2.4.2. Demand Components

The electrical network operation downstream of the primary substation was modelled to determine demand at each of the load points on the MV feeder circuit. The demand profile is composed of three components [32]:


To model the electrical network system peak and minimum load, the ESB electrical power flow analysis [32] for the following system load conditions are used:


Existing Demand on the MV Circuit Excluding the Project

Existing demand on the MV circuits includes the load points (distribution transformer substations) which provide electricity supply to the LV networks consisting of connections to customers. Ideally the actual values of the demands at each of these load points would be metered. In this study known load information was used to calculate the existing demand on the distribution transformers substation and at the large consumer substations which are connected to the existing MV network [32]. The project model includes the LV sections up to the street pillars, (the load points), in this study units were evenly spread across the 3 phases of 11 street pillars, 2 to 4 units per phase [32].

### Additional Demand on the MV Circuit Including the Project

The hourly loads of each unit are spikey in nature. In this study along with general loads, a heat pump is assumed to be used in each unit, the heat pump is assumed to consume a power input 2.14 kW to provide a power output 9 kW for an under-floor heating system and a hot water storage system. The timing of the usage or cycling of the heat pumps varies for each residential unit due to personal preferences and behaviours of occupants [32].

### Solar PV Electricity Output from Community Microgenerators

The solar PV electricity output from community microgenerators are estimated from weather profiles based on simulations [33] using weather data (with irradiance values) from the integrated weather database.

### *2.5. Energy Assessment of the Solar PV System*

The calculations for embodied energy and the energy payback time of the solar PV system, GHG emissions payback time and carbon credits are outlined.

### 2.5.1. Embodied Energy of the Solar PV System

Embodied energy of the solar PV system is defined as the energy consumed by the system for materials; manufacturing; transportation and installation [36]. The embodied energy of the solar PV system has been completed by evaluating the total energy required for each process [37].

The embodied energy of each component per m<sup>2</sup> of solar PV module *Ein* [37] for this study was calculated using Equation (5):

$$E\_{\rm in} = E\_{mf\_{\mathcal{K}}} + E\_{\rm nste} + E\_{\rm del} \tag{5}$$

where,

*Ein* = Embodied energy of solar PV system (kWh m<sup>−</sup>2);

*Emfg* = Total manufacturing energy (kWh m<sup>−</sup>2);

*Euse* =Total used energy in installation and operation and maintenance (kWh m<sup>−</sup>2);

*Edel* = Energy requirement to deliver from production to field site (kWh m<sup>−</sup>2).

The total manufacturing energy *Emfg* [37] is calculated using Equation (6):

$$E\_{\rm mf \, g} = E\_{\rm mpe} + E\_{\rm cop} \tag{6}$$

where,

*Empe* = Total material production energy in kWh m<sup>−</sup>2;

*Eeqp* = Total operation and maintenance energy of equipment in kWh m<sup>−</sup>2;

Total material production energy *Empe* [37] is calculated using Equation (7):

$$E\_{mpc} = \sum\_{i} \left( c\_{mpc,i} \cdot m\_i \right) \tag{7}$$

where,

*Empe*,*<sup>i</sup>* = Specific energy to produce ith material; *mi* = Total mass of ith product material.

The total used energy in installation and operation and maintenance *Euse* [37] is calculated using Equation (8):

$$E\_{\text{use}} = E\_{\text{inst}} + E\_{\text{am}} \cdot T\_{LS} \tag{8}$$

where,

*Einst* = Installation energy requirement for the experiment; *Eam* = Average energy operation and maintenance rate over the life of the PV system; *TLS* = Life of the system in years.

The energy requirement to deliver the product materials from production to field site *Edel* is calculated using Equation (9):

$$E\_{dcl} = \sum \left( E\_{trans\_{i \to i+1}} + E\_{pk\lg i \to i+1} \right) \tag{9}$$

where, *Epkg* and *Etrans* are the packaging and energy requirement for the transfer of the product materials respectively from production to field site.

The balance of system (BOS) components e.g., battery, inverter, electronic components, cables and miscellaneous items should also be included in the calculations [38]. The breakdown of embodied energy of each component per m<sup>2</sup> of solar PV module for this study is in Table A1. (Appendix A).

### 2.5.2. Energy Payback Time of the Solar PV System (EPBT)

Energy payback time of the solar PV system is defined as the time needed for the system to generate the energy used in its life cycle from the extraction of raw materials to the construction and decommissioning phase. The EPBT [39] is calculated using Equation (10):

$$EPBT = \frac{E\_{\text{mat}} + E\_{\text{manu}f} + E\_{\text{trans}} + E\_{\text{inst}} + E\_{\text{cal}}}{\frac{E\_{\text{avg}m}}{\frac{E\_{\text{avg}m}}{\frac{r\_{\text{ON}}}{r\_{\text{ON}}}} - E\_{\text{Od\&}M}}} \tag{10}$$

where,

*Emat* = Primary energy demand to produce materials comprising solar PV system;

*Emanu f* = Primary energy demand to manufacture solar PV system;

*Etrans* = Primary energy demand to transport materials used during the life cycle;

*Einst* = Primary energy demand to install solar PV system;

*Eeol* = Primary energy demand for end of life management;

*Eaegen* = Annual electricity generation by solar PV system;

*EO*&*M* = Annual primary energy demand for operation and maintenance of solar PV system;

η*G* = Grid efficiency, the average primary energy to electricity to electricity conversion efficiency at the demand side.

### *2.6. GHG Emissions and Carbon Credits*

The solar PV power generation is one of the cleanest sources of renewable energy [4]. In 2017, natural gas accounted for 51% of the fuel used for electricity generation in Ireland and the CO2 intensity of electricity is 437 g CO2 kWh−<sup>1</sup> or 0.000437 t CO2 kWh−<sup>1</sup> [40].
