4.2.1. Impact on the Primary Substation

Total demand on the primary substation during a winter peak was 7.19 MVA and the addition of the project increased the demand to 7.58 MVA (a 5.4% increase in substation capacity). The solar PV system contribution at the time of the winter peak was zero as the peak occurred at night [32]. During a summer minimum load demand was 4.93 MVA and the addition of the project increased the demand on the primary substation to 5 MVA (1.4% increase), while the addition of the solar PV covered the increase in demand from the project by reducing the demand on the primary substation back to 4.93 MVA [32]. The impact at the primary substation level is very small. The small contribution of the solar PV system would maintain the demand marginally within the continuous rating of single primary transformer by 0.07 MVA which is around 1.4% [32].

The primary substation is equipped with two 5 MVA, 38/10.47 kV transformers giving a total continuous supply capacity of 10 MVA, one unit is used to meet the electricity demand of customers and another kept in standby mode and brought into operation in the event of failure. By incorporating microgeneration, the demand on the primary substation transformers can be reduced which reduces the temperature hot spot within the winding of the transformer avoiding the most severe electric power outages and increasing the electrical power system security standards [32].

### 4.2.2. Impact on the MV Feeder Circuit

The total demand from all the 10.47 kV feeders, was 2.34 MVA and 1.91 MVA for the winter and summer peak load reading respectively. The additional electricity demand for the project increased the demand on the all the 10.47 kV feeders to 2.71 MVA and 1.98 MVA for the winter and summer peak load reading respectively (representing a 16.2% and 3.5% increase in feeder capacity respectively). The contribution of the solar PV system at the time of the winter peak is zero (peak occurred at night-time) while in summer it decreased feeder capacity to 1.91 MVA i.e., 3.5% [32]. Overall there is no significant relief to the MV overhead lines and underground cables in the feeder [32].

### 4.2.3. Impact on the Distribution Transformer and LV Network

The electricity demand on the distribution transformer for the project during a winter peak load reading was 374 kVA. The contribution from the solar PV system at the time of the peak is

zero because the peak occurred at night-time [32]. The demand on the distribution transformer during a summer minimum load reading was 68 kVA. The addition of the solar PV increased the demand on the distribution transformer by 56% to 121 kVA. This contribution will increase the demand within the continuous rating of single primary transformer by 53 kVA which is around 8.4% [32]. To allow expansion room for additional loads, the distribution substation should be equipped with one distribution transformer of 630 kVA, 10.47/0.400 kV designed for an emergency rating of 110% of the continuous rating i.e., 693 kVA for certain time period [32].

Incorporating microgeneration of solar PV system in the low voltage network, would increase the demand on the continuous rating of the distribution transformer, which in turn would increase the temperature hot spot within the winding of the transformer, however, the loading of the distribution transformer is significantly below the specified design limits contributing to increasing the electrical power system security [32].

The LV network is equipped 185 mm<sup>2</sup> cross sectional area conductor underground cable which consists of six feeders to supply the project. Each feeder is designed for a rated value of 246.64 kVA (total of 1480 kVA). ESB Network advise LV feeders should be loaded around 30% (74 kVA on each LV feeder or in total 444 kVA). In this study, the loading of the LV feeders is significantly below the specified design limits and further contributes to increasing the electrical power system security standards: avoiding short bursts of higher network losses in the LV and MV network; and voltage fluctuations [32].

### 4.2.4. Impact on the Network Losses

Total losses in the existing electrical network covering the primary substation and the MV network supplied from the substation during a winter peak load reading was 85 kW (1.18% of the total demand on the substation). The technical losses relate mainly to the primary transformers (40%) and the MV feeder circuit C15, which connected the residential units (44.7%) [32]. The addition of the project increased the technical losses to 106 kW (52.8%). There is no contribution to the time of peak losses from the solar PV system as the peak occurred outside the sunlight hours [32]. During a summer minimum load reading the total losses in the existing electrical network was 61 kW (1.23% of the total demand on the substation). The addition of the project increased technical losses to 64 kW (46.9%) [32]. The addition of the solar PV system reduced total losses to 62 kW which equates to 1.24% of the total demand on the substation. This contribution will maintain the demand marginally by decreasing the proportion of the losses occurring in MV feeder circuit C15 from 46.9% to 45.4% [32]. This suggests that wider deployment of solar PV system can have a significant impact on loss performance at distribution level, with potentially significant cost savings [32].

## 4.2.5. Impact on the Voltage Profile

The voltage profile at primary substation ranges from maximum 100% to minimum 98.1% at 16 km from the primary substation and at the distribution substation range from maximum 97.8% to minimum 96.2%. The voltage at the LV network entry point to further 170 m towards the project declined by another 2% [32]. The solar PV systems are typically located closer to the consumer load, which provides an opportunity for the electrical network to offset some of the reactive power requirements at the distribution system and provides benefits to the distribution system namely capital expenditure on the reinforcement due to power factor improvements, savings on voltage control equipment and reduced consumption of reactive power and is subject to the microgenerator connection point which is further depended upon the nature and topology of the connection method into the existing electrical distribution network [32].
