‘

MD ZAFAR ALAM

M.Tech 2nd Year(AHES)

E.No.- 13512017

AHEC, IIT Roorkee

IMPROVED TECHNIQUE TO EVALUATE PERFORMANCE OF SOLAR THERMAL

POWER PLANT

Under the guidance of:

Dr. R.P. SAINI

Associate Professor,

AHEC, IIT Roorkee

Contents

1. Introduction

2. Literature review

3. Gaps Identified

4. Objective of work

5. Factors Affecting Performance of solar thermal power plant (STPP)

6. Critical Parameters To Evaluate Performance of STPP

7. Parameters Used in Existing Technologies

8. Effect of wind speed on receiver heat loss

9. Solar collector assembly and optical efficiency

10. Performance Calculation of STPP

11. Power block efficiency calculation

12. Input to the solar field

13. Results calculation

14. Conclusion

15. References

Introduction

• Solar Thermal Power systems, also known as Concentrating Solar Power systems, use concentrated solar radiation as a high temperature energy source to produce electricity using thermal route.

Solar field

Power block

Parameters Considered in Existing Technologies of performance evaluation of STPP

Environmental temperature Varying radiation value Characteristics of collectors Circulating fluid etc.

Proposed Improved Technique Under this work an attempt is made to evaluate the performance of solar

thermal power plant (STPP) considering the convection losses due to wind

speed. As wind speed increases Nusselt no. increases which is directly related to

convection loss. So, the efficiency of each component and overall efficiency of STPP have

been evaluated by considering the effect of wind speed variation. To simulate the result System Analyzer Modeling (SAM) software

developed by NREL(National Renewable Energy Laboratory),USA is used.

Literature review

S. No. Author(s) Study(s) Result(s)

1 Joel Anderson et al

used CasADi to evaluate the performance

It is more user interactive, provide Symbolic/numeric algorithms and push the limit on mass flow rate & size.

2Clifford Ho et al.

probabilistic modeling of concentrating solar power plants

It consider input to the system in distributive form and provide result according to each value.

3 Juany M. Valenzuela

discussed performance of a 50 MW concentrating solar power plant

Used GateCycle and Set macro software. These types of macros assign a mathematical expression to a user-defined variable. In this case a variable under the name of “steam cycle efficiency” was created.

4 L.J. Yebra

analysis of Object Oriented Modelling of DISS Solar Thermal Power Plant

developed a dynamic models for use in simulation and control of this type of solar power plant

Objectives of the study

To identify critical parameters affecting

performance of solar thermal power plant (STPP).

To analyze the effect of wind speed on performance

of solar thermal power plant.

Mathematical formulation to evaluate the output

and losses at each section.

To determine the overall efficiency of STPP using

System Analyzer Modeling (SAM).

Factors Affecting Performance of STPP

Variations in solar radiation Characteristics of solar collectors Geometrical factors such as shadows, length of

collector, orientation etc. Losses due to convection, conduction and radiation. Losses in heat exchanger Change of phase of circulating fluid in power block. Velocity of cloud Dirt on concentrator

Critical Parameters To Evaluate Performance of STPP

Mass flow rate of fluid

Inlet temperature of working fluid

Outlet temperature of working fluid

Geometry of the system.

Optical parameters (such as absorptivity, transmissivity

and reflectivity)

Concentration ratio

Methods To Evaluate Performance of STPPThere are two methods to evaluate performance of STPPi. Deterministic Approach:

In deterministic evaluation of the system or component performance yield a single value for the simulated output such as levelized energy cost and power output. Input parameters are typically entered as specific values.

ii. Probabilistic Approach:

In probabilistic evaluation input data is entered as distribution of value rather than single value.

Heat Loss in Receiver

Receiver is like a tube through which heat transfer fluid (HTF)

passes and reflected solar radiation absorbed on it.

Losses in receiver occur by both convection and

radiation mode.

Modeling Approach of Receiver Heat Loss

.Figure shows the heat transfer network, conceptualized as a set

of thermal resistances in series and parallel. This is analogous to an

electrical resistance network:

Effect of wind speed on receiver heat loss

Convective loss from the receiver is given as:

Where h= convective heat transfer coefficient and it is directly proportional to Nusselt No. (Nu).

Convection heat loss from receiver depends on the wind speed, as wind speed increases, convective heat loss increase.

Convection heat loss is the function of convective heat transfer coefficient, Convective heat transfer coefficient is calculated by Nusselt number, Nusselt no. is proportional to Reynold’s number, Reynold’s number depends on wind speed, Hence, heat loss is directly related to wind speed.

for wind speed less than 0.1 m/s-

• Nusselt number is calculated using the Churchill & Chu correlation

For wind speed ≥0.1m/sNusselt number is calculated using Zhukauskas’ correlation

For Pr ≤ 10, n = .37, otherwise n = .36

Where, (V= wind speed)

From above relations we see that velocity is directly responsible to heat loss.

Reynolds No. Range c m

0 ≤Re<40 0.75 0.4

40 ≤Re<1000 0.51 0.5

1000 ≤Re<2*105 0.26 0.6

2*105 ≤Re<106 0.076 0.7

1. Solar collector assembly and optical efficiency• Collector is defined as the portion of the solar field that reflects irradiation

to the receiver. The optical calculations for the collector model extend to the point of determining the magnitude of solar flux that is incident on the receiver.

Efficiency Calculation of STPP

Optical Losses

End Description

Definition

End spillage losses

During hours when incoming solar radiation is not directly normal to the collector aperture some radiation is reflected off the end of the collector that doesn’t reach the receiver.

Row shadowing

Shadowing between rows generally occurs at extreme solar positions when the shadow cast by a collector closer to the sun obscures a portion of an adjacent collector.

Stow and Deploy Angles

The user can enforce limits on when the solar field will track the sun. This is given in terms of the solar elevation angle, and can be specified for the deploy event and stow event separately.

Incident Angle Modifier

The incident angle modifier IAM is a derate factor that accounts for collector aperture fore shortening glass envelope transmittance selective surface absorption, and any other losses that are a function of solar position.

Tracking error Inability of the collector to perfectly orient along the tracking angle twisting of the collector about the lengthwise axis

Fixed Losses

Geometry defects

Poor alignment of the mirror modules; deviation in the position of the receiver tube from the optical focus; warping or discontinuities along the reflective surface

Fixed Losses

Mirror reflectance

Specular reflectance within a cone angle defined by the collector and receiver geometry

Fixed Losses

Mirror soiling Dirt or soiling on the reflective surface that prevents irradiation from reflecting to the receiver.

Fixed Losses

General error Any effect not captured within the previous categories Fixed Losses

Figure: Row shadowing

Finally we get the total radiative energy incident on the receiver as:

Figure: End spillage

2. Solar Field

The solar field is the heat-collecting portion of the plant. It consists of one or more loops of solar collector assemblies with each loop laid out in parallel. A common header pipe provides each loop with an equal flow rate of heat transfer fluid (HTF) and a second header collects the hot HTF to return it either directly to the power cycle for power generation or to the thermal energy storage system for use at a later time.

Solar field loop

Cold header pipe

Hot header pipe

Nodal energy balance at collector

Energy balance is given as:

Here , m=mass of the HTF contained in the node, L = length of a single SCA, and Chtf = the specific heat of the HTF.An additional thermal inertia term (mc) bal,sca is included to account for the thermal mass of piping, joints, insulation, and other SCA components that thermally cycle with the HTF.

Finally output temperature from a node is given by

• Here input temperature, time difference, radiation energy from sun is known and mass in control volume is given as-

• The inlet temperature at the first node representing the inlet of the entire field .In a similar derivation process as the one describe “system” temperature is calculated for both the hot and cold sides of the solar field.

Efficiency of receiver:

Solar field efficiency:

Power block

The power cycle subsystem contains the equipment required to convert thermal energy from the solar field into useful mechanical or electrical energy. For utility-scale CSP systems, this most often entails a conventional steam Rankine cycle and electric generator.

Figure: Power block

Efficiency of the power block:

Overall efficiency :

In order to obtained the result a STPP of 100 MWe net capacity has been

considered. The STPP ha been assumed to be located at a site in Delhi for which

the required weather data is obtained from database of NREL, USA. For this

study data of 1st day of the month of January has been considered. Input to the SAM

Particulars ValueEstimate net output at design 100 MWe

Design inlet temp. to power block 391 °C

Design outlet temperature 293 °C

Single loop aperture 6540 m2

Actual no. of loops 130

No. of SCA/HCE assemblies per loop 8

Solar field area 548 acres

Row spacing 15 m

Hot piping thermal inertia 0.2 kWht/K-MWt

Cold piping thermal inertia 0.2 kWht/K-MWt

Field loop piping thermal inertia 4.5 Wht/K-m

Average surface-to-focus path length 1.8 m

Number of modules per assembly 12

Incidence angle modifier coef, F0 1

Incidence angle modifier coef, F1 0.0506

Incidence angle modifier coef, F2 -0.1763

Tracking error 0.99

Geometry effects 0.98

Mirror reflectance 0.935

Dirt on mirror 0.95

General optical error 0.99

Absorber absorptance 0.96

Annulus gas type Air

emittance

Internal surface roughness 4.5e-005

Incident radiation and wind speed data for Delhi

Time of day

DNI(W/m2) April(average)

DNI (W/m2)

August(average)

DNI(W/m2)January (average)

Wind speed (m/s)April (average)

Wind speed (m/s)August (average)

Wind speed January

(average)

1 0 0 0 1.18333 0.66129 0.448387

2 0 0 0 1.08 0.690323 0.493548

3 0 0 0 0.96 0.722581 0.532258

4 0 0 0 1.02 0.7 0.583871

5 0 0 0 1.05667 0.674194 0.622581

6 0 0 0 1.11333 0.648387 0.674194

7 8.7 0 0 1.46 1.12258 0.858065

8 231.433 145.806 0.193548 1.81667 1.59355 1.03871

9 477.133 285.677 240.71 2.16667 2.06774 1.15161

10 646.133 381.065 525.548 2.66 2.00645 1.57097

11 735.333 395.258 662.355 3.14667 1.97097 1.99032

12 773.333 370.097 723.129 3.67 1.94194 2.40968

13 788.267 381.129 749.871 3.90667 1.96129 2.54194

14 774.733 396.226 783.677 4.13667 1.96452 2.65484

15 726.1 366.968 746.355 4.36667 1.97742 2.7871

16 615.733 346.548 637.548 4.09333 1.73548 2.50645

17 411.467 256.194 385.516 3.83333 1.52903 2.22903

18 128.5 91.3226 16.0645 3.56 1.28387 1.94516

19 0 0 0 2.89333 1.13226 1.43871

20 0 0 0 2.24 1.00323 0.951613

21 0 0 0 1.57667 0.851613 0.445161

22 0 0 0 1.5 0.774194 0.425806

23 0 0 0 1.42333 0.674194 0.409677

0 2 4 6 8 10 12 14 16 18 20 22 240

100200300400500600700800

Beam Irradiance vs Time (April)

Time (in hr.)Be

am Ir

radi

ance

(w/m

2)

0 2 4 6 8 10 12 14 16 18 20 22 240

100200300400500600700800900

Beam irradiance vs Time(January)

Time in hr.

Beam

irra

dian

ce (W

/m2)

0 2 4 6 8 10 12 14 16 18 20 22 240

100

200

300

400

Beam Irradiance vs Time (August)

Time (in hr.)

Beam

Irra

dian

ce (w

/m2)

Result of variation of Wind speed vs Total receiver thermal and optical losses (1st January).

0 2 4 6 8 10 12 14 16 18 20 22 240

5

10

15

20

25

30

35

40

wind speed(m/s)Total receiver thermal and optical losses | (MWt)

Time

0.8 0.5 0.8 1.2 1.5 1.5 3.3 5.1 5.1 3.9 1.5 1.20

5

10

15

20

25

30

35

40

Wind speed

Tota

l rec

eive

r the

rmal

and

opti

cal l

osse

s

Time (in hr.) from

7 a.m. to 7 p.m.

wind speed

(m/s)

Total receiver thermal and optical losses (MWt)

Heat loss due to wind speed (MWt)

7 1.2 7.55715 7.558 1.3 18.1205 16.309 1.5 18.7181 10.4710 1.5 23.7775 9.51611 1.5 28.672 11.6212 2.4 29.3731 10.75913 3.3 30.4787 11.8614 4.2 34.7816 17.75215 5.1 36.2631 23.2016 5.1 37.8516 29.0817 5.1 36.7884 32.8318 5.1 24.9273 24.9219 3.9 13.529 13.52

Result of thermal output of the collector

0 2 4 6 8 10 12 14 16 18 20 22 240

50

100

150

200

250

300

350

400

450

500

Incident power at receiver(MW)

Thermal power produced by the field (MW)

Time

0 2 4 6 8 10 12 14 16 18 20 22 240

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8 Collector op-tical efficiency

Solar field ef-ficiency

Time

Efficie

ncy

Time (in hr.) from 7 a.m. to 7 p.m.

Total power incident on the field (MW)

Collector efficiency

Incident power at receiver

(MW)

Thermal power produced by the field (MW)

Solar field efficiency

7 0 0 0 0 0

8 73.1 0.0588 4.301 0 0

9 331.5 0.692 229.47 0 0

10 573.8 0.663 380.9 230.7 0.402

11 686.1 0.620 426.0 353.4 0.515

12 749.0 0.587 440.06 364.2 0.4862

13 749.0 0.573 429.75 356.1 0.4754

14 685.2 0.585 401.04 340.2 0.4965

15 525.4 0.617 324.25 290.8 0.5535

16 352.8 0.659 232.64 201.2 0.5703

17 158.9 0.702 111.61 80.1 0.5039

18 0 0 0 0 0

19 0 0 0 0 0

Table-Result of total energy output per hour and total efficiency of plant (1 st-January).

0 2 4 6 8 10 12 14 16 18 20 22 240

20000

40000

60000

80000

100000

120000Hourly energy output (kWh) vs Time (in hr.)

Time

Hour

ly e

nerg

y ou

tput

Time (in hr.) from 7a.m to 5 p.m.

Total power incident on the field (MW)

Hourly energy output (kWh) in a year

Total efficiency of plant (in %)

7 0 0 0

8 73.1172 0 0

9 331.578 0 0

10 573.885 0 0

11 686.111 84516.9 0.1802

12 749.026 95869.1 0.1701

13 749.026 94096.7 0.1663

14 685.261 98746.8 0.1737

15 525.424 101290 0.1937

16 352.833 94438.8 0.1996

17 158.987 0 0.1763

18 0 0 0

0 2 4 6 8 10 12 14 16 18 20 22 240

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.2

Overall efficiency of STPP vs TIME

Time (in hr.)

Ove

rall

efficie

ncy

Loss in Efficiency Due to Wind Speed

Particulars Value

Total Incident radiation on solar field 749.02 MWt

Thermal and optical loss 30.4 MWt

Losses due to wind speed 11.86 MWt

Percentage thermal loss by wind speed 1.58%

Solar field efficiency considering wind speed 47.5%

Solar field efficiency when wind speed is

not considered

49.08%

Power block efficiency 35%

Overall efficiency of STPP when wind speed

is not considered.

17.15 %

Overall efficiency considering wind speed 16.62 %

Hence change in efficiency due to wind

speed

0.53 %

ConclusionFor this study a STPP of 100 MWe net capacity has been considered. The

STPP ha been assumed to be located at a site in Delhi. For this study data of

1st day of the month of January at 1.00 p.m. has been considered. It is

concluded from the result that:

Total incident power at solar field is 749 MW from which 11.86 MWt power lost due to wind speed.

when wind speed is consider Solar field efficiency of the plant is 47.5% while when wind is not considered solar field efficiency is 49.05%.

When the effect of wind speed is considered overall efficiency of plant is 16.62% if wind speed is not considered solar field efficiency is found 17.15%. Hence there is a loss of 0.53 % of due to wind speed.

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Thank you…