# PV Microgrid Design for Rural Electrification

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## Abstract

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## 1. Introduction

- Being located in areas with difficult terrain such as hills, forests, deserts and islands. Being part of a protected forest area could isolate the village and prevent live conductors from being drawn through it.
- Being located far from the nearest existing grid.
- Very low population (below 500) and low number of households (ranging between 2 and 200).
- Low power demand, probably even in the near future, as the loads are mostly lighting.
- Minimal transport and communication facilities.
- Low income level and low affordability.
- Poor literacy levels and technical skills.

## 2. The Design Problem

_{k}is the power flowing in the kth line and k is the line number.

_{l}is voltage at the lth node (bus) and l is the node number. A node is the point of consumer connection on the network.

_{U}) and the maximum unavailability (Q

_{U}) for every consumer:

- Voltage drop limits the design: The loads are distributed over large distances, which increase the voltage drop at the extreme consumer point in a radial system.
- Losses costs are high: Moving relatively small amounts of power over long distances results in losses which are high in proportion to the amount of power delivered.
- Layout and customers are restricted to the road network.
- Loads vary from very small single-phase to medium sized three-phase. Water pumps for irrigation purpose may require three-phase supply.
- Reliability requirements are below average.

- What should be the network (microgrid) structure?
- What should be the size of the central PV system?
- Where the PV system should be located?
- What should be the specifications of cables, protective equipment?

- Spatially distributed ‘point’ loads and estimate of its magnitudes
- Location details and/or local resource availability
- Roads and other obstacles
- Expected load growth
- Cost of PV system and power network feeders
- ∙
- Installation cost
- ∙
- Operating cost

- The minimum PV system and battery bank size determined is adequate to ensure continuity of supply to the load
- Voltage at each bus/node should be within limits
- Feeder capacity should not be exceeded
- The energy losses are minimized
- The PV system design is based on parameters of practical components.

## 3. Methodology

- Siting of source PV system
- Size of PV system
- Slack bus voltage (p.u.)

#### 3.1. Case Study Systems

#### 3.1.1. Ghotiya Village in Raipur, Chattisgarh

#### 3.1.2. Rajmachi Village near Lonawala, Maharashtra

#### 3.2. PV System Location Siting Using Centre of Moments

#### 3.3. Network Topology Design

- Identify all the geographic constraints; areas that cannot be crossed, areas where construction is difficult etc.
- Identify all special opportunities; diagonal routes which contribute to lower cost.
- Identify a set of load points on the periphery of the area to be served by the feeder, as well as a load point that is the “worst case” in terms of each constraint
- One by one for each load points identified in step 3, work backward from it toward the substation (power source) trying to find out the shortest route(s). As feeders generally follow roads it is better to consider $D=\left|X\right|+\left|Y\right|$ than $D=\sqrt{{\left|X\right|}^{2}+{\left|Y\right|}^{2}}$ (X and Y are the feeder lengths along the two coordinates of the site map).
- As a shortest path from each point is traced, commonalities among the paths can be used as major trunk or branch routes.

- the type of source and cost of generating electricity
- the costs of running wire across different types of terrain
- the maximum low voltage line length. This input restricts the length of low voltage wire runs. It refers to the length of wire between a load point and the transformer to which it is connected. This restriction is meant to limit voltage drops and line losses.

#### 3.4. Parametric Analysis Based on Load Flow

- Voltage magnitudes and angles at all nodes of the feeder
- Line flow in each line section specified in kW and kVAr, amps and degree, or amps and power factor
- Power loss in each line section
- Total feeder input kW and kVAr
- Total feeder power loss
- Load kW and kVAr based upon the specified model for the load.

#### 3.5. PV System Sizing

#### 3.5.1. Pre-Sizing

_{d}). The total energy to be generated per day by the PV array (kWh/day

_{to be generated}) is determined using the inverter efficiency (η

_{inv}) as:

_{inv}is specific to the PV technology used (monocrystalline, polycrystalline, amorphous etc.) and the inverter topology (H5, HERIC etc. [23]). η

_{bat}is the battery round trip efficiency (the fraction of energy put into the storage that can be retrieved). An η

_{bat}of 80% can be assumed for lead acid batteries commercially available at present. With the current commercially available inverters, efficiency does not fall below 80% during PV generation hours.

_{t}, unit kW/m

^{2}) at the location can be identified from meteorological data or onsite recording using pyranometers. The average daily photovoltaic energy conversion efficiency (η) will depend mainly on the PV array orientation (tilt and azimuth) and the PV technology. An η of 10% can be assumed for crystalline silicon with the current commercially available PV modules. The area of PV array is then be calculated as:

#### 3.5.2. Detailed Design

## 4. Results and Discussion

#### 4.1. Location of PV System and Determination of Network Structure

#### 4.1.1. Location of Central PV System in Terms of Spatial Distribution of Load

_{i}), ${y}_{i}$ is the y- co-ordinate of the ith load and N is the total number of loads.

#### 4.1.2. Determination of Network Topology Using Simulated Annealing

#### 4.1.3. Parametric Analysis Using Load Flow

## 5. PV Microgrid Design Method for Rural Electrification

#### Illustration of Proposed Method

_{d}) at the location is 5.037 kWh/m

^{2}/day (source PVGIS CMSAF). Considering monocrystalline PV technology, the average daily system efficiency (η) is assumed to be 10%. The PV array is calculated using (4) as approx. 88 m

^{2}. A generic 75 Wp monocrystalline PV module of length 1208 mm and width 538 mm is considered. For an area of 10 m

^{2}, a series parallel arrangement of the 75 Wp module is equivalent to 1 kWp. Hence, the rating of the central PV system for Rajmachi is estimated as 8.9 kWp. Battery size calculated using (5) lead to an energy rating of 223 kWh. The autonomy considered was 2 days. The battery bank voltage is assumed to be 48 V. This gives the battery bank specification as 24 cells in series and 6 such strings in parallel.

#### Central PV System Design

## 6. Conclusions

## Author Contributions

## Funding

## Acknowledgments

## Conflicts of Interest

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**Figure 1.**Typical procedure followed by planners for design of photovoltaics (PV) based rural electrification.

**Figure 2.**Map of Ghotiya village (courtesy: Chattisgarh Renewable Energy Development Authority (CREDA)).

**Figure 4.**Map of Rajmachi village showing the customer load points (courtesy: Maharashtra Energy Development Agency (MEDA)).

**Figure 8.**Spatial distribution of load points on the map of village and location of source. The X-axis shows the distance of load or source points from the estimated origin of the map in the west to east direction. The Y-axis shows the distance of load or source points from the estimated origin of the map in the south to north direction.

**Figure 18.**Spatial distribution load and optimal location of PV source obtained for the Rajmachi system.

**Figure 19.**Network structure obtained for the Rajmachi system using simulated annealing. Also indicated is the actual location of PV source onsite.

From | To | Distance (m) | R (in p.u.) | X (in p.u.) |
---|---|---|---|---|

1 | 2 | 11 | 0.013 | 0.011 |

2 | 3 | 11 | 0.013 | 0.011 |

3 | 4 | 12 | 0.015 | 0.012 |

3 | 5 | 78 | 0.095 | 0.076 |

5 | 6 | 78 | 0.095 | 0.076 |

6 | 7 | 59 | 0.072 | 0.057 |

7 | 8 | 42 | 0.051 | 0.041 |

8 | 9 | 12 | 0.015 | 0.012 |

9 | 10 | 31 | 0.038 | 0.030 |

10 | 11 | 31 | 0.038 | 0.030 |

10 | 12 | 77 | 0.094 | 0.075 |

12 | 13 | 94 | 0.115 | 0.091 |

13 | 14 | 17 | 0.021 | 0.016 |

14 | 15 | 56 | 0.068 | 0.054 |

15 | 16 | 26 | 0.032 | 0.025 |

16 | 17 | 13 | 0.016 | 0.013 |

17 | 18 | 38 | 0.046 | 0.037 |

15 | 19 | 39 | 0.048 | 0.038 |

15 | 20 | 35 | 0.043 | 0.034 |

20 | 21 | 20 | 0.024 | 0.019 |

21 | 22 | 19 | 0.023 | 0.018 |

22 | 23 | 19 | 0.023 | 0.018 |

21 | 24 | 27 | 0.033 | 0.026 |

13 | 25 | 59 | 0.072 | 0.057 |

13 | 26 | 83 | 0.101 | 0.080 |

26 | 27 | 14 | 0.017 | 0.014 |

27 | 28 | 56 | 0.068 | 0.054 |

28 | 29 | 63 | 0.077 | 0.061 |

Load | No. of Units | Wattage | Coverage (fraction) | Connected Load (W) | No. of Households | Total |
---|---|---|---|---|---|---|

Domestic Lighting | 3 | 11 | 1 | 33 | 29 | 957 |

Street Lights | 1 | 11 | 0.5 | 5.5 | 29 | 159.5 |

Fans | 1 | 40 | 0.5 | 20 | 29 | 580 |

Refrigeration | 1 | 100 | - | 100 | 29 | 100 |

Television | 1 | 80 | 0.4 | 32 | 29 | 928 |

Radio | 1 | 5 | 0.4 | 1.75 | 29 | 58 |

Other Loads | 1 | 100 | 0.1 | 10 | 29 | 290 |

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

PV module technology | Monocrystalline Silicon |

Manufacturer and model | Ecosol PV tech Mono 75 Wp 36 cells |

No. of PV modules in series | 4 |

No. of parallel strings | 33 |

Array nominal (STC) power | 9.9 kWp |

MPPT converter maximum and European efficiencies | 97%/95% |

Battery technology | Lead acid |

Battery bank voltage | 48 V |

Nominal capacity | 7200 Ah |

Number of units | 24 in series × 8 in parallel |

© 2018 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

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**MDPI and ACS Style**

Mothilal Bhagavathy, S.; Pillai, G.
PV Microgrid Design for Rural Electrification. *Designs* **2018**, *2*, 33.
https://doi.org/10.3390/designs2030033

**AMA Style**

Mothilal Bhagavathy S, Pillai G.
PV Microgrid Design for Rural Electrification. *Designs*. 2018; 2(3):33.
https://doi.org/10.3390/designs2030033

**Chicago/Turabian Style**

Mothilal Bhagavathy, Sivapriya, and Gobind Pillai.
2018. "PV Microgrid Design for Rural Electrification" *Designs* 2, no. 3: 33.
https://doi.org/10.3390/designs2030033