basic principles of solar radiation and ste plants: eduardo zarza

Almería (Spain), June 27-28 , 2012“3rd SFERA Summer School” 1

Eduardo ZarzaCIEMAT-Plataforma Solar de Almería,

Apartado 22, Tabernas, E-04200 AlmeríaPhone: 950387931 E-mail: [email protected]

Basic principles of solar radiation and STE plants

3rd SFERA Summer School


Solar Concentrating Systems

Solar Thermal Electricity (STE) Plants

The Sun and the solar radiation

Índice de la Presentación

STE technologies comparison

Basic principles of Solar Radiation and STE Plants



Solar Thermal Electricity (STE) Plants



STE technologies comparison

Basic principles of Solar Radiation and STE Plants


The Sun and the Solar radiation

Sun is a huge nuclear reactor (7x105

km radius)

emitting a great amount of radiant energy (3,8x1023

kW, 5800ºK), which can be easily converted into thermal energy


Spectral Solar Irradiance

0,0 0,5 1,0 1,5 2,0 2,50

250

500

750

1000

1250

1500

1750

2000

2250

Extraterrestrial solar radiation

Wave length (μm)

Spe

ctra

l sol

ar ir

radi

ance

(W/m

2 ·μm

)

Solar radiation at ground level(Air Mass = 1.5)

LE

L

L/LE = 1.5



The Earth intercepts only 1,7x1014

kW of solar radiation (10 days ≅

known fossil fuels resources)

The solar irradiance outside the atmosphere is almost constant (its value is called “Solar Constant”, 1367 W/m2)

Solar radiation at ground level has two components: Direct Radiation and Difuse Radiation.


km radius)




Direct and Difuse Solar RadiationDi

rect

Radia

tion

Dire

ctRa

diatio

n

Dire

ctRa

diatio

n Diffuse Radiation

Diffuse RadiationDiffuse Radiation

b) d ≈ λ/4 c) d > λa) d < λ/10



The Earth intercepts only 1,7x1014

kW of solar radiation (10 days ≅

known fossil fuels resources)

The solar irradiance outside the atmosphere is almost constant (its value is called “Solar Constant”, 1367 W/m2)

Solar radiation at ground level has two components: Direct Radiation and Difuse Radiation.

Only Direct Solar Radiation can be concentrated.

Solar radiation reaching any point is not composed of a single ray, but of a cone of rays within a solid angle of 32”

(approx.).


km radius)





α

= inicidence angle β

= Reflection angle

α

= β

Reflecting surface

32”



Centrales Termosolares y Crecimiento Sostenible


Situación actual

Conclusiones


Introducción a los SistemasSolaresTérmicos deConcentración


Solar Radiation and its ConcentrationSolar Concentration: Why?

Since solar radiation suffers a significant attenuation in its way to the Earth (from 63,2 MW/m2 to 1 kW/m2) we have to concentrate solar radiation in order to compensate for its low flux density at the Earth surface and thus achieve higher temperatures and efficiencies.


Dependence of the Efficiency and the Optimum Working Temperature on the Solar Radiation Concentration Factor

η = f(C, T)

Efficiency versus concentration factor

0

0.25

0.5

0.75

1

0 1000 2000 3000 4000

Temperatura (K)

1.000

5.000

10.000

20.000

Carnot

C=250

0

0.25

0.5

0.75

1

0 1000 2000 3000 4000

Temperature (K)

Syst

em E

ffici

ency

1.000

5.000

10.000

20.000

Carnot

C=250


Solar Radiation and its Concentration

Solar Concentration: Why?Since solar radiation suffers a significant attenuation in its way to the Earth (from 63,2 MW/m2 to 1 kW/m2) we have to concentrate solar radiation in order to compensate for its low flux density at the Earth surface and thus achieve higher temperatures and efficiencies.

Ways to concentrate the direct solar radiationa) by Reflection

b) by Refraction


Direct radiation

Reflecting surface

Receiver

Direct radiation

a) by Reflection

Direct Solar Radiation can be concentrated by Reflection and by Refraction:

Receiver

Direct radiation

b) by Refraction

Fresnel lens




Limiting factors for solar concentration

Theoretical and practical limits for solar concentration• Point focus concentrators: 46200 (theoretical); 5000 y 10000 (practical)• Linear focus concentrators: 220, (theoretical); 20 –

80 (practical)

a) The apparent size of solar sphere is 32´as seen from the Earthb) Inaccuracies and optical errors of solar concentrators

Solar Concentration: Why?Since solar radiation suffers a significant attenuation in its way to the Earth (from 63,2 MW/m2 to 1 kW/m2) we have to concentrate solar radiation in order to compensate for its low flux density at the Earth surface and thus achieve higher temperatures and efficiencies.

Ways to concentrate the direct solar radiationa) by Reflection

b) by Refraction


32”

Actual shape

Theoretical shape

Concentration limit due to the Sun disk size

Concentration

= L/π·dd

L



Solar Thermal Electricity Plants


Situación actual

Conclusiones


Introducción a los SistemasSolaresTérmicos deConcentración


Solar Thermal Electricity PlantsWhat is a Solar Thermal Electricity (STE) plant ?A STE plant is a system where

solar radiation is concentrated and then converted intothermal energy at medium/high temperature (300ºC –

800ºC). This thermal energy is then used in a thermodynamic cycle to produce electricity.


Optical Concentrator

RECEIVER

Waste Heat

Heat

Thermallosses

Opticallosses

Simplified Scheme of a typical STE PlantSimplified Scheme of a typical STE PlantDirect Solar Radiation

ConcentratedSolar Radiation

ThermalStorage

Solar System

Mechanical energy

G Electricity generator

ThermodynamicCycle


What is a Solar Thermal Electricity (STE) plant ?

There is a huge market worldwide for these solar plants

These plants do not increase the emissions of CO2 :

-

Every GWh

of electricity produced by a STP plant saves 800 tons of CO2

There are many Countries with good solar radiation level

-

A STP plant saves 2000 Tons of CO2

per year and MWe

installed

Why are Solar Thermal Power plants interesting nowadays ?

These plants demand a lot of manpower for construction, as well as for O&M

It is already profitable in some Countries due to public subsidies or incentives

The technology is mature enough for commercial deployment

A STE plant is a system where

solar radiation is concentrated and then converted intothermal energy at medium/high temperature (300ºC –

800ºC). This thermal energy is then used in a thermodynamic cycle to produce electricity.



100 mHeliostat field

Receiver

Power Conversion System

Tower

Current Technologies for STE plants (I)Central Receiver Technology


Receiver Tube

Parabolic trough concentratorStructure

Current Technologies for STE plants (II)Parabolic Trough Collectors


Solar field

Power Conversion System

STE Plant with Parabolic Trough Collectors

Current Technologies for STE plants (II)


ConcentratorReceiver

Structure

Stirling DishesCurrent Technologies for STE plants (III)

Solar Stirling engine


Receiver pipe

Rectangular reflectors

Linear Fresnel ConcentratorCurrent Technologies for STE plants (and IV)


Technologies comparison

PTC CentralReceiver

ParabolicDishes

LFC

Unit plant powerWorking temperaturePeak efficiency (solar-electric) Yearly net Efficiency

15-200 MW390 ºC20 %

11-16 %

15-100 MW575 ºC23 %

7-20 %

9-25 kW750 ºC30 %

12-25 %

15-200 MW390ºC

1813

Current status

Technological riskStorage availabilityHybrid designs

Available

LowSiSi

Available

LowSiSi

Prototypes-Demonstration

LowSiSi

Available

High-MediumSiSi



End of Slide Show

! Thank you for your attention ¡

Basic principles of solar radiation and STE plants

3rd SFERA Summer School

basic principles of solar radiation and ste plants: eduardo zarza

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