5.1.1. System Constraints

In this study, battery charging and discharging mechanism and the distribution lines are ideal. Besides that, the inverter efficiency, battery efficiency and manufacturers' round-trip efficiency is constant regardless of the operation period. Since the battery cost is very high, the life span cost or total cost of the new battery system will be set to zero after achieving the life span of the battery operation. For any period, t, the total power supply from the solar PV-battery system must supply the total demand with a certain reliability criterion. This relation can be represented by Equation (24) as follows:

$$\rm P\_{PV} + P\_{Bat} \le P\_{load\\_actual} \tag{24}$$

This minimizes the excess power supply to the grid since the self-consumption of PV power or existing net consumption rate [MYR 0.365 (USD 0.08)/kWh] will be higher than net metering rate [MYR 0.238 (USD 0.05)/kWh].

### 5.1.2. Bounds of Design Variables

The proposed solar PV-battery system optimization parameters including the solar PV capacity, PPV\_kWp and maximum demand limit, PMD\_limit should be within a certain range:

$$\text{Load profile (Min)} < \text{P}\_{\text{PV\\_kWP}} < \text{Load profile (Max)} \tag{25}$$

$$\text{Load profile (Ave)} < \text{P}\_{\text{MD\\_limit}} < \text{Load profile (Max)} \tag{26}$$

The bounds of the design variable on PV and MD limit sizing is to maximize the self-consumption instead of surplus to the grid.

### *5.2. Validation of Numerical Results*

Experimental data on PV model using indirect method is verified using a 50 kWp PV system. The experimental data and figure are shown in Figure 6 and Table 9 respectively. Based on the results, based on the indirect method of Equation (4), at 1000 <sup>W</sup>/m<sup>2</sup> of measured solar irradiance, a 50 kWp solar PV system only delivers up to 35 kW of actual PV power and 38 kW of PV modelled power.

**Figure 6.** Modelled PV power (Indirect method).


**Table 9.** PV model validation data with 50 kWp PV system.

For this paper, load profile with actual MD load of 1050 kW has been used. Apart from that, two different phenomena of solar irradiance pattern with perfect data is used for solar PV-battery system integration to verify the MDRed scheme. For validation purposes, an MD limit of 750 kW and a PV-inverter rating of 1200 kWp are used to formulate the required battery capacity together with the financial data. Validation data is important to verify that the solar PV-battery system works according to MDRed scheme. In this paper, the MDRed control algorithm is based on a few conditions to achieve the new MD limit of 750 kW as shown in Table 10 and Figure 7.


**Table 10.** MDRed model validation data with solar PV-battery system.

**Figure 7.** MDRed model validation graph (for Table 10 data.)

Apart from that, the MDRed model shows the control algorithm battery managemen<sup>t</sup> system to cater for MD reduction with the support of solar PV power at preset MD limit. However, the rated sizing of solar PV-battery system is higher than the formulated optimal values since the calculation of rated values are based on Equations (5) and (8). The total savings is the combination of net consumption savings at rate of MYR 0.365/kWh, surplus power supplied to the grid at rate of MYR 0.238/kWh and maximum demand savings at rate of MYR 30.3/kW. Based on assumption, the annual total savings is calculated for 12 months period. Besides that, the cost of the solar PV-battery system will increase drastically due to additional cost of O&M and replacement apart from the interest rate of 7% incurred to the total cost of the system.

Control algorithm of MDRed modeling scheme falls under any of the conditions applied on Table 11 where battery managemen<sup>t</sup> system works based on maximum demand to maintain the MD limit setting of 750 kW. However, battery discharging mode will take place in between 8.00 a.m. until 10.00 p.m. and battery charging mode in between 10.01 p.m. until 7.59 a.m. everyday with respect to the MD limit of different load profiles.


