Stirling solare - Tesina per tecnico industriale

Renewable energy

Introduction

A renewable energy source is one that is replaced over a reasonable period of time by

natural processes; examples include wind, solar energy, hydroelectricity and geothermal

energy. About 16% of global final energy consumption comes from renewables, with 10%

coming from traditional biomass, which

is mainly used for heating, and 3.4%

from hydroelectricity. New renewables

(wind, solar and geothermal)

accounted for another 3% and are

growing very rapidly. While many

renewable energy projects are large-

scale, renewable technologies are also

suited to rural and remote areas, where

energy is often crucial in human

development. As of 2011, small solar

photovoltaic systems provide electricity

to a few million households, and micro-

hydro configured into mini-grids serves

even more. Over 44 million households

use biogas made in household-scale

digesters for lighting and/or cooking. United Nations' Secretary-General Ban Ki-

moon has said that renewable energy has the

ability to lift the poorest nations to new levels

of prosperity.

The most widely used forms of renewable

energy are: wind power, geothermal energy,

hydroelectricity and solar energy. These

sources of energy provide an alternate

‘cleaner’ source of energy, helping to negate

the effects of certain forms of pollution.

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Wind energy

Since ancient times man has harnessed the power of the wind, the earliest known wind

mills were vertical axis type, developed by the Persians in 500-900 A.D.

Wind power is the conversion of wind energy into a useful form of energy, such as using:

wind turbines to make electricity,

windmills for mechanical power, wind-

pumps for water pumping or drainage.

A wind farm is a group of wind

turbines in the same location used for

production of electricity. Wind farms

can be located onshoreor offshore.

In an farm a group of eolian

onshore

turbines, placed in the same area, are

interconnected by a middle-voltage

linking net. This net gathers the energy

created by each turbine, convoying it Onshore Wind-farm

to a collection station. Here a transformer

converts the middle-voltage electric energy in high-tension electric current, introducing it

in the distribution system. A large wind farm may have dozens of eolian generators and

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more than one hundred of single turbines, being placed on an area of several km

however, being the space of each generator very little, all the places between the turbines

could be used for agriculture or livestock holdings. United States of America currently own

the most quantity of wind farms, followed by Germany, Spain and Denmark. Italy is on the

fourth place.

The most recent wind farms are usually

placed on the sea or on the

offshore,

great lakes, far from the coasts, where

it is possible to exploit the strong winds

not delayed by obstacles. Unluckily, the

realization and maintenance costs of

these offshore wind farms are more

elevated than the onshore ones,

because of the transportation costs, the

great building problems, the difficulty

to anchor their towers on the bottom

and, in the end, the corrosive action of

the sea water on their structures.

Lillgrund Wind farm, Sweden 2

Anyway, these marine plants have great productivity advantages. On the sea surface, as

matter of fact, winds blow without any obstacle, with a higher speed. The offshore

placement of great wind farms also solve the acoustic and aesthetical problems, the tower

being placed beyond the line of the horizon, at least 3 km from the coast. The offshore

plants represent, according to the most part of the specialists of this sector, the true future

of the aeolian energy, for what concerns both the environmental problem and the

production potential. In 2007, the offshore plants produced about the 3,5% of the

European aeolian energy, owned for the most part from Denmark and United Kingdom,

followed by Holland and Sweden; in 2008 the largest aeolian offshore production

happened in the UK, followed by Denmark. At present, the largest offshore wind farm is

placed off the Lincolnshire coasts (Great Britain), with an installation power of 194 MW.

Geothermal energy

Geothermal energy is generated in the Earth’s almost 6,000 km beneath the Earth’s

core,

surface. The double-layered core is made up of very hot (melted rock) surrounding

magma

a solid iron center. Very high temperatures are continuously produced inside the Earth by

the slow decay of radioactive particles. This process is natural in all rocks. Geothermal

energy was used by ancient people for heating and bathing. Even today, hot springs are

used worldwide for bathing, and many people believe hot mineral waters have natural

healing powers. The exploitation of geothermal energy to produce electricity is a new

industry. A group of Italians first used it in 1904. The Italians used the natural steam

erupting from the Earth topower a turbine generator.

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There is more than one type of geothermal energy, but only one kind is widely used to

make electricity. It is called hydrothermal energy. have two

Hydrothermal resources

common ingredients: water (hydro) and heat (thermal). Depending on the temperature of

the hydrothermal resource, the heat energy can either be used for making electricity or for

heating.

Low Temperature Resources: Heating

•

Hydrothermal resources at low temperatures (50 to 300 degrees Fahrenheit) are used for

heating homes and buildings, growing

crops, and drying lumber, fruits, and

vegetables. In this application are used

Ground source heat pumps that are

special heating and cooling systems that

use heat from the ground to control

temperature inside a structure. In winter,

when homes and offices are chilled by the

low air temperatures above ground, a

geothermal heat pump will use the earth scheme of a plant at low temperature

below a structure as a heat source.

High Temperature Resources: Electricity

•

Hydrothermal resources at high temperatures (300 to 700 degrees Fahrenheit) can be used

to make electricity.

These high-temperature resources may come from either dry steam wells or hot water

wells. We can use these resources

by drilling wells into the Earth and

piping the steam or hot water to

the surface. Geothermal wells are

two to fourkm deep.

In a dry steam power plant, the

steamis piped directly from the

geothermal reservoir to a turbine

generator to make electricity. In a

hot water plant, some of the hot

water is turned into steam. The

steam powers a turbine generator

geothermalpower station in Iceland just like a dry steam plant. When

the steam cools, it condenses to water and is injected back into the ground to be used over

and over again. 4

Hydroelectricity

Hydroelectricity uses the energy of flowing water to produce electricity via a hydroelectric

power station.Hydroelectric power stations are usually powered by water that has been

captured in a dam or reservoir. The water from the dam is released into a pipeline and

through a turbine. The force of the water causes the turbine to spin that runs a generator.

This produces electricity which is transferred through a substation into the grid. Excess

water is released back into the waterways.

Hydropower is the most widely used form of renewable energy, accounting for 16 percent

of global electricity consumption. It is produced in 150 countries: China is the largest

hydroelectricity producer, with 721 terawatt-hours of production in 2010, representing

around 17 percent of domestic electricity use. Brazil, Canada, New Zealand, Norway,

Paraguay, Austria, Switzerland, and Venezuela have the majority of the internal electric

energy production from hydroelectric power. Paraguay produces 100% of its electricity

from hydroelectric dams, and exports 90% of its production to Brazil and to Argentina.

Norway produces 98–99% of its electricity from hydroelectric sources.

Solar energy

Every day, the sun radiates an enormous amount of energy, called solar energy. Like most

stars, the sun is a big gas ball made up mostly of hydrogen and helium gas. The sun makes

energy in its inner core in a process called nuclear fusion.

It takes the sun’s energy just a little over eight minutes to travel the 93 million miles to

Earth. Solar energy travels at a speed of 186,000 miles per second, the speed of light. Only

a small part of the radiant energy that the sun emits into space ever reaches the Earth, but

that is more than enough to supply all our energy needs. Every day enough amount of

solar energy reaches the Earth to supply our nation’s energy needs for a year! Solar energy

is considered a renewable energy source. There are many methods to exploit solar energy.

They will be seen in the following pages. 5

L’ENERGIA SOLARE

Cenni storici Il fotovoltaico basa il suo funzionamento sull’effetto fotoelettrico,

fenomeno osservato per la prima volta nel 1839 dallo scienziato

francese Alexandre Edmond Becquerel: egli immerse due elettrodi

metallici di platino in una soluzione acida ed espose l’intero

apparato alla luce del Sole. Riscontrò l’instaurarsi di una debole

differenza di potenziale. La fisica classica non fu in grado di

spiegare le osservazioni di Becquerel, per comprenderle fu

necessario attendere fino al 1905, anno in cui Einstein pubblicò la

sua teoria sull’effetto fotoelettrico, basata sui principi della fisica

quantistica, che gli valse il Nobel nel 1921. Le derivazioni tecniche

di queste scoperte rimasero tuttavia inapplicate per lungo tempo.

Si costruirono, infatti, le prime celle a semiconduttori, ma la loro

efficienza era purtroppo irrisoria: le prime celle al selenio avevano

Edmond Becquerel,

fisico francese un rendimento dell’1%, mentre quelle più innovative al silicio,

scoperte dall’americana Bell Telephone negli anni successivi, rendevano al massimo il 6%.

Fu necessario l’intervento del programma spaziale americano negli anni ’50 per

rivitalizzare un settore ormai in stallo. L’incessante

ricerca di nuove fonti di energia per rifornire di

elettricità i satelliti in orbita portò l’industria

aereospaziale a orientarsi sul fotovoltaico; anzi, si

può, di fatto, dire che fu il programma spaziale

americano a creare l’industria del fotovoltaico. In

seguito, negli anni ’60 e ’70, il settore ricevette un

ulteriore impulso dall’enorme sviluppo dei

semiconduttori, grazie alla nascita della moderna

elettronica. Nel corso di trent’anni le celle solari

hanno registrato uno straordinario abbattimento.

dei costi, ancora in corso, un aumento dell’efficienza e Albert Einstein, fisico tedesco

una maggiore penetrazione del mercato. .

“L’Energia del sole”

L'energia solare è una delle principali fonti di energia rinnovabile, è la fonte "madre" di

tutte le fonti energetiche sulla Terra. In modo diretto o indiretto, tutte le fonti di energia

derivano dall'attività solare e la stessa vita non esisterebbe sul nostro pianeta.

La radiazione solare ha consentito di creare le condizioni ideali per la vita vegetale tramite

la fotosintesi. 6

Senza l'energia solare fossile, immagazzinata nel carbone, nel petrolio e nel gas, l'uomo

non avrebbe potuto avviare il processo di rivoluzione industriale della propria società. Per

energia solare s’intende la produzione di energia termica o elettrica sfruttando

direttamente la radiazione solare in arrivo sulla Terra. Mediamente la potenza radiante che

incide sulla superficie terrestre al livello del mare è di circa 1000 W/m2. Ogni Paese a livelli

modalità di sfruttamento

diversi può accedere alla radiazione solare e sfruttarla. Le

dell’energia solare possono essere divise in tre categorie principali.

Pannelli fotovoltaici

I pannelli solari fotovoltaici convertono la luce solare direttamente in energia elettrica. Un

pannello è composto da una serie di moduli che a loro volta sono gruppi di più unità base,

le celle fotovoltaiche. Il settore che si

occupa della conversione diretta di energia

solare in energia elettrica prospetta

consistenti miglioramenti: il fotovoltaico è,

infatti, il campo energetico con le maggiori

possibilità di sviluppo futuro. Su di esso si

concentrano ingenti investimenti,

soprattutto per promuovere la ricerca, per

via della concreta possibilità che ha questo