AbstractIn this work transient simulation results of a hybrid solar tower power plant with openvolumetric receiver technology are presented for several locations in China. The openvolumetric receiver uses ambient air as heat transfer fluid and the hybridization can be realized with additional firing. The solar receiver and/or the additional firing heat up the air which is then passed through a boiler of a conventional Rankine cycle. The simulated plantis based on the configuration of the solar thermal test and demonstration power plant located in Jülich (STJ). The investigatedplant operates in hybrid - parallelmode which allows a constant power generation. The meteorological data for the different sites in China was taken from the software Meteonorm in a time resolution of one hour. The solar tower power simulation tool was developed in the simulation environment MATLAB/Simulink

Alexoupoulos, S.

Kronhardt, V.

Latzke, M.

Rendón, C.

Sattler, J.

Elsevier - Publisher Connector 

Comparison of Potential Sites in China for Erecting a Hybrid Solar Tower Power Plant with Air Receiver 

 Energy Procedia  69 ( 2015 )  1327 – 1334 
Available online at www.sciencedirect.com
ScienceDirect
1876-6102 © 2015 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license 
(http://creativecommons.org/licenses/by-nc-nd/4.0/).
Peer review by the scientific conference committee of SolarPACES 2014 under responsibility of PSE AG
doi: 10.1016/j.egypro.2015.03.142 
International Conference on Concentrating Solar Power and Chemical Energy Systems, 
SolarPACES 2014 
Comparison of potential sites in China for erecting a hybrid solar 
tower power plant with air receiver 
M. Latzkea,*, S. Alexoupoulosa, V. Kronhardta, C. Rendóna, J. Sattlera 
aFH Aachen, Aachen University of Applied Sciences, Solar-Institut Jülich (SIJ), Heinrich-Mussmann-Str. 5,52428 Jülich, Germanny 
Abstract 
In this work transient simulation results of a hybrid solar tower power plant with open volumetric receiver technology are 
presented for several locations in China. The open volumetric receiver uses ambient air as heat transfer fluid and the 
hybridization can be realized with additional firing. The solar receiver and/or the additional firing heat up the air which is then 
passed through a boiler of a conventional Rankine cycle. The simulated plant is based on the configuration of the solar thermal 
test and demonstration power plant located in Jülich (STJ). The investigated plant operates in hybrid - parallel mode which 
allows a constant power generation. The meteorological data for the different sites in China was taken from the software 
Meteonorm in a time resolution of one hour. The solar tower power simulation tool was developed in the simulation environment 
MATLAB/Simulink. 
 
© 2015 The Authors. Published by Elsevier Ltd. 
Peer review by the scientific conference committee of SolarPACES 2014 under responsibility of PSE AG. 
Keywords: hybrid concept; solar tower power plant; transient simulation; open volumetric air receiver; China 
1. Introduction  
The world’s first solar tower power plant based on the open volumetric receiver technology is in operation in 
Jülich, Germany, since December 2008. This test and demonstration plant is operated by the German Aerospace 
Center (DLR). At the heart of the solar tower power plant Jülich is the open volumetric receiver technology which 
 
 
* Corresponding author. Tel.: +49-241-6009-53551; fax:+49-241-6009-53570. 
E-mail address: latzke@sij.fh-aachen.de 
© 2015 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license 
(http://creativecommons.org/licenses/by-nc-nd/4.0/).
Peer review by the scientific conference committee of SolarPACES 2014 under responsibility of PSE AG
1328   M. Latzke et al. /  Energy Procedia  69 ( 2015 )  1327 – 1334 
consists of porous ceramic absorber modules [1]. The receiver transforms concentrated solar irradiation from the 
heliostat field into heat. The receiver is cooled with ambient air which blowers suck through the absorber modules. 
The air heats up to 680 °C as it passes through the absorber modules. The hot air is then passed through a heat 
recovery steam generator (HRSG) of a conventional steam Rankine cycle. 
Nomenclature 
DNI direct normal irradiation 
HRSG heat recovery steam generator 
LCOE levelized cost of electricity 
2. Selection of locations 
Simulation results of a hybrid concept of such air receiver solar power tower were carried out and analyzed for 
locations in the middle of the north of China. Figure 1 shows the mean annual values of the solar irradiation 
calculated through Meteonorm for the year 2005 for seven potential sites. 
Fig. 1. Direct solar radiation (mean annual values) in China [2] 
Out of the seven sites, three were selected for further analysis: 1. The desert region of Alxa Zuoqi in Inner 
Mongolia east of the city of Yinchuan, 2. Yinchuan-City and 3. Taiyuan-City. The selected locations satisfy the 
following criteria: access to natural gas supply, dissimilar values of DNI and altitude. The used geographical and 
solar data are shown in Table 1. 
  Table 1. Geographic coordinates and solar conditions of selected locations 
Location  Latitude [°] 
Longitude 
[°] 
Altitude 
[m] 
DNI 
[KWh/(m²a)] 
Location 1: Desert 38.79 N 104.54 E 1345 1074.73 
Location 2: Yinchuan –City 38.48 N 106.23 E 1111 977.97 
Location 3: Taiyuan –City 37.87 N 112.54 E 788 668.73 
 
A representation of a monthly distribution of the diffuse and global solar radiation of the three selected locations 
is shown in Figure 2. Additionally, the monthly ambient Temperatures for these locations are illustrated in Figure 3.  
 
 M. Latzke et al. /  Energy Procedia  69 ( 2015 )  1327 – 1334 1329
 a.    b.    c. 
Fig. 2. Monthly solar radiance (a) Location 1, (b) Location 2, (c) Location 3 [3] 
 a.    b.    c. 
Fig. 3. Monthly ambient Temperature (a) Location 1, (b) Location 2, (c) Location 3 [3] 
Location 2 and 3 show a higher diffuse radiation in comparison to location 1. These higher diffuse irradiation 
values possibly arise due to influencing air pollution caused by the nearby densely populated regions as well as 
higher humidity levels in the air especially during summer time. Location 1 and location 2 have very similar global 
irradiation values. The direct irradiation levels from location 1 are slightly higher than at the other locations due to 
the effect of clear sky and lack of vegetation which is typical of desert regions. All three locations have a similar 
ambient Temperature distribution throughout the year. 
3. Plant configuration of the hybrid solar tower concept  
This kind of solar thermal power plant allows the uncomplicated integration of a natural gas burner into the air 
piping system (Figure 4). In the presented concept, a thermal energy storage system is not considered as the 
supplementary firing will provide the thermal power difference required for the steam cycle to operate at nominal 
conditions at times when solar radiation is insufficiently high or (temporarily) unavailable.  
 
 
 
 
 
 
 
 
Fig. 4. Schematic of the hybrid open volumetric solar tower power plant 
1330   M. Latzke et al. /  Energy Procedia  69 ( 2015 )  1327 – 1334 
The objective of the hybrid operation strategy is to keep the mass flow and temperature of the hot air entering the 
HRSG constant and close to the design condition in order to reach a high thermal efficiency. During night time the 
Rankine cycle will be operated by the gas burner only allowing 24 hour operation of the plant. 
 
The access to natural gas supply piping plays an important role for the location of the plant. The gas price 
considered for the evaluation of the hybrid concept is 0.45 €/m³. The electricity price for the heavy industrial sector 
is assumed to be 0.06 €/kWh [4][5]. The presented plant configuration (cf. Fig. 4) is taken for the simulation of all 
three simulated power tower sites. The boundary conditions of the plant are listed in Table 2. A constant and 
identical air mass flow rate was considered for all three locations. 
Table 2. Technical data of the hybrid concept 
 Value Unit 
Operational concept Parallel solar-hybrid (burner) - 
Heliostat field area 25,000 m² 
Tower height 60 m 
Hot air Temperature 680 °C 
Steam turbine power  1.8 MWe 
Cooling concept Dry air cooling - 
4. Simulation tool 
4.1. Description of used simulation model and abilities 
For being able to compute the annual electricity production of a solar thermal power plant with air receiver, a 
complex software tool was developed at the Solar-Institut Jülich (SIJ) [6] over the past few years. The simulation 
model was programmed in MATLAB/Simulink [7] and is based on a model library (cf. Fig. 2) which includes most 
of the components of the power plant. A plant is built up by interconnecting individual components. Most 
components are represented as steady-state models and are programmed either with underlying physical models or 
user-defined performance maps. For some of the components with high thermal inertia such as the receiver, the 
thermal energy storage system, the HRSG and the deaerator, transient models were developed. The combination of 
steady-state and transient models allows maintaining a fast computation speed [8][9]. 
 
    
Fig. 5. Model libraries for solar cycle (left), Rankine (middle) and hybrid (right) components 
To increase the HSRG model accuracy, a more detailed transient HRSG model was developed to include all 
effects that describe the transient behavior caused by the fluctuating solar power. These transient models also 
consider variations of the gas mixture entering the HRSG and fluctuations of the water steam cycle conditions 
 M. Latzke et al. /  Energy Procedia  69 ( 2015 )  1327 – 1334 1331
caused by the change of the ambient temperature. This detailed transient HRSG model was used for the simulations 
of the presented work. 
 
For validating the software tool and especially of the transient models, the simulated values were compared to 
measured data of the STJ. Validations of individual components such as the HRSG [9] as well as of the complete 
power plant system were carried out. First validations of the electrical output of simulation and real plant data show 
good agreement. 
4.2. Simulation of hybrid concept for locations in China 
The hybrid concept presented in this work was implemented in MATLAB/Simulink by interconnecting the 
individual plant component models according to the described plant layout (cf. Fig. 4). Using Meteonorm weather 
data for the period of January to December 2005, the hybrid concept was simulated for the three locations in China 
(cf. Table 1). For each simulation a set of parameters was specified and used as input for the simulation. The 
implemented operation strategy defined for the hybrid plant facility for the annual simulation is based on constant 
nominal electrical power generation. When the DNI profile decreases, the thermal power output of the receiver drops 
down as a result. In solar only mode there are two possible applicable operation strategies: i) maintaining a constant 
air temperature level by continuously adapting the mass flow to the solar radiation input or ii) maintaining a constant 
air mass flow which results in the air temperature to fluctuate according to the level of solar radiation input. For the 
investigated hybrid concept the air mass flow was kept constant at nominal level during night time and periods of the 
day with low solar radiation. A fuel mass flow rate control was implemented for the burner to maintain the set point 
air temperature at the boiler inlet. The temperature of the condenser was simulated by taking into account ambient 
temperature variation and a constant cooling system power.  
4.3. Results 
The operation strategy implemented for the simulation fulfills a parallel hybrid operation with a gas burner as 
described in 4.2. Figure 6 shows the DNI, fuel mass flow rate and the generated electrical power of the steam 
turbine’s generator from 26th to 27th May 2005. The day 26 May 2005 was an operation day with fluctuating solar 
irradiation whereas the 27 May 2005 showed a solar irradiation profile with little fluctuations. Figure 7 shows the 
simulated temperature profiles of the air at the receiver outlet and burner outlet, the steam temperature at the steam 
turbine inlet as well as the air mass flow rate. 
 
 
 
 
 
 
 
 
 
Fig. 6. Fuel mass flow rate and electrical power generation for days with different DNI profile. 
1332   M. Latzke et al. /  Energy Procedia  69 ( 2015 )  1327 – 1334 
 
Fig. 7. Simulated temperatures levels at receiver, burner and steam turbine, and mass flow at the burner output. 
The air mass flow in the boiler remains almost constant at the normalized nominal mass flow value. The 
normalized air mass flow slightly increases during night operation due to the increased fuel mass flow which is 
mixed into the air mass flow when the solar irradiation decreases. This increase in air mass flow as well as a 
decreased condenser temperature at night time led to a low increase of the electrical power generation. Due to the 
decrease of the ambient Temperature during the night, the Temperature of the cooling fluid in the condenser also 
drops down. Figure 8 shows the air ambient Temperature profile during the 26th and 27th May. The temperature in 
the supplementary firing system is automatically switched on when the available solar irradiation cannot provide the 
thermal power required to maintain the set point gas temperature. 
Fig. 8. Ambient temperature level  
In Figure 6 and 7 it is shown that at low solar irradiation the maximum air temperature reaches only 75 % of the 
nominal temperature. In this period the burner operates in parallel with the solar receiver to increase the nominal 
temperature to 100 %. In this period of parallel operation the burner’s fuel mass flow is above 25 %. On the second 
day of operation (cf. Fig. 6-7) the receiver temperature reaches nominal level between 11:40 a.m. and 1:20 p.m. and 
consequently the burner is switched off during that period; instead, the electrical power decreases slightly due to the 
 M. Latzke et al. /  Energy Procedia  69 ( 2015 )  1327 – 1334 1333
missing fuel mass flow rate from the burner side. Significant reduction of the fuel consumption is noticed on days 
with clear sky and steady solar irradiation. During the night hours the burner operates at nominal power and the fuel 
mass flow is accordingly high. The calculated annual operation costs of the hybrid solar tower power plant concept 
for the three investigated locations are illustrated in Figure 9 below. 
 
 
 
 
 
 
Fig. 9. Operation cost for (a) Location 1, (b) Location 2, (c) Location 3 
The cost of the consumed fuel represents a share of 66 % of the total operation costs at Location 1. This is 
followed by labor costs with 22 % of the total operation costs. The main electrical power consumer with respect to 
parasitic costs due to own consumption are the air blowers. Maintaining a constant air flow rate throughout the 
plant’s operation, the air blowers contribute 6 % of the total cost. In comparison to the other two locations, 
Location 1 has the lowest fuel consumption because it has slightly higher monthly direct solar radiation values. 
With 1 % and 2 % respectively, the difference in fuel consumption of Location 2 and 3 compared Location 1 is very 
small. Further calculated results of fuel consumption, solar share and LCOE for the different locations are 
summarized in Table 3. 
 Table 3. Normalized fuel consumption and LCOE 
 Unit Location 1 Location 2 Location 3 
Fuel consumption  - 1.000 1.017 1.080 
Solar share  % 16 14 10 
LCOE - 1.000 1.008 1.037 
 
The fuel consumption at Location 2 and Location 3 is 1.7 % and 8 % higher than at Location 1. As a consequence 
of the high fuel consumption, the LCOE at Location 3 is 3.7 % higher than at Location 1. With a difference of 0.8 % 
in LCOE and 1.26 % in solar share between Locations 1 and 2 are fairly similar. The lowest solar share was 
calculated for Location 3; only about 9.67 % of the thermal energy required for nominal operation is provided by the 
solar side. 
5. Conclusion 
The simulation tool developed at the SIJ can be used for carrying out detailed and transient simulations of hybrid 
plant concepts for any defined site. The investigated sites with high annual solar irradiation energy resource have 
lower gas consumption costs due to the higher solar share. This leads to an increase in the solar tower power plant’s 
investment costs for installing the necessary infrastructure. Further investigation regarding the selection of an ideal 
location should be carried out for large hybrid solar tower power plants and should include costs for installing 
necessary piping infrastructure. 
Despite of the large differences in the DNI profile between the three investigated locations, small variation in fuel 
consumption, solar share und LCOE were predicted. Even for Location 1, which has the best solar conditions 
throughout the year among the investigated sites, the consumption of natural gas for the operation of the burner 
1334   M. Latzke et al. /  Energy Procedia  69 ( 2015 )  1327 – 1334 
during night operation is foreseen to be high. Based on the solar and weather conditions of the two simulated days, a 
hybrid plant of small capacity as presented here therefore has a fossil fuel dependency of about 85 % when operated 
round-the-clock.  
The highest solar share of about 15 % is achieved for Location 1 while the solar share for Location 3 
is 6 % lower. This difference in solar share leads to an additional annual fuel consumption of 8 % compared to 
Location 1. The fuel consumption to solar share ratio is approximately 1.33. 
The potential sites in China to erect a hybrid solar tower power plant are locations with annual solar radiation 
resources above 950 kWh/(m²a). Significant differences between Location 1 and 2 are hardly seen.  
Acknowledgements 
The authors gratefully acknowledge the financial support for the solar tower demonstration project given by the 
German Federal Ministry for Environment, Nature Conservation, Building and Nuclear Safety (BMU), the Federal 
Ministry of Economics and Technology (BMWi). The research in plant simulation is supported by the German 
Ministry of Education and Research (BMBF). 
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Comparison of Potential Sites in China for Erecting a Hybrid Solar Tower Power Plant with Air Receiver

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