Solar Heating
(JR125)
Introduction
Solar heating is the conversion of sunlight into heat for water heating or air heating or using a solar thermal collector. A variety of configurations are
available at varying cost to provide solutions in different climates and latitudes.
SHs are widely used for residential and some industrial applications. Although
in Pakistan SHs are not often used by residences or by industry, in spite of
the fact that gas supplies are dwindling.
Principles
A sun-facing collector heats a working fluid that passes into a storage system for later use. SH are active
(pumped) and passive (convection-driven). They use water only, or
both water and a working fluid. They are heated directly or via
light-concentrating mirrors. They operate independently or as hybrids with
electric or gas heaters. In large-scale installations, mirrors may concentrate
sunlight into a smaller collector.
The
heart of a solar heating system is the collector. A flat-plate solar collector,
the most prevalent collector form, is made up of a selectively layered absorber
that serves to absorb the incoming solar radiation and transforms it into heat.
This absorber is embedded in a thermally insulated box with a transparent cover
(usually glass) to minimize thermal loss.
A
heat conducting liquid (usually a mixture of water and non-environmentally
damaging anti-freeze) flows through the absorber and circulates between the
collector and the warm water storage tank. Thermal solar energy systems will be
brought into operation through a solar automatic controller. As soon as the
temperature on the collector exceeds the temperature in the storage tank by a
few degrees, the regulator switches on the solar circulation pump and the heat
conducting liquid transports the heat received from the collector to the
storage tank.
Elements of
a solar heating system for hot water:
·
Automatic
solar controller
·
Temperature
sensor on collector
·
Temperature
sensor on storage tank
·
Solar
circulation pump
·
Cold
water inflow
·
Hot
water run-off
·
Expansion
tank
·
Temperature
sensor for additional heating
·
Charging
circuit- solar circulation pump
The conventional
heater guarantees, with the charging circuit, that enough warm water will be
available even when the solar heating system supplies little or no heat at all.
Solar heating systems can be integrated into buildings without a problem. Thus,
a modern solar heating system, with at least twenty years life expectancy
exceeds that of a boiler, and ideally supplements conventional heating
technology.
Types
The type, complexity and size of a solar water heating system are
mostly determined by:
·
Changes in ambient
temperature and solar radiation between summer and winter
·
Changes in ambient
temperature during the day-night cycle
·
Possibility of the
potable water or collector fluid overheating or freezing
The minimum requirements of the system are typically determined
by the amount or temperature of hot water required during winter, when a
system's output and incoming water temperature are typically at their lowest.
The maximum output of the system is determined by the need to prevent the water
in the system from becoming too hot.
Economics
The
sun, however, supplies its energy free of charge. The relatively high initial
investment at first sight suggests that the systems are, in general, very
expensive. But from the time of installation of the system on, there are no
more operating costs, except very low costs for maintenance and pump
electricity.
Freeze protection
Freeze
protection measures prevent damage to the system due to the expansion of
freezing transfer fluid. Drain back systems drain the transfer fluid from the
system when the pump stops. Many indirect systems use antifreeze e.g., propylene
glycol in the heat transfer fluid.
In
some direct systems, collectors can be manually drained when freezing is
expected. This approach is common in climates where freezing temperatures do
not occur often, but can be less reliable than an automatic system as it relies
on an operator.
.
Overheat protection
When
no hot water has been used for a day or two, the fluid in the collectors and
storage can reach high temperatures in all non-drain back systems. When the
storage tank in a drain back system reaches its desired temperature, the pumps
stop, ending the heating process and thus preventing the storage tank from
overheating.
Some
active systems deliberately cool the water in the storage tank by circulating
hot water through the collector at times when there is little sunlight or at
night, losing heat. This is most effective in direct or thermal store plumbing
and is virtually ineffective in systems that use evacuated tube collectors, due
to their superior insulation. Any collector type may still overheat. High
pressure, sealed solar thermal systems ultimately rely on the operation of temperature and pressure relief valves. Low pressure, open vented heaters have simpler, more
reliable safety controls, typically an open vent.
Design
Simple
designs include a simple glass-topped insulated box with a flat solar absorber
made of sheet metal, attached to copper heat exchanger pipes and dark-colored, or a set of metal tubes surrounded by an
evacuated (near vacuum) glass cylinder. In industrial cases a parabolic mirror
can concentrate sunlight on the tube. Heat is stored in a hot water storage tank. The volume of this tank needs to be larger with solar
heating systems to compensate for bad weather and because the
optimum final temperature for the solar collector[ is lower than a
typical immersion or combustion heater. The heat transfer fluid (HTF) for the
absorber may be water, but more commonly (at least in active systems) is a
separate loop of fluid containing anti-freeze and a corrosion inhibitor
delivers heat to the tank through a heat
exchanger (commonly a coil of copper heat exchanger tubing within the tank). Copper is an important component in
solar thermal heating and cooling systems
because of its high heat conductivity, atmospheric and water corrosion
resistance, sealing and joining by soldering and mechanical strength. Copper is
used both in receivers and primary circuits (pipes and heat exchangers for
water tanks).
Another
lower-maintenance concept is the 'drain-back'. No anti-freeze is required;
instead, all the piping is sloped to cause water to drain back to the tank. The
tank is not pressurized and operates at atmospheric pressure. As soon as the
pump shuts off, flow reverses and the pipes empty before freezing can occur.
How a solar
hot water system works
Residential
solar thermal installations fall into two groups: passive (sometimes called
"compact") and active (sometimes called "pumped") systems.
Both typically include an auxiliary energy source (electric heating element or
connection to a gas or fuel oil central heating system) that is activated when
the water in the tank falls below a minimum temperature setting, ensuring that
hot water is always available. The combination of solar water heating and
back-up heat from a wood stove chimney can enable a hot water system
to work all year round in cooler climates, without the supplemental heat
requirement of a solar water heating system being met with fossil fuels or
electricity.
When
a solar water heating and hot-water central heating system are used together,
solar heat will either be concentrated in a pre-heating tank that feeds into
the tank heated by the central
heating, or the solar heat exchanger will
replace the lower heating element and the upper element will remain to provide
for supplemental heat. However, the primary need for central heating is at
night and in winter when solar gain is lower. Therefore, solar water heating
for washing and bathing is often a better application than central heating
because supply and demand are better matched. In many climates, a solar hot
water system can provide up to 85% of domestic hot water energy. This can
include domestic non-electric concentrating solar thermal systems. In many northern European countries, combined hot
water and space heating systems (solar
combisystems) are used to provide 15 to 25% of
home heating energy. When combined with storage, large scale solar heating can provide 50-97% of annual
heat consumption for district
heating.
Heat transfer
Direct or open loop systems circulate potable water through
the collectors. They are relatively cheap. Drawbacks include:
·
They offer little or no overheat
protection unless they have a heat export pump.
·
They offer little or no freeze
protection, unless the collectors are freeze-tolerant.
·
Collectors accumulate scale in hard water areas, unless an ion-exchange softener is
used.
The
advent of freeze-tolerant designs expanded the market for SWH to colder
climates. In freezing conditions, earlier models were damaged when the water
turned to ice, rupturing one or more components.
Indirect or
closed loop systems use a heat
exchanger to transfer heat from the "heat-transfer fluid" (HTF) fluid
to the potable water. The most common HTF is an antifreeze/water mix that
typically uses non-toxic propylene
glycol. After heating in the panels, the
HTF travels to the heat exchanger, where its heat is transferred to the potable
water. Indirect systems offer freeze protection and typically overheat
protection.
Propulsion
Passive systems rely on heat-driven convection or heat pipes to
circulate the working fluid. Passive systems cost less and require low or no
maintenance, but are less efficient. Overheating and freezing are major
concerns.
Active systems use one or more pumps to circulate water and/or
heating fluid. This permits a much wider range of system configurations.
Pumped
systems are more expensive to purchase and to operate. However, they operate at
higher efficiency can be more easily controlled.
Active
systems have controllers with features such as interaction with a backup
electric or gas-driven water heater, calculation and logging of the energy
saved, safety functions, remote access and informative displays.
Integrated
collector storage (ICS) system
An integrated collector storage (ICS or batch heater)
system uses a tank that acts as both storage and collector. Batch heaters are
thin rectilinear tanks with a glass side facing the sun at noon. They are simple and less costly than plate and tube
collectors, but they may require bracing if installed on a roof (to support
400–700 lb (180–320 kg) lbs of water), suffer from significant heat
loss at night since the side facing the sun is largely un insulated and are
only suitable in moderate climates.
A convection heat storage unit (CHS) system is similar to
an ICS system, except the storage tank and collector are physically separated
and transfer between the two is driven by convection. CHS systems typically use
standard flat-plate type or evacuated tube collectors. The storage tank must be
located above the collectors for convection to work properly. The main benefit
of CHS systems over ICS systems is that heat loss is largely avoided since the
storage tank can be fully insulated. Since the panels are located below the
storage tank, heat loss does not cause convection, as the cold water stays at
the lowest part of the system.
Active indirect systems
Pressurized
antifreeze systems use a mix of antifreeze (almost always non-toxic propylene glycol) and water
mix for HTF in order to prevent freeze damage.
Though
effective at preventing freeze damage, antifreeze systems have drawbacks:
·
If the HTF gets too hot the glycol
degrades into acid and then provides no freeze protection and begins to
dissolve the solar loop's components.
·
Systems without drainback tanks must
circulate the HTF – regardless of the temperature of the storage tank – to
prevent the HTF from degrading. Excessive temperatures in the tank cause
increased scale and sediment build-up, possible severe burns if a tempering
valve is not installed, and if used for storage, possible thermostat failure.
·
The glycol/water HTF must be
replaced every 3–8 years, depending on the temperatures it has experienced.
·
Some jurisdictions require
more-expensive, double-walled heat exchangers even though propylene glycol is
non-toxic.
·
Even though the HTF contains glycol
to prevent freezing, it circulates hot water from the storage tank into the
collectors at low temperatures (e.g. below 40 °F (4 °C)), causing
substantial heat loss.
A
drainback system is an active indirect system where the HTF (usually
pure water) circulates through the collector, driven by a pump. The collector
piping is not pressurized and includes an open drainback reservoir that is
contained in conditioned or semi-conditioned space. The HTF remains in the
drainback reservoir unless the pump is operating and returns there (emptying
the collector) when the pump is switched off. The collector system, including
piping, must drain via gravity into the drainback tank. Drainback systems are
not subject to freezing or overheating. The pump operates only when appropriate
for heat collection, but not to protect the HTF, increasing efficiency and
reducing pumping costs
Collector
Solar thermal collectors capture and retain heat from the sun
and use it to heat a liquid. Two important physical principles govern the
technology of solar thermal collectors:
·
Any hot object
ultimately returns to thermal equilibrium with its environment, due to heat
loss from conduction, convection and radiation. Efficiency
(the proportion of heat energy retained for a predefined time period) is
directly related to heat loss from the collector surface. Convection and
radiation are the most important sources of heat loss. Thermal insulation is
used to slow heat loss from a hot object. This follows the Second law of thermodynamics (the 'equilibrium effect').
·
Heat is lost more
rapidly if the temperature difference between a hot object and its environment
is larger. Heat loss is predominantly governed by the thermal gradient between
the collector surface and the ambient temperatures. Conduction, convection and
radiation all occur more rapidly over large thermal gradients (the delta-t effect).
Flat-plate solar
thermal collector, viewed from roof-level
Flat plate
Flat plate collectors are an extension of the idea to place a
collector in an 'oven'-like box with glass directly facing the Sun. Most flat plate collectors have two horizontal
pipes at the top and bottom, called headers, and many smaller vertical pipes
connecting them, called risers. The risers are welded (or similarly connected)
to thin absorber fins. Heat-transfer fluid (water or water/antifreeze mix) is
pumped from the hot water storage tank or heat exchanger into the collectors'
bottom header, and it travels up the risers, collecting heat from the absorber
fins, and then exits the collector out of the top header. Serpentine flat plate
collectors differ slightly from this "harp" design, and instead use a
single pipe that travels up and down the collector. However, since they cannot
be properly drained of water, serpentine flat plate collectors cannot be used
in drainback systems.
The type of glass used in flat plate collectors is almost always
low-iron, tempered glass. Such glass can withstand significant hail
without breaking, which is one of the reasons that flat-plate collectors are
considered the most durable collector type.
Unglazed or formed collectors are similar to flat-plate
collectors, except they are not thermally insulated nor physically protected by
a glass panel. Consequently, these types of collectors are much less efficient.
For pool heating applications, the water to be heated is often colder than the
ambient roof temperature, at which point the lack of thermal insulation allows
additional heat to be drawn from the surrounding environment
Evacuated tube
Evacuated tube solar
water heater on a roof
Evacuated tube collectors (ETC) are a way to reduce the heat
loss inherent in flat plates. Since heat loss due to convection cannot
cross a vacuum, it forms an efficient isolation mechanism to keep heat inside
the collector pipes. Since two flat glass sheets are generally not
strong enough to withstand a vacuum, the vacuum is created between two
concentric tubes. Typically, the water piping in an ETC is therefore surrounded
by two concentric tubes of glass separated by a vacuum that admits heat from
the sun (to heat the pipe) but that limits heat loss. The inner tube is coated
with a thermal absorber Vacuum life varies from collector to collector,
from 5 years to 15 years.
Flat plate collectors are generally more efficient than ETC in
full sunshine conditions. However, the energy output of flat plate collectors
is reduced slightly more than ETCs in cloudy or extremely cold conditions. Most ETCs are made out of annealed
glass, which is susceptible to hail, failing given
roughly golf ball -sized particles. ETCs made from "coke glass,"
which has a green tint, are stronger and less likely to lose their vacuum, but
efficiency is slightly reduced due to reduced transparency. ETCs can gather
energy from the sun all day long at low angles due to their tubular shape.
Pump
One
way to power an active system is via a photovoltaic (PV) panel. To ensure proper pump performance and longevity, the (DC)
pump and PV panel must be suitably matched. Although a PV-powered pump does not
operate at night, the controller must ensure that the pump does not operate
when the sun is out but the collector water is not hot enough.
PV
pumps offer the following advantages:
·
Simpler/cheaper installation and
maintenance
·
Excess PV output can be used for
household electricity use or put back into the grid.
·
Can dehumidify living space.[29]
·
Can operate during a power outage.
·
Avoids the carbon consumption from
using grid-powered pumps.
Bubble Pump
A bubble pump (also known as geyser pump) is suitable for flat
panel as well as vacuum tube systems. In a bubble pump system, the closed HTF
circuit is under reduced pressure, which causes the liquid to boil at low
temperature as the sun heats it. The steam bubbles form a geyser, causing an
upward flow. The bubbles are separated from the hot fluid and condensed at the
highest point in the circuit, after which the fluid flows downward toward the
heat exchanger caused by the difference in fluid levels. The HTF
typically arrives at the heat exchanger at 70°C and returns to the circulating
pump at 50°C. Pumping typically starts at about 50 C and increases as the
sun rises until equilibrium is reached.
Controller
A differential controller senses temperature differences
between water leaving the solar collector and the water in the storage tank
near the heat exchanger. The controller starts the pump when the water in the
collector is sufficiently about 8–10 C warmer than the water in the tank,
and stops it when the temperature difference reaches 3–5 C. This ensures
that stored water always gains heat when the pump operates and prevents the pump
from excessive cycling on and off. (In direct systems the pump can be triggered
with a difference around 4 C because they have no heat exchanger.)
Tank
The simplest collector is a water-filled metal tank in a sunny
place. The sun heats the tank. This was how the first systems worked This setup
would be inefficient due to the equilibrium effect: as soon as heating of the
tank and water begins, the heat gained is lost to the environment and this
continues until the water in the tank reaches ambient temperature. The
challenge is to limit the heat loss.
·
The storage tank can
be situated lower than the collectors, allowing increased freedom in system
design and allowing pre-existing storage tanks to be used.
·
The storage tank can
be hidden from view.
·
The storage tank can
be placed in conditioned or semi-conditioned space, reducing heat loss.
·
Drainback tanks can be
used.
Insulated tank
ICS or batch collectors reduce heat loss by thermally insulating
the tank.
This is achieved by
encasing the tank in a glass-topped box that allows heat from the sun to reach
the water tank. The
other walls of the box are thermally insulated, reducing convection and
radiation. The box
can also have a reflective surface on the inside. This reflects heat lost from
the tank back towards the tank. In a simple way one could consider an ICS solar
water heater as a water tank that has been enclosed in a type of 'oven' that
retains heat from the sun as well as heat of the water in the tank. Using a box
does not eliminate heat loss from the tank to the environment, but it largely
reduces this loss.
Standard ICS collectors have a characteristic that strongly
limits the efficiency of the collector: a small surface-to-volume ratio Since
the amount of heat that a tank can absorb from the sun is largely dependent on
the surface of the tank directly exposed to the sun, it follows that the
surface size defines the degree to which the water can be heated by the sun.
Cylindrical objects such as the tank in an ICS collector have an inherently
small surface-to-volume ratio. Collectors attempt to increase this ratio for
efficient warming of the water. Variations on this basic design include
collectors that combine smaller water containers and evacuated glass tube
technology, a type of ICS system known as an Evacuated Tube Batch (ETB)
collector
Evacuated tube
ETSCs can be more useful than other solar collectors during
winter season. ETCs can be used for heating and cooling purposes in industries
like pharmaceutical and drug, paper, leather and textile and also for
residential houses, hospitals nursing home, hotels swimming pool etc. An ETC can
operate at a range of temperatures from medium to high for solar hot water,
swimming pool, air conditioning and solar cooker.
ETCs higher operational temperature range (up to 200°C (392°F))
makes them suitable for industrial applications such as steam generation, heat
engine and solar drying.
Swimming pools
Pool covering systems, whether solid sheets or floating
disks, act as insulation and reduce heat loss. Much heat loss occurs through
evaporation, and using a cover slows evaporation.
STCs for non potable pool water use are often made of plastic. Pool water is mildly corrosive due to chlorine.
Water is circulated through the panels using the existing pool filter or
supplemental pump. In mild environments, unglazed plastic collectors are more
efficient as a direct system. In cold or windy environments evacuated tubes or
flat plates in an indirect configuration are used in conjunction with a heat
exchanger. This reduces corrosion. A fairly simple differential
temperature controller
is used to direct the water to the panels or heat exchanger either by turning a
valve or operating the pump. Once the pool water has reached the required
temperature, a diverter valve is used to return water directly to the pool
without heating. Many systems are configured as drainback
systems where the water drains into the pool when the water pump is switched
off.
The collector panels are usually mounted on a nearby roof, or
ground-mounted on a tilted rack. Due to the low temperature difference between
the air and the water, the panels are often formed collectors or unglazed flat
plate collectors. A simple rule-of-thumb for the required panel area needed is
50% of the pool's surface area.[37] This is for areas where pools are used
in the summer season only. Adding solar collectors to a conventional outdoor
pool, in a cold climate, can typically extend the pool's comfortable usage by
months and more if an insulating pool cover is used. Most solar hot water systems are capable
of heating a pool by around 5-8ᵒ C and often by as much as 10ᵒ C.
An active solar energy system analysis program may be used to optimize the
solar pool heating system before it is built.
Energy
production
The amount of heat delivered by a solar water heating system
depends primarily on the amount of heat delivered by the sun at a particular
place (insolation).
In the tropics insolation can be relatively high, e.g. 7 kWh/m2 per day, Average
insolation can vary a great deal from location to location due to differences
in local weather patterns and the amount of overcast. Calculators are available
for estimating insolation at a site.
Costs
In sunny, warm locations, where freeze protection is not
necessary, an ICS (batch type) solar water heater can be cost effective In
higher latitudes, design requirements for cold weather add to system complexity
and cost. This increases initial costs, but not life-cycle costs. The
biggest single consideration is therefore the large initial financial outlay of
solar water heating systems. Offsetting
this expense can take years. The payback period is longer in temperate
environments. Since solar energy is free, operating
costs are small. At higher latitudes, solar heaters may be less effective due
to lower insolation, possibly requiring larger and/or dual-heating systems. In some countries government incentives
can be significant.
Cost factors (positive and negative) include:
·
Price of solar water
heater (more complex systems are more expensive)
·
Efficiency
·
Installation cost
·
Electricity used for
pumping
·
Price of water heating
fuel (e.g. gas or electricity) saved per kWh
·
Amount of water
heating fuel used
·
Initial and/or
recurring government subsidy
·
Maintenance cost (e.g.
antifreeze or pump replacements)
·
Savings in maintenance
of conventional (electric/gas/oil) water heating system
Payback times can vary greatly due to regional sun, extra cost
due to frost protection needs of collectors, household hot water use etc. For
instance in central and southern Florida the payback period could easily be 7
years or less rather than the 12.6 years indicated on the chart for the U.S.
Country
|
System
cost
|
Effective
cost
|
Payback
period years
|
|
|
2
|
2500
|
4.2
|
|
|
14000
|
11900
|
5.5
|
|
|
|
3000
|
6.9
|
|
|
|
2000
|
8.3
|
|
|
|
3500
|
12.6
|
|
|
|
4800
|
18.2
|
The payback period is shorter given greater insolation. However,
even in temperate areas, solar water heating is cost effective. The payback
period for photovoltaic systems has historically been much longer. Costs and payback period are shorter if no
complementary/backup system is required. thus extending the payback period of such a
system.
Energy footprint
The
source of electricity in an active SWH system determines the extent to which a
system contributes to atmospheric carbon during operation. Active solar thermal
systems that use mains electricity to pump the fluid through the panels are
called 'low carbon solar'. In most systems the pumping reduces the energy
savings by about 8% and the carbon savings of the solar by about 20%. However, low power
pumps operate with 1-20W.
Assuming a solar collector
panel delivering 4 kWh/day and a pump running intermittently from mains
electricity for a total of 6 hours during a 12-hour sunny day, the potentially
negative effect of such a pump can be reduced to about 3% of the heat produced.
However,
PV-powered active solar thermal systems typically use a 5–30 W PV panel and a
small, low power diaphragm pump or
centrifugal pump
to circulate the water. This reduces the operational carbon and energy
footprint.
Alternative
non-electrical pumping systems may employ thermal expansion and phase changes
of liquids and gases.
Life cycle energy assessment
Recognised
standards can be used to deliver robust and quantitative life cycle assessments (LCA). LCA considers the financial and environmental costs
of acquisition of raw materials, manufacturing, transport, using, servicing and
disposal of the equipment. Elements include:
·
Financial costs and gains
·
Energy consumption
·
CO2 and other
emissions
In
terms of energy consumption, some 60% goes into the tank, with 30% towards the
collector thermosiphon flat
plate in this case). In Italy, some 11
giga-joules of electricity are used in producing SWH equipment, with about 35%
goes toward the tank, with another 35% towards the collector. The main
energy-related impact is emissions. The energy used in manufacturing is
recovered within the first 2–3 years of use (in southern Europe).
By
contrast the energy payback time in the UK is reported as only 2 years. This
figure was for a direct system, retrofitted to an existing water store, PV
pumped, freeze tolerant and of 2.8 sqm aperture. For comparison, a PV
installation took around 5 years to reach energy payback, according to the same
comparative study
In
terms of CO2 emissions, a large fraction of the emissions saved is
dependent on the degree to which gas or electricity is used to supplement the
sun. Using the Eco-indicator 99 points system as a yardstick (i.e. the yearly
environmental load of an average European inhabitant) in Greece, a purely gas-driven system may have fewer
emissions than a solar system. This calculation assumes that the solar system
produces about half of the hot water requirements of a household.
A
test system in Italy produced about 700 kg of CO2, considering all
the components of manufacture, use and disposal. Maintenance was identified as
an emissions-costly activity when the heat transfer fluid (glycol-based) was
replaced. However, the emissions cost was recovered within about two years of
use of the equipment
In
Australia, life cycle emissions were also recovered. The tested SWH system had
about 20% of the impact of an electrical water heater and half that of a gas
water heater
System specification and installation
Most SWH installations require backup
heating.
·
The amount of hot
water consumed each day must be replaced and heated. In a solar-only system,
consuming a high fraction of the water in the reservoir implies significant
reservoir temperature variations. The larger the reservoir the smaller the
daily temperature variation.
·
SWH systems offer
significant scale economies in collector and tank costs. Thus the most economically efficient
scale meets 100% of the heating needs of the application.
·
Direct systems (and
some indirect systems using heat exchangers) can be retrofitted to existing
stores.
·
Equipment components
must be insulated to achieve full system benefits. The installation of
efficient insulation significantly reduces heat loss.
·
The most efficient PV
pumps start slowly in low light levels, so they may cause a small amount of
unwanted circulation while the collector is cold. The controller must prevent
stored hot water from this cooling effect.
·
Evacuated tube
collector arrays can be adjusted by removing/adding tubes or their heat pipes,
allowing customization during/after installation.
·
Above 45 degrees
latitude, roof mounted sun-facing collectors tend to outproduce wall-mounted
collectors. However, arrays of wall-mounted steep collectors can sometimes
produce more useful energy because gains in used energy in winter can offset
the loss of
·
A solar water heater is one of the most effective ways to reduce
the overall carbon footprint of a home or office. As opposed to employing a
boiler (and, therefore, fossil fuels) to heat water, the renewable power of the
sun is harnessed. Although designs may vary depending upon the manufacturer,
there are several common components within the typical solar water heater.The
first portion of the unit is known as a collector. This is normally mounted on
a roof or a similar area that receives a great deal of sunlight. A collector
may consist of an insulated box and a dark-coloured “absorber” made of sheet
metal or a similar substance. A heating fluid is then pumped through this
collector. The overall purpose of this collector can be easily understood. By
focusing the solar rays within a small environment, water will be heated up to
time. It can then be distributed to various areas of the home.
·
Once this water is heated to an agreeable temperature, it is
then sent to a hot water storage tank. One of the issues that some homes will
encounter is that the storage tank will need to be significantly larger than
that associated with a traditional boiler. This is intended to account for bad
weather or days when there is little sunlight available. Also, many solar water
heaters will have a backup power system if the overall temperature of the
reservoir falls below a certain temperature (normally around 55ºC). Should this
occur, a standard energy source will make up for the lack of solar power.
Normally, this energy is derived from electrical or natural gas sources.
·
A final consideration to take into account regarding a solar
water heater is that some areas of the world will not be able to employ this
technology. This has much to do with the angle of the sun (latitude) as well as
how many pleasant days there is each year. While this system may be perfectly
suited for areas within the Mediterranean or South America, Northern England or
Finland are not likely to enjoy the benefits that are provided. This may very
well change if solar panels and their individual cells continue to become more
efficient regarding energy production.
·
SOlr Water heaters available in Pakistan
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more beautiful tank side cover. These technologies distinguishes JXL from other
competitors in the market. It attracts more customers’ attention and brings our
agents more benefits compared with normal solar water heaters.Besides, JXL is
the first company to realize WiFi control of solar water heaters in the
industry. JXL’s mobile app enables users to monitor the temperature and control
electric heating element anywhere as long as there is WiFi access.
Price Rs.
57000
Price
Rs.20000 to 50000
Solar water heating collectors capture and
retain heat from the sun and transfer this heat to a liquid. Solar thermal heat
is trapped using the “greenhouse effect,” in this case is the ability of a
reflective surface to transmit short wave radiation and reflect long wave
radiation. Heat and infrared radiation (IR) are produced when short wave
radiation light hits a collector’s absorber, which is then trapped inside the
collector. Fluid, usually water, in contact with the absorber collects the
trapped heat to transfer it to storage.
Popular type of collector is called
evacuated tube, which has a long, skinny absorber that is inside a glass tube.
The tube has the air evacuated out of it, which makes it highly insulated—not
too different from a thermos used to keep drinks hot.
There are two types of solar water heater
or Solar Geyser systems:
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