Solar technology

Solar technology

Content

1 introduction

2 classification

3 Active solar technology

3.1 Photovoltaic cell

3.1.1 working

3.1.2 type of solar panel

3.1.3 photovoltaic solar plant work

4 solar thermal technology

4.1 type of solar thermal collector

4.1.1 low thermal collector

4.1.2 medium thermal collector

4.1.3 high thermal collector

5 passive solar technology

6 conclusion

1 Introduction Sun is an ultimate source of energy, it continuously emits radiant energy know as solar

energy, which supports all form of life on our earth.

The Earth receives 174 pet watts (PW) of incoming solar radiation (insolation) at

the upper atmosphere. Approximately 30% is reflected back to space while the rest is absorbed

by clouds, oceans and land masses.

By 1873, concerns of running out of coal prompted experiments with using solar

energy. Development of solar engines continued until the outbreak of World War I. The

importance of solar energy was recognized in a 1911Scientific American article: "in the far distant

future, natural fuels having been exhausted [solar power] will remain as the only means of

existence of the human race".

Solar energy, radiant light and heat from the sun, is harnessed using a range of ever-

evolving technologies such as solar heating, photovoltaics, concentrated solar power, solar

architecture and artificial photosynthesis.

In this entire topic we will discuss different type of technique that we are using to harness

the solar energy, the development in the technology and some of the application of them. We

first start with of classification of the technology that we are using and then we will discuss each

one by one with some of the application of them.

2 Classification of solar technology

Solar technologies are broadly characterized as either passive solar or

active solar depending on the way they capture, convert and distribute solar energy. Passive solar

techniques include orienting a building to the Sun, selecting materials with favorable thermal

mass or light dispersing properties, and designing spaces that naturally circulate air.

Active solar technologies encompass solar thermal energy, using solar collectors for heating,

and solar power, converting sunlight into electricity either directly using photovoltaics (PV), or

indirectly using concentrated solar power (CSP)

3 Active solar technology

As we discuss above, in active solar technology we use solar collector, converting solar energy

to electricity by using photovoltaic cell. In an active solar technology we can harness solar energy

by two ways

1 photovoltaic cell

2 Solar thermal technology

We will discuss them one by one

3.1 Photovoltaic cell Photovoltaic cell can be defined as devices which convert sunlight into electricity. An array of

closely interconnected solar cells makes a solar panel which is use to convert solar energy in to

electrical energy.

3.1.1 Working of photovoltaic cell

To understand how a solar cells works, we must first take the time to understand the properties

of the materials used in the construction of a solar cell. Consider the primary type solar cell that

is constructed from a single crystal of silicon semiconductor.

Fig: - Czochralski process

to be useful in electronics and for generating electrical power from solar energy,

silicon must be highly purified. To purify silicon to such a high degree requires special processing.

One purification method is the Czochralski process. In it, a seed crystal is dipped into a crucible of

molten silicon and withdrawn slowly, pulling out a cylindrical single crystal out of the molten

silicon that had crystallized on the seed. The cylindrical crystal is called a Boule. The Boule can be

cut up with a diamond saw into slices (called wafers) and is used to make electrical components.

Fig: - Cell structure

Pure silicon does not conduct electricity; in fact it’s an insulator. Each silicon atom has four

electrons in its outer shell. Each atom fills its outer electron shell to eight electrons by sharing its

four electrons with four other silicon atoms. The atoms form into a tight crystalline structure

where all the electrons are held strongly in place. Without any free electrons to act as charge

carriers pure silicon a good insulator. What makes silicon so useful in electronics is that by adding

a small amount of impurities to the silicon while it is being manufactured alters its electrical

properties in a very useful way. The impurities are called dopants in the industry, and the process

of adding the impurities is called doping. By the process of doping we get p-type and n-type.

Silicon is

cut into tiny disks and transformed into silicon wafers. This silicon wafer, not more than a

centimeter thick are then polished carefully.The process of polishing makes the surface of silicon

free from any outside impurities.

Metal conductors that are laid across each disk of silicon crystal help carry electric current within

the solar cell and complete the circuit inside the solar panel as a whole system. Metal connectors

are typically in the form of flat ribbons or thin wires. These kinds of connections between two or

more solar cells are packaged tightly into modules. Solar panels are then covered inside the

sheet of glass (typically tampered glass) on to the front side, so as to be transparent to the light

energy (photons) and hit the solar cells lying within

3.1.2Type of solar panel

Solar panel are classified in to three category

Monocrystalline

this type of solar panel are unique in their use of a single, very pure crystal of silicon.

They are among the oldest, most efficient and most dependable ways to produce electricity from

the sun.

Each module is made from a single silicon crystal, and is more efficient, though more expensive,

than the newer and cheaper polycrystalline and thin-film PV panel technologies. You can typically

recognize them by their color which is typically black or iridescent blue.

Polycrystalline

Polycrystalline cells are made from similar silicon material except that instead of being grown into

a single crystal, they are melted and poured into a mold. This forms a square block that can be cut

into square wafers with less waste of space or material than round single-crystal wafers. As the

material cools, it crystallizes in an imperfect manner, forming random crystal boundaries.The

efficiency of energy conversion is slightly lower.marginally less expensive to produce than

monocrystalline

3.1.3 Photovoltaic solar plants work

As light hits the solar panels, the solar radiation is converted into direct current electricity (DC).

The direct current flows from the panels and is converted into alternating current (AC) used by

local electric utilities. Finally, the electricity travels through transformers, and the voltage is

boosted for delivery onto the transmission lines so local electric utilities can distribute the

electricity to homes and businesses.

4 Solar thermal technology

. 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 We use solar thermal technology to cook food and on a big scale to generate

electricity.

Solar collectors capture and concentrate sunlight to heat a synthetic oil called therminol, which

then heats water to create steam. The steam is piped to an onsite turbine-generator to produce

electricity, which is then transmitted over power lines. On cloudy days, the plant has a

supplementary natural gas boiler. The plant can burn natural gas to heat the water, creating

steam to generate electricity

4.1 Type of solar thermal collector

4.1.1 Low thermal collector

Systems for utilizing low-temperature solar thermal energy include means for heat collection;

usually heat storage, either short-term or interseasonal; and distribution within a structure or a

district heating network. In some cases more than one of these functions is inherent to a single

feature of the system. Some systems are passive, others are active.

MIT's Solar House built in 1939 used seasonal thermal energy storage(STES) for year round

heating.

4.1.2Medium thermal collector

These collectors could be used to produce approximately 50% and more of the hot water needed

for residential and commercial use in the United States. It is commonly used in solar drying,

cooking and distillation.

Solar drying

Solar thermal energy can be useful for drying wood for construction and wood fuels such as wood

chips for combustion. Solar is also used for food products such as fruits, grains, and fish. Crop

drying by solar means is environmentally friendly as well as cost effective while improving the

quality. Technologies in solar drying include ultralow cost pumped transpired plate air collectors

based on black fabrics. Solar thermal energy is helpful in the process of drying products such as

wood chips and other forms of biomass by raising the temperature while allowing air to pass

through and get rid of the moisture.

Cooking

Solar cookers use sunlight for cooking, drying and pasteurization. Solar cooking offsets fuel costs,

reduces demand for fuel or firewood, and improves air quality by reducing or removing a source

of smoke. Concentrating solar cookers use reflectors to concentrate solar energy onto a cooking

container. The most common reflector geometries are flat plate, disc and parabolic trough type.

These designs cook faster and at higher temperatures up to 350 °C but require direct light to

function properly.

The Solar Bowl above the Solar Kitchen in Auroville, India concentrates sunlight on a movable

receiver to produce steam for cooking.

Distillation

solar can be used to make drinking water in areas where clean water is not common. Solar

distillation is necessary in these situations to provide people with purified water. Solar energy

heats up the water in the still. The water then evaporates and condenses on the bottom of the

covering glass.

4.1.3 High-temperature collectors

this is mainly use to produce electricity on a big scale. solar radiation is concentrated by mirrors

or lenses to obtain higher temperatures – a technique called Concentrated Solar Power (CSP).

Here use of solar tracking system is very necessary so that the reflector can track the solar

position n efficiently concentrate the light on their focal point . we use different type of design to

concentrate the solar light

Parabolic trough designs

Here we use a curved, mirrored trough which reflects the direct solar radiation onto a glass tube

containing a fluid running the length of the trough, positioned at the focal point of the reflectors.

The receiver may be enclosed in a glass vacuum chamber. The vacuum significantly reduces

convective heat loss.

A fluid passes through the receiver and becomes very hot. Common fluids are synthetic oil,

molten salt and pressurized steam. The fluid containing the heat is transported to a heat

engine where about a third of the heat is converted to electricity.

Power tower designs

Power towers capture and focus the sun's thermal energy with thousands of tracking mirrors .

A tower resides in the center of the heliostat field. The heliostats focus concentrated sunlight on a

receiver which sits on top of the tower. Within the receiver the concentrated sunlight heats

molten salt to over 538 °C. The heated molten salt then flows into a thermal storage tank where it

is stored, maintaining 98% thermal efficiency, and eventually pumped to a steam generator. The

steam drives a standard turbine to generate electricity.

Dish designs

In this design we use reflective, parabolic dish .It focuses all the sunlight that strikes the dish up

onto a single point above the dish, where a receiver captures the heat and transforms it into a

useful form. Typically the dish is coupled with a Stirling engine in a Dish-Stirling System, but also

sometimes a steam engine is used.These create rotational kinetic energy that can be converted to

electricity using an electric generator.

A parabolic solar dish concentrating the sun's rays on the heating element of a Stirling engine. The entire unit acts as a solar tracke.

Fresnel technologies

In this technology we use a series of long, narrow, shallow-curvature mirrors to focus light onto

one or more linear receivers positioned above the mirrors. On top of the receiver a small

parabolic mirror can be attached for further focusing the light.. This is similar to the trough design

The receiver is stationary and so fluid couplings are not required .The mirrors also do not need to

support the receiver, so they are structurally simpler. When suitable aiming strategies are used

this can allow a denser packing of mirrors on available land area.

Fresnel reflector

5 Passive solar technology

Passive solar technologies use sunlight without active mechanical systems . Such technologies

convert sunlight into usable heat, cause air-movement for ventilating, or future use, with little

use of other energy sources. Passive solar technologies include direct and indirect solar gain for

space heating, solar water heating systems.

Passive solar heating techniques generally fall into one of three categories: direct

gain, indirect gain, and isolated gain. Direct gain is solar radiation that directly penetrates, and is

stored in, the living space. Indirect gain technology collects, stores, and distributes solar radiation

using some thermal storage material. Conduction, radiation, or convection then transfers the

energy indoors. Isolated gain systems collect solar radiation in an area that can be selectively

closed off or opened to the rest of the house

a passive solar home work to reduce energy bills and increase comfort in winter

10:00 am to 5:00 pm

Sunlight enters south-facing windows and strikes the thermal mass inside the home. The sunlight

is converted to heat energy, which heats both the air and thermal mass materials. On most sunny

days, solar heat maintains comfort during the mid-morning to late afternoon periods.

5:00 pm to 11:00 pm

As the sun sets, it stops supplying heat to the home. However, a substantial amount of heat has

been stored in the thermal mass. These materials release the heat slowly into the passive solar

rooms, keeping them comfortable on most winter evenings. If temperatures fall below the

comfort level, supplemental heat is needed.

11:00 pm to 6:30 am

The home owner sets the thermostat back at night, so less backup heating is needed. Energy-

efficient features in the home minimize heat losses to the outside.

6:30 am to 10:00 am

Providing a comfortable temperature with passive solar heating systems is toughest in the cool

early morning hours. The thermal mass has usually given up most of its heat, and the sun has not

risen enough to begin heating the home. During this period, the home owner may have to rely on

supplemental heat. Energy-efficient features in the home minimize the need for supplemental

heating.

Conclusion

solar energy is renewable source of energy and it does not cause any

environmental pollution like non- renewable source of energy cause. We have many type of

technology to use solar energy for different purposes and we are continuously trying to advance

the technology so that we increase the efficiency of harnessing the solar energy or to maximize

the use of solar energy with lowest price.

We have photovoltaic technology which is used in most of the places like

calculator, watch, to power house hold devices , boiling water etc. it is use almost all satellite to

give them power. We have solar thermal technology which is use to cook food , boil water etc.

most important it is use to generate a electricity on a big scale . we can established a big power

plant based on this technology and give electricity to entire city. We have passive technology

which we can design our home so that we can get maximum benefit from solar energy. Engineers

are constantly trying to improve all these technology so that we can harness solar energy more

efficiently with lower cost.