Solar thermal energy

1. Solar thermal energy
Solar thermal energy (STE) is a form of energy and a technology for harnessing solar energy to
generate thermal energy or electrical energy for use in industry, and in the residential and
commercial sectors.
Solar thermal collectors are classified as low-, medium-, or high-temperature collectors.
Low-temperature collectors are generally unglazed and used to heat swimming pools or to heat
ventilation air.
Medium-temperature collectors are also usually flat plates but are used for heating water or air
for residential and commercial use.
High-temperature collectors concentrate sunlight using mirrors or lenses and are generally used
for fulfilling heat requirements up to 300 deg C / 20 bar pressure in industries, and for electric
power production. Two categories include Concentrated Solar Thermal (CST) for fulfilling heat
requirements in industries, and Concentrated Solar Power (CSP) when the heat collected is used
for power generation. CST and CSP are not replaceable in terms of application.
The first installation of solar thermal energy equipment occurred in the Sahara approximately in
1910 by Frank Shuman when a steam engine was run on steam produced by sunlight. Because
liquid fuel engines were developed and found more convenient, the Sahara project was
abandoned, only to be revisited several decades later.

2. Solar thermal energy is one of the most cost effective forms of green
energy.
Solar heating systems take advantage of some basic principles about how solar energy is
converted into solar thermal energy and the physical behavior of heat. The first principle you
need to understand about solar home heating is how solar energy is captured and converted into
heat.
Solar Energy Collectors
A solar collector captures the radiant energy from the Sun and converts it into heat.
How does a solar collector convert solar energy into heat?
By taking advantage of a process known as the greenhouse effect.
The basic idea is that the solar energy passes through a layer of glazed glass where it is absorbed
by the underlying material. The solar energy excites the molecules in the underlying material
resulting in heat. The glazing of the glass prevents the heat from escaping, thereby effectively
capturing the heat.
Once that heat is captured we can put it to good use! But in order to use it, you first need to
understand some of the basic principles of heat...
Basic Principles of Heat
Heat is simply a form of energy associated with the motion of molecules.
When the electromagnetic waves coming from the Sun hit an object, they excite the molecules of
that object causing them to move. This molecular movement is heat.
Heat is always moving from higher to lower temperatures until the temperatures are equal. This
is known as heat transfer. If you place two objects next to each other, the warmer object will
cool down as its heat is transferred to the cooler object. The cooler object in turn will warm up.
This heat transfer is driven by the difference in temperatures of the objects. The heat transfer
rate is proportional to the difference in temperature. The larger the difference in temperature
between the objects, the faster the heat moves.

3. Understanding Heat Movement
To really understand solar thermal energy, you need to understand about heat movement. This is
especially important for passive solar energy applications.
There are three basic physical ways that heat moves...
 Conduction
 Convection
 Radiation
Conduction is the transfer of heat through a solid material, or from one material to another
where their surfaces are touching. Heat is conducted more easily through a solid material than
through layers of material, even when the layers are held together tightly. This is important as the
conduction of heat through building materials is a major source of heat loss.
Convection is the transfer of heat by a moving fluid, usually air or water. Natural convection is
caused by the heating and cooling of the air in a room as it contacts objects. As air is warmed, it
expands resulting in it having a lower density than the cooler air around it. Since its density is
lower than the cool air, it will rise. As the air cools, it's density increases and it will sink, starting
the process all over again. This movement of air is known as a convection current.
Radiation is the direct transfer of heat through space by electromagnetic waves coming from a
warmer object to a cooler object. Heat radiates in all directions from a warm material and will
warm all surfaces that are in direct line of sight of the material. Most objects that block visible
light will also block radiant energy. You've experienced this when you move into the shade on a
hot summer day to cool down. You are moving out of the direct line of sight of the Sun's radiant
energy, and as a result, you get cooler.
SolarHeating Applications
Now that you understand the basics about solar thermal energy, take a look at the
different solar heating applications that you can use for solar home heating...

4.  Solar Space Heating
 Solar Water Heating
 Solar Pool Heating
Flat Plate Solar Collectors
A typical flat-plate collector is a metal box with a glass or plastic cover (called glazing) on top
and a dark-colored absorber plate on the bottom. The sides and bottom of the collector are
usually insulated to minimize heat loss.

5. Sunlight passes through the glazing and strikes the absorber plate, which heats up, changing solar
energy into heat energy. The heat is transferred to liquid passing through pipes attached to the
absorber plate. Absorber plates are commonly painted with "selective coatings," which absorb
and retain heat better than ordinary black paint. Absorber plates are usually made of metal—
typically copper or aluminum—because the metal is a good heat conductor. Copper is more
expensive, but is a better conductor and less prone to corrosion than aluminum. In locations with
average available solar energy, flat plate collectors are sized approximately one-half- to one-
square foot per gallon of one-day's hot water use.
Applications: The main use of this technology is in residential buildings where the demand for
hot water has a large impact on energy bills. This generally means a situation with a large family,
or a situation in which the hot water demand is excessive due to frequent laundry washing.
Commercial applications include laundromats, car washes, military laundry facilities and eating
establishments. The technology can also be used for space heating if the building is located off-
grid or if utility power is subject to frequent outages. Solar water heating systems are most likely
to be cost effective for facilities with water heating systems that are expensive to operate, or with
operations such as laundries or kitchens that require large quantities of hot water.

6. Specifications of the solar collectors
The solar panels core components of solar thermal systems, must meet minimum
quality requirements. These services are certified by an accredited and must follow
a defined laboratory test protocol.
The technical information you need to know about a solar collector is as follows:
 Instant performance curves made by an accredited laboratory.
 Catchment Area.
 Weight
 Transport and handling instructions of the sensor.
 Capacity and type of heat transfer fluid recommended by the manufacturer.
 Recommended flow rates and pressure drops.
 Maximum operating pressure and test pressure.
 Constitution of the absorber materials and fluid circuit.
 Materials and constitution of the cover of the box.
 Sealing System.
 Types and thicknesses of insulation.
 Temperature stagnation.
 Requirements for maintenance.
Physical principles of operation of the solar collector plane
The solar collector operates from the application of the following physical
principles:
The black body (absorber)
The solar radiation is partially absorbed by the body. The rest is reflected or passes
through them.
The relationship between these effects depends
 The nature of the body.
 The state of the surface.
 The bulk of the body.
 The type of radiation. The wavelength.

7.  The angle of the sun.
The dark bodies and kill better capture solar radiation than any other color; so the
absorber of the solar collector is usually dark colors, to maximize sun laradiación.
The greenhouse effect
This effect is generated in some transparent bodies, which are normally only
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This radiation is reflected can not go into again. A portion of this energy heats the
glass and the glass forwards in and out.
Some plastics (such as polycarbonate) have a glass-like behavior (let through
shortwave radiation from the sun and stop long-wave emissions coming from the
absorber plate).
insulation
The third of the physical principles involved in the operation of the sensors is the
insulation of the assembly from the outside, usually consists of an inner coating of
the container box.
Components of a flat solar collector
The flat solar collector with cover glaze is the facilities used to produce hot water.
This team consists of the following elements:
absorber
It is the element that intercepts the solar radiation inside the sensor and is
responsible for converting solar energy into thermal energy.
The absorber is formed usually by a metal foil, typically copper (good thermal
conductor) which darkens basically
1. A thin film of heat black paint, which can withstand temperatures above 100 ° C
work.
2. A selective treatment based on electrochemical deposition or paints with metallic
oxides having a high absorption of solar radiation (shortwave) and a low emission
of heat (long wave).
The absorber includes a grid of pipes through which circulate the heat transfer
fluid.

8. transparent cover
Its function is to isolate the sensor for external environmental conditions, though let
sunlight - that cause the greenhouse effect. It usually consists of a single sheet of
tempered glass (resistant) with low iron content (very transparent) 4 mm thick
approximately.
Insulation
This element, as in other applications, serves to prevent heat loss from inside the
sensor -specifically the absorbidor- outward and usually consists of sheets of
synthetic foam (polyurethane, cyanide, fiber glass, etc.) located on the sides and in
the back of the pickup.
Housing
The housing serves to accommodate the other components. This closure is typically
formed by an anodised aluminum that will ensure joint resistance even in extreme
conditions. Also, the housing will have a condensate drain holes in the bottom.
flat solar collectors
The flat plate solar collector has a good cost / effectiveness in moderate climates
and a large number of applications (domestic hot water, pool heating, support for
heating, preheating industrial fluids, etc adapted correctly .).
We can distinguish two basic types of flat plate collectors, depending on the
configuration of the absorber: the parallel of "grid type" in the vertical and
horizontal versions and the series of "coil type". Basically, the difference between
the two is:
 The parallel configuration favors that can stratify the temperature sensor with the
largest circulation of water through the branches inside the sensor and obtain
a temperaturedifferential of about 10 in good yield.
 The series configuration consists of a single continuous circuit with low volume
of circulating water and a temperature differential higher, in good yield.
Operation of flat solar collector
The operation of a sensor is very basic. In fact, any Solrecibe body exposed to an
energy flow which heats and therefore increases the temperature.
A body at a given temperature emits energy around it, in the form of radiation, and
this depends directly on the temperature difference between the body temperature
and room temperature.

9. If refrigerate the sensor by passing a fluid through the interior, this heat is used,
whereby it is achieved that a part of the collected energy is transmitted to the fluid
as useful energy. The rest is still losing energy as radiation from the sensor to the
external environment. In this case, the temperature is always less than equilibrium.
If we get good performance, the sensors have to work at the lowest
possible temperature, as long as it is sufficient for the intended use given.
The harnessed energy is removed from the sensor by the heat transfer fluid,
generally consisting of a mixture of water with antifreeze and corrosion inhibitors.
parabolic trough solar collectors
The solar concentrator systems are specially designed for high temperatures. Its
principle of operation is based on the projection of the whole incident a reflective
surface on a particular point radiation.
Until recently, the use of solar thermal systems CCP concentration was restricted to
the field of research, industry and electricity generation, as this technology
requiring complex tracking systems to locate and supermarkets.
Domestically, it was not justifiable to install sensors with these requirements to
reach high temperatures of over 200 ° C.
But currently available in the market, concentration sensors "compact parabolic
trough" (CPC) and having a format similar to the dimensions of the flat plate
collectors.
The sensors consist of a pipeline with a selective coating which longitudinally
traverse the sensor and acting absorber.
These pipes are solar radiation reflected by the curved walls that surround them,
thus achieving a higher amount of energy per unit area of the absorber (W / m2).
The result of all this is a sensor capable of generating high temperatures up to 200 °
C with standard radiation levels.
Therefore, such sensors are used both to produce and support sanitary hot
water heating or cooling equipment to feed by adsorption or absorption.