INTERNATIONAL JOURNAL OF ENERGY RESEARCH

Int. J. Energy Res. 2011; 35:909–922

Published online 27 July 2010 in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/er.1748

Evaluation of solar aided thermal power generationwith various power plants

Qin Yan1, Eric Hu2,�,y, Yongping Yang1,z,y and Rongrong Zhai1

1School of Energy Power and Mechanical Engineering, Beijing Key Laboratory of Energy Safety and Clean Utilization, North China

Electric Power University, Beijing 102206, People’s Republic of China2School of Mechanical Engineering, The University of Adelaide, Adelaide SA5005, Australia

SUMMARY

Solar aided power generation (SAPG) is an efficient way to make use of low or medium temperature solar heat forpower generation purposes. The so-called SAPG is actually ‘piggy back’ solar energy on the conventional fuel firedpower plant. Therefore, its solar-to-electricity efficiency depends on the power plant it is associated with. In thepaper, the developed SAPG model has been used to study the energy and economic benefits of the SAPG with 200and 300MW typical, 600MW subcritical, 600MW supercritical, and 600 and 1000MW ultra-supercritical fuelpower units separately. The solar heat in the temperature range from 260 to 901C is integrated with above-mentioned power units to replace the extraction steam (to preheat the feedwater) in power boosting and fuel-savingoperating modes. The results indicate that the benefits of SAPG are different for different steam extracted positionsand different power plants. Generally, the larger the power plant, the higher the solar benefit if the same level solaris integrated. Copyright r 2010 John Wiley & Sons, Ltd.

KEY WORDS

solar aided thermal power generation; solar energy to electricity efficiency; coal consumption rate

Correspondence

*Eric Hu, School of Mechanical Engineering, The University of Adelaide, Adelaide SA5005, Australia.yE-mail: eric.hu@adelaide.edu.auzYongping Yang, School of Energy Power and Mechanical Engineering, Beijing Key Laboratory of Energy Safety and Clean Utilization,

North China Electric Power University, Beijing 102206, People’s Republic of China.yE-mail: yyp@ncepu.edu.cn

Received 3 January 2010; Revised 12 May 2010; Accepted 15 May 2010

1. INTRODUCTION

Solar energy is one of the clean and renewable green

resources, but its intermittent and low intensity nature,

thus low efficiency, constrain its application or increase

the costs significantly [1]. Therefore, the conventional

coal or gas-fired power plants are still dominant way to

generate base load electricity in the world for decades

to come [2,3], despite the pollution, green house gas

emission, and fossil fuel resource reduction draw more

and more critique to the conventional power plants [4].

Although the new designed ultra-supercritical coal-

fired plants have improved efficiencies to nearly

50% [5], they still cannot generate ‘green’ electricity

as solar and wind powers do. The conventional power

industry is under huge pressure with the forthcoming

renewable energy targets and carbon taxes set by

various governments. A real technical revolution is

needed to help the power industry to become cleaner

than before. Solar energy aided power [6] or equipment

[7] have been noticed and done some groping research

works in the whole world.

In this paper, solar thermal energy below 3001C (as

low as 901C) was assumed to be integrated with dif-

ferent capacities coal-fired power plants separately

(200 and 300MW typical, 600MW subcritical,

600MW supercritical and 600 and 1000MW ultra-

supercritical power units). In the integrations, steam

extractions from steam turbines are replaced by the

thermal oil from solar collectors to heat feedwater in

the thermal oil heater in both power boosting and fuel-

saving operating modes. The energy and economic

benefits after integration will be analyzed and dis-

cussed based on the developed models. The model will

Copyright r 2010 John Wiley & Sons, Ltd.

include steam turbine stages model, condenser model,

feedwater heater model, water mixer model, boiler

model, evaluating model and so on.

2. SYSTEM DESCRIPTION

2.1. Coal-fired power plant

Coal-fired power plants have been used for more than

one hundred years. In a typical regenerative and

reheating Rankine steam system, the boiler is com-

posed of furnace, drum, risers, superheaters, feedwater

heaters and economizer [8]. The combustion of coal

takes place in the boiler. The unsaturated feed-water

from condenser enters boiler after going through low-

pressure feedwater heaters and a deaerator, and then

enters high-pressure feedwater heaters. The super-

heated steam from the boiler enters the high-pressure

turbine to expand i.e. generate power, after reheated in

the boiler. The steam expands further through inter-

mediate pressure and lower pressure stages of the

turbine. At the end, the final exhaust steam is

condensed in the condenser. To increase the thermal

efficiency of the cycle, i.e. increasing the average heat

input temperature, parts of the steam is extracted at

the different locations of the turbine to pre-heat the

feedwater in the feedwater heaters. The deaerator is

actually an open type water heater in which steam mix

with the feedwater to preheat the feedwater and

remove the oxygen and other incoagulable gas from

the water. The feedwater heaters are typical shell-and-

tube closed type heaters.

2.2. Solar collector systems

There are two basic types of solar collectors, focusing

and non-focusing. Solar tower, solar dish and para-

bolic trough are three kinds of typical focusing

collectors. Linear parabolic concentrators in parabolic

trough type are used to focus sunlight to the receiver

running along the focal line of the collector. The solar

energy is absorbed by the heat transfer working fluid,

such as heat transfer oil or water/steam [9]. The

parabolic trough collector is typical medium tempera-

ture type, which can generate temperature up to 5001C.

Solar tower and solar dish are point focusing types;

they can generate higher temperature solar fluid. The

highest temperatures the solar tower can generate are

nearly 10001C [10]. If the focusing collectors are used

in a typical solar alone power station, the peak

thermal-electricity efficiency is about 20% [10,11].

A typical commercial medium temperature focusing

parabolic trough collector system is LS-2 in U.S.,

manufactured by LUZ Company. The collector system

has been used for the generation for the past two

decades. Table I lists the main parameters of the

system.

The vacuum tube and flat plate are non-focusing

type of collectors. Compared with focusing type col-

lectors, their investment costs are lower and almost

maintenance free, as the sun tracking system is not

required. However, a typical vacuum tube collector

with the selective coating can generate heat at maximal

temperature about 2001C, and a flat plat solar collector

can generate to 1001C [14].

2.3. Solar aided thermal power generation(SAPG)

Almost all combustion-based steam power plants are

running regenerative Rankine cycle thermodynami-

cally, in which part of the steam is bled-off/extracted

from the turbine to be used to pre-heat the boiler

feedwater from about 401C (from the condenser) to

3001C (to the boiler) [15]. By doing this, the overall

cycle thermal efficiency is increased, but the power

generated per unit steam passing through boiler is

reduced. In the SAPG, the bled-off steam is partly or

totally replaced by solar heat carried by heat transfer

fluid to preheat the feedwater, as shown in Figure 1.

Therefore, the saved bled-off steam continues to

expand in the turbine, to generate power. In Figure 1,

if the solar input cannot satisfy the demand to heat all

the distributed feedwater in cloudy days, the valves 1

and 2 can be adjusted to distribute part of the

feedwater to be heat by solar thermal oil. The ratio

of water flow through steam heater or thermal oil

heater is decided by sun radiation condition and

feedwater flow rate. In the nighttime, the valve 1 will

be opened and valve 2 closed, then the extracted steam

can heat the feedwater in original heater again. The

operating mode is back to conventional working

condition without integration.

Therefore, the advantages of the SAPG include:

(1) various temperature levels of solar heat can be in-

tegrated into various stages of the feedwater heaters;

(2) the solar to electricity conversion rate, i.e. efficiency

that is the power generated by the saved bled-off steam

to the solar heat input, is no longer limited by the

temperature of solar fluid as the solar does not directly

generate power; (3) the solar collectors using thermal

oil as the heat carrier can be used and (4) the benefit to

power station can come from either additional power

Table I. The system main parameters of the LS-2 system [12,13].

Name Parameters Value Unit

Solar collectors Length of single collector 47.1 m

Width of single collector 5 m

Area of single collector 235 m2

Focal length of the collector 1.84 m

Focal ratio of the collector 71 —

Absorber external diameter 70 mm

Envelope external diameter 115 mm

Evaluation of solar aided thermal power generationQ. Yan et al.

Int. J. Energy Res. 2011; 35:909–922 r 2010 John Wiley & Sons, Ltd.

DOI: 10.1002/er

910

generation with the same fuel consumption i.e. solar

boosting mode, or fuel and emission reduction while

keeping the same generating capacity i.e. fuel-saving

mode, shown in Figure 2. But in power boosting op-

erating mode, the output power exceeds the rated load

to reduce coal-fired energy consumption rate. In gen-

eral, the maximum safe power output (so-called

T-MCR working condition for a steam turbine) is

much higher than rated load, but the energy con-

sumption rate in the above working condition is also

much higher than in rated working condition. For

example, the maximum safe load for a 600MW unit is

about 645MW or much larger, 200MW unit has about

220MW maximum load.

3. MODELING AND VALIDATION OFCOAL-FIRED POWER SYSTEM

The mathematic simulation model to understand the

efficiencies of SAPG with various coal or gas fired

power plants has been developed and validated by their

designed values. Power units are grouped into sub-

critical, supercritical and ultra-supercritical according

to their designed steam parameters. The critical status

of water is 22.115MPa and 374.151C in thermody-

namics [5]. In a subcritical power plant, the steam

pressure and temperature from the boiler is lower than

the critical condition. If the steam’s parameters are

higher than the critical condition, but less than 25MPa

and 5931C, it is called supercritical. The ultra-super-

critical is defined as pressure higher than 25MPa and

temperature higher than 5931C [15,16]. Increasing

steam parameters to supercritical or ultra-supercritical

can get higher cycle efficiency and lower pollution

emission rate [17].

200 and 300MW subcritical units were the main

generating units in China before 2005. The perfor-

mance parameters of typical subcritical 200, 300

and 600MW, supercritical 600MW and ultra-super-

critical 600 and 1000MW are listed in Table II. The

steam and water flow and thermal system parameters

of a typical 600MW supercritical plant are drawn in

Figure 3. Other units’ descriptions are listed in

Table III.

The serial numbers in Table III are noted in

Figure 3. They are all important parameters to de-

scribe and evaluate a thermal system. The ‘—’ of

200MW unit means the vacant parameter, because the

selected 200MW unit only sets two high-pressure

feedwater heaters.

Steam

Heater

1

2Feedwater

Thermal oil heater

Solar collector

Oilpump

Figure 1. Schematic scheme of solar thermal energy replacing

one of bled-off steams.

0Power boosting mode

Pow

er o

utpu

t

Pow

er o

utpu

t

Fuel saving mode

Fuel

Fuel

Solar

Solar

2412 420(Hours)186 12 (Hours)186

Figure 2. Two operation modes of SAPG.

Evaluation of solar aided thermal power generation Q. Yan et al.

911Int. J. Energy Res. 2011; 35:909–922 r 2010 John Wiley & Sons, Ltd.

DOI: 10.1002/er

Table II. The main designed values of the selected units in 100% load.

Parameters Units

200 MW

subcritical

300 MW

subcritical

600 MW

subcritical

600 MW

supercritical

600 MW ultra

supercritical

1000 MW ultra

supercritical

Manufacturer — Beizhong — Hitachi Shangqi Shangqi Hitachi

Capacity MW 201.36 308.404 600 600 600 1000

Main steam parameters MPa 16.18 17.0 17.0 24.2 25.0 25.0

/1C 530 537 538 566 600 600

/1C 530 537 538 566 600 600

Feedwater flow rate t h�1 590.00 935.00 1810.383 1655.897 1598.77 2733.434

Condenser P kPa 5.4 5.5 5.41 4.9 4.9 4.5/5.7

Feedwater temp. 1C 246.13 268.84 271/5 273.8 283.7 294.8

Heat con. rate kJ kWh�1 7985.2 8005.71 7888.31 7517 7408 7354

Steam con. rate kg kWh�1 2.930 3.032 3.017 2.758 2.663 2.734

A C

D

E F G H

G.CHTR1HTR2HTR3HTR4HTR6HTR8

HTR5

273.8

1199.7

205.6

889.4

253.8

1104.5

211.2

903.2

180.2

779.0

137.8

580.4

99.98

419.0

105.5

442.5

86.36

361.6

56.51

236.5

80.80

338.3

50.95

213.2

39.19

164.1

33.63

140.8 99.04

415.0

32.54

136.3

174.9

741.1

To boiler

32.54

2346.9Boiler

HP IP LP LPIP

600.315 MW

B C DGH

301.2

2965.9

566.0

3598.8

--

3185.7

HTR7

185.7

788.5

248.3

1080.4

566.0

3396.0 24.2 MPa 1655.897 t/h

A

B

3.585 MPa

F E

0.919 MPa

5.688

3050.4

101.549

A3.863

2965.9

143.375

B1.747

3375.3

59.844

C0.891

3187.3

77.739

D0.3668

2972.0

81.237

E0.1117

2730.3

40.622

F0.05466

2616.3

60.499

G0.01481

2474.7

33.821

H--

--

1.499

I

I

Temperature C

Enthalpy kJ /kg

Pressure MPa

Enthalpy kJ /kg

Flow t/h

(1)

(2)(3)(4)(5)

(6)

(7)

(8)(9)

(10)

Figure 3. Steam and water flow and thermal system parameters of a 600 MW supercritical unit.

Table III. System parameters of other selected units.

1 2 3 4 5 6 7 8 9 10

Parameters MW 1C 1C 1C 1C 1C 1C 1C 1C 1C

200 MW subcritical 201.36 36.45 77.20 103.92 123.32 143.55 164.61 193.07 — 246.13

300 MW subcritical 308.40 35.69 83.12 103.34 124.52 145.75 169.23 198.31 242.25 268.83

600 MW subcritical 600.00 34.90 77.50 100.00 118.10 157.70 183.50 202.10 246.80 271.50

600 MW ultra-supercritical 600.27 33.67 53.97 74.09 94.89 134.80 171.00 207.80 248.40 283.00

1000 MW ultra-supercritical 1000.00 36.00 84.90 108.10 132.50 154.70 182.30 216.40 258.60 294.80

Evaluation of solar aided thermal power generationQ. Yan et al.

Int. J. Energy Res. 2011; 35:909–922 r 2010 John Wiley & Sons, Ltd.

DOI: 10.1002/er

912

As introduced before, an integrated thermal system

model is consisted of steam turbine stages model,

condenser model, feedwater heater model, water mixer

model, boiler model, evaluating model and so on. The

basic descriptions of the submodels are provided below.

3.1. Steam turbine stages model

The ideal process in a steam turbine stages is an

isentropic process in thermodynamical concept, sin 5

sout. Therefore, the ideal outlet steam specific enthalpy

hout can be calculated or found from steam tables when

the Pout and sout are known [18].

The ideal specific enthalpy change in the stages is:

Dh ¼ hin � hout ð1Þ

The real specific enthalpy change is:

Dh0 ¼ estage � Dh ¼ hin � h0out ð2Þ

where estage is the isentropic efficiency of the stages, %.

The real power output is:

Wout ¼ Fin � Dh0 ð3Þ

The real outlet steam enthalpy is:

h0out ¼ hin � Dh0 ð4Þ

The inlet steam flow rate entering next stages is the

difference of inlet flow of this stages and extraction

flow Fex. All the units of above enthalpies are kJ kg�1.

3.2. Condenser model

Condenser is one of the main equipments for maintaining

steam turbine backpressure. Its working performance

affects the units’ characters directly. In theory, the

condenser can be divided to pipe and shell sides,

according to its heat transfer principle. In pipe side,

cooling water is heated by condensed steam. The cooling

effect is decided by water flow rate, pipe structure and so

on. The shell side is consisted of steam section, condensed

water section and non-condensing gas section [19].

(1) Steam mass in shell side

d

dtMs ¼

XFsin �

XFsout ð5Þ

where Fsin is inlet steam mass, kg h�1; Fsout is outlet

steam mass, kg h�1.

(2) Air mass in shell side

d

dtMa ¼

XFain �

XFaout ð6Þ

where Fain is inlet air mass, kg h�1; Faout is outlet air

mass, kg h�1.

(3) Condensed steam mass

The vacuum in condenser is caused by condensed

steam, and its condensing effect also affects con-

denser’s working conditions. The condensed steam

mass is calculated by energy conversation.

Fc ¼as � Au � ðTs � TcÞ

Hs �Hcwð7Þ

where as is the condensing heat transfer efficiency

(W (m21C)�1), Au is the heat transfer area in shell side

(m2), Ts is the average temperature in condenser (1C),

Tc is the temperature of cooling water (1C) Hs is the

average steam enthalpy in condenser (kJ kg�1), Hcw is

the saturated water enthalpy in condenser (kJ kg�1).

(4) Partial steam pressure in shell side

State equation for ideal gas is applied for steam,

Ps � V ¼Ms � Rs � ðTs1273Þ. The partial differential of

the equation is

Ps ¼ P0s1dMsRs � ðTs1273Þ

Vð8Þ

where Ps is partial steam pressure in condenser (MPa),

P0s is the partial steam pressure at previous calculating

time (MPa), Rs is steam gas constant (J (kgK)�1), V is

the condenser’s volume (m3).

(5) Partial air pressure in shell side

As described in steam pressure, the partial air pres-

sure in shell side is

Pa ¼ P0a1dMaRa � ðTa1273Þ

Vð9Þ

where Ma is air mass in condenser (kg h�1), Pa is

partial air pressure in shell side (MPa), P0a is the partial

air pressure at previous calculating time (MPa), Ra is

air gas constant (J (kgK)�1).

(6) Pressure in shell side

The total pressure in shell side is the sum of partial

steam and air pressures.

P ¼ Ps1Pa ð10Þ

(7) Cooling water outlet temperature

According to energy balance in condenser,

McwCwd

dtT11T2

2

� �¼ Qc �DwCwðT2 � T1Þ ð11Þ

where T1 and T2 are cooling water inlet and outlet

temperature (1C), Qc is absorbed heat by cooling water

(kJ), Dw is cooling water mass flow rate (kg h�1), Cw is

cooling water thermal capacity (kJ (kg 1C)�1), Mcw is

the kept cooling water in condenser (kg).

3.3. Feedwater heater model

Feedwater heaters are typical close heaters, the feed-

water is heated by extracted steam from steam turbine.

The heater can be sorted into higher-pressure and

lower-pressure heaters, according to the inlet steam

parameters. The heater consists of steam side and air

side in shell side, and the pipe side is feedwater side.

The main mathematic descriptions are

(1) Average steam enthalpy in steam side

The average steam enthalpy in feedwater heaters is

calculated by energy and mass balance principles.

Hsteama ¼Fsteam �Hsteam1

PF �Hc

Fsteam1P

Fð12Þ

where Hsteama is the average steam enthalpy (kJ kg�1),

Fsteam and Hsteam are mass flow rate and enthalpy of

Evaluation of solar aided thermal power generation Q. Yan et al.

913Int. J. Energy Res. 2011; 35:909–922 r 2010 John Wiley & Sons, Ltd.

DOI: 10.1002/er

extracted steam (kg h�1 and kJ kg�1),P

F �Hc is total

vaporized steam energy (kJ).

(2) Condensed steam mass in steam side

Fcon ¼Kcon � F0:8

win � ð1� foulÞHsteama �Hcw

�Twin � Twout

2ð13Þ

where Kcon is heat transfer efficiency in feedwater side

(W (m21C)�1), Fwin is feedwater mass flow rate

(kg h�1), foul is fouling factor in feedwater side, Hcw is

saturated feedwater enthalpy in special pressure

(kJ kg�1), Twin and Twout are inlet and outlet feedwater

temperature (1C).

(3) Feedwater heater pressure

The total pressure of heater is the sum of partial

steam pressure and air pressure.

Pr ¼ Prs1Pra ð14Þ

(4) Outlet feedwater temperature

The outlet temperature of heated feedwater by ab-

sorbed condensed steam can be calculated by the fol-

lowing equation.

dcw �Mw � ðTwin1TwoutÞ

dt¼ Fwin � cw � ðTwin � TwoutÞ1Fcon � ðHsteam �HcwÞ

ð15Þ

where cw is water specific heat capacity (kJ (kg 1C)�1),

Mw is water mass in pipe side (kg h�1).

3.4. Deaerator model

Deaerator in coal-fired power plant is used for

removing oxygen in feedwater, by heating water to

saturated state. Oxygen in feedwater can corrupt

steel equipments and harm safety and economic

characters. In this study, the deaerator is only an

open water-steam heater. So the basic heat balance

equation is

where Hwater is outlet feedwater enthalpy (kJ kg�1),

Hsteam and Fsteam are enthalpy and mass flow rate of

extracted steam (kJ kg�1 and kg h�1), Hfeedwater and

Ffeedwater are feedwater enthalpy and mass flow rate

from lower-pressure heaters (kJ kg�1 and kg h�1),

Hdrain and Fdrain are drain water enthalpy and mass

flow rate from higher-pressure heaters (kJ kg�1

and kg h�1), Hother and Fother are enthalpy and

mass flow rate of other inlet water or steam (kJ kg�1

and kg h�1).

3.5. Boiler model

Boiler is the main equipment in thermal power plants

to combust fuel to heat water or steam. Boiler is the

energy resource for an integrated thermal circle. Its

main characteristic parameters are superheated and

reheated steam temperature, pressure, flow rate and

fuel consumption rate. As described in deaerator

model, boiler is considered as a ‘black box’ with input

and output parameters of temperature, enthalpy, mass

flow rate and pressure.

The standard coal consumption rate can be calcu-

lated by energy balance principle.

where Mscoal is the standard coal consumption rate

(kg h�1), Hmsteam and Fmsteam are enthalpy and mass

flow rate of main steam (kJ kg�1 and kg h�1), Hmwater

is main feedwater enthalpy (kJ kg�1), Hrsteamout and

Frsteamout are outlet enthalpy and mass flow rate of

reheated steam (kJ kg�1 and kg h�1), Hrsteamin is inlet

reheated steam enthalpy (kJ kg�1), qscoal is standard

coal thermal value (kJ kg�1).

3.6. System evaluating model

The benefits in terms of efficiency and fuel saving of

various levels of solar heat in various power stations

are modeled in this study. To evaluate the benefit or

the efficiency of the solar heat utilization, the solar to

power efficiency (Zse) and solar percentage (psolar) in

the above solar aided thermal power generation is

defined as follows:

Zse ¼DWe

Qsolar� DQboiler� 100% ð18Þ

psolar ¼Qsolar

Qboiler1Qsolar� 100% ð19Þ

where DWe is the increased power output after the

solar replacement (kW), Qsolar is the solar heat

transferred into the feedwater heater (kW), DQboiler is

the possible change of the thermal energy load in boiler

after replacement, e.g. boiler reheating load would

increase if the replaced bled-off is before re-heating

(kW). The other impacts after the solar integration,

e.g. the minor changes of pumps work for steam

and oil are not included in the calculation. ‘7’ in

Equation (18) means the changed boiler heat demands,

it is ‘1’ if the integration adds boiler heat load, but ‘�’when decreasing boiler heat load.

Mscoal ¼ðHmsteam �HmwaterÞ � Fmsteam1ðHrsteamout �HrsteaminÞ � Frsteamout

qscoalð17Þ

Hwater ¼Hsteam � Fsteam1Hfeedwater � Ffeedwater1Hdrain � Fdrain1Hother � Fother

Fsteam1Ffeedwater1Fdrain1Fotherð16Þ

Evaluation of solar aided thermal power generationQ. Yan et al.

Int. J. Energy Res. 2011; 35:909–922 r 2010 John Wiley & Sons, Ltd.

DOI: 10.1002/er

914

Other criteria used in the study are specific steam

consumption rate, heat consumption rate and standard

coal consumption rate, which are defined as below:

Specific steam consumption rate is the mass of steam

(passing trough boiler) for per kWh electrical power

generated (kg kWh�1) defined as

d ¼D

Wð20Þ

where D is boiler steam flow rate (kg h�1), W is elec-

trical energy output the plant (kWhh�1).

Heat consumption rate is the per kWh fuel heat

consumption, for per kWh electrical power generated

(kJ kWh�1) defined as

q ¼Q

Wð21Þ

where Q is the total heat load in boiler per hour (kJh�1).

Standard coal consumption rate (generating coal

consumption rate) is standard coal consumption for

per kWh (g kWh�1) defined as

b ¼M

Wð22Þ

where M is the coal consumption (per hour) converted

to the standard coal (29 298 kJ kg�1), in kg h�1.

The feedwater heating system of the selected

200MW subcritical unit is more complex than others,

with the additional five drain water heat exchangers

and two water mixers. The thermodynamic submodels

developed for the conventional power plant can accu-

rately simulate the performance of the power plants.

The main sub models will be connected and debugged

according to the real steam and water flow direction.

Then, all the modeled power plants are validated with

simulated and designed values in Table IV.

The advantages of the supercritical and ultra-su-

percritical units are clear. The selected six units are

typical in steam flow and structure. Therefore, other

similar unit in capacity has analogous characters. The

error percentages in Table IV indicate the great pre-

cision between the designed and simulated results. The

main error source is the neglected parts of gland lea-

kages and make-up water flows, especially for 200MW

subcritical unit with more water mixing and hybrid. In

general, the total model precision can satisfy project

modeling demands.

4. ANALYSIS OF SOLAR AIDEDTHERMAL POWER SYSTEM

As discussed above, the purpose of extracted steam

from turbine is to preheat the feedwater, thus reducing

the heat demand in boiler resulting the higher cycle

efficiency. However, the steam passing the turbine

and power generated are reduced due to the extraction.

In the SAPG system, the solar heat carried by thermal

oil is to replace the extraction steam to preheat

the feedwater while the saved steam is allowed to

continue through the turbine to generate power. In the

system, medium temperature solar heat less than

3001C, from non-concentration types of solar collec-

tors, can be used to generate power through saved

extraction steam because the highest and lowest

temperatures required for feedwater heaters are less

than 260 and 901C respectively in normal power

stations. The assumed temperature differences between

thermal oil and feedwater demands are all about 151C

here. The differences are normal in industry and they

are easy to achieve.

Table IV. Comparison between simulated and designed values.

Parameters Units

200 MW

subcritical

300 MW

subcritical

600 MW

subcritical

600 MW

supercritical

600 MW ultra-

supercritical

1000 MW ultra-

supercritical

Output power DV� MW 201.36 308.404 600 600.315 600.274 1000.000

SV�� MW 200.24 308.673 600.00 600.314 600.271 1000.163

(error) (%) (0.56) (0.087) (0) (0) (0.005) (0.02)

Feedwater temperature DV 1C 246.13 268.83 271.5 273.8 283.00 294.80

SV 1C 245.58 269.08 271.45 275.93 284.55 294.77

(error) (%) (0.22) (0.093) (0.015) (0.78) (0.55) (0.01)

Steam consumption rate DV kg kWh�1 2.930 3.032 3.017 2.758 2.663 2.734

SV kg kWh�1 2.946 3.031 3.017 2.758 2.663 2.733

(error) (%) (0.55) (0.033) (0) (0) (0) (0.04)

Heat consumption rate DV kJ kWh�1 7985.20 8005.71 7888.31 7517 7408.00 7354.00

SV kJ kWh�1 8072.04 8010.67 7897.99 7533.88 7388.74 7330.37

(error) (%) (0.01) (0.062) (0.12) (0.22) (0.26) (0.32)

Coal consumption rate DV g kWh�1 272.83 273.53 269.52 256.83 253.11 251.26

SV g kWh�1 275.79 273.70 269.85 257.41 252.45 250.45

(error) (%) (0.01) (0.062) (0.12) (0.22) (0.26) (0.32)

�DV, designed value; ��SV, simulated values.

Evaluation of solar aided thermal power generation Q. Yan et al.

915Int. J. Energy Res. 2011; 35:909–922 r 2010 John Wiley & Sons, Ltd.

DOI: 10.1002/er

4.1. 200 MW subcritical unit

As described in Table II, the solar heat can be used to

replace the steams entering the first high-pressure

heater (HTR7), the second high-pressure heater

(HTR6), the first low-pressure heater (HTR4) and

the last low-pressure heater (HTR1), which are at 260,

215, 160 and 901C, respectively. And the temperature

difference between feedwater demand and the solar

thermal oil temperature of HTR7 is 141C, with outlet

feedwater temperature 2461C; HTR6 is 201C, HTR4

171C and HTR1 131C. The results for integrating solar

into the 200MW subcritical power unit are shown in

Table V. Four replacements are operated in power

boosting and fuel-saving modes to analyze separately.

In Table V, four cases of solar replacements are si-

mulated and analyzed in two operating modes. In the

case of replacing HTR7 steam, the coal consumption

rate in power boosting mode is reduced by 20 g kWh�1,

while increasing 20MW power output. But it is not

recommended to long-term running in this mode due

to safety limitation unless the unit is retrofitted. In fuel-

saving mode, the coal consumption rate is reduced by

18 g kWh�1 in the replacing HTR7 case, while main-

taining the base load 200MW. In the case of replacing

HTR4, the original steam entering HTR4 is 13.28 t h�1

extraction steam mixed with 3.65 t h�1 gland leakage

steam, after extraction steam is replaced by solar heat;

the gland leakage steam now enters the next heater

HTR3. The 901C solar heat can also achieve reduced

coal consumption rate by about 3 g kWh�1.

4.2. 300 MW subcritical unit

The results for integrating solar energy into the

300MW subcritical power unit are shown in Table VI.

Compared with the results in Table V, there are

slight differences, because of the different steam

parameters and heat demands. It should be noted that

the power generation efficiency of 901C thermal oil

from solar energy is higher as 13.65%, which is very

difficult for any solar (alone) thermal power generating

systems to achieve in industry.

4.3. 600 MW subcritical unit

For the 600MW subcritical unit in Table III, the

second high-pressure heater (HTR7), the third high-

pressure heater (HTR6), the second low-pressure

heater (HTR3) and the first low-pressure heater

(HTR1) are selected to be replaced by 260, 215, 160

and 901C thermal oil in both power boosting and fuel-

saving operating modes. The results are listed in

Table VII.

It seems that the benefits of the larger power gen-

eration unit with solar aiding are more obvious than 200

and 300MW units listed above. The solar heat (at

2601C) to electricity efficiency is 40%. When replacing

the first high-pressure HTR7, the gland leakage steam

10 mixing with extraction 8 is moved to mix with steam

9 to enter into the gland steam heater G.C., the feed-

water temperature from G.C. will have a few increasing.

4.4. 600 MW supercritical unit

The thermal balance diagram of a 600MW super-

critical unit is shown in Table III, which has the similar

structure to the 600MW subcritical one. The solar

thermal oil is used to replace the second high-pressure

heater HTR7 at 2601C, the third high-pressure heater

HTR6 at 2151C, the forth low-pressure heater HTR4

at 1601C and the second low-pressure heater HTR2 at

901C separately. The simulation results are shown in

Table VIII.

In Table VIII, the greater reduction of heat (coal)

consumption rates indicates that the solar integration

Table V. Comparisons of the 200 MW subcritical unit in different replacements.

Replacing HTR7

steam

Replacing HTR6

steam

Replacing HTR4

steam

Replacing HTR1

steam

Schemes

Parameters Units

Base

case

Power

boosting

Fuel

saving

Power

boosting

Fuel

saving

Power

boosting

Fuel

saving

Power

boosting

Fuel

saving

Oil temp.demand 1C — 260 260 215 215 160 160 90 90

Feedwater temp. 1C 245.58 245.52 245.54 249.85 251.09 245.54 246.08 245.58 246.92

Feedwater flow t h�1 589.99 589.99 541.69 589.99 577.89 589.99 584.30 589.99 584.60

Condenser flow t h�1 434.39 496.37 448.07 453.49 441.39 447.67 441.98 434.39 429.00

Output power MW 200.24 219.72 200.12 205.02 200.12 202.55 200.24 202.40 200.21

Coal con. t h�1 55.17 56.19 51.58 54.79 53.54 55.17 54.58 55.17 54.54

Heat con. rate kJ kWh�1 8072.04 7492.55 7551.45 7829.59 7838.07 7890.53 7986.14 7985.85 7980.73

Steam con. rate kg kWh�1 2.946 2.685 2.707 2.878 2.888 2.913 2.918 2.915 2.920

Coal con. rate g kWh�1 275.79 256.00 258.01 267.51 267.80 272.67 272.86 272.85 272.68

Input solar heat MW 0 46.88 37.53 23.56 21.60 10.34 9.05 21.14 20.85

Solar to power eff % 0 36.58 — 25.48 — 22.33 — 10.65 —

Solar percentage % 0 10.25 8.94 5.28 4.96 2.30 2.04 4.71 4.70

Evaluation of solar aided thermal power generationQ. Yan et al.

Int. J. Energy Res. 2011; 35:909–922 r 2010 John Wiley & Sons, Ltd.

DOI: 10.1002/er

916

has greater advantage in the supercritical plant. The

solar-to-electricity efficiency is also higher than that in

the subcritical unit in Table VI, but the solar heat

demand is also increasing.

4.5. 600 MW ultra-supercritical unit

The thermal balance diagram of a 600MW ultra-

supercritical unit is given in Table III. The solar

heat at the same temperature levels (as previous

cases) is integrated. The simulated benefits in terms

of power boosting and fuel saving are listed in

Table IX.

In the ultra-supercritical unit, the extracted steam in

low-pressure heaters are all from low-pressure stages of

the turbine with lower steam quality. Therefore, the

benefits of using solar to replace the extracted steam

are limited when compared with the above 600 and

300MW sub or supercritical units.

4.6. 1000 MW ultra-supercritical unit

The 1000MW ultra-supercritical unit modeled is a

product of Hitachi, in Table III. Solar heat was

integrated into the third high-pressure heater (HTR6),

the third and forth low-pressure heaters (HTR4 6 and

HTR3) and the last heater (HTR1).

From Table X it can be seen that for the 1000MW

ultra-supercritical unit, the benefits, i.e. the reduced

energy consumption rate and solar-to-electricity effi-

ciency, are smaller than that in the supercritical units.

But the average coal consumption rate difference be-

tween ultra-supercritical and subcritical units are all

about 15 g kWh�1, with great energy-saving potential.

Table VI. Comparisons of the 300 MW subcritical unit in different replacements.

Replacing

HTR7 steam

Replacing

HTR6 steam

Replacing

HTR4 steam

Replacing

HTR1 steam

Schemes

Parameters Units

Base

case

Power

boosting

Fuel

saving

Power

boosting

Fuel

saving

Power

boosting

Fuel

saving

Power

boosting

Fuel

saving

Oil temp.demand 1C — 260 260 215 215 160 160 90 90

Feedwater temp. 1C 269.08 269.08 270.96 269.24 270.51 269.08 270.53 269.08 270.96

Feedwater flow t h�1 935.64 935.64 874.54 933.25 915.40 935.64 924.14 935.64 926.14

Condenser flow t h�1 735.34 815.23 754.13 767.79 749.94 735.34 723.84 735.34 725.84

Output power MW 308.67 334.31 308.65 316.16 308.67 313.51 308.68 312.65 308.66

Coal con. t h�1 84.40 85.77 79.88 84.15 82.33 84.40 83.13 84.40 83.26

Heat con. Rate kJ kWh�1 8010.67 7516.78 7582.65 7798.26 7814.69 7887.13 7890.50 7908.74 7902.78

Steam con. Rate kg kWh�1 3.013 2.799 2.833 2.952 2.966 2.984 2.994 2.993 3.001

Coal con. rate g kWh�1 273.70 256.82 259.07 266.44 267.00 269.48 269.59 270.22 270.01

Input solar heat MW 0 59.54 44.03 31.12 27.62 19.38 17.88 29.15 28.76

Solar to power eff % 0 36.24 — 24.08 — 22.79 — 13.65 —

Solar percentage % 0 8.53 6.77 4.54 4.12 2.82 2.64 4.24 4.24

Table VII. Comparisons of the 600 MW subcritical unit in different replacements.

Replacing HTR7

steam

Replacing HTR6

steam

Replacing HTR3

steam

Replacing HTR1

steam

Schemes

Parameters Units

Base

case

Power

boosting

Fuel

saving

Power

boosting

Fuel

saving

Power

boosting

Fuel

saving

Power

boosting

Fuel

saving

Oil temp. demand 1C — 260 260 215 215 160 160 90 90

Feedwater temp. 1C 271.45 271.45 273.26 271.45 272.37 271.45 272.56 271.45 273.07

Feedwater flow t h�1 1810.38 1810.383 1687.143 1810.383 1784.413 1810.383 1796.223 1810.383 1794.903

Condenser flow t h�1 1444.55 1603.416 1480.176 1517.789 1458.778 1444.548 1430.388 1444.548 1429.068

Output power MW 600.00 652.89 600.00 611.15 600.00 606.08 600.00 606.64 600.00

Coal con. t h�1 161.74 164.40 152.66 161.75 159.12 161.75 160.15 161.75 159.89

Heat con. Rate kJ kWh�1 7897.99 7377.45 7454.62 7754.00 7769.79 7818.80 7820.00 7811.51 7807.32

Steam con. Rate kg kWh�1 3.017 2.773 2.812 2.962 2.974 2.987 2.994 2.984 2.992

Coal con. Rate g kWh�1 269.85 252.06 254.70 264.93 265.47 267.14 267.18 266.89 266.75

Input solar heat MW 0 109.96 78.87 35.77 30.69 37.68 36.62 53.33 53.25

Solar to power eff % 0 40.26 — 31.16 — 16.13 — 12.46 —

Solar percentage % 0 8.23 6.36 2.72 2.37 2.87 2.81 4.06 4.10

Evaluation of solar aided thermal power generation Q. Yan et al.

917Int. J. Energy Res. 2011; 35:909–922 r 2010 John Wiley & Sons, Ltd.

DOI: 10.1002/er

Table VIII. Comparisons of the 600 MW supercritical unit in different replacements.

Replacing

HTR7 steam

Replacing

HTR6 steam

Replacing

HTR4 steam

Replacing

HTR2 steam

Schemes

Parameters Units

Base

case

Power

boosting

Fuel

saving

Power

boosting

Fuel

saving

Power

boosting

Fuel

saving

Power

boosting

Fuel

saving

Oil temp. demand 1C — 260 260 215 215 160 160 90 90

Feedwater temp. 1C 275.93 275.66 277.81 275.76 277.15 275.81 278.42 275.89 277.20

Feedwater flow t h�1 1655.895 1665.273 1548.732 1655.895 1618.715 1655.895 1624.595 1655.895 1644.915

Condenser flow t h�1 1273.388 1426.141 1309.600 1333.232 1296.052 1273.388 1242.088 1273.388 1262.408

Output power MW 600.314 654.70 600.317 617.50 600.147 614.721 600.115 605.213 600.090

Coal con. t h�1 154.37 158.43 146.76 154.40 150.50 154.39 150.75 154.38 153.00

Heat con. Rate kJ kWh�1 7533.88 7089.88 7162.35 7325.83 7346.95 7358.49 7359.89 7473.28 7469.78

Steam con. rate kg kWh�1 2.758 2.544 2.580 2.682 2.697 2.694 2.707 2.736 2.741

Coal con. Rate g kWh�1 257.41 242.24 244.71 250.30 251.02 251.42 251.46 255.34 252.22

Input solar heat MW 0 102.00 72.50 56.12 48.73 59.61 55.92 36.75 36.25

Solar to power eff % 0 41.22 — 30.94 — 23.27 — 12.75 —

Solar percentage % 0 7.91 6.07 4.44 3.98 4.72 4.56 2.91 2.91

Table IX. Comparisons of the 600 MW ultra-supercritical unit in different replacements.

Replacing

HTR7 steam

Replacing

HTR6 steam

Replacing

HTR4 steam

Replacing

HTR2 steam

Schemes

Parameters Units

Base

case

Power

boosting

Fuel

saving

Power

boosting

Fuel

saving

Power

boosting

Fuel

saving

Power

boosting

Fuel

saving

Oil temp. demand 1C — 260 260 215 215 160 160 90 90

Feedwater temp. 1C 284.55 284.55 286.722 284.55 286.43 284.55 287.14 284.55 285.24

Feedwater flow t h�1 1598.772 1598.772 1505.912 1598.722 1556.912 1598.772 1570.532 1598.771 1593.429

Condenser flow t h�1 1206.641 1332.717 1239.857 1275.251 1233.391 1206641 1178.401 1206.641 1201.299

Output power MW 600.271 645.512 600.279 620.655 600.265 614.028 600.272 602.866 600.264

Coal con. t h�1 151.38 154.18 144.63 151.38 146.85 151.38 148.01 151.38 150.70

Heat con. rate kJ kWh�1 7388.74 6997.83 7058.90 7146.07 7167.73 7223.20 7223.84 7356.93 7355.21

Steam con.rate kg kWh�1 2.663 2.477 2.509 2.576 2.594 2.604 2.616 2.652 2.655

Coal con. Rate g kWh�1 252.45 239.09 241.18 244.16 244.90 246.79 246.81 251.38 251.30

Input solar heat MW 0 104.30 79.19 72.81 63.49 55.67 52.79 28.63 28.48

Solar to power eff % 0 35.61 — 28.00 — 24.71 — 9.06 —

Solar percentage % 0 8.31 6.71 5.91 5.31 4.50 4.38 2.32 2.31

Table X. Comparisons of the 1000 MW ultra-supercritical unit in different replacements.

Replacing

HTR6 steam

Replacing

HTR4 steam

Replacing

HTR3 steam

Replacing

HTR1 steam

Schemes

Parameters Units

Base

case

Power

boosting

Fuel

saving

Power

boosting

Fuel

saving

Power

boosting

Fuel

saving

Power

boosting

Fuel

saving

Oil temp. demand 1C — 260 260 215 215 160 160 90 90

Feedwater temp. 1C 294.77 294.76 296.57 294.77 296.47 294.77 296.49 294.77 296.94

Feedwater flow t h�1 2733.434 2733.434 2664.434 2733.434 2699.234 2733.434 2703.834 2733.434 2705.655

Condenser flow t h�1 2076.699 2184.318 2115.318 2076.699 2042.499 2076.699 2047.099 2076.699 2048.920

Output power MW 1000.163 1033.53 1000.038 1016.701 1000.102 1014.407 1000.04 1013.606 1000.123

Coal con. t h�1 250.24 250.24 242.95 250.24 246.29 250.24 246.72 250.24 246.70

Heat con. Rate kJ kWh�1 7330.37 7093.76 7117.74 7211.14 7215.07 7227.45 7228.06 7233.16 7227.04

Steam con. Rate kg kWh�1 2.733 2.645 2.664 2.689 2.699 2.695 2.704 2.697 2.705

Coal con. rate g kWh�1 250.45 242.37 243.19 246.38 246.51 246.94 246.96 247.13 246.92

Input solar heat MW 0 106.57 91.73 55.77 51.32 66.26 63.68 119.45 117.82

Solar to power eff % 0 31.31 — 29.65 — 21.50 — 11.25 —

Solar percentage % 0 5.24 4.64 2.74 2.56 3.38 3.17 5.87 5.87

Evaluation of solar aided thermal power generationQ. Yan et al.

Int. J. Energy Res. 2011; 35:909–922 r 2010 John Wiley & Sons, Ltd.

DOI: 10.1002/er

918

5. THERMAL AND ECONOMICBENEFIT ANALYSIS

The solar-to-electricity (power) efficiency, the reduced

fuel consumption rate and solar percentage are selected

to compare the merits of solar integration among

various power plants in power boosting and fuel-

saving modes. The results of solar-to-electricity effi-

ciencies for all six different units in same solar

temperatures in power boosting operating mode are

shown in Figure 4.

Table XI shows the reduced coal consumption rate

breduced and the solar percentage psolar in different in-

tegrations in fuel-saving operating modes. It can be

seen that generally, the higher the solar heat tem-

perature, more significant the benefits for the same

unit. But the rates of input solar heat in different steam

extraction structures and parameters are changed with

different units. Input solar heat under 901C for

1000MW unit is much more than the 2601C working

condition, but the other units are the opposite. The

reason for the difference of 1000MW unit is that the

designed increased temperature (heat demand) of the

replaced lower-pressure heater is higher than others.

To show the comparison of solar integration clearly,

the results of three 600MW units all in power boosting

operating models are shown in Figure 5. Apparently,

subcritical and supercritical power plants are more

beneficial for solar integration, especially for low

temperature solar heat, compared with ultra-super-

critical plants. The solar percentages for replacing

2151C extracted stream in the 600MW ultra-super-

critical unit is higher than subcritical and supercritical

units, but the reduced coal consumption rate is less

than the two units. Meanwhile, the coal consumption

rates in fuel-saving operating mode will increase a bit

when compared with the power boosting mode.

For some integrating modes, especially in replacing

the higher pressure extraction steam, if the power out-

put exceeds the long-term safe limitation in power

boosting mode, then the integration system could adjust

valves 1 and 2 in Figure 1 to decrease the power output

05

1015202530354045

90 160 215 260

200MW sub critical unit 300MW sub critical unit

600MW sub critical unit 600MW super critical unit

600MW ultra supercritical unit 1000MW ultra supercritical unit

Solar Thermal Oil Temperature ( C)

Sola

r to

ele

ctri

city

eff

icie

ncy

(%)

1-

4-

12 3 4

56

2-

5-

3-

6-

1

2

3

4 56

12

3 45 6 6

5

43

21

Figure 4. Comparison analysis of the solar to electricity

efficiencies (in power boosting mode).

Tab

leX

I.C

om

parison

analy

sis

of

the

reduced

coalconsum

ption

rate

sand

sola

rperc

enta

ges

(In

fuelsavin

gm

ode).

200

MW

subcriticalunit

300

MW

subcriticalunit

600

MW

subcriticalunit

600

MW

superc

riticalunit

600

MW

ultra

-superc

ritical

unit

1000

MW

ultra

-superc

ritical

unit

Para

mete

rsb

reduced

psola

r(Q

sola

r)b

reduced

psola

r(Q

sola

r)b

reduced

psola

rb

reduced

psola

rb

reduced

psola

rb

reduced

psola

r

Therm

aloil

tem

pera

ture

gkW

h�

1%

(MW

)g

kW

h�

1%

(MW

)g

kW

h�

1%

(MW

)g

kW

h�

1%

(MW

)g

kW

h�

1%

(MW

)g

kW

h�

1%

(MW

)

901C

3.1

14.7

3.6

94.2

43.1

04.1

5.1

92.9

11.1

52.3

13.5

35.8

7

(20.8

5)

(28.7

6)

(53.2

5)

(36.2

5)

(28.4

8)

(117.8

2)

1601C

2.9

32.0

44.1

12.6

42.6

72.8

15.9

54.5

65.6

44.3

83.4

93.1

7

(9.0

5)

(17.8

8)

(36.6

2)

(55.9

2)

(52.7

9)

(63.6

8)

2151C

7.9

94.9

66.7

04.1

24.3

82.3

76.3

93.9

87.5

55.3

13.9

42.5

6

(21.6

0)

(27.6

2)

(30.6

9)

(48.7

3)

(63.4

9)

(51.3

2)

2601C

17.8

88.9

414.6

36.7

715.1

56.3

612.7

06.0

711.2

76.7

17.2

64.6

4

(37.5

3)

(44.0

3)

(78.8

7)

(72.5

0)

(79.1

9)

(91.7

3)

Evaluation of solar aided thermal power generation Q. Yan et al.

919Int. J. Energy Res. 2011; 35:909–922 r 2010 John Wiley & Sons, Ltd.

DOI: 10.1002/er

or change to fuel-saving operating mode. In other ways,

if the weather condition often changes, adjusting system

will work frequently. In order to avoid the parameter

fluctuating, a small heat storage system can be set to

stabilize the temperature changes between solar col-

lector and thermal oil heater. But the installed heat

storage system will increase investment cost apparently.

In addition, the solar heat demands in fuel-saving mode

is smaller than the power boosting mode for same re-

placement in Tables V–X. But the reduced coal con-

sumption rates are also a little small compared with the

power boosting operating mode. Meanwhile, the units

operated in fuel-saving mode are much safer, because

the power output is always below the rated load.

In economic analysis, the capital cost for the typical

parabolic trough solar collector system (maximum

temperature below 3501C) is about 2000 h kW�1 in

international market [20], less than 1500 h kW�1 in

China. But the coal price is about 55–80 h t�1 in China.

Therefore, the payback period of the integration is

acceptable, especially under the encouraged policy

from the government. For example, in China, the

prices of electricity output from sustainable energy

(including solar energy, wind energy and so on) are

much higher than the conventional coal-fired power

plants. The potential carbon tax will also accelerate the

process of energy-saving reform. The benefits of the

SAPG are much more observable in the future.

In addition, the above-mentioned integrating modes

studied only the effect and benefits of replacing single

feedwater heater. If the solar collector system can af-

ford enough heat demands to satisfy replacing two or

more heaters, the benefits will be more remarkable.

6. CONCLUSIONS

In this paper, using SAPG concept [21], i.e. integrating

solar heat at various temperature levels of 260, 215,

160 and 901C in the 200MW typical, 300 and 600MW

subcritical, 600MW supercritical and 600 and

1000MW ultra-supercritical power plants are modeled.

Thus their benefits in terms of integrated with solar

energy to preheat the feedwater both in power

boosting and fuel-saving models are studied and

compared.

The results indicate that the SAPG technique can

achieve higher solar (to power) efficiency compared to

the solar alone power plant and is more suitable to be

adopted in subcritical and supercritical plants than in

ultra-supercritical plants. The solar energy can play a

significant (up to 20%) and ecumenically competitive

role in providing base load power generation once the

SAPG principle. Therefore, the SAPG is proved the-

oretically to be the most efficient way to make use of

solar energy especially at low-to-medium temperature

ranges for power generation purposes.

NOMENCLATURE

SAPG 5 solar aided power generation

P 5 pressure (MPa)

temp. 5 temperature (1C)

con. 5 consumption

sin 5 inlet steam entropy (kJ kg�1)

sout 5 outlet steam entropy (kJ kg�1)

hin 5 inlet steam-specific enthalpy (kJkg�1)

hout 5 ideal outlet steam-specific enthalpy

(kJ kg�1)

h0out 5 real outlet steam-specific enthalpy

(kJ kg�1)

Dh 5 ideal enthalpy change (kJ kg�1)

Dh0

5 real enthalpy change (kJ kg�1)

estage 5 the isentropic efficiency of the stages

(%)

Fin 5 inlet steam mass flow rate (kg h�1)

Wout 5 real power output (kW)

0

5

10

15

20

25

30

35

40

45

90 160 215 260

600MW sub critical unit solar to electricity eff. 600MW sub critical unit solar percentage

600MW 600MW super critical unit solar percentage

600MWultra super critical unit solar to electricity eff. 600MWultra super critical unit solar percentage

Solar Thermal Oil Temperature(oC)

Sola

r to

ele

ctri

city

eff

icie

ncy

(%)

/Sol

ar p

erce

ntag

e (%

)

super critical unit solar to electricity eff.

1-

2-

3-

1

1

1

1

2

2

2

2

3

33

3

a-

b-

c-

a b c ab c

ab c

a b c

Figure 5. Solar to electricity efficiencies and solar percentages in 600 MW power boosting operating modes.

Evaluation of solar aided thermal power generationQ. Yan et al.

Int. J. Energy Res. 2011; 35:909–922 r 2010 John Wiley & Sons, Ltd.

DOI: 10.1002/er

920

Fex 5 steam extraction flow rate (kg h�1)

Ms 5 steam mass in shell side of the

condenser (kg h�1)

Fsin 5 inlet steam mass of the condenser

(kg h�1)

Fsout 5 outlet steam mass of the condenser

(kg h�1)

Ma 5 air mass in shell side of the con-

denser (kg h�1)

Fain 5 inlet air mass of the condenser

(kg h�1)

Faout 5 outlet air mass of the condenser

(kg h�1)

Fc 5 condensed steam mass of the con-

denser (kg h�1)

as 5 the condensing heat transfer effi-

ciency (W (m21C)�1)

Au 5 the heat transfer area in shell side

(m2)

Ts 5 the average temperature in conden-

ser (1C)

Tc 5 the temperature of cooling water

(1C)

Hs 5 the average steam enthalpy in con-

denser (kJ kg�1)

Hcw 5 the saturated water enthalpy in con-

denser (kJ kg�1)

Ps 5 partial steam pressure in condenser

(MPa)

P0s 5 partial steam pressure at previous

calculating time (MPa)

Rs 5 steam gas constant (J (kgK)�1)

V 5 condenser’s volume (m3)

Ma 5 air mass in condenser (kg h�1)

Pa 5 partial air pressure in shell side of the

condenser (MPa)

P0a 5 partial air pressure at previous cal-

culating time (MPa)

Ra 5 air gas constant (J (kgK)�1)

P 5 pressure in shell side of the conden-

ser (MPa)

Mcw 5 the kept cooling water in condenser

(kg)

Cw 5 cooling water thermal capacity

(kJ (kg 1C)�1)

Dw 5 cooling water mass flow rate (kg h�1)

Qc 5 absorbed heat by cooling water (kJ)

T1 5 cooling water inlet temperature (1C)

T2 5 cooling water outlet temperature (1C)

Hsteama 5 the average steam enthalpy (kJ kg�1)

Fsteam 5mass flow rate of extracted steam

(kg h�1)

Hsteam 5 enthalpy of extracted steam (kJ kg�1)PF �Hc 5 total vaporized steam energy (kJ)

Fcon 5 condensed steam mass in steam side

of the feedwater heater (kg h�1)

Kcon 5 heat transfer efficiency in feedwater

side (W (m21C)�1)

Fwin 5 feedwater mass flow rate (kg h�1)

foul 5Fouling factor in feedwater side

Hcw 5 saturated feedwater enthalpy in spe-

cial pressure (kJ kg�1)

Twin 5 inlet feedwater temperature (1C)

Twout 5 outlet feedwater temperature (1C)

Pr 5 feedwater heater pressure (MPa)

Pr,s 5 partial steam pressure of the feed-

water heater (MPa)

Pra 5 partial air pressure of the feedwater

heater (MPa)

Twin 5 inlet temperature of heated feed-

water (1C)

Twout 5 outlet temperature of heated feed-

water (1C)

cw 5water specific heat capacity

(kJ (kg 1C)�1)

Mw 5water mass in pipe side of the heater

(kg h�1)

Hwater 5 outlet feedwater enthalpy (kJ kg�1)

Hsteam 5 enthalpy of extracted steam (kJ kg�1)

Fsteam 5mass flow rate of extracted steam

(kg h�1)

Hfeedwater 5 feedwater enthalpy from lower-pres-

sure heaters (kJ kg�1)

Ffeedwater 5 feedeater mass flow rate from lower-

pressure heaters (kg h�1)

Hdrain 5 drain water enthalpy from higher-

pressure heaters (kJ kg�1)

Fdrain 5 drain water mass flow rate from

higher-pressure heaters (kg h�1)

Hother 5 enthalpy of other inlet water or

steam (kJ kg�1)

Fother 5mass flow rate of other inlet water or

steam (kg h�1)

Mscoal 5 the standard coal consumption rate

(kg h�1)

Hmsteam 5 enthalpy and mass flow rate of main

steam (kJ kg�1)

Fmsteam 5mass flow rate of main steam

(kg h�1)

Hmwater 5main feedwater enthalpy (kJ kg�1)

Hrsteamout 5 outlet enthalpy of reheated steam

(kJ kg�1)

Frsteamout 5 outlet mass flow rate of reheated

steam (kg h�1)

Hrsteamin 5 inlet reheated steam enthalpy

(kJ kg�1)

qscoal 5 standard coal thermal value (kJ kg�1)

Zse 5 the solar to power efficiency (%)

psolar 5 the solar percentage (%)

DWe 5 the increased power output after the

solar replacement (kW)

Qsolar 5 the solar heat transferred into the

feedwater heater (kW)

DQboiler 5 the possible change of the thermal

energy load in boiler after replace-

ment (kW)

Evaluation of solar aided thermal power generation Q. Yan et al.

921Int. J. Energy Res. 2011; 35:909–922 r 2010 John Wiley & Sons, Ltd.

DOI: 10.1002/er

d 5 specific steam consumption rate

(kg kWh�1)

D 5 boiler steam flow rate (kg h�1)

W 5 electrical energy output the plant

(kWhh�1)

q 5 heat consumption rate (kJ kWh�1)

Q 5 the total heat load in boiler per hour

(kJ h�1)

b 5 standard coal consumption rate

(g kWh�1)

M 5 the coal consumption (per hour)

converted to the standard coal

(29 298 kJ kg�1) (kg h�1)

breduced 5 the reduced coal consumption rate

(kg kWh�1)

DV 5 designed value

SV 5 simulated values

ACKNOWLEDGEMENTS

We are grateful for the project (No. 2009CB219801),funding from National Basic Research Program ofChina-973 program, and China National NaturalScience Fund Project (No. 50776028) to support theresearch.

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