur 4
conditions, or to be bypassed completely (Harrison J,
Tiedeman T, 1997).
Integral collector storage (ICS) systems
In integral collector storage (ICS) or batch systems,
water is heated directly by the sun and the storage tank
serves as the solar collector. Batch water heaters are
almost always passive systems in which hot water is
delivered from the solar heated tank to a backup tank or
the point of use by the water pressure in the house.
Most designs use local main water pressure to circulate
water in the collector. Water may also flow due to
buoyancy forces set up due to differential heating on
the collector and valves control the flow direction.
These systems are relatively cheaper than
thermosyphon systems. The system is simple because
pumps and controllers are not required. On demand,
cold water from the house flows into the collector and
hot water from the collector flows to a standard hot
water auxiliary tank within the house. A freeze
protection valve installed in the top plumbing near the
collector opens to allow relatively warm water to flow
through the collector to prevent freezing (Harrison J,
Tiedeman T, 1997).
Direct active systems
Direct (Open Loop) Active Systems are similar to
thermosyphon systems in that they are direct systems
that use a solar collector separate from the storage tank.
The difference with direct active systems is that they
use an electric pump to circulate water from the storage
tank to the collector, and back to the storage tank.
These systems always require a check valve to prevent
reverse thermosyphoning at night (Harrison J,
Tiedeman T, 1997).
Indirect active systems
Glycol antifreeze systems are active, indirect systems
with a heat exchanger. Freeze resistant propylene
glycol is circulated through the solar collector(s) and
heat exchanger, while household water is circulated
from the storage tank through the heat exchanger. The
household water is heated inside the heat exchanger
and then stored inside the tank until needed. The
antifreeze and water (if an external heat exchanger is
used) are circulated using either AC pumps powered
from the utility grid or DC pumps powered by a solar
electric PV module.
The most common types of solar water heating system
in temperature climate regions are indirect active
systems mainly to protect the systems against freezing.
Direct active systems are used in tropical climates
where freezing is not a problem and domestic water is
treated, or in cases water is fed directly from water
utility supply line (which normally treats domestic
water). Active system whether direct or indirect can be
easily retrofitted to already existing water heaters
because the storage tank can be placed at any place
unlike thermosyphon systems which require a storage
tank always above the collector (Harrison J, Tiedeman
T, 1997).
Solar energy collectors work in a similar manner to
heat exchangers in that they transform one form of
energy, solar radiation to another in the form of hot
water. The component that allows this exchange of
energy is a solar collector. The solar collector absorbs
radiation and converts it into heat. This heat is then
transferred to a fluid which is usually water or a glycol
mixture, flowing through the collector. The energy that
is collected from the process just described is then
transferred from the fluid either directly to where it is
required or to a solar water heating storage tank from
which it can be used when necessary. There are two
ways that solar collectors can be mounted; stationary or
tracking. If the collector is to be mounted in a
stationary position calculations are carried out at the
design stage as to the optimum inclination of the panels
for location and usage. The collectors will then remain
fixed to this tilt angle all year round and for the
lifespan of the system. In a tracking position the
collector’s inclination will change as the sun’s angle in
the sky changes hour to hour and day to day in order to
receive the optimum amount of radiation (Kalogirou,
S.A, 2004).
Flat plate collectors
Flat plate collectors currently are currently
manufactured in two different forms. Firstly collectors
using liquid with no glazing are manufactured using a
black absorbent polymer coating without an insulated
backing. The manufacturing costs of these particular
collectors is extremely low but with this comes a
negative as they also have high heat losses to the
environment making them inefficient. Such collectors
are not suitable when used in low temperature
applications such as swimming pools and industrial
The second form of flat plate collector uses glazing
(Fig. 3) and makes use of an absorber plate that absorbs
the solar radiation and in turn heats the copper tubes
that contain the transfer liquid. The side of the casing
and underside of the absorber plate are heavily
insulated to reduce conduction losses while in
operation. The liquid tubes are sometimes welded to
the absorbing plate, or they can be manufactured as
part of the plate. These tubes are then connected at both
ends by large diameter header tubes. These collectors
NCEVT’14 Sachin - Keyur 5
also utilize a transparent cover to reduce the convection
losses from the absorber plate by trapping a layer of
stagnant air between the absorber plate and the glass
(Kalogirou, S.A, 2004).
Fig. 3 Flat plate collector
Evacuated tube collectors
Evacuated tube collectors are in most cases more
efficient than most flat plate collectors, but as a result
of this increased efficiency are also more costly due to
their complex design. Due to the absorber being
mounted in an evacuated and pressure-proof glass tube,
conductive and convective losses are minimized
increasing efficiency. Evacuated tubes work efficiently
at low radiation levels with high absorber temperatures
and can provide higher output temperatures than flat
plate collectors and they can be used in applications
where the demand temperature is 50–95 °C or in colder
climates. There are currently two principal types of
evacuated tube collectors on the current market, direct
flow and heat pipe. The first type is known as a direct
flow evacuated tube and as shown in Fig. 4 below
where the heat transfer liquid is pumped in the tubes.
Fig. 4 Evacuated tube collector
The second type of collector shown in Fig. 5 utilizes
heat pipes inside vacuum sealed glass tubes with a
reflector also used to further increase the ability to
absorb radiation. The collector operates by vapour
rising to the heat exchanger shown on the left of Fig. 5,
where heat is then transferred to the systems primary
circuit and condensed fluid flows back down the heat
pipe. Choosing the correct collector can depend on the
temperature of hot water required in the system and the
climate where the system is installed. The suitability of
a collector to a system therefore depends on the rated
efficiency of the panel and suitability to the
application. The vacuum envelopes in evacuated tube
collectors reduce conduction and convection losses,
which enables the collectors to operate at higher
temperatures than flat plate collectors. This advantage
means that these collectors are always used for high
temperature applications. They also have the ability to
absorb both direct and diffuse radiation like flat plate
collectors but at lower incident angles their efficiency
is greater. This effect tends to give Evacuated Tube
Collectors an advantage over Flat Plate Collectors in
day-long performance (Kalogirou, S.A, 2004).
Fig. 5 Heat pipe solar collector
Parabolic concentrating collectors
Parabolic concentrators shown below in Fig. 6 are
rarely used in the European climate but they are very
useful for high temperature applications from 100-
200°C, where the efficiency of the collector
outperforms that of vacuum tube collectors. In very hot
countries where solar cooling systems are used,
temperatures levels of 150°C or higher are easily
Fig.6 Parabolic concentrating collectors
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Some feasibility studies and concept designs exist
where parabolic concentrators can be used on
commercial buildings however to date they have not
been used in that scenario. Parabolic collectors rely
heavily on direct irradiance and climates with a high
direct irradiance proportion and little cloud cover are
best suited for their use. According to Eicker (2003
p.48) “The investment costs of parabolic collectors are
about 300€/m². The solar heat costs can be as low as
0.045 €/kWh on a Turkish site with 1900 kWh/m²
direct normal irradiance and 0.11 €/kWh on a southern
German site with 890 kWh/m²” (Eicker. U, 2003).
There are two main types of solar water heater systems:
passive and active. Active systems integrate pumps and
rotary elements and are therefore very expensive.
Passive systems use natural water circulation, gravity,
and/or pressurized water systems. Passive solar water
heater systems are much less expensive than their
active counterparts and are easier to maintain and
(Soteris A. Kalogirou, 2004) presents a survey of the
various types of solar thermal collectors and
applications. All the solar systems which utilize the
solar energy and its application depends upon the solar
collector such as flat-plate, compound parabolic,
evacuated tube, parabolic trough, Fresnel lens,
parabolic dish and heliostat field collectors which are
used in these system. The solar collectors are used for
domestic, commercial and industrial purposes. These
include solar water heating, which comprise
thermosyphon, integrated collector storage, direct and
indirect systems and air systems, space heating and
cooling, which comprise, space heating and service hot
water, air and water systems and heat pumps,
refrigeration, industrial process heat, which comprise
air and water systems and steam generation systems,
desalination, thermal power systems, which comprise
the parabolic trough, power tower and dish systems,
solar furnaces, and chemistry applications.
Table 1. Comparison of the Collectors
(K. Sivakumar) represent the design of Elliptical heat
pipe flat plat solar collector and tested with a collector
tilt angle of 11° to the horizontal. Experimental
analysis of the effect of condenser length/evaporator
length (Lc/Le) ratio of the heat pipe, different cooling
water mass flow rates and different inlet cooling water
temperature were analyses. Five numbers of elliptical
heat pipes with stainless steel wick has been fabricated
and used as transport tubes in the collector. Copper
tube has been used as container material with methanol
as working fluid of the heat pipe. These heat pipes
were fixed to the absorber plate of the solar collector
and the performance of elliptical heat pipe solar
collector has been studied and results were compared.
It has been found from the experimental trials that the
elliptical heat pipe solar collector having Lc/Le ratio of
0.1764 achieved higher instantaneous efficiency.
(B Sivaraman and N Krishna Mohan, 2005)
represents experiments on the effect of L/d ratio of heat
pipe on heat pipe solar collector. Two solar collectors
with different L/d
have been designed and fabricated.
A heat pipe with stainless steel wick replaces the
transport tubes of the solar collector. Copper and
stainless steel were used as container and wick material
and methanol was used as working fluid of heat pipe.
Heat pipes are designed to have heat transport factor of
around 194 W and 260 W of thermal energy.
Experiments were conducted during summer season
with a collector tilt angle of 13o to the horizontal. The
collector with L/d
ratio of 52.63 was found to be more
efficient than the collector with L/d
ratio of 58.82. This
improved efficiency is due to increase in heat transport
factor of heat pipe, which increase with decrease in
(Hussain Al-Madani, 2006) studied a batch solar
water heater in Bahrain consisting of an evacuated,
cylindrical glass tube. Water runs through copper coils,
which act as collectors, located within the glass tube.
Side-by-side testing of prototypes resulted in a
maximum temperature difference between the inlet and
outlet of the cylindrical batch system of 27.8°C with a
maximum efficiency of 41.8%. Al-Madani determined
the cost of manufacturing the cylindrical batch system
to be $318, slightly less expensive than typical flat
plate collectors of $358.
(Dharamvir Mangal, Devander Kumar Lamba,
Tarun Gupta, Kiran Jhamb, 2010) presents
acknowledgement to one of the latest solar water heater
which is evacuated solar water heater based on a
thermo siphon principle used for heating water for
domestic purposes in household by utilizing solar
radiations. As the air is evacuated from the solar tube
to form a vacuum, this greatly reduces conductive and
convective heat loss from the interior of tube. As a
result wind and cold temperature have less effect on the
NCEVT’14 Sachin - Keyur 7
efficiency of evacuated solar water heater. Result of
less heat loss is fast heating of water as compared to
flat plate solar water heater/collector. This paper
introduced the benefits of evacuated tube solar water
heater. In India, it is still new model of solar water
heater which can be used in our household to face the
challenge of climate change, global warming, energy
crisis etc. When comparing peak efficiency levels it
may seem that there is little difference between flat
plate and evacuated tubes, in fact flat plate may
actually be higher, but this is during minimal heat loss
conditions. When averaged over a year evacuated tube
collector have a clear advantage.
(K. S. Ong and W. L. Tong, 2011) presents a System
performance of solar water heaters depend upon
collector and storage tank design and sizing and
weather conditions (solar radiation intensity and
ambient temperature). Short and long term
performance tests were conducted on natural and force
convection U-tube and heat pipe evacuated tube solar
water heaters. The test procedures employed enabled
comparative performances of solar water heating
systems to be made even when they were tested at
different times of the year. The experimental results
showed that the natural convection heat pipe system
was capable of heating water to 100˚C and performed
best among the systems tested.
The energy saved from using a solar water heating
system helps to reduce domestic energy demand from
power utilities. A solar water heater is a long-term
investment that will save money spent on water heating
after the system has paid for itself. In addition to the
reduced electrical energy and cost savings from water
heating, there are several other benefits derived from
using the sun’s energy to heat water. Most solar water
heaters come with an additional water tank, which
feeds the conventional hot water tank. Users benefit
from the larger hot water storage capacity and the
reduced likelihood of running out of hot water.
Some solar water heaters do not require electricity to
operate. For these systems, hot water supply is secure
from power outages, as long as there is sufficient
sunlight to operate the system. Solar water heating
systems can also be used to directly heat swimming
pool water, with the added benefit of extending the
swimming season for outdoor pool applications (Ret
screen, 2012).
Most of the solar energy applications are concerned
with trapping sunlight as photovoltaic (PV) heat.
Because of the low energy density of sunlight, the
higher the temperature needed the more complicated
and expensive the system will be. Depending on the
range of temperature use, solar thermal applications are
divided into the three broad categories:
1) Low-temperature applications (below 100°C), such
as solar drying, hot water supplies, cooking.
2) Medium-temperature applications (below 150°C),
such as refrigeration, industrial process heat, etc.
3) High-temperature (above 150°C) applications, such
as electricity generation (Roger Taylor, 2006).
Renewable energy research has become increasingly
important since the signing of the Kyoto Protocol.
Solar water heating (SWH) is one of the most effective
technologies to convert solar energy into thermal
energy and is considered to be a developed and
commercialized technology. However, there exist
opportunities to further improve the system
performance to increase its reliability and efficiency. A
concise review primarily on the design features and
related technical advancements of the SWH systems in
terms of both energy efficiency and cost effectiveness
has been presented. Several solar water heating designs
have been introduced in the market and are more
commonly utilized in the tropical regions of developing
countries. Recent developments in heat pipe based
solar collector technology exhibit a promising design to
utilize solar energy as a reliable heating source for
water heating applications in solar adverse regions.
Heat pipe based solar water heating is influenced by
many factors including the nature of the refrigerant,
due to the environmental concerns.
Al-Madani, Hussain (2006). “The performance of a
cylindrical solar water heater.” Renewable Energy Vol. 31,
pp 1751-1763.
Bennet T. (2007). “Solar thermal water heating, a simplified
modeling approach”.
B Sivaraman and N Krishna Mohan (2005). “Experimental
analysis of heat pipe solar collector with different L/di ratio
of heat pipe”, Journal of Scientific & Industrial Research,
Vol. 64, pp 698-701.
Charles Smith (1995). “History of Solar Energy Revisiting,
Past Solar Power Technology Review”.
Data-Annual Report (2001). “International Energy Agency of
Solar Heating and Cooling Programme”.
Dharamvir Mangal, Devander Kumar Lamba, Tarun Gupta,
Kiran Jhamb (2010). “Acknowledgement of Evacuated
Tube Solar Water Heater Over Flat Plate Solar Water
Heater” International Journal of Engineering (IJE), Vol. 4,
pp 279-284.
Duffie J.A and Beckman W.A. (1991). “Solar Engineering of
Thermal Processes”, Second Edition, Wiley-Interscience,
New York.
Eicker, U (2003). “Solar Technologies for Buildings” West
NCEVT’14 Sachin - Keyur 8
Harrison J, Tiedeman T (1997). “Solar Water Heating
Options in Florida”, Florida Solar Energy Centre. Rpt:
Ken Butti, John Perlin (1980) “A Golden Thread,” Van
Nostrand Reinhold Company.
K. Sivakumar, N. Krishna Mohan and B. Sivaraman (2005)
“Performance analysis of elliptical heat pipe solar
collector” Indian Journal of Science and Technology.
K. S. Ong, W. L. Tong, Sheriwati, K. Low (2011). “System
Performance of Heat Pipe Solar Water Heaters” 10th IHPS,
Taipei, Taiwan, pp 261-266.
Ret screen (2012).
Roger Taylor (2006). Solar thermal technology and
applications”, NREL, pp 7.
SOPAC Technical Report 297 (1999). “Energy Unit, South
Pacific Applied Geosciences Commission”.
Soteris A. Kalogirou (2004). “Solar thermal collectors and
applications.”, Progress in Energy and Combustion Science
30, pp 231–295.
... There are two main types of solar hot water systems: active and passive (Fig. 1) [6,35,39]. In active systems (Fig. 1b) a pump is used for the circulation of water between the tank and the solar collectors, in passive (thermosyphon) systems the circulation of water is due to gravitational forces. ...
... Therefore, solar systems are becoming increasingly popular not only in the southern regions, but also in temperate climates regions. The main elements of such systems are usually solar collectors, which depending on the design features can be of different types [35]. The most common are flat collectors, the effectiveness of which has been confirmed by a number of scientific papers [3,8,37], as well as vacuum solar collectors [33]. ...
Full-text available
The article is devoted to solving the urgent problem of assessing the efficiency of flat solar collectors in hot water supply systems of single-family homes in temperate climate regions. Ten cities of Ukraine with different geographical location and climatic parameters were selected for comparison. Evaluation of the efficiency of solar collectors was carried out by two indicators: the solar share and the efficiency of the solar collector. Graphical dependences of results of analytical researches of an estimation of efficiency of use of flat solar collectors are resulted. It is determined that the average annual solar fraction for selected cities of Ukraine is quite high and is 0.61. The average annual efficiency of the solar collector for selected cities of Ukraine is 0.55, which allows us to say about the sufficient efficiency of flat solar collectors in hot water supply systems of single-family homes. It is established that the intensity of solar radiation and ambient air temperature in this region have the greatest influence on the efficiency of a flat solar collector in hot water supply systems.KeywordsRenewable energy sourcesEnergy saving technologiesHot water supply systemSolar collectorSolar fractionSolar collector efficiency
... The PTSC system is the most important type of solar concentrators because it produces a high output power [6,7]. The PTSC system is a parabolic-shaped reflector that focuses the solar radiation from the sun on a receiver tube at its focal point [8]. The collector tracks the sun to make sure the exact focus of the solar radiation is on the receiver tube [9]. ...
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A solar water heating system has been fabricated and tested to analyze the thermal performance of Parabolic Trough Solar Collector (PTSC) using twisted tape insert inside absorber tube with twisted ratio about TR=y/w=1.33. The performance of PTSC system was evaluated by using three main important indicators: water outlet temperature (Tout), useful energy and thermal efficiency (ηth) under the effect of mass flow rate (ṁ) ranges between 0.02 and 0.04 Kg/s with the corresponding of Reynolds number (Re) range (2000 to 4000). In a parallel, a fuzzy-logic model was proposed to predict the thermal efficiency (ηth) and Nusselt number (Nu) of PTSC depending on the experimental results. The fuzzy model consists of five input and two output parameters. The input parameters include: solar intensity (I), receiver temperature (Tr), water inlet temperature (Tin), water outlet temperature (Tout) and water mass flow ( ) while, the output include the thermal efficiency (ηth) and Nu. The final results indicate that, owing to the mixture of the swirling flow of the perforated twisted-tape insert, the perforated twist tape insert enhances the heat transfer characteristics and the thermal efficiency of the PTSC system. More specifically, the use of perforate twist tape inserts enhanced the thermal efficiency by 4% to 4.5% higher than smooth absorber tube. Also, the predicted values were found to be in close agreement with the experimental counterparts with accuracy of ~92 %. So, the suggested Fuzzy model system would have high validity and precision in forecasting the success of a PTSC system compared to that of the traditional model. Pace, versatility, and the use of expert knowledge for estimation relative to those of the traditional model are the advantages of this approach.
... Recently utilizing solar water heating systems in the residential sector is arguably one of the most energy-efficient technique of producing domestic hot water, as the primary source "sunlight" for energy is renewable, competitive and cost effective. Most solar water heaters come with auxiliary heaters that make users benefit from reduced running out of hot water [1][2] [3]. Also, some SWH do not require electricity to operate, where systems are directly used to heat water, as in the swimming pool applications to extend the outdoor swimming season [4]. ...
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Legionella is a kind of bacteria that has been detected by many researchers in different Water Heating Electrical (EWH) or solar (SWH) systems installed at various places. In the capital city Tripoli-Libya, most of water heater systems used are of electric type. Simultaneously, over 100 solar water heating (SWH) systems provided with electric heaters were installed under the supervision of the Centre for Solar Energy Research and Studies (CSERS) in the residential buildings in Tripoli in the period between (2000 and 2020). Ten hot water samples were collected from the outlet points in SWH systems and 43 water samples from different water draining points at Corinthia hotel and Palm City Residences water systems, for the purpose of legionella detection and enumeration in the systems. A questionnaire was designed and distributed to be filled by the 10 SWH system users whom the ten water samples were taken from. The purpose was to collect information about the building, the hot water system, and the user's satisfaction. As the water source is untreated ground water from private wells, analysis of Escherichia coli (E.coli), total Coliform bacteria and total bacterial count were conducted to see whether any other probable bacteria kind is available. According to the results obtained, both 43 samples and 10 SWH samples investigated are free of legionella bacteria, while the total bacteria count for 4 out of 10 SWH systems was less than 60 CFU/g. This was due to water temperature not lowered to the bacteria colonisation temperature, and the daily water temperature gained from solar energy was high enough to be more than 55°C for at least an hour daily and maximum daily temperature exceeds 60°C for 80 days in addition to summer time, which is high enough to destroy legionella bacteria
... Solar water heaters are classified according to their dependency on the heating capacity and fluid applied for heat transfer (water or antifreeze fluid) through the collector. Solar water heaters are usually classified into two groups, namely, direct or indirect, which can be further subdivided into active or passive systems [54]. In direct systems water is heated inside the collectors, whereas indirect systems require a heat exchanger between the collector and a hot water storage tank. ...
It is estimated that the solar energy provided to the Earth in 1 h could satisfy the global energy needs for 1 year. Solar energy is an abundant, clean, and inexhaustible source of energy. Therefore it is necessary to find an efficient way of harnessing this energy, and the solar tracking system is a result of this quest. The efficiency of solar systems increases by using solar tracking systems which can track the position of the sun according to the season and time. Solar energy has many applications such as solar water heating, solar heating of buildings, solar cooking, electric power generation, and many more. Algae cultivation utilizes light, carbon dioxide, and water simultaneously to produce biomass in which light is the most crucial factor. Solar trackers help to overcome photoinhibition, thereby stabilizing photosynthesis to maximize the yield of biomass in the cultivation of algae. Microalgal biomass is an unique energy source since it profitably stores solar energy which can then be converted further into expedient biofuels. The cost of harnessing solar energy includes the costs of procurement, operation, maintenance, and end of cycle. This chapter provides an extensive account of the utilization of solar radiation in the cultivation of algae and the subsequent thermal conversion for bioenergy production.
... Taking into account the low solar irradiance in U.K. the authors have concluded that the potential of solar thermal systems to contribute to a more sustainable domestic energy supply in U.K. is limited. A review of solar water heating systems has been presented by Vinubhai et al. [12]. The authors have stated that solar water heating is one of the most effective technologies to convert solar energy into thermal energy and it is currently a developed and commercialized technology. ...
Conference Paper
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The main aim of this experimental work is enhancing the thermal performance of a modified PTSC system by using a corrugated absorber tube with a Fuzzy model system to predict the thermal efficiency (ηth) and Nusselt number (Nu). The experimental work is carried out at mass flow rates (m˚) of 0.02 Kg/s, 0.025 Kg/s, 0.03 Kg/s, 0.035 Kg/s, and 0.04 Kg/s. The Reynolds number (Re) were determined in the ranges of 2000 to 4000. According to the data are obtained in the experimental work, the fuzzy model of the PTSC system has been created considering five inputs and two outputs data. The input parameters include the inlet water temperature (Tin), the outlet water temperature (Tout), receiver temperature (Tr), mass flow rate (m˚), and solar intensity (I). While the output parameters include the thermal efficiency (ηth) and Nusselt number (Nu) of the PTSC system. The triangular MFs and the Mamdani-style of model systems are used in this modeling. The final results show that the inner geometry modified technique enhanced the heat transfer coefficient and the thermal efficiency of the PTSC system to generated vortex in the flow. More specifically, the use of a using a corrugated absorber tube enhanced the collector efficiency by 5.1% to 5.5% compared with a smooth absorber tube. Also, the predict value are founding to been in near settlement with the investigational counterparts with accuracy of ∼92 %. Therefore, the proposed Fuzzy model system has high validity and accuracy for predicting a PTSC system's performance relative to that of the conventional model. The benefits of this approach are speed, flexibility, and the using of specialist information for predict as compared to that of the conventional model.
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System performance of solar water heaters depend upon collector and storage tank design and sizing and weather conditions (solar radiation intensity and ambient temperature). Nocturnal reverse flow and tank insulation dictate the degree of overnight water temperature drop in the storage tank. A tropical country like Malaysia has widely fluctuating and intermittent solar radiation. It is neither practical nor feasible to conduct outdoor tests such as that proposed by International Standards. Indoor collector tests are expensive to conduct and would not provide meaningful information to the domestic or commercial end user. Outdoor system tests would be more informative to consumers who would like to compare the water temperatures that could be achieved in order to choose from the wide range of commercial products available. This paper reports the results of outdoor tests conducted on several evacuated tube solar collectors (U-tube and heat pipe types) under natural and forced convection. Although tested at different times, the long and short term test procedures employed allowed us to compare the performances of the various systems as if they were tested simultaneously side-by-side. It was found that the natural convection heat pipe system performed best among them.
A complete overview of solar technologies relevant to the built environment, including solar thermal energy for heating and cooling, passive solar energy for daylighting and heating supply, and photovoltaics for electricity production. Provides practical examples and calculations to enable component and system simulation e.g. Calculation of U-values, I-V curve parameters and radiance distribution modelling. Discusses the new trends in thermal energy use, including the architectural integration of collector systems, integrated ventilation photovoltaics facades and solar powered absorption cooling systems. Coverage of cutting-edge applications such as active and passive cooling techniques and results from ongoing research projects.
Elliptical heat pipe flat plat solar collector was designed, constructed and tested with a collector tilt angle of 11° to the horizontal. Experimental analysis of the effect of condenser length/evaporator length (Lc/Le) ratio of the heat pipe, different cooling water mass flow rates and different inlet cooling water temperature were analysed. Five numbers of elliptical heat pipes with stainless steel wick has been fabricated and used as transport tubes in the collector. Copper tube has been used as container material with methanol as working fluid of the heat pipe. These heat pipes were fixed to the absorber plate of the solar collector and the performance of elliptical heat pipe solar collector has been studied and results were compared. It has been found from the experimental trials that the elliptical heat pipe solar collector having Lc/Le ratio of 0.1764 achieved higher instantaneous efficiency.
Heat pipe solar collector has better collecting efficiency compared to the conventional collectors. In this paper, experiments on the effect of L/d ratio of heat pipe on heat pipe solar collector are presented. Two solar collectors with different L/di have been designed and fabricated. A heat pipe with stainless steel wick replaces the transport tubes of the solar collector. Copper and stainless steel were used as container and wick material and methanol was used as working fluid of heat pipe. Heat pipes are designed to have heat transport factor of around 194 W and 260 W of thermal energy. Experiments were conducted during summer season with a collector tilt angle of 13° to the horizontal. The collector with L/di ratio of 52.63 was found to be more efficient than the collector with L/di ratio of 58.82. This improved efficiency is due to increase in heat transport factor of heat pipe, which increase with decrease in L/di ratio.
This trip was undertaken to participate in and represent the United States Industry at the International Energy Agency (IEA) Solar Heating and Cooling Program (SHCP) Task 14 Workshop. The meeting took place at the A1 Bani Hotel in Rome Italy.