# D6.1 Measurement Technique and Experimental Protocols for the Testing and Evaluation of the Prototype of Plant

Alain Ferriere, Frédéric Pithoud

► To cite this version:

Alain Ferriere, Frédéric Pithoud. D6.1 Measurement Technique and Experimental Protocols for the Testing and Evaluation of the Prototype of Plant. [Research Report] European Union. 2022. hal-04750964

HAL Id: hal-04750964

https://cnrs.hal.science/hal-04750964v1

Submitted on 28 Oct 2024

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_1.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
<figure><img src="image_2.png" /></figure>

<figure><img src="image_3.png" /></figure>

POLYPHEM

THE FUTURE OF SMALL-SCALE CSP PLANTS

POLYPHEM
Small-Scale Solar Thermal Combined Cycle

# D6.1 Measurement techniques and experimental protocols for the testing and evaluation of the prototype of plant

Date of delivery 19/05/2022

Author(s) Alain FERRIERE, Frédéric PITHOUD

Institution/Company CNRS

<figure><img src="image_4.png" /></figure>

<figure><img src="image_5.png" /></figure>

This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 764048.
## Document tracks

<table><tr><td>Identification</td><td>POLYPHEM_D6.1_Measurement techniques &amp; experimental protocols for testing &amp; evaluation_final</td></tr><tr><td>TITLE OF DELIVERABLE</td><td>Measurement techniques and experimental protocols for the testing and evaluation of the prototype of plant</td></tr><tr><td>Author(s)</td><td>Alain Ferriere, Frédéric Pithoud</td></tr><tr><td>Reviewers(s)</td><td>Simon Schütrumpf, Richard Aumann, Esther Rojas</td></tr><tr><td>Related Work Package (s)</td><td>WP6: Testing and validation of the technology</td></tr><tr><td>Beneficiary responsible of delivery</td><td>CNRS</td></tr><tr><td>Due date of delivery</td><td>31/10/2021</td></tr><tr><td>Actual date of submission/revision</td><td>19/05/2022</td></tr><tr><td>Number of pages</td><td>43</td></tr><tr><td>SUMMARY</td><td>This document is the deliverable D6.1 of the project POLYPHEM. The instrumentation is composed of sensors installed on the process at appropriated locations to measure the physical parameters which are relevant for the control of the plant and for the performance assessment. The sensors are connected to a data acquisition system capable of real time monitoring and recording of all data.<br>The experimental protocols describe the operation parameters needed to validate the technology and assess the performance of each component and of the overall plant.</td></tr><tr><td>Dissemination level</td><td>Public (PU)</td></tr><tr><td>Repository</td><td>https://dms.POLYPHEM-project.eu</td></tr></table>

## Document History and Validation

<table><thead><tr><td>Date</td><td>Name</td><td>Comments</td></tr></thead><tbody><tr><td>15/02/2021</td><td>Frédéric Pithoud</td><td>Creation</td></tr><tr><td>26/04/2022</td><td>Alain Ferriere</td><td>Completion</td></tr><tr><td>05/05/2022</td><td>Simon Schütrumpf</td><td>Review</td></tr><tr><td>10/05/2022</td><td>Richard Aumann</td><td>Review</td></tr><tr><td>12/05/2022</td><td>Esther Rojas</td><td>Review</td></tr><tr><td>13/05/2022</td><td>Alain Ferriere</td><td>Final version</td></tr></tbody></table>

All information in this document only reflects the author's view. The European Commission is not responsible for any use that may be made of the information it contains.
## Background: about the POLYPHEM project

<table><tr><td>FULL TITLE</td><td>SMALL-SCALE SOLAR THERMAL COMBINED-CYCLE</td></tr><tr><td>Acronym</td><td>POLYPHEM</td></tr><tr><td>Call identifier</td><td>H2020 LCE-07-2017-RES-RIA-TwoStage</td></tr><tr><td>Instrument</td><td>Research and Innovation Action (RIA)</td></tr><tr><td>Grant Agreement N°</td><td>764048</td></tr><tr><td>Starting Date</td><td>01/04/2018</td></tr><tr><td>Duration</td><td>48 months</td></tr><tr><td>Website</td><td>https://www.POLYPHEM-project.eu</td></tr><tr><td>Keywords</td><td>Renewable electricity; Energy collection, conversion and storage; Renewable energy</td></tr><tr><td>Additional keywords</td><td>Concentrated solar power; Solar tower system; Combined cycle; Gas-turbine; Thermal energy storage; Organic Rankine cycle; Process control</td></tr><tr><td>Beneficiaries</td><td>CNRS, CEA, CIEMAT, Arraela S.L., Fraunhofer ISE, Kaefer SE, Orcan Energy, Euronovia, Aalborg CSP</td></tr></table>

The POLYPHEM project is a research and innovation action funded by the European Union's H2020 program. It is implemented by a European consortium of 4 research centres and 5 industrial partners. The aim is to increase the flexibility and improve the performance of small solar tower power plants. The concept of POLYPHEM consists in implementing a combined cycle formed by a solarized micro gas-turbine and a Rankine organic cycle machine, with an integrated thermal storage device between the two cycles. The need for cooling is minimal.

Developed from a patented technology by CNRS and CEA, the pressurized air solar receiver is integrated in the micro-turbine cycle. The thermal efficiency targeted for the receiver is 80% with a cost of 400 €/kW. The innovative thermal storage uses a thermal oil and a single thermocline tank with a technical concrete filler material.

The main expected impact of this project is to enhance the competitiveness of low-carbon energy production systems through the technology developed. The expected progress is a better fitting of electricity generation to variable local needs, an overall conversion efficiency of solar energy into electricity of 18% for an investment cost of less than 5 €/W and a low environmental impact. By 2030, the cost of electricity production targeted by the POLYPHEM technology is 165 €/MWh for an annual direct normal irradiation of 2600 kWh/m²/year (North Africa and Middle East) and 209 €/MWh under 2050 kWh/m²/year (Southern Europe). In addition to decentralized power generation, other applications are considered for the deployment of this technology used in poly-generation: industrial heat production, solar heating and cooling, desalination of seawater or brackish water.

A prototype plant of 60 kWel with a thermal storage of 1300 kWh is designed, built and installed on the site of the experimental solar tower of Themis in Targasonne (France). The objective of the project is to validate the technical choices under test conditions representative of actual operating conditions.

*This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 764048*
Table of content

<table><tr><td>1. SUMMARY</td><td>7</td></tr><tr><td>2. SHORT DESCRIPTION OF THE PROCESS</td><td>7</td></tr><tr><td>2.1 Air circuit of the POLYPHEM plant</td><td>7</td></tr><tr><td>2.2 HTF circuit of the POLYPHEM plant</td><td>7</td></tr><tr><td>2.3 Process of the prototype plant</td><td>8</td></tr><tr><td>3. MEASUREMENT TECHNIQUES</td><td>12</td></tr><tr><td>3.1 Solar resource assessment</td><td>12</td></tr><tr><td>3.1.1 Meteo station</td><td>12</td></tr><tr><td>3.1.2 Sunshape measurement</td><td>13</td></tr><tr><td>3.2 Instrumentation of solar receiver</td><td>15</td></tr><tr><td>3.3 Instrumentation of gas-turbine and power block (top cycle)</td><td>16</td></tr><tr><td>3.4 Instrumentation of the recovery heat exchanger</td><td>17</td></tr><tr><td>3.5 Instrumentation of the thermal storage tank</td><td>17</td></tr><tr><td>3.5.1 Temperature in the thermal storage tank</td><td>19</td></tr><tr><td>3.5.2 Level in the thermal storage tank</td><td>21</td></tr><tr><td>3.6 Instrumentation of Organic Rankine Cycle</td><td>21</td></tr><tr><td>3.6.1 Temperature in the ORC</td><td>21</td></tr><tr><td>3.6.2 Pressure in the ORC</td><td>21</td></tr><tr><td>3.6.3 Further instruments in the ORC</td><td>23</td></tr><tr><td>3.7 Instrumentation of Balance of Plant</td><td>23</td></tr><tr><td>3.7.1 Mass flowrate in the BOP</td><td>23</td></tr><tr><td>3.7.2 Temperature in the BOP</td><td>23</td></tr><tr><td>3.7.3 Pressure in the BOP</td><td>24</td></tr><tr><td>3.7.4 Level in the HTF tank</td><td>24</td></tr><tr><td>4. EXPERIMENTAL PROTOCOLS</td><td>24</td></tr><tr><td>4.1 Process flow diagrams</td><td>24</td></tr><tr><td>4.2 Operation of the gas-turbine in fuel mode</td><td>25</td></tr><tr><td>4.2.1 Start-up</td><td>25</td></tr><tr><td>4.2.2 Power generation in fuel mode</td><td>26</td></tr><tr><td>4.2.3 Stop</td><td>26</td></tr><tr><td>4.3 Operation of the gas-turbine in solar mode</td><td>26</td></tr><tr><td>4.3.1 Start-up of gas-turbine in solar mode</td><td>26</td></tr><tr><td>4.3.2 Power generation in solar mode</td><td>26</td></tr><tr><td>4.3.3 Normal stop of gas-turbine in solar mode</td><td>27</td></tr><tr><td>4.3.4 Testing of the emergency stop procedure in solar mode</td><td>27</td></tr><tr><td>4.4 Thermal charging of the TES</td><td>27</td></tr><tr><td>4.4.1 Charging in electric mode</td><td>27</td></tr><tr><td>4.4.2 Isothermal method in electric mode</td><td>28</td></tr><tr><td>4.4.3 Charging in solar mode</td><td>29</td></tr><tr><td>4.4.4 Isothermal method in solar mode</td><td>30</td></tr><tr><td>4.4.5 Cooling-down mode of the TES</td><td>31</td></tr><tr><td>4.5 Off-sun operation of the ORC: discharging of the TES</td><td>31</td></tr><tr><td>4.6 Operation of the ORC in solar mode</td><td>32</td></tr></table>
4.6.1 Low demand of electricity: TES charging 32

4.6.2 High demand of electricity: TES discharging 32

5. PERFORMANCE ASSESSMENT 32

5.1 Performance of solar receiver 33

5.2 Performance of gas-turbine power block 33

5.3 Performance of recovery heat exchanger 35

5.4 Performance of electrical heater 36

5.5 Performance of ORC power block 36

5.6 Performance of thermal energy storage 37

6. SUPERVISORY CONTROL AND DATA ACQUISITION 38

REFERENCES 43

List of Figures

Figure 1: Process and Instrumentation Diagram of the POLYPHEM plant: air circuit 9

Figure 2: Process and Instrumentation Diagram of the POLYPHEM plant: HTF circuit 10

Figure 3: Final version of the P&ID of POLYPHEM prototype plant 11

Figure 4: Meteo station of CNRS at Themis: solar irradiance (a) and other meteorological parameters (b) 12

Figure 5: Recorded image of the sun which is used for the CSR calculation 13

Figure 6: Radial distribution of the sun image 13

Figure 7: Example evaluation of DNI (orange), theoretical DNI (green) and measured CSR values (red dotted) on a clear summer day 14

Figure 8: Example evaluation of DNI (orange), theoretical DNI (green) and measured CSR values (red dotted) on a cloudy summer day. Attention: CSR y-scale is changed 14

Figure 9: histogram of all the CSR measurements taken in august 2020 in Freiburg. Most of the measured values of CSR are around 2% – 5% 14

Figure 10: Instrumentation of the solar receiver 15

Figure 11: Instrumentation of the recovery heat exchanger 17

Figure 12: Instruments of the thermal energy storage tank (vertical cross section) 18

Figure 13: Instruments of the thermal energy storage tank (horizontal cross section) 19

Figure 14: P&ID of the organic Rankine Cycle system in POLYPHEM 22

Figure 15: Protocol for thermal charging of the TES in electric mode 28

Figure 16: Protocol for the assessment of the thermal loss by the isothermal method in electric mode 29

Figure 17: Protocol for the thermal charging of the TES in solar mode 30

Figure 18: Protocol for the assessment of the thermal loss by isothermal method in solar mode 31

Figure 19: Protocol for the off-sun operation of the ORC (left: demand of electricity is met, right: electricity generation may be reduced when the thermocline zone is harvested) 31

Figure 20: Protocols for the operation of the ORC in solar mode (Left: low demand of electricity, Right: high demand of electricity) 32

Figure 21: Typical ideal Brayton cycle (left: p,V diagram – right: T,s diagram) 34

Figure 22: Control cabinet of POLYPHEM by CNRS (left) and control cabinet or ORC by ORCAN (right) 38

Figure 23: Screenshot of the supervision - Example of display of the process and of measured signals 40
## List of Tables

<table><tr><td>Table 1: thermocouples and their positions in the TES tank</td><td>20</td></tr><tr><td>Table 2: Configurations of plant for the experiment</td><td>25</td></tr><tr><td>Table 3: Maximum acceptable temperature for each component</td><td>33</td></tr><tr><td>Table 4: KPIs of Solar Receiver</td><td>33</td></tr><tr><td>Table 5: KPI of Gas-Turbine</td><td>34</td></tr><tr><td>Table 6: KPIs of Recovery Heat Exchanger (RHX)</td><td>35</td></tr><tr><td>Table 7: KPI of electrical Heater (elHe)</td><td>36</td></tr><tr><td>Table 8: KPIs of the Organic Rankine Cycle power block</td><td>36</td></tr><tr><td>Table 9: KPIs of the Thermal Energy Storage system (TES)</td><td>37</td></tr><tr><td>Table 10: Template of datafile: time series of measured values</td><td>39</td></tr><tr><td>Table 11: List of measured signals</td><td>41</td></tr></table>

## List of Acronyms and Abbreviations

<table><thead><tr><td>Acronym/abbreviation</td><td>Meaning/full text</td></tr></thead><tbody><tr><td>BOP</td><td>Balance of Plant</td></tr><tr><td>CSP</td><td>Concentrated Solar Power</td></tr><tr><td>CSR</td><td>Circumsolar Radiation</td></tr><tr><td>DNI</td><td>Direct Normal solar Irradiance</td></tr><tr><td>GT (µGT)</td><td>Gas-Turbine (micro Gas-Turbine)</td></tr><tr><td>HMI</td><td>Human Machine Interface</td></tr><tr><td>HTF</td><td>Heat Transfer Fluid</td></tr><tr><td>HTR</td><td>Electrical Heater</td></tr><tr><td>IR</td><td>Infrared</td></tr><tr><td>IR</td><td>Infrared</td></tr><tr><td>KPI</td><td>Key Performance Indicator</td></tr><tr><td>ORC</td><td>Organic Rankine Cycle</td></tr><tr><td>P&ID</td><td>Process & Instrumentation Diagram</td></tr><tr><td>PI</td><td>Pressure Indicator</td></tr><tr><td>PICC</td><td>Power Induced Catalytic Combustor</td></tr><tr><td>PLC</td><td>Programmable Logic Controller</td></tr><tr><td>Pt</td><td>Platinum (in Pt-100)</td></tr><tr><td>PT</td><td>Pressure Transmitter</td></tr><tr><td>RHX</td><td>Recovery Heat Exchanger</td></tr><tr><td>RTD</td><td>Resistance Temperature Detector</td></tr><tr><td>TC</td><td>Thermocouple</td></tr><tr><td>TES</td><td>Thermal Energy Storage</td></tr><tr><td>TIT</td><td>Turbine Inlet Temperature</td></tr><tr><td>TT</td><td>Temperature Transmitter</td></tr><tr><td>TSH</td><td>Temperature Switch High</td></tr><tr><td>UAV</td><td>Unmanned Aerial Vehicle</td></tr></tbody></table>
# 1. SUMMARY

This report defines the instrumentation of the POLYPHEM plant. The process includes:

* In the focal area at the top of the tower (79 m): the top cycle with the air receiver, the gas-turbine and the recovery heat exchanger (RHX)

* In the tower: the branch of the oil circuit making the junction between the top and bottom cycle

* On the ground at the bottom of the tower: the bottom cycle with the organic Rankine cycle (ORC) and the thermal energy storage (TES).

A prototype plant is constructed and operated in the experimental phase of the project POLYPHEM (WP6) in order to assure the validation of the technology and to study the performance assessment of each component and of the overall plant.

In August 2021, it was decided to give up the installation of the solar receiver at the Themis site, after a major failure in the manufacturing process of this component. This sequence is reported in the deliverable D5.2. Eventually, the prototype plant erected in Themis slightly differs from the POLYPHEM plant initially designed, and it will be operated off-sun. The decision was made to give up the installation of the gas-turbine at Themis site, since the operation of this component in fuel mode has already been demonstrated in the test facility of KAEFER. This sequence is reported in the deliverable D2.7.

In practice, the test program will be restricted to the demonstration of the RHX, the TES system and the ORC. Nevertheless, the experimental protocols described in this report are related to the test program of the original POLYPHEM plant and of its main components as they were scheduled according to the design of the plant before August 2021. In particular, the instrumentation and the test protocols required to assess the performance of the solar receiver and of the gas-turbine have been designed prior to the change of configuration, and are reported in this document (see §3.2, §3.3, §4.2, §4.3, §4.4.3, §4.6, §5.1, §5.2)

The testing of the prototype plant in its new configuration preserves the main objectives of the experimental phase mentioned above (for further information see §4.1).

The instrumentation is composed of sensors installed on the process at appropriated locations to measure the physical parameters which are relevant for the control of the plant and for the performance assessment. The sensors are connected to a data acquisition system capable of real time monitoring and recording of all data.

# 2. SHORT DESCRIPTION OF THE PROCESS

## 2.1 AIR CIRCUIT OF THE POLYPHEM PLANT

The air circuit of the POLYPHEM plant is presented in Figure 1. It is composed of the gas-turbine and the generator set, the solar receiver and the recovery heat exchanger (RHX).

The air is taken from the outside at ambient conditions of temperature and pressure. The air flows through the compressor, the solar receiver and the expander. At the exhaust of the expander, the air is directed to the RHX and it is rejected to the ambient through a chimney. When there is no need for heat recovery, or in case of overheating of Heat Transfer Fluid (HTF) in the RHX, the exhaust air is directly rejected to the ambient with a by-pass valve.

## 2.2 HTF CIRCUIT OF THE POLYPHEM PLANT

The HTF circuit of the POLYPHEM plant is presented in Figure 2. The installation consists of a closed circuit of HTF. It is subdivided in three sub-loops:

* The primary sub-loop includes the sources of heat: the RHX and the electrical heater.

* The secondary sub-loop includes the heat sink: the ORC. Both primary and secondary sub-loops are interfaced with the manual valves V-401 and V-501.
* The third sub-loop is connected in parallel to the secondary loop. It includes the thermal energy storage tank (TES). The "hot" branch is connected to the primary sub-loop, the "cold" branch is connected to the secondary sub-loop.

A set of 2 motor pumps P401 and P101 forms the main pump group. According to the variations of heat input in the RHX, the servo control of the pump receives the feedback of the temperature sensor TT-120 and thus regulates the temperature of the HTF at the outlet of the RHX at a setpoint value.

A safety thermostat is installed at the outlet of the RHX (TSH 120 in Figure 2). Its signal is connected directly to the turbine control cabinet, allowing hot gases to be redirected into a by-pass of the RHX to prevent overheating of the HTF.

When the RHX is unavailable, or when additional heat needs to be added to the fluid, the electric heater is switched on. Its servo control receives the feedback of TT-404 and regulates the temperature of the HTF at the outlet of the electrical heater at a setpoint value. A minimum mass flowrate of HTF, indicated by FIT-401, is required to switch on the electrical heater.

The bottom circuit (electrical heater, TES and ORC) is protected against overpressure by a set of two valves. The regulation valve VR-109 is servo controlled by the feedback of the pressure downstream, measured by PT-109. The safety valve EV109 (normally closed) is servo controlled by a pressure switch PSH109.

In charge mode, the thermal energy is supplied to the TES by the RHX (or by the electrical heater). The valve EV709 on the inlet tube of the TES opens and let the hot oil flow into the TES when the temperature TT701 exceeds the minimum value required to charge the TES, typically 300°C. The pumps P401 and P101 manage the flow of HTF through the RHX as described here above. The motor pump P501 is not used until the temperature of the HTF extracted at the bottom of the TES begins to increase. This takes place at the end of the TES charging sequence, when the thermocline zone reaches the bottom of the TES tank. The motor pump P501 is servo controlled by the feedback of the temperature sensor TT-403 and thus regulates the temperature of the HTF at the inlet of the RHX (or of the electrical heater) at a setpoint value. When the TES is fully charged, the ORC takes all the heat delivered by the RHX (or by the electrical heater).

In discharge mode, the thermal energy required by the ORC is supplied by the TES. The pumps P401 and P101 are stopped. The valve EV709 is opened. The motor pump P501 extracts the "hot" HTF at the top of the TES and directs it to the ORC. The "cold" HTF is then returned from the outlet of the ORC back to the bottom of the TES. The thermal power converted by the ORC is determined by the mass flowrate of HTF delivered by the pump P501 and by the difference of temperature of HTF between the inlet and the outlet of the ORC.

The temperature of the HTF at the inlet of the ORC must remain below a maximum value which defines a setpoint. It is typically set at 168°C. When the temperature of the "hot" HTF is higher than this setpoint, a fraction of the flowrate of "cold" HTF returned from the ORC is recirculated by the 3-ways valve EV-501. The servo control of the 3-ways valve receives the feedback of the temperature sensor TT-502 and thus regulates the temperature of the HTF at the inlet of the ORC at the setpoint value. On the top of that, a by-pass of the ORC is implemented to avoid overheating at the inlet. A safety thermostat TSH, typically set at 170°C, feeds the servo-controllers of a main valve and of a by-pass valve. The safety thermostat and the 2 valves are supplied by ORCAN.

## 2.3 PROCESS OF THE PROTOTYPE PLANT

The P&ID of the prototype plant constructed at Themis and operated in the project is presented in Figure 3. The configuration of the prototype plant is reduced to the recovery heat exchanger (RHX), the thermal energy storage (TES), and the organic Rankine cycle (ORC). The engineering of the thermal oil circuit has been entirely revised by CNRS in Q3 of 2021. It was therefore agreed to simulate the exhaust gas flow of the gas-turbine using a combustor to supply hot air to the RHX. The heat supply is guaranteed all the time, so there is no need for a back-up electrical heater. The construction of the burner and of the oil circuits started in Q4 of 2021. The final version of the P&ID of the prototype plant has been issued in December 2021.
<figure><img src="image_6.png" /><figcaption>Figure 1: Process and Instrumentation Diagram of the POLYPHEM plant: air circuit</figcaption></figure>
<figure><img src="image_7.png" /><figcaption>Figure 2: Process and Instrumentation Diagram of the POLYPHEM plant: HTF circuit</figcaption></figure>
<figure><img src="image_8.png" /><figcaption>Figure 3: Final version of the P&ID of POLYPHEM prototype plant</figcaption></figure>
## 3. MEASUREMENT TECHNIQUES

The devices and techniques presented in this section refer to the instruments defined for the needs of the assessment of the entire POLYPHEM plant. The items related to the solar resource, solar receiver and gas-turbine are not implemented in the POLYPHEM prototype plant installed in Themis.

The measurement techniques are based on the implementation of sensors in best suited locations for measuring the relevant physical parameters:

* Direct Normal Irradiance (DNI)

* Temperature, pressure, humidity of ambient air

* Speed and direction of wind (security of heliostats)

* Temperature, pressure and mass flowrate of working fluid (air) upstream and downstream the main components: compressor, solar receiver, expander, RHX.

* Temperature, pressure and mass flowrate of HTF (thermal oil) upstream and downstream the main components: RHX, electrical heater, TES, ORC, pumps.

* Level of HTF in tanks (TES, main oil tank).

* Electrical power generated by the power blocks: gas-turbine (GT), Organic Rankine Cycle (ORC)

* Electrical power consumed by pumps, valves, heater, controllers.

### 3.1 SOLAR RESOURCE ASSESSMENT

#### 3.1.1 Meteo station

The solar resource harvested by POLYPHEM is the direct normal solar irradiance (DNI). It is measured by a pyrheliometer, which is the standard instrument commonly used in the sector of concentrated solar power (CSP). In the case of the meteo station of CNRS at Themis, it is composed of one pyrheliometer and 2 pyranometers (Kipp & Zonen), used to measure the global hemispherical solar irradiance and the diffuse solar irradiance. These instruments are mounted on a solar tracker (Solys). The meteo station is completed by a series of sensors installed on a pylon to measure the ambient temperature, humidity, wind speed and direction. All these sensors are installed at the top of the Themis tower, and are connected to a data acquisition system. A picture of the meteo station of CNRS at Themis is shown in Figure 4.

<figure><img src="image_9.png" /><figcaption>Figure 4: Meteo station of CNRS at Themis: solar irradiance (a) and other meteorological parameters (b)</figcaption></figure>
### 3.1.2 Sunshape measurement

The pyrheliometer measures the solar radiation in the wavelength band 0.3 µm – 2.8 µm received under an angle of view of 5°. The solar disc is viewed from the Earth under the angle of 9.28 mrad (0.532°) ± 1.7%. However, a fraction of the solar radiation scattered in the atmosphere of the Earth is received outside this angle, still accounting for a significant amount of energy. This energy is called the circumsolar radiation. It might be captured and concentrated by the solar field, according to the actual acceptance angle of the optics. The determination of the circumsolar ratio (CSR) in the overall DNI, and the investigation of the influence of the CSR on the performance of the solar field and solar receiver assuming their acceptance angle, are part of the objectives of the project POLYPHEM. To this end, a specific instrument has been developed by Fraunhofer ISE to measure the profile of solar radiation in the radial direction -sunshape- over a wide angle of view. This instrument is called CSR camera. It is installed near the meteo station.

A CSR camera has been developed and is tested and evaluated at Fraunhofer ISE. The new camera is based on an image sensor with optical filters, specially designed for reducing the sun's intensity. The design was adapted with the goal to obtain best contrasts over the CSR region on the taken images. The camera has a spatial resolution of 0.1 mrad with a maximum acceptance angle of 35 mrad. For (solar) heat protection, the front glass is covered by a mirror with a hole at the position of the camera optics.

The camera is mounted on a sun-tracker, it continuously faces the sun. CSR is measured automatically at least every 5 minutes between sunrise and sunset. At night the camera returns into standby. The camera can operate in the temperature range of -10 C to +60 C. A microcontroller-based temperature control has been implemented to achieve cooling and front-glass heating of the camera casing, and therefore address harsh ambient temperature conditions. The complete CSR-setup is controlled by a LabVIEW program running on an Industrial PC below the camera. Recorded images and CSR data are stored on the internal SSD.

The radial distributions of the sun-disc and of the circumsolar region are considered for the CSR calculation. Since the half-opening angle of the sun slightly changes during a year, the size of the sun-disc is calculated according to the current date. A false-colored image of the sun can be seen in Figure 5. By integrating the gray values of the image in the angular ranges of solar disc and aureole, the CSR value is determined by putting the sums in relation to each other: $CSR(\text{circumsolar ratio}) = \frac{l_{CSR}}{l_{Total}} = \frac{l_{CSR}}{l_{sun}+l_{CSR}}$. The corresponding radial distribution can be seen in Figure 6.

<figure><img src="image_10.png" /><figcaption>Figure 5: Recorded image of the sun which is used for the CSR calculation</figcaption></figure>

<figure><img src="image_11.png" /><figcaption>Figure 6: Radial distribution of the sun image</figcaption></figure>

The camera is installed at a Fraunhofer ISE test site, on a solar tracker. The images in Figure 7 and Figure 8 show two evaluation examples that were taken in the summer 2020. The x-bar displays the UTC+1 time. The measured CSR values are plotted on the right y-bar (red dotted line). An external measured DNI is plotted on the left y-bar for comparison (orange line). An additional clear-sky model was also plotted (green line). Figure 7 shows the CSR over the day of a clear summer day. CSR is nearly constant and DNI does not much differ
from the clear sky model. In Figure 8 the same is plotted for a cloudy summer day. CSR values rises when DNI falls. Data was recorded all of August 2020 at Fraunhofer test site. With this data, a CSR histogram could be plotted, which is shown in Figure 9.

<figure><img src="image_12.png" /><figcaption>Figure 7: Example evaluation of DNI (orange), theoretical DNI (green) and measured CSR values (red dotted) on a clear summer day</figcaption></figure>

<figure><img src="image_13.png" /><figcaption>Figure 8: Example evaluation of DNI (orange), theoretical DNI (green) and measured CSR values (red dotted) on a cloudy summer day.
Attention: CSR y-scale is changed</figcaption></figure>

<figure><img src="image_14.png" /><figcaption>Figure 9: histogram of all the CSR measurements taken in august 2020 in Freiburg. Most of the measured values of CSR are around 2% - 5%</figcaption></figure>

Data analysis at the Fraunhofer ISE test site in Freiburg is still ongoing. The installation at the THEMIS facility of CNRS was delayed because of the travel restrictions due to COVID-19 situation, and finally cancelled after the cancellation of the installation of the solar receiver.
## 3.2 INSTRUMENTATION OF SOLAR RECEIVER

The energy of the beam delivered by the solar field at the aperture of the solar receiver is measured by an image-based method using a reflective moving target in the aperture plane. The target is a flat band of 30 cm in width covered by a white diffuse paint and equipped with an embedded fast response flux gauge. To measure the distribution of flux density and the incoming solar power at the receiver, the target scans the aperture plane of the receiver in about 1s. The fast scanning does not impact the thermal balance of the receiver. Series of images of the beam reflected by the target during a scan are taken by a fast video camera and are recorded with timestamping. In parallel, the signal of the flux gauge is recorded for calibration purpose. The image post-processing results in the concentrated solar flux distribution on the aperture plane and the input solar power in the receiver. This method has been developed, validated and reported in previous work (A. Ferriere, 2015).

The instrumentation of the solar receiver is composed of temperature and pressure gauges. The location of these sensors is presented in the scheme of Figure 10.

<figure><img src="image_15.png" /><figcaption>Figure 10: Instrumentation of the solar receiver</figcaption></figure>

The temperature of the outer surface of the receiver (Ni-based alloy 230) is measured on the back side with K-type thermocouples (Ø 1mm) welded onto the metal: for each module, one thermocouple (TC) is installed close to the air inlet and the other is installed close to the air outlet. In total, 8 TCs are used to assess the distribution of temperature on the back side of the receiver.

In addition to that, the distribution of temperature on the outer surface of the front side of the receiver is measured with an infrared camera (IR) on-board an Unmanned Aerial Vehicle (UAV). The camera is kept in static position in front of the focal area, at about 10 m from the receiver, outside from the solar beam. The best suited position of the camera is determined by pre-tests and it is then reproduced with high accuracy using GPS coordinates.

The temperature of the air is measured at the inlet and at the outlet of the receiver with K-type thermocouples (Ø 1mm) installed in the air flow: 2 TCs are installed on the inlet manifold and 2 TCs are installed on the outlet manifold, close to the flanges. The TCs pass through sealed passages welded onto small and short tubes. The air pressure is measured at the same location with pressure take-off lines (Ø 6mm) connected to a manometer.
The temperature of the air is also measured at the inlet and at the outlet of the internal tubes, with TCs placed in the middle of the tubes without contact with the tube wall (see Figure 10, bottom left). One TC is placed in the middle of each module at the inlet, and 6 TCs are placed at the outlet of each module (2 TCs in tubes of row #1 -front, 2 TCs in tubes of row #3 -middle, 2 TCs in tubes of row #7 -back). In total, 30 TCs are used to assess the distribution of the air temperature at strategic locations inside the receiver. Uneven distribution of mass flowrate and/or solar flux density will be detected and assessed.

## 3.3 INSTRUMENTATION OF GAS-TURBINE AND POWER BLOCK (TOP CYCLE)

The mass flowrate $\dot{m}_{air}$ of the air was planned to be measured at the air intake, using either a built-in mass flowmeter (Coriolis- or Venturi-type) or a venturi device with pressure and temperature sensors. In this latter case, the temperature, and the pressure will be measured upstream the venturi device to determine the mass density, and the pressure drop $\Delta p$ is measured using a differential pressure transmitter. This value is used to derive the mass flowrate of air $\dot{m}_{air}$, according to the temperature and to physical parameters of the venturi device: $\dot{m}_{air} = K\sqrt{\rho_{air}} \Delta p$

Due to the change of the project plan (no gas turbine operation in Themis), these air flow measurement devices have not been purchased. The corresponding funds will be made available for the project consortium.

The **temperature of the air** flowing into the compressor, into the expander and into the RHX is measured with Resistance Temperature Detectors (RTD). The type of temperature gauge is Pt-100. This gauge is accurate, stable, reliable, and suited to measure high temperature. The Pt-100 gauges are temperature transmitters (TT). They are installed in thermowells welded onto the air ducts. In total, 12 Pt-100 gauges are installed at strategic locations (all measurements are doubled with two gauges):

* Upstream the venturi device (CT001, CT002). The temperature is used to assess the mass density of the air flowing through the venturi.

* Upstream the compressor (CT102-1, CT102-2)

* Downstream the compressor (CT103-1, CT103-2)

* Upstream the expander (CT108-1, CT108-2)

* Downstream the expander (CT112-1, CT112-2)

* Downstream the RHX (CT116-1, CT116-2)

The measured values are used to monitor the air temperature along the gas cycle and to quantify the heat gained or extracted in each subcomponent.

The **pressure of the air** is measured with absolute manometers mounted onto pressure take-off lines. The manometers are transmitters (PT). In total, 6 absolute manometers are installed at the same locations as the temperature sensors:

* Upstream the venturi device (CP001). The pressure is used to assess the mass density of the air flowing through the venturi.

* Upstream the compressor (CP102)

* Downstream the compressor (CP103)

* Upstream the expander (CP108)

* Downstream the expander (CP112)

* Downstream the RHX (CP116)

The **rotation speed** of the turbine and the generator are measured using two different methods. The first method utilizes the rotation speed of the generator which is given by the frequency converter of the generator. This value is multiplied by the gear reduction ratio. As this method is not fully accurate, a separate digital speed sensor with two pulses per rotation is installed in the turbine housing on the turbine shaft. Furthermore, this two-method measurement provides redundancy, as the first method does not provide data in case of a malfunction of the power electronics. Consequently, the rotation speed of the gas-turbine is controlled by the speed of the generator.
The vibrations of rotating devices are controlled by a mobile device which is the property of KAEFER, not charged to the project POLYPHEM.

The temperature of the gearbox is measured directly in the oil flow and the oil back-flow. To enable monitoring of heat dissipation of the gearbox (and efficiency of the gearbox), flow sensors are installed within the oil circuit. Furthermore, a thermocouple is installed on the surface of the gearbox casing.

The electrical power generated or consumed by the power block is measured with the power electronics respectively with the frequency converter of the generator.

## 3.4 INSTRUMENTATION OF THE RECOVERY HEAT EXCHANGER

The temperature of the gas (air) is measured at the inlet and at the outlet with thermocouples (J-type) immerged in the gas flow. The TCs are installed through fluid-tight packing which are mounted on the inlet and outlet gas pipes, close to the flanges. The temperature of the thermal oil is measured at the inlet and at the outlet with temperature gauges Pt-100. The RHX is entirely thermally insulated by a layer of mineral wool, 10 cm thick. The temperature of the skin of the body of the RHX and the temperature of the outer surface of the insulation are measured with two J-type thermocouples. The instrumentation of the RHX is presented in Figure 11.

<figure><img src="image_16.png" /><figcaption>Figure 11: Instrumentation of the recovery heat exchanger</figcaption></figure>

## 3.5 INSTRUMENTATION OF THE THERMAL STORAGE TANK

The thermal storage tank is a dodecagonal cylindrical tank, made of thick concrete walls. Bricks of filler material are stacked inside the tank and form the solid structured bed which serves as main thermal storage material in addition to the thermal oil which occupies the porosity of the bed. On the top of the filler bed, a sufficient volume is left to accommodate the thermal expansion of the thermal oil in operation. The top free surface of the oil is at ambient pressure. The thermal oil flows in and out of the tank with 2 pipes located at the bottom of the tank and at the top of the filler bed. The drawings of the tank are presented in Figure 12 and Figure 13.

The pressure and the temperature of the oil are measured in the pipes near both inlet and outlet connections.

The other instruments are described in §3.5.1 and §3.5.2 au-dessous.
<figure><img src="image_17.png" /><figcaption>Figure 12: Instruments of the thermal energy storage tank (vertical cross section)</figcaption></figure>
<figure><img src="image_18.png" /><figcaption>Figure 13: Instruments of the thermal energy storage tank (horizontal cross section)</figcaption></figure>

### 3.5.1 Temperature in the thermal storage tank

The temperature of the thermal oil and of the filler inside the thermal storage tank and the temperature of the walls of the tank is measured by thermocouples (TCs). This technology is suited for measuring temperature in location with difficult access. The sensor is made by thin wires of two different metals welded and protected by an Inconel sheath. The sensors are long enough to be installed inside the tank whereas the connections with compensation cables remain outside. The diameter of the sheath is 1.5 mm. Most sensors are J-type thermocouples (iron/constantan). Some TCs are K-type (NiCr/NiAl). The accuracy of both types of TC is typically ±1°C.

The 16 TCs used to measure the horizontal distribution of temperature (e.g. radial profile) are placed along the separators (metallic grids) in the room between two stacks of filler bricks. The tips of the TCs used to measure the temperature of the inner face of the tank wall are placed in contact with the wall, using the stiffness of the sheath to form a spring slightly bended.

12 TCs are used to measure the temperature inside the tank wall and on the outer face (TW1 to TW12 in Figure 12). These TCs are installed during the construction of the tank, they are embedded in the concrete wall. Similarly, 2 TCs are embedded in the bottom slab of the tank (TF1 and TF2). 2 TCs are placed at the inside and outside faces of the cover (TW13 and TW14).
The 32 TCs used to measure the vertical distribution of temperature (e.g. axial profile) along the central axis of the tank are grouped to form 5 bundles which are placed along the central axis.

6 K-type TCs (TB1 to TB6 in Figure 12) measure the temperature of the insulation slab under the tank. The insulation slab is placed on the ground, the tank is erected just above it. This slab is a pavement of blocks made of insulating concrete. Each block is 1m x 0.6m x 0.5m. The TCs are placed at the upper side, and 20 cm and 40 cm beneath.

In total, 80 TCs are installed into the thermal storage tank. They are connected to a cabinet located inside a container on the ground 5 m far from the storage tank (see §2.6). The names and positions of the TCs are summarized in Table 1.

<table><caption>Table 1: thermocouples and their positions in the TES tank
(the origin is the position of T01: bottom centre of the tank, inside)</caption><thead><tr><th>TC</th><th>X (mm)</th><th>Y (mm)</th><th>Z (mm)</th><th>TC</th><th>X (mm)</th><th>Y (mm)</th><th>Z (mm)</th></tr></thead><tbody><tr><td>TB1</td><td>0</td><td>0</td><td>-55</td><td>TB4</td><td>116</td><td>0</td><td>-55</td></tr><tr><td>TB2</td><td>0</td><td>0</td><td>-75</td><td>TB5</td><td>116</td><td>0</td><td>-75</td></tr><tr><td>TB3</td><td>0</td><td>0</td><td>-95</td><td>TB6</td><td>116</td><td>0</td><td>-95</td></tr><tr><td>TF1</td><td>0</td><td>0</td><td>-25</td><td>TD1</td><td></td><td></td><td></td></tr><tr><td>TF2</td><td>0</td><td>0</td><td>-50</td><td>TD2</td><td></td><td></td><td></td></tr><tr><td>T01</td><td>0</td><td>0</td><td>0</td><td>T02</td><td>63</td><td>0</td><td>0</td></tr><tr><td>T11</td><td>0</td><td>0</td><td>13</td><td>T03</td><td>116</td><td>0</td><td>0</td></tr><tr><td>T21</td><td>0</td><td>0</td><td>23</td><td>T22</td><td>63</td><td>0</td><td>23</td></tr><tr><td>T31</td><td>0</td><td>0</td><td>33</td><td>T23</td><td>116</td><td>0</td><td>23</td></tr><tr><td>T41</td><td>0</td><td>0</td><td>43</td><td>T24</td><td>126</td><td>0</td><td>23</td></tr><tr><td>T51</td><td>0</td><td>0</td><td>53</td><td>T25</td><td>0</td><td>63</td><td>23</td></tr><tr><td>T61</td><td>0</td><td>0</td><td>63</td><td>T26</td><td>0</td><td>116</td><td>23</td></tr><tr><td></td><td></td><td></td><td></td><td>TW1</td><td>150</td><td>0</td><td>23</td></tr><tr><td></td><td></td><td></td><td></td><td>TW2</td><td>174</td><td>0</td><td>23</td></tr><tr><td>T71</td><td>0</td><td>0</td><td>73</td><td>T72</td><td>63</td><td>0</td><td>73</td></tr><tr><td>T81</td><td>0</td><td>0</td><td>86</td><td>T73</td><td>116</td><td>0</td><td>73</td></tr><tr><td>T91</td><td>0</td><td>0</td><td>96</td><td>TW13</td><td>116</td><td>0</td><td>320</td></tr><tr><td>T101</td><td>0</td><td>0</td><td>106</td><td>TW14</td><td>116</td><td>0</td><td>340</td></tr><tr><td>T111</td><td>0</td><td>0</td><td>116</td><td></td><td></td><td></td><td></td></tr><tr><td>T121</td><td>0</td><td>0</td><td>126</td><td>T122</td><td>63</td><td>0</td><td>126</td></tr><tr><td>T131</td><td>0</td><td>0</td><td>139</td><td>T123</td><td>116</td><td>0</td><td>126</td></tr><tr><td>T141</td><td>0</td><td>0</td><td>149</td><td>T124</td><td>126</td><td>0</td><td>126</td></tr><tr><td>T151</td><td>0</td><td>0</td><td>159</td><td>T125</td><td>0</td><td>63</td><td>126</td></tr><tr><td>T161</td><td>0</td><td>0</td><td>169</td><td>T126</td><td>0</td><td>116</td><td>126</td></tr><tr><td></td><td></td><td></td><td></td><td>TW3</td><td>150</td><td>0</td><td>126</td></tr><tr><td></td><td></td><td></td><td></td><td>TW4</td><td>174</td><td>0</td><td>126</td></tr><tr><td>T171</td><td>0</td><td>0</td><td>179</td><td>T172</td><td>63</td><td>0</td><td>179</td></tr><tr><td>T181</td><td>0</td><td>0</td><td>192</td><td>T173</td><td>116</td><td>0</td><td>179</td></tr><tr><td>T191</td><td>0</td><td>0</td><td>202</td><td></td><td></td><td></td><td></td></tr><tr><td>T201</td><td>0</td><td>0</td><td>212</td><td></td><td></td><td></td><td></td></tr><tr><td>T211</td><td>0</td><td>0</td><td>222</td><td></td><td></td><td></td><td></td></tr><tr><td>T221</td><td>0</td><td>0</td><td>232</td><td>T222</td><td>63</td><td>0</td><td>232</td></tr><tr><td>T231</td><td>0</td><td>0</td><td>244</td><td>T223</td><td>116</td><td>0</td><td>232</td></tr><tr><td>T241</td><td>0</td><td>0</td><td>257</td><td>T224</td><td>126</td><td>0</td><td>232</td></tr><tr><td></td><td></td><td></td><td></td><td>T225</td><td>0</td><td>63</td><td>232</td></tr><tr><td></td><td></td><td></td><td></td><td>T226</td><td>0</td><td>116</td><td>232</td></tr><tr><td></td><td></td><td></td><td></td><td>TW5</td><td>150</td><td>0</td><td>232</td></tr><tr><td></td><td></td><td></td><td></td><td>TW6</td><td>174</td><td>0</td><td>232</td></tr><tr><td>T251</td><td>0</td><td>0</td><td>270</td><td>T254</td><td>126</td><td>0</td><td>270</td></tr><tr><td>T261</td><td>0</td><td>0</td><td>280</td><td>TW7</td><td>150</td><td>0</td><td>270</td></tr><tr><td></td><td></td><td></td><td></td><td>TW8</td><td>174</td><td>0</td><td>270</td></tr><tr><td>T271</td><td>0</td><td>0</td><td>290</td><td>T274</td><td>126</td><td>0</td><td>290</td></tr><tr><td>T281</td><td>0</td><td>0</td><td>300</td><td>TW9</td><td>150</td><td>0</td><td>290</td></tr><tr><td></td><td></td><td></td><td></td><td>TW10</td><td>174</td><td>0</td><td>290</td></tr><tr><td>T291</td><td>0</td><td>0</td><td>310</td><td>T294</td><td>126</td><td>0</td><td>310</td></tr><tr><td>T301</td><td>0</td><td>0</td><td>320</td><td>TW11</td><td>150</td><td>0</td><td>310</td></tr><tr><td>T311</td><td>0</td><td>0</td><td>330</td><td>TW12</td><td>174</td><td>0</td><td>310</td></tr></tbody></table>
### 3.5.2 Level in the thermal storage tank

The level of thermal oil in the storage tank is strongly affected by the thermal expansion. It is measured with a level sensor using radar technology (LT-715). The temperature and the properties of the oil do not impact the signal of this sensor. The sensor is mounted on a short vertical tube that goes through the top cap of the tank and through the insulation layer. The electromagnetic wave emitted by the sensor is reflected by the free surface of the thermal oil and the reflected wave is finally captured by the sensor. This signal is used to check that the upper diffuser is always immersed into the liquid HTF, and to detect the overflow of HTF at the top of the tank.

## 3.6 INSTRUMENTATION OF ORGANIC RANKINE CYCLE

The ORC in POLYPHEM basically has four different circuits which can be recognized by their numbers in the P&ID of the ORC (see Figure 14):

* 200: Thermal oil circuit

* 300: Refrigerant circuit

* 400: Lubrication oil circuit (for the expansion machine ORC)

* 500: Electrical cabinet

The instrumentation is based on temperature sensors, pressure sensors, one flow meter, leakage sensor, and one flow switch.

### 3.6.1 Temperature in the ORC

Several temperature sensors are installed in the ORC. All of them are installed in a thermowell and the types are pT-100. So, in case of a sensor error or failure, it is possible to replace them without draining the system. The sensors are installed in:

* Oil inlet: TE201

* Oil outlet: TE202

* Live vapor: TE302

* Exhaust vapor: TE306

* Condensate: TE307

An external safety temperature limiter (STB max) is also installed to protect the ORC against overheating. If this device detects a too high temperature of the thermal oil, the controller closes the valve V201 to the ORC and opens the by-pass V202.

In order to validate proper function of the twin screw and generator unit during operation with elevated live vapor temperature, which are beyond current state of the art for twin screw expansion machines, 12x thermocouples (type K) are integrated in the winding packet of the generator within the expansion machine. Due to the thermocouples, it is possible to measure the impact on the winding which results from elevated temperature of oil and higher live vapor temperature. One additional temperature sensor pT-1000 is installed on the current plate of the expander (TE308).

### 3.6.2 Pressure in the ORC

The pressure is measured on different fluids and at different locations in the ORC. All the pressure sensors are installed on a Schrader valve, so they can be replaced without draining the system (in case of sensor failure). All the sensors are transmitters and they measure the absolute pressure.

The pressure sensors are installed in:

Oil: PE201

Live steam: PE301

Condensate: PE303

Injection: PE304
<figure><img src="image_19.png" /><figcaption>Figure 14: P&ID of the organic Rankine Cycle system in POLYPHEM</figcaption></figure>
### 3.6.3 Further instruments in the ORC

A Coriolis type mass flowmeter is integrated in the feed line of the ORC (FE301) to measure the mass flowrate of the working fluid. Hence the heat input to the ORC is derived from the mass flowrate, and the efficiency of the system is assessed very accurately.

A second mass flowmeter (FE302) is installed in a special pipe which is used to inject cold liquid working fluid in the expander, after the expansion of the vapor has taken place. This additional injection enhances the cooling of the exhaust vapor, which is used itself to cool the generator. It is thus planned to compensate for the higher live steam temperature, and to quantify the impact on the temperature of the windings in the generator.

A flow switch (FE403) is used in the lubrication oil circuit to check if there is sufficient oil flow to the bearings of the expansion machine.

The ORC also contains a leakage sensor (QE501) that triggers an alarm to the system in case of leakage of refrigerant.

Finally, the ambient temperature in the cabinet (TE502) and the ambient outdoor air temperature (TE501) are also measured. Both sensors are pT-100.

## 3.7 INSTRUMENTATION OF BALANCE OF PLANT

The balance of plant (BOP) is composed of the thermal oil circuits with pumps, valves and tanks, the recovery heat exchanger (RHX) and the electrical heater. The electrical heater is used as back-up to compensate for the lack of solar radiation, or it is used to charge the thermal energy storage under controlled conditions. In this latter situation, the objective is to test the bottom cycle as an island separated from the top cycle.

Most part of the BOP is installed inside a container (6m x 2.5m x 2.5m), located on the ground close to the bottom of the tower. The electrical heater, some circuits and some electrical cabinets are therefore sheltered from rain and snow.

### 3.7.1 Mass flowrate in the BOP

The mass flowrate of HTF in the oil circuits is critical to transfer the thermal energy from the RHX (or from the electrical heater) to the TES and to the ORC at design or at targeted temperature. 2 flowmeters are installed in the circuit: FT-401 is located upstream the main pump of the primary loop P-101, and FIT-501 is located upstream the pump P-501 of the ORC loop. These gauges measure the mass flowrate $m_{RHX}$ circulating in the primary loop (RHX) and $m_{ORC}$ circulating in the ORC loop, respectively.

The technology of flowmeter is based on the Coriolis effect. The sensor features a small portion of U-tube which is continuously vibrated at a given frequency. The mass flowrate of the liquid yields a phase shift between the two branches of the U-tube. The mass flowrate is reported to the phase shift which is detected and measured by the sensor. The measurement is accurate (typically 0.1%) and does not require any additional data about the properties of the fluid.

The mass flowrate $m_{TES}$ circulating in the TES tank is derived from the two mass flowrates measured in the RHX and in the ORC loops: $m_{TES} = m_{RHX} - m_{ORC}$.

### 3.7.2 Temperature in the BOP

The temperature of the thermal oil (HTF) is measured with Resistance Temperature Detectors (RTD). The type of gauge is Pt-100. This type of gauge is accurate, stable, reliable and suited to measure high temperature and to serve in harsh environment. The Pt-100 gauges are all temperature transmitters (TT). They are installed in thermowells welded onto the oil tubes. In total, 10 Pt-100 gauges are installed at strategic locations:

* upstream and downstream of the RHX (TT-110 and TT-120), of the TES tank (TT-701 and TT-702) and of the ORC (TT-502 and TT-503). These gauges are used to regulate the temperature of HTF and to quantify the heat gained or extracted in each component.
* downstream of the electrical heater (TT-404). This gauge is used to regulate the temperature of the HTF in electrical charging mode.

* at the separation of the branches to/from the TES tank (TT-501 and TT-403). TT-501 is used to protect the TES from unexpected input of HTF at temperature lower than the high temperature of the TES. TT-403 is used to regulate the temperature of HTF at the main pump suction.

* inside the HTF tank (TT-301). This gauge is used to check the temperature of the HTF before filling the circuits.

In addition, a thermostat sensor (TSH-120) is installed at the outlet of the RHX to detect overheating of the HTF in the RHX. The technology used is the thermal expansion of liquid. The signal of this thermostat sensor (switch on/off) is read by the controller of the gas-turbine (PLC): in case of overheating of HTF, the gas-turbine is stopped in emergency.

Another thermostat sensor of same technology is installed at the inlet of the ORC oil circuit. It is connected to the controller of the ORC. The signal is used to shut down the flow of HTF in the ORC circuit and by-pass the ORC when the temperature of the HTF exceeds the maximum value accepted by the ORC circuit.

### 3.7.3 Pressure in the BOP

The pressure of the HTF is measured with absolute or differential manometers mounted onto pressure take-off lines. The manometers are either transmitters (PT) or indicators (PI). In total, 8 absolute manometers are installed at strategic locations:

* upstream of the RHX (PT-110), of the TES tank (PT-701) and of the ORC (PT-506 and PI-503)

* upstream and downstream of the main pumps (PT-402, PT-403 and PI-110)

* upstream and downstream of the pressure regulation valve (PT-410 and PT-109)

In addition, 3 differential manometers measure the pressure drops of HTF in the RHX (DPT-130), in the TES tank (DPT-702) and in the ORC (DPT-507). The pressure drop is part of the performance assessment of the components. It also serves to detect fouling -or plugging- of the HTF tube in a component (RHX, TES, ORC).

### 3.7.4 Level in the HTF tank

The level of HTF is measured in the main HTF tank with a level sensor using a probe and float technology (LIT-301). The probe is immersed into the HTF. The signal is used to control the amount of thermal oil in the circuits.

## 4. EXPERIMENTAL PROTOCOLS

### 4.1 PROCESS FLOW DIAGRAMS

In practice, the test program will be restricted to the demonstration of the RHX, the TES system and the ORC. Nevertheless, the experimental protocols described in this section are related to the test program of the POLYPHEM plant and of its main components as they were scheduled according to the design of the plant before August 2021.

The experimental protocols and performance assessment of the solar receiver and gas-turbine refers to the P&ID of Figure 1. The performance assessment of the electrical heater refers to the P&ID of Figure 2. The performance assessment of the other components refers to the P&ID of Figure 3.

The configurations for the testing of the plant are listed in Table 2. In this table, icons represent the options selected for each component. The test-matrix is built on this basis: a series of runs is performed for each configuration, covering an extended range of operating conditions which are defined in section 5 (page 32).
<table><caption>Table 2: Configurations of plant for the experiment</caption><thead><tr><th>Config.</th><th>GT</th><th>RHX</th><th>El. Heater</th><th>TES</th><th>ORC</th></tr></thead><tbody><tr><td>1-a</td><td>!</td><td>↑</td><td>◎</td><td>↔</td><td>✗</td></tr><tr><td>1-b</td><td>!</td><td>↔</td><td>◎</td><td>↑</td><td>✗</td></tr><tr><td>1-c</td><td>!</td><td>↔</td><td>◎</td><td>↑</td><td>✓</td></tr><tr><td>2-a</td><td>+</td><td>↑</td><td>◎</td><td>↔</td><td>✗</td></tr><tr><td>2-b</td><td>+</td><td>↔</td><td>◎</td><td>↑</td><td>✗</td></tr><tr><td>2-c</td><td>+</td><td>↔</td><td>◎</td><td>↑</td><td>✓</td></tr><tr><td>2-d</td><td>+</td><td>↔</td><td>◎</td><td>↓</td><td>✓</td></tr><tr><td>3</td><td>~</td><td>↑</td><td>◎</td><td>↓</td><td>✓</td></tr><tr><td>4-a</td><td>~</td><td>↑</td><td>◎</td><td>↑</td><td>✗</td></tr><tr><td>4-b</td><td>~</td><td>↑</td><td>◎</td><td>↑</td><td>✓</td></tr><tr><td>5</td><td>~</td><td>↑</td><td>◎</td><td>↔</td><td>✗</td></tr></tbody></table>

<figure><img src="image_20.png" /></figure>

GT in fuel mode

<figure><img src="image_21.png" /></figure>

GT in solar mode

<figure><img src="image_22.png" /></figure>

Night time

<figure><img src="image_23.png" /></figure>

Cloudy day

<figure><img src="image_24.png" /></figure>

RHX by-passed

<figure><img src="image_25.png" /></figure>

RHX active

<figure><img src="image_26.png" /></figure>

Elec. Heater OFF

<figure><img src="image_27.png" /></figure>

Elec. Heater ON

<figure><img src="image_28.png" /></figure>

TES inactive

<figure><img src="image_29.png" /></figure>

TES in charging mode

<figure><img src="image_30.png" /></figure>

TES in discharging mode

<figure><img src="image_31.png" /></figure>

TES in up-keeping mode

<figure><img src="image_32.png" /></figure>

ORC in generation mode

<figure><img src="image_33.png" /></figure>

ORC stopped

## 4.2 OPERATION OF THE GAS-TURBINE IN FUEL MODE

The gas-turbine used in POLYPHEM is provided by KAEFER. It is made of commercially available components. The machine has been composed using existing, proven, and robust sub-components, for an easy and inexpensive maintenance and high reliability. The machine is assembled at KAEFER's facilities in Bremen (Germany). It is capable to be operated either in fuel mode or in solar mode. The configuration in fuel mode is implemented and tested in Bremen. The combustor used for this test campaign is called Power Induced Catalytic Combustor (PICC). This sub-component was developed by KAEFER to burn methane gases and hence to contribute to climate change mitigation in the energy sector. The PICC reactor has been developed by KAEFER outside the project POLYPHEM and is provided free of charge to the project.

### 4.2.1 Start-up

The frequency converter linked to the high-speed generator allows for smooth and continuous start-up procedure. When the start-up sequence begins, the generator runs in motor mode and rotates the compressor, and also the expander as both items are mounted on one single shaft. The generator -motor - consumes electrical power. The rotation speed is controlled by the frequency converter, under the supervision of the operator. When the minimum desired rotation speed is achieved, the combustor is ignited. The compressed air is then heated up and the expander begins to generate mechanical power. The turbine inlet temperature (TIT) is controlled by the rate of fuel injection. The TIT is progressively and continuously increased. When the TIT is sufficient, the turbine generates enough mechanical power to fully compensate for the motor and hence it rotates the compressor at the same rotation speed without electricity consumption. At that point, the engine is in idle mode. From that point and by increasing the injection of fuel in the combustor, the operator can ramp-up the rotation speed at the same TIT. The machine runs at constant speed and the delivered electrical power is controlled by the amount of thermal power provided by the combustor.
### 4.2.2 Power generation in fuel mode

When the rotation speed reaches the design point, the power can be generated at full load. The operation consists of keeping the rotation speed constant and varying the generated power by rating the fuel injection.

### 4.2.3 Stop

To stop the engine, the fuel injection is cut off. From that moment, the compressed air is not heated any more, the TIT drops down, the generated power decreases accordingly. The rotation speed cannot be maintained, the engine slows down. When idle mode is reached, the free shaft rotates at low velocity and the engine cools down.

## 4.3 OPERATION OF THE GAS-TURBINE IN SOLAR MODE

In solar mode, the combustor is substituted by the solar receiver. KAEFER has designed and engineered the air ducts from the compressor outlet to the solar receiver inlet and from the solar receiver outlet back to the expander inlet. Due to the change of the project plan (no gas turbine operation in Themis), these air ducts have not been purchased. The corresponding funds will be made available for the project consortium. Compensators are installed to accommodate for the thermal expansion of the ducts. The major parameter driving the operation in solar mode is the thermal condition of the solar receiver. This latter sub-component must be pre-heated before it can supply hot air to the expander. Once the solar receiver is hot, the solar energy input is governed by the number of heliostats focused on its aperture and by the direct normal irradiation delivered by the sun. The variation of solar energy input -caused by cloud passing- is smoothed by the thermal inertia of the receiver.

### 4.3.1 Start-up of gas-turbine in solar mode

The start-up in solar mode slightly differs from the start-up in fuel mode. The protocol in solar mode integrates the preheating of the solar receiver. When the start-up sequence begins, the generator runs in motor mode and rotates the compressor (and also the expander). The generator-motor- consumes electrical power. The rotation speed is controlled by the frequency converter, under the supervision of the operator. At the same time, the operator sets the solar field in tracking mode, with an aiming point outside from the tower but near the tower, called "stand-by target". When the minimum desired rotation speed is achieved, solar energy is progressively directed to the solar receiver. The compressed air flows at low flowrate in the receiver. Heliostats are moved one by one from the stand-by target to the aperture of the solar receiver. The solar receiver is heated up. The temperature of the air at the outlet of the receiver increases until the thermal equilibrium is reached. The time needed to achieve this equilibrium depends on the initial temperature of the receiver, on the power of the solar beam and on the air mass flowrate. The expander begins to generate mechanical power. The TIT is progressively and continuously increased by increasing the solar power (number of heliostats aiming at the aperture of the receiver). When the TIT is sufficient, the turbine generates enough mechanical power to fully compensate for the compression forces at the same rotation speed. Hence the compressor is rotated without electricity consumption. At that point, the engine is in idle mode. From that point and by increasing the solar power in the receiver, the operator can ramp-up the rotation speed at the same TIT. The machine runs at constant speed and the delivered electrical power is controlled by the amount of thermal power provided by the solar receiver.

### 4.3.2 Power generation in solar mode

**Design mode:** when the rotation speed reaches the design point, the solar receiver is cooled by the flow of compressed air. The solar power input is set to the design value and the power is generated at full load.

**Off-design mode:** the operation consists of keeping the rotation speed constant and varying the generated power by rating the solar beam. To this end, the minimum incremental increase/decrease of solar power is obtained by focusing/defocusing one single heliostat. If needed, some mirrors will be partly masked/unmasked with opaque veil.
### 4.3.3 Normal stop of gas-turbine in solar mode

The solar power is switched off by defocusing the solar beam from the aperture of the receiver while the rotation is maintained at design speed. The core of the solar receiver cools down, and the TIT decreases accordingly. Consequently, the power generated on the rotating shaft also decreases, down to the idle mode. From that point, the rotation speed is released by the frequency controller, the exciting current of the stator is switched-off. The air mass flowrate and the air temperature drop down rapidly. The thermal power transferred to the expander drops down accordingly and the engine stops in a short time.

### 4.3.4 Testing of the emergency stop procedure in solar mode

The emergency stop of the engine is required when:

* dramatic overheating of the HTF is observed in the RHX and by-pass of the RHX on the air side is not fast enough to prevent overheating

* fire is detected and emergency stop of the overall plant is imposed by the safety system at prior level of control

The emergency stop consists of the fast defocusing of the solar beam to switch-off the thermal power and simultaneously opening of a waste-gate to release the hot air from the inlet of the expander. Consequently, no more power is generated on the shaft and the gas-turbine stops immediately. In parallel, the HTF pumps are stopped, and the circuits are drained by gravity. The HTF is collected in the main tank located beneath the lowest level of the circuits. The thermal power at the inlet of the ORC is cut off, hence the ORC stops.

The testing of the emergency stop procedure is part of the commissioning. In this step, the configuration of the operation is set in safe mode: the solar field focuses the beam on the stand-by target, the generator of the gas-turbine is operated in motor mode, the HTF flows into the circuits at low temperature. In this configuration, the emergency stop button of the plant is pushed and the sequence is observed.

## 4.4 THERMAL CHARGING OF THE TES

The thermal charging of the TES is carried out when HTF is extracted at low temperature from the bottom of the TES tank and it is returned back at the top of the tank at high temperature. Thermal energy is supplied to the HTF by the RHX in solar mode or by the electrical heater. While the HTF flows through the TES tank, the region at high temperature grows at the top while the region at low temperature decreases at the bottom. The two regions are separated by the so-called thermocline zone.

### 4.4.1 Charging in electric mode

The thermal oil circuit in the tower is by-passed. The gas-turbine is stopped, or it is operated independently when the solar resource is sufficient and power generation is required. In this latter case the gas side of the RHX is by-passed and the exhaust gas of the turbine is directly rejected to the outside.

The electrical heater HTR, which is regulated by a controller on a setpoint temperature (typically at design high temperature of 300°C), increases the temperature of the thermal oil (HTF).

The protocol of charging in electric mode includes several steps illustrated by the schemes in Figure 15.

**Step #0:** In the initial configuration, the temperature of the HTF is low, the pumps are stopped and there is no heat input.

**Step #1:** The operator sets the main pump at the minimum speed. The valve to the TES is closed. The circulation is established through the ORC.

**Step #2:** The HTR is set on, the electrical power input is regulated by the controller of the heater using the temperature of the HTF measured at the outlet of the HTR ($T_{out-HTR}$). The setpoint value is set by the operator to the low temperature of the HTF in the TES ($T_L$).
**Step #3:** The setpoint for T<sub>out-HTR</sub> is switched to the high temperature targeted T<sub>H</sub>. Simultaneously, the circulation of HTF is established through the TES, by opening the valve to the TES and closing the 3-ways valve to the ORC. The charging mode is now operated, at low heat input.

**Step #4:** The speed of the main pump governs the operation regime. The regulation of the HTR keeps the temperature of the HTF at T<sub>H</sub>.

**Step #5:** When the TES is almost fully charged, the thermocline zone reaches the bottom of the tank and the temperature of the HTF extracted from the tank increases according to the profile of the thermocline. The heat input power in the HTR is reduced and the HTF mass flowrate is reduced accordingly by the regulation until the lower limit is reached. At this moment, the TES is considered as fully charged and the temperature of HTF in the tank is almost uniform.

<figure><img src="image_34.png" /><figcaption>Step #0: Initial configuration</figcaption></figure>

<figure><img src="image_35.png" /><figcaption>Step #1: start-up, no heat input</figcaption></figure>

<figure><img src="image_36.png" /><figcaption>Step #2: start-up, low heat input</figcaption></figure>

<figure><img src="image_37.png" /><figcaption>Step #3: thermal charging of TES at low heat input</figcaption></figure>

<figure><img src="image_38.png" /><figcaption>Step #4: thermal charging of TES at high heat input</figcaption></figure>

<figure><img src="image_39.png" /><figcaption>Step #5: charging of the thermocline zone</figcaption></figure>

**Figure 15: Protocol for thermal charging of the TES in electric mode**

### 4.4.2 Isothermal method in electric mode

The isothermal method is an operation mode specifically carried out to assess the thermal losses of the TES tank. The preparation step for this mode is a full charging of the TES in electric mode at a given (target) temperature set by the operator. When the TES is fully charged, the temperature profile in the tank is constant and features an almost uniform temperature (T<sub>H</sub> at the top and T<sub>H</sub>− at the bottom). From that moment, the mass flowrate is set to a high value and the charging of the TES is continued in electric mode.
The setpoint is conserved at the same constant temperature T<sub>out-HTR</sub>. This latter is set in order to maintain the temperature T<sub>H</sub> at the top of the tank. The power delivered by the heater mitigates the overall thermal losses in the circuits and in the TES. The heat balance between the inlet at T<sub>H</sub> and the outlet at T<sub>H</sub>- precisely reflects the heat loss of the TES tank.

The implementation of this method is illustrated by the scheme of Figure 16.

<figure><img src="image_40.png" /><figcaption>**Figure 16: Protocol for the assessment of the thermal loss by the isothermal method in electric mode**</figcaption></figure>

### 4.4.3 Charging in solar mode

The HTF extracted from the TES tank is directed to the RHX at the top of the tower. The gas-turbine is started and operated, the exhaust gas is directed to the RHX. The heat input is driven by the solar resource, which is variable. The temperature of the HTF at the outlet of the RHX is maintained constant at set point (typically at design high temperature of 300°C) by the regulation of the main pumps P-101 and P-401. The HTF flow heated in the RHX is returned back to the top of the TES tank. The protocol of charging in solar mode includes several steps, illustrated by the schemes in Figure 17.

**Step #0:** In the initial configuration, the temperature of the HTF is low, the pumps are stopped and there is no heat input.

**Step #1:** The operator sets the main pump at the maximum speed. The circulation is established through the RHX and the ORC, the valve to the TES is closed.

**Step #2:** The exhaust gas of the µGT is admitted in the RHX. The thermal power input is regulated by the temperature of the HTF measured at the outlet of the RHX (T<sub>out-RHX</sub>). The setpoint value is set by the operator to the low temperature of the HTF in the TES (T<sub>L</sub>). The heat input is not converted to power neither sent to the TES. This step ends when the pipes are preheated at T<sub>L</sub>.

**Step #3:** The setpoint for T<sub>out-RHX</sub> is switched to the high temperature targeted T<sub>H</sub>. Simultaneously, the circulation of HTF is established through the TES, by opening the valve to the TES and closing the 3-ways valve to the ORC. The charging of the TES is running, according to the exhaust heat of the µGT available at the RHX. There is no power generation by the ORC.

**Step #4:** When the TES is almost fully charged, the thermocline zone reaches the bottom of the tank and the temperature of the HTF extracted from the tank and directed to the RHX increases according to the profile of the thermocline. The recirculation pump and the ORC engine are started. The regulations of the main pump, of the recirculation pump P-501 and of the 3-ways valve EV-501 maintain the temperature of the HTF within acceptable range at the inlet and outlet of the RHX and at the inlet of the ORC. The heat extracted from the RHX is transferred to the TES and to the ORC at once. The share of flowrate directed to the ORC progressively increases while the share of flowrate directed to the TES decreases. The operator controls the status of the charging of the TES by setting the value of the temperature at the inlet of the RHX. The TES is fully charged when this setpoint temperature equals the temperature of the HTF at the outlet of the ORC. At that moment, the protocol is stopped or the operation mode switches from the "thermal charging of the TES in solar mode" to the "operation of the ORC in solar mode" (see § 4.6 au-dessous).
<figure><img src="image_41.png" /><figcaption>**Figure 17: Protocol for the thermal charging of the TES in solar mode**</figcaption></figure>

#### 4.4.4 Isothermal method in solar mode

The preparation step for this mode is a full charging of the TES in solar mode at a given (target) temperature set by the operator. The ORC is operated at the end of the charging to support the full charging of the tank (see step #4 of the charging sequence). When the TES is fully charged, the temperature profile in the tank is constant and features an almost uniform temperature ($T_H$ at the top and $T_{H-}$ at the bottom). From that moment, the charging of the TES is continued in solar mode and the mass flowrate is regulated to maintain the temperature $T_{out-HTR}$ at the unchanged setpoint. The power delivered by the RHX mitigates the overall thermal losses in the circuits and in the TES. The heat balance between the inlet at $T_H$ and the outlet at $T_{H-}$ precisely reflects the heat loss of the TES tank.

The implementation of the isothermal method in solar mode is illustrated by the scheme of Figure 18.
<figure><img src="image_42.png" /><figcaption>Figure 18: Protocol for the assessment of the thermal loss by isothermal method in solar mode</figcaption></figure>

### 4.4.5 Cooling-down mode of the TES

The cooling-down mode is carried out when the charging or discharging of the TES is stopped and the TES tank is left without any forced interaction with the environment (no circulation of HTF, no active input or output of heat). This mode enables to assess the long-term stability of the thermocline zone and it also provides information about the heat loss of the TES.

The evolution of the distribution of temperature inside the TES tank is observed. The drivers are the heat losses of the TES tank and of the circuits (boundary condition), the natural convection inside the tank and the diffusion in the HTF and in the filler.

## 4.5 OFF-SUN OPERATION OF THE ORC: DISCHARGING OF THE TES

This mode is operated when power generation is required to fulfil the demand of electricity in off-sun situation. The HTF does not flow through the RHX. Heat is extracted from the TES and is converted into electricity by the ORC. To this end, the recirculation pump P-501 is started, the “hot” HTF is pumped out of the top of the TES tank at high temperature and it is directed to the ORC. The flowrate is set by the operator to meet the demand of electrical power. The 3-ways valve EV-501 regulates the temperature of the HTF at the inlet of the ORC at the setpoint value selected by the operator in the range 140°C-170°C, by recirculating part of the “cold” HTF from the outlet of the ORC and mixing it with the “hot” HTF extracted from the TES.

When the TES is almost fully discharged, the thermocline zone reaches the top of the tank and the temperature of the HTF extracted from the TES decreases according to the profile of the thermocline. The 3-ways valve EV-501 decreases the recirculation to maintain the temperature $T_{in-ORC}$ at the inlet of the ORC at the setpoint value. By decreasing this setpoint value until the minimum temperature acceptable for the ORC (around 110°C), the operator allows to fully extract the thermocline zone out of the TES tank. The electricity generated by the ORC is maintained constant as much as possible by increasing the mass flowrate of HTF by pump P-501, until the maximum flowrate is reached. From this moment, the electricity generated decreases. ORC stops when the temperature of the oil at the inlet of the ORC drops under the minimum acceptable.

The protocol is illustrated by the schemes of Figure 19.

<figure><img src="image_43.png" /><figcaption>Figure 19: Protocol for the off-sun operation of the ORC (left: demand of electricity is met, right: electricity generation may be reduced when the thermocline zone is harvested)</figcaption></figure>
## 4.6 OPERATION OF THE ORC IN SOLAR MODE

This mode is operated when power generation is required to fulfil the demand of electricity during sunny periods and the power generated by the gas-turbine is too low to meet this demand. The temperature of the HTF at the outlet of the RHX is regulated at the setpoint value by the controller of the pump P-401. The 3-ways valve EV-501 regulates the temperature of the HTF at the inlet of the ORC at the setpoint value selected by the operator in the range 140°C-170°C. The flowrate imposed by the recirculation pump P-501 is set by the operator to meet the demand of electrical power generated by the ORC. Two situations are observed, depending on the demand of electricity compared to the available heat recovered from the gas-turbine. Both protocols are illustrated by the schemes of Figure 20 and are described in §4.6.1 and §4.6.2 au-dessous.

<figure><img src="image_44.png" /><figcaption>Figure 20: Protocols for the operation of the ORC in solar mode (Left: low demand of electricity, Right: high demand of electricity)</figcaption></figure>

### 4.6.1 Low demand of electricity: TES charging

The heat recovered at the exhaust of the gas-turbine and transferred to the HTF circuit in the RHX exceeds the heat needed by the ORC to meet the demand of electricity.

The ORC converts part of the thermal energy provided by the RHX, the rest of this thermal energy is directed to the TES for charging. The plant is operated in combined mode "TES charging" and "power generation by ORC", simultaneously. This mode is similar to the end of TES charging in solar mode (see § 4.4.3 au-dessus and Figure 17 step #4), the difference being that the pump P-501 is not regulated by the temperature of thermal oil. The pump P-501 delivers the mass flowrate needed to meet the demand of electricity generated by the ORC.

### 4.6.2 High demand of electricity: TES discharging

The thermal energy recovered at the exhaust of the gas-turbine and transferred to the HTF circuit in the RHX is too small to meet the demand of electricity.

The thermal energy transferred to the HTF in the RHX is entirely directed to the ORC, and additional thermal energy is extracted from the TES to feed the ORC. The plant is operated in combined mode "TES discharging" and "power generation by ORC", simultaneously. The flowrate delivered by the circulation pump P-401 is smaller than the flowrate directed to the ORC with pump P-501.

## 5. PERFORMANCE ASSESSMENT

Key performance indicators (KPI) are associated to the main components of the plant: the solar receiver, the gas-turbine power block (top cycle), the RHX, the electrical heater, the TES and the ORC. The KPIs are directly measured by sensors, or more generally they are derived from measurements of physical parameters using expressions. The KPIs will be assessed within an extended range of operating conditions, covering design and off-design operating conditions. The range of operating conditions is defined by the minimum and maximum acceptable thermal load which will be determined for each component. In practice, conservative values of maximum acceptable temperature are set. They are summarized in Table 3.
<table><caption>Table 3: Maximum acceptable temperature for each component</caption><thead><tr><th>Component</th><th>SR</th><th>GT</th><th>RHX</th><th>TES</th><th>ORC</th></tr></thead><tbody><tr><th>Critical temperature</th><td>Metal surface</td><td>Air inlet</td><td>Air inlet</td><td>HTF</td><td>HTF inlet</td></tr><tr><th>Max value</th><td>950°C</td><td>800°C</td><td>500°C</td><td>340°C</td><td>170°C</td></tr></tbody></table>

## 5.1 PERFORMANCE OF SOLAR RECEIVER

The Key Performance Indicators of the solar receiver are summarized in Table 4.

<table><caption>Table 4: KPIs of Solar Receiver</caption><thead><tr><th>KPI</th><th>Notation and unit</th><th>Expression</th><th>Measurement</th><th>Notation and unit</th></tr></thead><tbody><tr><td rowspan="2">Solar energy input</td><td rowspan="2">$Q_{Rec\_in}$ [W]</td><td rowspan="2">$\iint \delta q_{Rec\_in}(x, y) \delta x \delta y$</td><td>Fast camera: images of beam reflected (see §3.2)</td><td>$Im_{[t_1...t_N]}(x, y)$</td></tr><tr><td>Flux sensor: flux density (see §3.2)</td><td>$\varphi_{cal}(x, 0, t)$ [W/m²]</td></tr><tr><td rowspan="3">Heat transferred to air</td><td rowspan="3">$Q_{Rec\_air}$ [W]</td><td rowspan="3">$\dot{m}_{air}(h_{Rec\_out} - h_{Rec\_in})$</td><td>Air mass flowrate (see §3.3)</td><td>$\dot{m}_{air}$ [kg/s]</td></tr><tr><td>Temperature sensor: air inlet temperature (CT103 in Figure 1)</td><td>$T_{Rec\_in}$ [°C]</td></tr><tr><td>Temperature sensor: air outlet temperature (CT108 in Figure 1)</td><td>$T_{Rec\_out}$ [°C]</td></tr><tr><td>Thermal loss</td><td>$Q_{Rec\_loss}$ [W]</td><td>$Q_{Rec\_in} - Q_{Rec\_air}$</td><td></td><td></td></tr><tr><td>Thermal efficiency</td><td>$\eta_{Rec}$ [-]</td><td>$\frac{Q_{Rec\_air}}{Q_{Rec\_in}}$</td><td></td><td></td></tr><tr><td>Pressure loss [bar]</td><td>$\Delta p_{Rec}$ [hPa]</td><td>$\Delta p_{Rec}$</td><td>Differential pressure</td><td>$\Delta p_{Rec}$ [hPa]</td></tr></tbody></table>

## 5.2 PERFORMANCE OF GAS-TURBINE POWER BLOCK

The typical ideal Brayton cycle is presented in the scheme (T,s) of Figure 21.

Assuming that air is a perfect gas and the cycle is ideal, the actual temperature $T_{2s}$ at node 2 and $T_{4s}$ at node 4 are expressed by: $T_{2s} = T_1 \left(\frac{P_2}{P_1}\right)^{\frac{\gamma-1}{\gamma}}$ and $T_{4s} = T_3 \left(\frac{P_4}{P_3}\right)^{\frac{\gamma-1}{\gamma}}$ with $\gamma=1.4$

Consequently, the compressor and expander isotropic efficiencies are expressed by:

$$ \eta_{Comp-iso} = \frac{T_{GT\_2s} - T_{GT\_1}}{T_{GT\_2r} - T_{GT\_1}} = \frac{\left(\frac{P_{GT\_2}}{P_{GT\_1}}\right)^{\frac{\gamma-1}{\gamma}} - 1}{\frac{T_{GT\_2r}}{T_{GT\_1}} - 1} \quad \text{and} \quad \eta_{Exp-iso} = \frac{T_{GT\_3} - T_{GT\_4r}}{T_{GT\_3} - T_{GT\_4s}} = \frac{1 - \frac{T_{GT\_4r}}{T_{GT\_3}}}{1 - \left(\frac{P_{GT\_4}}{P_{GT\_3}}\right)^{\frac{\gamma-1}{\gamma}}} $$
<figure><img src="image_45.png" /><figcaption>Figure 21: Typical ideal Brayton cycle (left: p,V diagram – right: T,s diagram)</figcaption></figure>

(1: air intake; 2r: actual compressor outlet; 2s: isentropic compressor outlet; 3: expander inlet; 4r: actual expander outlet; 4s: isentropic expander outlet; Q<sub>add</sub>: input heat from solar/combustor; Q<sub>re</sub>: exhaust heat; W<sub>c</sub>: compression work; W<sub>T</sub>: expansion work)

The Key Performance Indicators of the gas-turbine are summarized in Table 5.

<table><caption>Table 5: KPI of Gas-Turbine</caption><thead><tr><th>KPI</th><th>Notation and unit</th><th>Expression</th><th>Measurement</th><th>Notation and unit</th></tr></thead><tbody><tr><td rowspan="4">Gas-turbine thermal efficiency</td><td rowspan="4">η<sub>GT-th</sub></td><td rowspan="4">1 - <sup>T<sub>GT_4r</sub> - T<sub>GT_1</sub></sup>&frasl;<sub>T<sub>GT_3</sub> - T<sub>GT_2r</sub></sub></td><td>Air temperature at compressor inlet (CT102 in Figure 1)</td><td>T<sub>GT_1</sub> [K]</td></tr><tr><td>Air temperature at compressor outlet (CT103 in Figure 1)</td><td>T<sub>GT_2r</sub> [K]</td></tr><tr><td>Air temperature at expander inlet (CT108 in Figure 1)</td><td>T<sub>GT_3</sub> [K]</td></tr><tr><td>Air temperature at expander outlet (CT112 in Figure 1)</td><td>T<sub>GT_4r</sub> [K]</td></tr><tr><td rowspan="2">Gas-turbine conversion efficiency</td><td rowspan="2">η<sub>GT-el</sub></td><td rowspan="2">Q<sub>GT-elec</sub> / ṁ<sub>air</sub>(h<sub>GT_3</sub> - h<sub>GT_2r</sub>)</td><td>Power generated</td><td>Q<sub>GT-elec</sub> [W]</td></tr><tr><td>Air mass flowrate</td><td>ṁ<sub>air</sub> [kg/s]</td></tr><tr><td rowspan="2">Compression isentropic efficiency</td><td rowspan="2">η<sub>Comp-iso</sub></td><td rowspan="2">(p<sub>GT_2</sub>/p<sub>GT_1</sub>)<sup>γ-1/γ</sup> - 1 / (T<sub>GT_2r</sub>/T<sub>GT_1</sub> - 1)</td><td>Air pressure at compressor inlet (CP102 in Figure 1)</td><td>p<sub>GT_1</sub> [hPa]</td></tr><tr><td>Air pressure at compressor outlet (CP103 in Figure 1)</td><td>p<sub>GT_2</sub> [hPa]</td></tr><tr><td rowspan="2">Expansion isentropic efficiency</td><td rowspan="2">η<sub>Exp-iso</sub></td><td rowspan="2">1 - (T<sub>GT_4r</sub>/T<sub>GT_3</sub>) / (1 - (p<sub>GT_3</sub>/p<sub>GT_4</sub>)<sup>1-γ/γ</sup>)</td><td>Air pressure at expander inlet (CP108 in Figure 1)</td><td>p<sub>GT_3</sub> [hPa]</td></tr><tr><td>Air pressure at expander outlet (CP112 in Figure 1)</td><td>p<sub>GT_4</sub> [hPa]</td></tr></tbody></table>
## 5.3 PERFORMANCE OF RECOVERY HEAT EXCHANGER

The Key Performance Indicators of the recovery heat exchanger are summarized in Table 6.

<table><caption>Table 6: KPIs of Recovery Heat Exchanger (RHX)</caption><thead><tr><th>KPI</th><th>Notation and unit</th><th>Expression</th><th>Measurement</th><th>Notation and unit</th></tr></thead><tbody><tr><td rowspan="2">RHX Thermal pinch</td><td rowspan="2">δT<sub>RHX</sub> [K]</td><td rowspan="2">T<sub>RHX.air_out</sub> - T<sub>RHX.oil_in</sub></td><td>Air temperature at RHX outlet (TT-Air-03 &amp; TT-Air-04 in Figure 3)</td><td>T<sub>RHX.air_out</sub> [°C]</td></tr><tr><td>Oil temperature at RHX inlet (TT-08 in Figure 3: Final version of the P&ID of POLYPHEM prototype plant)</td><td>T<sub>RHX.oil_in</sub> [°C]</td></tr><tr><td>RHX heat transfer efficiency</td><td>η<sub>RHX.hx</sub></td><td>1 - δT<sub>RHX</sub> / (T<sub>RHX.air_in</sub> - T<sub>RHX.oil_in</sub>)</td><td>Air temperature at RHX inlet (TT-Air-01 &amp; TT-Air-02 in Figure 3)</td><td>T<sub>RHX.air_in</sub> [°C]</td></tr><tr><td rowspan="2">Heat transferred to thermal oil</td><td rowspan="2">Q<sub>RHX.oil</sub> [W]</td><td rowspan="2">ṁ<sub>RHX.oil</sub>(h<sub>RHX.oil_out</sub> - h<sub>RHX.oil_in</sub>)</td><td>Oil mass flowrate (FT-02 in Figure 3)</td><td>ṁ<sub>RHX.oil</sub> [kg/s]</td></tr><tr><td>Oil temperature at RHX outlet (TT-01 in Figure 3)</td><td>T<sub>RHX.oil_out</sub> [°C]</td></tr><tr><td>RHX thermal efficiency</td><td>η<sub>RHX.th</sub></td><td>Q<sub>RHX.oil</sub> / (ṁ<sub>air</sub>(h<sub>RHX.air_in</sub> - h<sub>RHX.air_out</sub>))</td><td>Air mass flowrate (*)</td><td>ṁ<sub>air</sub> [kg/s]</td></tr><tr><td rowspan="2">RHX thermal loss</td><td rowspan="2">Q<sub>RHX(loss)</sub> [W]</td><td rowspan="2">A<sub>RHX</sub> κ<sub>insu</sub> / d<sub>insu</sub> (T<sub>RHX.sk</sub> - T<sub>RHX_ext</sub>)</td><td>Skin temperature of RHX (TT_RHXSkin)</td><td>T<sub>RHX.sk</sub> [°C]</td></tr><tr><td>Outer temperature of RHX (TT_RHX_ext)</td><td>T<sub>RHX_ext</sub> [°C]</td></tr><tr><td>RHX thermal efficiency</td><td>η<sub>RHX.th</sub></td><td>1 - Q<sub>RHX_loss</sub> / (Q<sub>RHX air</sub> + Q<sub>RHX loss</sub>)</td><td></td><td></td></tr><tr><td rowspan="2">Pressure loss in thermal oil flow</td><td rowspan="2">ΔP<sub>RHX_oil</sub></td><td rowspan="2">p<sub>RHX air</sub> - p<sub>RHX_oil_in</sub></td><td>Thermal oil pressure at outlet (CP-01 in Figure 3)</td><td>p<sub>RHX air</sub> [hPa]</td></tr><tr><td>Thermal oil pressure at inlet (CP-08 in Figure 3)</td><td>p<sub>RHX_oil_in</sub> [hPa]</td></tr></tbody></table>

<footnote>(*) The air mass flowrate is not measured in the prototype plant installed according to the final version of P&ID in Figure 3: Final version of the P&ID of POLYPHEM prototype plant</footnote>

<footnote>, because the mass flowrate was planned to be measured in the gas turbine and solar receiver piping. Therefore, it was decided to assess the heat loss of the RHX by measuring the skin and outer temperature,</footnote>
and then to derive the thermal efficiency from this heat loss assessment. This method is less accurate than the previous one based on the air mass flowrate. The thermal efficiency will be roughly assessed.

## 5.4 PERFORMANCE OF ELECTRICAL HEATER

The Key Performance Indicator of the electrical heater is the thermal efficiency of this component. It is indicated in Table 7 and the measurements refer to Figure 2.

<table><caption>Table 7: KPI of electrical Heater (elHe)</caption><thead><tr><th>KPI</th><th>Notation and unit</th><th>Expression</th><th>Measurement</th><th>Notation and unit</th></tr></thead><tbody><tr><td rowspan="3">El. Heater thermal efficiency</td><td rowspan="3">η<sub>elHe_th</sub></td><td rowspan="3">$\frac{\dot{m}_{oil}(h_{oil\_out} - h_{oil\_in})}{Q_{elHe}}$</td><td>Oil mass flowrate (FIT-401 in Figure 2)</td><td>$\dot{m}_{oil}$ [kg/s]</td></tr><tr><td>Oil temperature at heater outlet (TT-404 in Figure 2)</td><td>$T_{oil\_out}$ [°C]</td></tr><tr><td>Oil temperature at heater inlet (TT-403 in Figure 2)</td><td>$T_{oil\_out}$ [°C]</td></tr></tbody></table>

## 5.5 PERFORMANCE OF ORC POWER BLOCK

The ORC is considered as a loop including the ORC group and the recirculation of thermal oil. The thermal energy transferred to this loop is assessed and reported to the electrical power generated by the power block. The Key Performance Indicators of the ORC power block are summarized in Table 8.

<table><caption>Table 8: KPIs of the Organic Rankine Cycle power block</caption><thead><tr><th>KPI</th><th>Notation and unit</th><th>Expression</th><th>Measurement</th><th>Notation and unit</th></tr></thead><tbody><tr><td rowspan="4">Thermal oil temperature inlet ORC</td><td rowspan="4">$T_{ORC\_in}$ [K]</td><td rowspan="4">$T_{TES\_oil\_in} + \frac{\dot{m}_{RHX\_oil}}{\dot{m}_{ORC\_oil}}(T_{oil\_hot} - T_{TES\_oil\_in})$</td><td>Hot oil temperature (TT-02 in Figure 3: Final version of the P&amp;ID of POLYPHEM prototype plant)</td><td>$T_{oil\_hot}$ [°C]</td></tr><tr><td>TES inlet oil temperature (“hot”) (TT-04 in Figure 3)</td><td>$T_{TES\_oil\_in}$ [°C]</td></tr><tr><td>Oil mass flowrate in RHX (FT-02 in Figure 3)</td><td>$\dot{m}_{RHX\_oil}$ [kg/s]</td></tr><tr><td>Oil mass flowrate in ORC loop (FT-01 in Figure 3)</td><td>$\dot{m}_{ORC\_oil}$ [kg/s]</td></tr><tr><td>$T_{ORC\_out}$ [K]</td><td>$T_{TES\_oil\_out} - \frac{\dot{m}_{RHX\_oil}}{\dot{m}_{ORC\_oil}}(T_{TES\_oil\_out} - T_{oil\_cold})$</td><td>TES outlet oil temperature (“cold”)</td><td>$T_{TES\_oil\_out}$ [°C]</td></tr></tbody></table>
<table><tr><td>Thermal oil temperature outlet ORC</td><td></td><td>(TT-03 in Figure 3)</td><td></td></tr><tr><td>ORC gross conversion efficiency</td><td>η<sub>ORC-gross</sub></td><td><div style="text-align: center;"><div style="border-bottom: 1px solid black; padding-bottom: 1px;">Q<sub>ORC-gross</sub></div><div style="padding-top: 1px;">ṁ<sub>ORC_oil</sub>(h<sub>ORC_oil_in</sub> - h<sub>ORC_oil_out</sub>)</div></div></td><td>Cold oil temperature (TT-07 in Figure 3)</td><td>T<sub>oil_cold</sub> [°C]</td></tr><tr><td>ORC net conversion efficiency</td><td>η<sub>ORC-net</sub></td><td><div style="text-align: center;"><div style="border-bottom: 1px solid black; padding-bottom: 1px;">Q<sub>ORC-net</sub></div><div style="padding-top: 1px;">ṁ<sub>ORC_oil</sub>(h<sub>ORC_oil_in</sub> - h<sub>ORC_oil_out</sub>)</div></div></td><td>Gross electrical power generated by ORC</td><td>Q<sub>ORC_gross</sub> [W]</td></tr><tr><td></td><td></td><td></td><td>Net electrical power generated by ORC</td><td>Q<sub>ORC_net</sub> [W]</td></tr></table>

## 5.6 PERFORMANCE OF THERMAL ENERGY STORAGE

The assessment of the performance of the thermal energy storage is a major outcome of the experimental work. The stability of the thickness of the thermocline region under series of charging and discharging steps is an indicator of successful behavior of the thermocline storage. The quality of the storage is also assessed by the efficiency of charge and discharge. The experimental work performed in Task 3.2 for the validation of the filler material using the Microsol-R test bench at CNRS will serve as a reference for the processing of the data, as it was reported in the deliverable D3.4 (A. Ferriere, 2022). The contribution of the walls of the tank to the storage capacity and to the charging and discharging dynamics will be carefully analyzed.

The Key Performance Indicators of the Thermal Energy Storage system are summarized in Table 9.

<table><caption>Table 9: KPIs of the Thermal Energy Storage system (TES)</caption><thead><tr><th>KPI</th><th>Notation and unit</th><th>Expression</th><th>Measurement</th><th>Notation and unit</th></tr></thead><tbody><tr><td rowspan="2">High temperature threshold</td><td rowspan="2">T<sub>H</sub> [K]</td><td rowspan="2">T<sub>TES,max</sub> - τ(T<sub>TES,max</sub> - T<sub>TES,min</sub>)<br>τ = 20%</td><td>Maximum temperature of thermal oil in TES</td><td>T<sub>TES_max</sub> [°C]</td></tr><tr><td>Minimum temperature of thermal oil in TES</td><td>T<sub>TES_min</sub> [°C]</td></tr><tr><td>Low temperature threshold</td><td>T<sub>L</sub> [K]</td><td>T<sub>TES,min</sub> + τ(T<sub>TES,max</sub> - T<sub>TES,min</sub>)<br>τ = 20%</td><td></td><td></td></tr><tr><td>Thickness of thermocline region</td><td>δ<sub>therm</sub> [m]</td><td>h(T<sub>H</sub>) - h(T<sub>L</sub>) (*)</td><td></td><td></td></tr><tr><td>Thermal capacity of TES</td><td>Ω<sub>TES</sub> [J]</td><td>∫<sub>T<sub>TES_min</sub></sub><sup>T<sub>TES_max</sub></sup> [Σ<sub>i</sub> m<sub>i</sub>Cp<sub>i</sub>(T)] ∂T</td><td></td><td></td></tr><tr><td rowspan="2">Thermal oil mass flowrate in TES</td><td rowspan="2">ṁ<sub>oil</sub> [kg/s]</td><td rowspan="2">ṁ<sub>RHX_oil</sub> - ṁ<sub>ORC_oil</sub></td><td>Oil mass flowrate in ORC loop (FT-01 in Figure 3)</td><td>ṁ<sub>ORC_oil</sub> [kg/s]</td></tr><tr><td>Oil mass flowrate in RHX (FT-02 in Figure 3)</td><td>ṁ<sub>RHX_oil</sub> [kg/s]</td></tr><tr><td>Input/output thermal power</td><td>Q<sub>oil</sub> [W]</td><td>ṁ<sub>oil</sub> ∫<sub>T<sub>oil_out</sub></sub><sup>T<sub>oil_in</sub></sup> Cρ<sub>oil</sub>(T) ∂T</td><td>Thermal oil TES inlet temp. (TT-04 in Figure 3)</td><td>T<sub>oil_in</sub> [°C]</td></tr></tbody></table>
<table><thead><tr><th></th><th></th><th></th><th>Thermal oil TES<br>outlet temp. (TT-03<br>in Figure 3)</th><th>T<sub>oil_out</sub><br>[°C]</th></tr></thead><tbody><tr><td>Heat loss</td><td>Q<sub>loss</sub><br>[W]</td><td>f(T<sub>oil_in</sub>, T<sub>oil_out</sub>)</td><td></td><td></td></tr><tr><td>Thermal energy<br>charged/discharged</td><td>Σ<sub>TES</sub><br>[J]</td><td>∫<sub>0</sub><sup>t</sup> [Q<sub>oil</sub>(t) - Q<sub>loss</sub>(t)] ∂t</td><td></td><td></td></tr><tr><td>Efficiency of<br>charge/discharge</td><td>Ψ</td><td>Σ<sub>TES</sub>(t<sub>end</sub>) / Ω<sub>TES</sub></td><td></td><td></td></tr></tbody></table>

## 6. SUPERVISORY CONTROL AND DATA ACQUISITION

The supervisory control and data acquisition system (SCADA) is composed of a human-machine interface (HMI) which communicates via Ethernet links with the control cabinet supplied by CNRS and with the programmable logic controller (PLC) of the ORC group supplied by ORCAN (see Figure 22).

<figure><img src="image_46.png" /><figcaption>Figure 22: Control cabinet of POLYPHEM by CNRS (left) and control cabinet or ORC by ORCAN (right)</figcaption></figure>

The HMI serves for the remote control of the plant, for the monitoring of the signals measured and for the recording of data files. The operation software is developed by CNRS using Labview™ environment. The actuators and sensors of the process are connected to the control cabinet via I/O terminals. Some data supplied by the PLC of the ORC are transferred to the HMI via Ethernet connection.

The values of the measured signals are displayed in real time in a schematic process diagram on the screen of the supervisor. An example is shown in Figure 23.

A datafile is created when a test is carried out. 124 input terminals are collected and the signals are converted into physical values. 111 terminals are connected to sensors and 13 terminals are not connected (NC). The frequency of the data acquisition is set by the operator. The minimum period (time stp) is 500 ms. In practice, a typical period between 5 s and 60 s is suited to catch the variation of the physical signals.

The datafiles are created in format txt (text file). The heading summarizes the date of the test, the starting and ending time and the operating conditions. The time series are presented in columns in a table. The labels are indicated in the first line. The 1st column is the time, the columns 2 to 125 are the values of the signals

<footnote>(*) The thickness of the thermocline zone is determined from the profile of temperature h(T) along the vertical direction in the storage tank.</footnote>
expressed in physical unit, labelled by their name and ranked in a constant order (SigName-1 to SigName-124). The template of datafile is given in Table 10.

<table><caption>Table 10: Template of datafile: time series of measured values</caption><thead><tr><th>TIME</th><th>SigName-1</th><th>SigName-2</th><th>SigName-3</th><th>SigName-n</th></tr></thead><tbody><tr><td>hh:mm:s</td><td>value</td><td>value</td><td>value</td><td>value</td></tr><tr><td>hh:mm:s</td><td>value</td><td>value</td><td>value</td><td>value</td></tr><tr><td>hh:mm:s</td><td>value</td><td>value</td><td>value</td><td>value</td></tr><tr><td>hh:mm:s</td><td>value</td><td>value</td><td>value</td><td>value</td></tr></tbody></table>

The signals ordered by signal names and transposed in column are listed in Table 11. The notation used in this report for each signal and a short description of the signals are also indicated in Table 11.
<figure><img src="image_47.png" /><figcaption>Figure 23: Screenshot of the supervision - Example of display of the process and of measured signals</figcaption></figure>
<table><caption>Table 11: List of measured signals</caption><thead><tr><td>SigName</td><td>Notation</td><td>Unit</td><td>Signal description</td><td>Sensor</td></tr></thead><tbody><tr><td>T01</td><td>T<sub>TES_oil_01</sub></td><td>°C</td><td>Thermal oil temp. in TES (0,0,0)</td><td>TC-type J</td></tr><tr><td>T02</td><td>T<sub>TES_oil_02</sub></td><td>°C</td><td>Thermal oil temp. in TES (63,0,0)</td><td>TC-type J</td></tr><tr><td>T03</td><td>T<sub>TES_oil_03</sub></td><td>°C</td><td>Thermal oil temp. in TES (116,0,0)</td><td>TC-type J</td></tr><tr><td>T11</td><td>T<sub>TES_oil_11</sub></td><td>°C</td><td>Thermal oil temp. in TES (0,0,13)</td><td>TC-type J</td></tr><tr><td>T21</td><td>T<sub>TES_oil_21</sub></td><td>°C</td><td>Thermal oil temp. in TES (0,0,23)</td><td>TC-type J</td></tr><tr><td>T22</td><td>T<sub>TES_oil_22</sub></td><td>°C</td><td>Thermal oil temp. in TES (63,0,23)</td><td>TC-type J</td></tr><tr><td>T23</td><td>T<sub>TES_oil_23</sub></td><td>°C</td><td>Thermal oil temp. in TES (116,0,23)</td><td>TC-type J</td></tr><tr><td>T24</td><td>T<sub>TES_oil_24</sub></td><td>°C</td><td>Thermal oil temp. in TES (126,0,23)</td><td>TC-type J</td></tr><tr><td>T25</td><td>T<sub>TES_oil_25</sub></td><td>°C</td><td>Thermal oil temp. in TES (0,63,23)</td><td>TC-type J</td></tr><tr><td>T26</td><td>T<sub>TES_oil_26</sub></td><td>°C</td><td>Thermal oil temp. in TES (0,116,23)</td><td>TC-type J</td></tr><tr><td>T31</td><td>T<sub>TES_oil_31</sub></td><td>°C</td><td>Thermal oil temp. in TES (0,0,33)</td><td>TC-type J</td></tr><tr><td>T41</td><td>T<sub>TES_oil_41</sub></td><td>°C</td><td>Thermal oil temp. in TES (0,0,43)</td><td>TC-type J</td></tr><tr><td>T51</td><td>T<sub>TES_oil_51</sub></td><td>°C</td><td>Thermal oil temp. in TES (0,0,53)</td><td>TC-type J</td></tr><tr><td>T61</td><td>T<sub>TES_oil_61</sub></td><td>°C</td><td>Thermal oil temp. in TES (0,0,63)</td><td>TC-type J</td></tr><tr><td>T71</td><td>T<sub>TES_oil_71</sub></td><td>°C</td><td>Thermal oil temp. in TES (0,0,73)</td><td>TC-type J</td></tr><tr><td>T72</td><td>T<sub>TES_oil_72</sub></td><td>°C</td><td>Thermal oil temp. in TES (63,0,73)</td><td>TC-type J</td></tr><tr><td>T73</td><td>T<sub>TES_oil_73</sub></td><td>°C</td><td>Thermal oil temp. in TES (116,0,73)</td><td>TC-type J</td></tr><tr><td>T81</td><td>T<sub>TES_oil_81</sub></td><td>°C</td><td>Thermal oil temp. in TES (0,0,86)</td><td>TC-type J</td></tr><tr><td>T91</td><td>T<sub>TES_oil_91</sub></td><td>°C</td><td>Thermal oil temp. in TES (0,0,96)</td><td>TC-type J</td></tr><tr><td>T101</td><td>T<sub>TES_oil_101</sub></td><td>°C</td><td>Thermal oil temp. in TES (0,0,106)</td><td>TC-type J</td></tr><tr><td>T111</td><td>T<sub>TES_oil_111</sub></td><td>°C</td><td>Thermal oil temp. in TES (0,0,116)</td><td>TC-type J</td></tr><tr><td>T121</td><td>T<sub>TES_oil_121</sub></td><td>°C</td><td>Thermal oil temp. in TES (0,0,126)</td><td>TC-type J</td></tr><tr><td>T122</td><td>T<sub>TES_oil_122</sub></td><td>°C</td><td>Thermal oil temp. in TES (63,0,126)</td><td>TC-type J</td></tr><tr><td>T123</td><td>T<sub>TES_oil_123</sub></td><td>°C</td><td>Thermal oil temp. in TES (116,0,126)</td><td>TC-type J</td></tr><tr><td>T124</td><td>T<sub>TES_oil_124</sub></td><td>°C</td><td>Thermal oil temp. in TES (126,0,126)</td><td>TC-type J</td></tr><tr><td>T125</td><td>T<sub>TES_oil_125</sub></td><td>°C</td><td>Thermal oil temp. in TES (0,63,126)</td><td>TC-type J</td></tr><tr><td>T126</td><td>T<sub>TES_oil_126</sub></td><td>°C</td><td>Thermal oil temp. in TES (0,116,126)</td><td>TC-type J</td></tr><tr><td>T131</td><td>T<sub>TES_oil_131</sub></td><td>°C</td><td>Thermal oil temp. in TES (0,0,139)</td><td>TC-type J</td></tr><tr><td>T141</td><td>T<sub>TES_oil_141</sub></td><td>°C</td><td>Thermal oil temp. in TES (0,0,149)</td><td>TC-type J</td></tr><tr><td>T151</td><td>T<sub>TES_oil_151</sub></td><td>°C</td><td>Thermal oil temp. in TES (0,0,159)</td><td>TC-type J</td></tr></tbody></table>

<table><tr><td>T161</td><td>T<sub>TES_oil_161</sub></td><td>°C</td><td>Thermal oil temp. in TES (0,0,169)</td><td>TC-type J</td></tr><tr><td>T171</td><td>T<sub>TES_oil_171</sub></td><td>°C</td><td>Thermal oil temp. in TES (0,0,179)</td><td>TC-type J</td></tr><tr><td>T172</td><td>T<sub>TES_oil_172</sub></td><td>°C</td><td>Thermal oil temp. in TES (63,0,179)</td><td>TC-type J</td></tr><tr><td>T173</td><td>T<sub>TES_oil_173</sub></td><td>°C</td><td>Thermal oil temp. in TES (116,0,179)</td><td>TC-type J</td></tr><tr><td>T181</td><td>T<sub>TES_oil_181</sub></td><td>°C</td><td>Thermal oil temp. in TES (0,0,192)</td><td>TC-type J</td></tr><tr><td>T191</td><td>T<sub>TES_oil_191</sub></td><td>°C</td><td>Thermal oil temp. in TES (0,0,202)</td><td>TC-type J</td></tr><tr><td>T201</td><td>T<sub>TES_oil_201</sub></td><td>°C</td><td>Thermal oil temp. in TES (0,0,212)</td><td>TC-type J</td></tr><tr><td>T211</td><td>T<sub>TES_oil_211</sub></td><td>°C</td><td>Thermal oil temp. in TES (0,0,222)</td><td>TC-type J</td></tr><tr><td>T221</td><td>T<sub>TES_oil_221</sub></td><td>°C</td><td>Thermal oil temp. in TES (0,0,232)</td><td>TC-type J</td></tr><tr><td>T222</td><td>T<sub>TES_oil_222</sub></td><td>°C</td><td>Thermal oil temp. in TES (63,0,232)</td><td>TC-type J</td></tr><tr><td>T223</td><td>T<sub>TES_oil_223</sub></td><td>°C</td><td>Thermal oil temp. in TES (116,0,232)</td><td>TC-type J</td></tr><tr><td>T224</td><td>T<sub>TES_oil_224</sub></td><td>°C</td><td>Thermal oil temp. in TES (126,0,232)</td><td>TC-type J</td></tr><tr><td>T225</td><td>T<sub>TES_oil_225</sub></td><td>°C</td><td>Thermal oil temp. in TES (0,63,232)</td><td>TC-type J</td></tr><tr><td>T226</td><td>T<sub>TES_oil_226</sub></td><td>°C</td><td>Thermal oil temp. in TES (0,116,232)</td><td>TC-type J</td></tr><tr><td>T231</td><td>T<sub>TES_oil_231</sub></td><td>°C</td><td>Thermal oil temp. in TES (0,0,244)</td><td>TC-type J</td></tr><tr><td>T241</td><td>T<sub>TES_oil_241</sub></td><td>°C</td><td>Thermal oil temp. in TES (0,0,257)</td><td>TC-type J</td></tr><tr><td>T251</td><td>T<sub>TES_oil_251</sub></td><td>°C</td><td>Thermal oil temp. in TES (0,0,270)</td><td>TC-type J</td></tr><tr><td>T254</td><td>T<sub>TES_oil_254</sub></td><td>°C</td><td>Thermal oil temp. in TES (126,0,270)</td><td>TC-type J</td></tr><tr><td>T261</td><td>T<sub>TES_oil_261</sub></td><td>°C</td><td>Thermal oil temp. in TES (0,0,280)</td><td>TC-type J</td></tr><tr><td>T271</td><td>T<sub>TES_oil_271</sub></td><td>°C</td><td>Thermal oil temp. in TES (0,0,290)</td><td>TC-type J</td></tr><tr><td>T274</td><td>T<sub>TES_oil_274</sub></td><td>°C</td><td>Thermal oil temp. in TES (126,0,290)</td><td>TC-type J</td></tr><tr><td>T281</td><td>T<sub>TES_oil_281</sub></td><td>°C</td><td>Thermal oil temp. in TES (0,0,300)</td><td>TC-type J</td></tr><tr><td>T291</td><td>T<sub>TES_oil_291</sub></td><td>°C</td><td>Thermal oil temp. in TES (0,0,310)</td><td>TC-type J</td></tr><tr><td>T294</td><td>T<sub>TES_oil_294</sub></td><td>°C</td><td>Thermal oil temp. in TES (126,0,310)</td><td>TC-type J</td></tr><tr><td>T301</td><td>T<sub>TES_oil_301</sub></td><td>°C</td><td>Thermal oil temp. in TES (0,0,320)</td><td>TC-type J</td></tr><tr><td>T311</td><td>T<sub>TES_oil_311</sub></td><td>°C</td><td>Thermal oil temp. in TES (0,0,330)</td><td>TC-type J</td></tr><tr><td>TW1</td><td>T<sub>TES wall_1</sub></td><td>°C</td><td>Wall temp. in TES (150,0,23)</td><td>TC-type J</td></tr><tr><td>TW2</td><td>T<sub>TES wall_2</sub></td><td>°C</td><td>Wall temp. in TES (174,0,23)</td><td>TC-type J</td></tr><tr><td>TW3</td><td>T<sub>TES wall_3</sub></td><td>°C</td><td>Wall temp. in TES (150,0,126)</td><td>TC-type J</td></tr><tr><td>TW4</td><td>T<sub>TES wall_4</sub></td><td>°C</td><td>Wall temp. in TES (174,0,126)</td><td>TC-type J</td></tr><tr><td>TW5</td><td>T<sub>TES wall_5</sub></td><td>°C</td><td>Wall temp. in TES (150,0,232)</td><td>TC-type J</td></tr><tr><td>TW6</td><td>T<sub>TES wall_6</sub></td><td>°C</td><td>Wall temp. in TES (174,0,232)</td><td>TC-type J</td></tr></table>
<table><tr><td>TW7</td><td>T<sub>TES wall_7</sub></td><td>°C</td><td>Wall temp. in TES (150,0,270)</td><td>TC-type J</td></tr><tr><td>TW8</td><td>T<sub>TES wall_8</sub></td><td>°C</td><td>Wall temp. in TES (174,0,270)</td><td>TC-type J</td></tr><tr><td>TW9</td><td>T<sub>TES wall_9</sub></td><td>°C</td><td>Wall temp. in TES (150,0,290)</td><td>TC-type J</td></tr><tr><td>TW10</td><td>T<sub>TES wall_10</sub></td><td>°C</td><td>Wall temp. in TES (174,0,290)</td><td>TC-type J</td></tr><tr><td>TW11</td><td>T<sub>TES wall_11</sub></td><td>°C</td><td>Wall temp. in TES (150,0,310)</td><td>TC-type J</td></tr><tr><td>TW12</td><td>T<sub>TES wall_12</sub></td><td>°C</td><td>Wall temp. in TES (174,0,310)</td><td>TC-type J</td></tr><tr><td>TW13</td><td>T<sub>TES wall_13</sub></td><td>°C</td><td>Top cap temp. in TES (116,0,320)</td><td>TC-type J</td></tr><tr><td>TW14</td><td>T<sub>TES wall_14</sub></td><td>°C</td><td>Top cap temp. in TES (116,0,340)</td><td>TC-type J</td></tr><tr><td>TD1</td><td>T<sub>bot man oil</sub></td><td>°C</td><td>Thermal oil temp., bottom manifold</td><td>TC-type J</td></tr><tr><td>TD2</td><td>T<sub>top man oil</sub></td><td>°C</td><td>Thermal oil temp., top manifold</td><td>TC-type J</td></tr><tr><td>TB1</td><td>T<sub>base_1</sub></td><td>°C</td><td>Basement temp. in TES (0,0,-55)</td><td>TC-type J</td></tr><tr><td>TB2</td><td>T<sub>base_2</sub></td><td>°C</td><td>Basement temp. in TES (0,0,-75)</td><td>TC-type J</td></tr><tr><td>TB3</td><td>T<sub>base_3</sub></td><td>°C</td><td>Basement temp. in TES (0,0,-95)</td><td>TC-type J</td></tr><tr><td>TB4</td><td>T<sub>base_4</sub></td><td>°C</td><td>Basement temp. in TES (116,0,-55)</td><td>TC-type J</td></tr><tr><td>TB5</td><td>T<sub>base_5</sub></td><td>°C</td><td>Basement temp. in TES (116,0,-75)</td><td>TC-type J</td></tr><tr><td>TB6</td><td>T<sub>base_6</sub></td><td>°C</td><td>Basement temp. in TES (116,0,-95)</td><td>TC-type J</td></tr><tr><td>TF1</td><td>T<sub>bot slab_1</sub></td><td>°C</td><td>Bottom slab temp. in TES (0,0,-25)</td><td>TC-type J</td></tr><tr><td>TF2</td><td>T<sub>bot slab_2</sub></td><td>°C</td><td>Bottom slab temp. in TES (0,0,-50)</td><td>TC-type J</td></tr><tr><td>TT_Air_01</td><td>T<sub>RHX air in</sub></td><td>°C</td><td>Air temp. at RHX inlet</td><td>TC-type J</td></tr><tr><td>TT_Air_02</td><td>T<sub>RHX air in</sub></td><td>°C</td><td>Air temp. at RHX inlet</td><td>TC-type J</td></tr><tr><td>TT_Air_03</td><td>T<sub>RHX air out</sub></td><td>°C</td><td>Air temp. at RHX outlet</td><td>TC-type J</td></tr><tr><td>TT_Air_04</td><td>T<sub>RHX air out</sub></td><td>°C</td><td>Air temp. at RHX outlet</td><td>TC-type J</td></tr><tr><td>TT_Air_00</td><td>T<sub>CMB air out</sub></td><td>°C</td><td>Air temp. at combustor outlet</td><td>TC-type K</td></tr><tr><td>TT_Air_06</td><td>T<sub>CMB air out</sub></td><td>°C</td><td>Air temp. at combustor outlet</td><td>TC-type K</td></tr><tr><td>TT_RHXSkin</td><td>T<sub>RHX skin</sub></td><td>°C</td><td>Skin temp. of RHX</td><td>TC-type J</td></tr><tr><td>TT_RHX_ext</td><td>T<sub>RHX out</sub></td><td>°C</td><td>Outer temp. of RHX</td><td>TC-type J</td></tr><tr><td>TT_amb_in</td><td>T<sub>CONT amb</sub></td><td>°C</td><td>Ambient temp. inside the container</td><td>TC-type J</td></tr><tr><td>TT_amb_out</td><td>T<sub>OUT amb</sub></td><td>°C</td><td>Outdoor ambient temp.</td><td>TC-type J</td></tr><tr><td>NC</td><td></td><td></td><td></td><td></td></tr><tr><td>NC</td><td></td><td></td><td></td><td></td></tr><tr><td>NC</td><td></td><td></td><td></td><td></td></tr><tr><td>NC</td><td></td><td></td><td></td><td></td></tr></table>

<table><tr><td>NC</td><td></td><td></td><td></td><td></td></tr><tr><td>NC</td><td></td><td></td><td></td><td></td></tr><tr><td>TT-01</td><td>T<sub>RHX oil out</sub></td><td>°C</td><td>Thermal oil RHX outlet temp.</td><td>Pt-100</td></tr><tr><td>TT-02</td><td>T<sub>oil hot</sub></td><td>°C</td><td>Hot thermal oil temp.</td><td>Pt-101</td></tr><tr><td>TT-03</td><td>T<sub>TES oil out</sub></td><td>°C</td><td>Thermal oil TES outlet temp. (cold)</td><td>Pt-102</td></tr><tr><td>TT-04</td><td>T<sub>TES oil in</sub></td><td>°C</td><td>Thermal oil TES inlet temp. (hot)</td><td>Pt-103</td></tr><tr><td>TT-05</td><td>T<sub>ORC oil in</sub></td><td>°C</td><td>Thermal oil ORC inlet temp.</td><td>Pt-104</td></tr><tr><td>TT-06</td><td>T<sub>ORC oil out</sub></td><td>°C</td><td>Thermal oil ORC outlet temp.</td><td>Pt-105</td></tr><tr><td>TT-07</td><td>T<sub>oil cold</sub></td><td>°C</td><td>Cold thermal oil temp.</td><td>Pt-106</td></tr><tr><td>TT-08</td><td>T<sub>RHX oil in</sub></td><td>°C</td><td>Thermal oil RHX inlet temp.</td><td>Pt-107</td></tr><tr><td>TT-09</td><td>T<sub>TANK oil</sub></td><td>°C</td><td>Thermal oil temp. in tank</td><td>Pt-108</td></tr><tr><td>NC</td><td></td><td></td><td></td><td></td></tr><tr><td>NC</td><td></td><td></td><td></td><td></td></tr><tr><td>NC</td><td></td><td></td><td></td><td></td></tr><tr><td>PT-01</td><td>p<sub>RHX oil out</sub></td><td>hPa</td><td>Thermal oil press. at RHX outlet</td><td>Si sensor</td></tr><tr><td>PT-02</td><td>p<sub>TES oil out</sub></td><td>hPa</td><td>Thermal oil press. at TES outlet (cold)</td><td>Si sensor</td></tr><tr><td>PT-03</td><td>p<sub>TES oil in</sub></td><td>hPa</td><td>Thermal oil press. at TES inlet (hot)</td><td>Si sensor</td></tr><tr><td>PT-05</td><td>p<sub>ORC oil in</sub></td><td>hPa</td><td>Thermal oil press. at ORC inlet</td><td>Si sensor</td></tr><tr><td>PT-06</td><td>p<sub>ORC oil out</sub></td><td>hPa</td><td>Thermal oil press. at ORC outlet</td><td>Si sensor</td></tr><tr><td>PT-08</td><td>p<sub>RHX oil in</sub></td><td>hPa</td><td>Thermal oil press. at RHX inlet</td><td>Si sensor</td></tr><tr><td>FT-01</td><td>m<sub>ORC</sub></td><td>kg/s</td><td>Oil mass flowrate in ORC loop</td><td>Vortex</td></tr><tr><td>FT-02</td><td>m<sub>RHX</sub></td><td>kg/s</td><td>Oil mass flowrate in RHX</td><td>Vortex</td></tr><tr><td>LT-01</td><td>Z<sub>TES oil</sub></td><td>m</td><td>Level in TES</td><td>Radar</td></tr><tr><td>LT-02</td><td>Z<sub>TANK oil</sub></td><td>m</td><td>Level in thermal oil tank</td><td>Radar</td></tr><tr><td>NC</td><td></td><td></td><td></td><td></td></tr><tr><td>NC</td><td></td><td></td><td></td><td></td></tr><tr><td>NC</td><td></td><td></td><td></td><td></td></tr><tr><td>NA</td><td></td><td></td><td></td><td></td></tr><tr><td>P_ORC_gross</td><td>Q<sub>ORC gross</sub></td><td>W</td><td>Gross elec. power generated by ORC</td><td></td></tr><tr><td>P_ORC_net</td><td>Q<sub>ORC net</sub></td><td>W</td><td>Net elec. power generated by ORC</td><td></td></tr></table>
## REFERENCES

**A. Ferriere L.Padilla** Report on the Lab-Test of the thermocline storage system, Deliverable D3.4. - [s.l.] : POLYPHEM GA n°764048, 2022.

**A. Ferriere M. Volut, A. Perez, Y. Volut** In-situ Measurement of Concentrated Solar Flux and Distribution at the Aperture of a Central Solar Receiver [Conference] // SolarPACES. - 2015.

**T. Fasquelle Q. Falcoz, P. Neveu, J.-F. Hoffmann** A temperature threshold evaluation for thermocline energy storage in concentrated solar power plants.