# Hybrid PV System with High Speed Flywheel Energy Storage for Remote Residential Loads

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## Abstract

**:**

_{2}emissions of diesel generator are detrimental factors which have inspired searches for more cost effective and cleaner technologies. The integration of an energy storage system (ESS) in islanded system along with generator not only reduces generator maintenance costs but also reduces the CO

_{2}emissions by limiting its operating hours. This paper proposes an islanded PV hybrid microgrid system (PVHMS) utilizing flywheel energy storage systems (FESS) as an alternative to battery technology to support the PV system and meet the peak demand of a small residential town with 100 dwellings. The diesel generator is used in the islanded system as a spinning reserve to maintain the stability of the islanded system when the PV system and flywheel storage cannot meet the load demand. Results of analysis of such a system demonstrate that flywheel energy storage technology of appropriate size offers a viable solution to support the operation of the standalone PV system. Furthermore, the reduction in CO

_{2}emissions and fuel consumption has been quantified as compared with the case with flywheel energy storage systems which means the diesel generator but always be operating.

## 1. Introduction

_{2}emissions by reducing the operation of DGen. Additionally, operation of FESS together with DGen can increase the efficiency of DGen and save costs due to lesser consumption of diesel fuel. This paper studies the use of FESS in a microgrid together with a stand-alone PV system and DGen to demonstrate how the FESS can act as a power bridge in a microgrid to ensures the constant supply of power to the load when power from the DGen and/or the PV system is not sufficient. The operation scenarios are created based on the three load profiles for day and nighttime. The compliance of the FESS operation is demonstrated according to the activity of the residents and their inhabitance.

## 2. Modelling of FESS and Its Control Structure

#### 2.1. Modelling of FESS

^{2}) and spinning at an angular velocity of $\omega $ (rad/s), stores kinetic energy $E$ (joules) as given by Equation (1).

^{3}) and length $l$ (m), angular velocity can be expressed by Equation (2);

#### 2.2. Modelling of Control Structure

## 3. Modelling and Operation of Photovoltaic Hybrid Mini-Grid System (PVHMS)

#### 3.1. Operation of the FESS

#### 3.2. Modelling of Load Profiles

## 4. Methodology

^{2}). When photovoltaic power output reduces, MSC allows the FESS to provide the power back to DC bus. In the load profiles presented above (Figure 6, Figure 8 and Figure 10), output of the PV system is zero because of the zero-input solar irradiance from 00:00 in the midnight till 6:00 in the morning. During this time there is very less total electricity demand due to less activities in the dwellings. Therefore, at nighttime, the DGen can be used to meet the load demand and charge the flywheel. The DGen will only operate until flywheel is charged enough to meet the load demand or the PV system generates enough power compared to the electricity consumption. During the day when there is maximum solar irradiance and the PV produces more power than the residential load power, the excess power can be used to charge the flywheel in order to store the kinetic energy. The stored energy can be converted into the electrical energy which can be used to feed the residential load when the power generated by PV system is not sufficient. Figure 11 shows the concept map of the proposed logic control scheme studied in this paper.

## 5. Results and Analysis

_{2}emissions produced due to running of DGen. In order to ensure stability of the system, the DGen must be operated all the time since the PV power can fall away at any time with cloud passing and if the DGen was every switched off, it would take several seconds to start up and come back on line.

#### 5.1. Islanded Operation without Flywheel Energy Storage

#### 5.1.1. Load Profile 1

#### 5.1.2. Load Profile 2

#### 5.1.3. Load Profile 3

#### 5.2. Islanded Operation with Flywheel Energy Storage

_{2}emissions, fuel costs and hours of running of the Dgen. The PV system can generate up to 90 kW of power for all load profiles. The Dgen is sized according to the maximum demand as it can provide with the maximum load demand when neither PV and nor flywheel are available.

#### 5.2.1. Load Profile 1

#### 5.2.2. Load Profile 2

#### 5.2.3. Load Profile 3

_{2}emissions and the fuel cost. The fuel consumption analysis of the DGen with and without the FESS is provided in the next section.

## 6. Diesel Generator Fuel Consumption and CO_{2} Emission Analysis

_{2}emission and fuel cost are presented in following sections.

#### 6.1. Diesel Fuel Consumption Analysis

_{2}emissions. Therefore, adding energy storage along with RES in islanded system is best solution to save the cost and the environment, provided that ESS is itself environmentally friendly such as the flywheel. The percentage loading of the DGen is categorized in three loading levels in order to calculate the consumption according the manufacturer specifications.

#### 6.2. Diesel CO_{2} Emission Analysis

_{2}emission depends on the type of the fuel and amount of its consumption by DGen. The diesel fuel emits 2.7 kg of CO

_{2}per liter. Different types of fuels have different carbon contents; however, an average carbon content in diesel fuel can be considered in order to estimate the CO

_{2}[17].

_{2}emission analysis; it can be seen that there is huge reduction in carbon emissions with integration of flywheel technology in PVHMS. In the case of load profile 3 without the flywheel, the DGen emits 12 kg of CO

_{2}during 17 min of operation, which drops to 6.1kg of CO

_{2}when flywheel is added in the system. The significant drop can be seen in case in load profile 1 and 3 as well. However, the emissions can further be reduced if size of the energy storage is increased or another type of ESS is integrated in the system besides the flywheel such as battery system.

## 7. Conclusions

_{2}emission and fuel cost savings was also discussed and analyzed.

## Author Contributions

## Funding

## Informed Consent Statement

## Data Availability Statement

## Conflicts of Interest

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

Stator Resistance $({\mathit{R}}_{\mathit{s}})$ | 11.85 mΩ |

Rotor Resistance $({\mathit{R}}_{\mathit{r}})$ | 9.29 mΩ |

Stator leakage inductance $\left({\mathit{L}}_{\mathit{l}\mathit{s}}\right)$ | 0.2027 mH |

Rotor leakage inductance $\left({\mathit{L}}_{\mathit{l}\mathit{r}}\right)$ | 0.2027 mH |

Mutual Inductance $\left({\mathit{L}}_{\mathit{m}}\right)$ | 9.295 mH |

Rated magnetic flux $\left({\mathit{\lambda}}_{\mathit{m}}\right)$ | 0.75 Weber |

Power rating | 100 kW |

Maximum speed | 20 krpm |

Minimum speed | 10 krpm |

Switching frequency | 20 kHz |

DC bus voltage | 600 V |

Flywheel rotor outer diameter $\left({\mathit{D}}_{\mathit{r}0}\right)$ | 0.4 m |

Shaft diameter $\left({\mathit{D}}_{\mathit{s}}\right)$ | 0.025 m |

Source Type | Specification | Value/Description | |
---|---|---|---|

Synchronous Diesel Generator | Nominal Power | 100 (kW) | |

Nominal Frequency | 50 (Hz) | ||

Power Factor | 0.8 | ||

% Load | liter/h | ||

Fuel Consumption | 100 | 26.7 | |

75 | 20.2 | ||

50 | 14.1 | ||

Model | 1104C-44TAG2 | ||

Engine Speed | 1800 (rpm) | ||

Engine Make | PERKINS | ||

Solar Photovoltaic System | Model | SunPower SPR-305E-WHT-D | |

Maximum power | 305.226 (W) | ||

Temperature | 40 (°C) | ||

Maximum irradiance | 1200 (W/m^{2}) | ||

Maximum power point current | 5.58 (A) | ||

Maximum power point voltage | 54.7 (V) | ||

Parallel strings | 50 | ||

Series connected strings | 5 |

Operation Scenario | Operation Ratio at % Load | Total Fuel Consumption (Liters) | ||||
---|---|---|---|---|---|---|

50% | 75% | 100% | 50% | 75% | 100% | |

Load Profile 1 | 47% | 7.5% | 15% | 1.9 | 0.505 | 1.26 |

Load Profile 2 | 93.5% | 6.5% | 0% | 3.6 | 0.24 | 0 |

Load Profile 3 | 56% | 15% | 18% | 2.16 | 0.841 | 1.33 |

Operation Scenario | Operation Ratio at % Load | Total Fuel Consumption (Liters) | ||||
---|---|---|---|---|---|---|

50% | 75% | 100% | 50% | 75% | 100% | |

Load Profile 1 | %0 | %0 | 17.5% | 0 | 0 | 1.4 |

Load Profile 2 | %0 | %0 | 23.7% | 0 | 0 | 1.27 |

Load Profile 3 | %0 | %0 | 31% | 0 | 0 | 2.26 |

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**MDPI and ACS Style**

Soomro, A.; Pullen, K.R.; Amiryar, M.E.
Hybrid PV System with High Speed Flywheel Energy Storage for Remote Residential Loads. *Clean Technol.* **2021**, *3*, 351-376.
https://doi.org/10.3390/cleantechnol3020020

**AMA Style**

Soomro A, Pullen KR, Amiryar ME.
Hybrid PV System with High Speed Flywheel Energy Storage for Remote Residential Loads. *Clean Technologies*. 2021; 3(2):351-376.
https://doi.org/10.3390/cleantechnol3020020

**Chicago/Turabian Style**

Soomro, Abid, Keith R. Pullen, and Mustafa E. Amiryar.
2021. "Hybrid PV System with High Speed Flywheel Energy Storage for Remote Residential Loads" *Clean Technologies* 3, no. 2: 351-376.
https://doi.org/10.3390/cleantechnol3020020