# Thermodynamic Performance Analysis of Solar Based Organic Rankine Cycle Coupled with Thermal Storage for a Semi-Arid Climate

^{*}

## Abstract

**:**

## 1. Introduction

^{2}is used as a heat source, and a phase change material tank with a surface area of 25.82 m

^{2}is used as a heat storage device for configurations. Selecting a working fluid is essential for efficient power generation from ORC, as the thermodynamic properties of the working fluid affect the thermal efficiency of the system [24]. R245fa and water were selected as the working fluids for direct and indirect SORC systems. Wang et al. [25] studied how the off-design model of an ORC cycle operated by solar energy is presented with the CPC collector to collect the solar radiation, and how the thermal storage is deployed to achieve the continuous operation of the entire system. The system is analyzed under different time frame conditions and decreased ambient temperature, where the system manages to produce the maximum average exergy efficiency in December and maximum net power output in July or in September. Wang et al. [26] established the mathematical models to simulate solar-driven regenerative ORC under steady-state conditions. It was added that by utilizing heat storage into the system, constant and smooth performance can be attained over a long period. Li et al. [27] discuss the dynamic performance of SORC with TES. The impact of storage capacity, solar variation, and evaporation temperature were examined. It was stated that storage capacity should be preferred according to solar variation to retrain dynamic impact. Freeman et al. [28] introduced a small domestic-scale combined solar heat and power system combined with ORC to analyze the capability of the system in the UK. The authors identified two factors to boost the performance of the system: increasing the efficiency of the solar collector while keeping the operating temperature ideal and allowing the cycle to attain a smooth, steady power output for progressing load profile.

- Temperature profile variation during the charging and discharging mode is indicated and compared under the hottest and coldest month of weather conditions on an hourly basis.
- The thermodynamic performance of the system is based on the variation in the system efficiencies and net power output.

## 2. System Description

## 3. Thermodynamic Modeling

#### 3.1. Solar Collectors

#### 3.2. Thermal Energy Storage Tank

^{−3}, ${C}_{p}$ = 0.46 kJ kg

^{−1}K

^{−1}). Additionally, 0.02 m-thick glass wool insulation material was used to completely insulate it. It is presumed that the starting temperature of the TES was 45 °C.

#### 3.3. Organic Rankine Cycle

- Pressure drops in the heat exchanger, condenser, and connecting pipes are neglected;
- The system is assumed to be in steady-state condition;
- The isentropic efficiency of the pump and expander are chosen, respectively.

## 4. Results and Discussion

#### 4.1. Performance of July (Hottest) Month on an Hourly Basis

#### 4.1.1. Variation in the Tank Temperature Profiles during Charging Mode

#### 4.1.2. Variation in the Tank Temperature Profiles during Discharging Mode

#### 4.1.3. Variation in the System Efficiencies and Net Power Output

#### 4.2. Performance of January (Coldest) Month on an Hourly Basis

#### 4.2.1. Variation in the Tank Temperature Profiles during Charging Mode

#### 4.2.2. Variation in the Tank Temperature Profiles during Discharging Mode

#### 4.2.3. Variation in the System Efficiencies and Net Power Output

## 5. Conclusions

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Conflicts of Interest

## Nomenclature

$A$ | area (${\mathrm{m}}^{2}$) |

$N$ | number of collectors |

T | temperature (°C) |

$\eta $ | efficiency (%) |

$Q$ | heat rate (W) |

$m$ | mass flow (Kg-s) |

$dt$ | time |

$\rho $ | density (Kg/${\mathrm{m}}^{3}$) |

$V$ | volume $({\mathrm{m}}^{3})$ |

$U$ | loss coefficient (W/m^{2}K) |

$\mathrm{h}$ | specific enthalpy (J/kg) |

s | specific entropy (J/kg·K) |

Abbreviations | |

CPC | compound parabolic collector |

TES | thermal energy storage |

SORC | solar organic Rankine cycle |

ORC | organic Rankine cycle |

DNI | direct normal irradiation (Wh/${\mathrm{m}}^{2})$ |

Subscripts | |

$amb$ | ambient temperature (°C) |

$co$ | collector |

cond | condenser |

$cp$ | specific heat capacity (J/kg·K) |

$env$ | outside tank temperature (°C) |

exp | expander |

hx | heat exchanger |

P | pump |

$stor$ | thermal energy storge |

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**Figure 2.**Climatic data of Riyadh, Saudi Arabia, (average hourly profile): (

**a**) hottest month; and (

**b**) coldest month.

**Figure 4.**Variation in the tank temperature profiles during the charging and discharging mode in July.

**Figure 6.**Variation in the tank temperature profiles during the charging and discharging mode in January.

**Figure 7.**Variations in system efficiencies (

**a**) and net power output (

**b**) during the month of January.

**Table 1.**Design parameters of compound parabolic concentrators (CPC) [27].

Efficiency Coefficient | First Heat Loss Coefficient | Second Heat Loss Coefficient |
---|---|---|

${a}_{0}$ | ${a}_{1}\left(\mathrm{W}/{\mathrm{m}}^{2}\mathrm{K}\right)$ | ${a}_{2}\left(\mathrm{W}/{\mathrm{m}}^{2}\mathrm{K}\right)$ |

0.6831 | 0.2125 | 0.001672 |

**Table 2.**Properties of working fluid R245fa [24].

Property | Value |
---|---|

Molar mass (Kg/kmol) | 134.05 |

Critical temperature (°C) | 154.01 |

Critical pressure (MPa) | 3.651 |

ODP | 0 |

GWP | 820 |

Parameter | Value | Unit |
---|---|---|

Number of CPC | 75 | - |

Size of CPC | 2 | ${\mathrm{m}}^{2}$ |

Height of TES | 2 | $\mathrm{m}$ |

The diameter of TES | 1 | $\mathrm{m}$ |

Thickness | 0.006 | $\mathrm{m}$ |

Expander efficiency | 0.85 | % |

Pump efficiency | 0.80 | % |

Pinch point temperature in the evaporator | 5 | °C |

Pressure inlet to the expander | 1300 | kPa |

Pressure outlet from the expander | 180 | kPa |

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Almefreji, N.M.A.; Khan, B.; Kim, M.-H.
Thermodynamic Performance Analysis of Solar Based Organic Rankine Cycle Coupled with Thermal Storage for a Semi-Arid Climate. *Machines* **2021**, *9*, 88.
https://doi.org/10.3390/machines9050088

**AMA Style**

Almefreji NMA, Khan B, Kim M-H.
Thermodynamic Performance Analysis of Solar Based Organic Rankine Cycle Coupled with Thermal Storage for a Semi-Arid Climate. *Machines*. 2021; 9(5):88.
https://doi.org/10.3390/machines9050088

**Chicago/Turabian Style**

Almefreji, Nasser Mohammed A., Babras Khan, and Man-Hoe Kim.
2021. "Thermodynamic Performance Analysis of Solar Based Organic Rankine Cycle Coupled with Thermal Storage for a Semi-Arid Climate" *Machines* 9, no. 5: 88.
https://doi.org/10.3390/machines9050088