**Abstract**

Energy storage technologies is transforming the way the world and utility companies utilize, control and dispatch electrical energy. In several countries, the consequential effect of meeting electrical demands continues to burden the electrical infrastructure leading to violation of statutory operating limits. Such violations constrain a power system's ability to supply suitable energy whilst meeting daily load and growth demands. While optimization techniques can be used to reduce violations, these are still limited do not provide effective short-term solutions when dealing with constrained networks in dense and radial distribution systems. Battery energy storage systems (BESS) and solar rooftop photovoltaics (RTPV) are a viable distributed energy resource to alleviate violations which are constraining medium voltage (MV) networks.

**Keywords:** battery energy storage systems (BESS), rooftop solar-photovoltaics (RTPV), power distribution, voltage limits, thermal limits, technical performance

### **1. Introduction**

In designing and operating electric power networks or implementing major expansions to existing networks, a number of key issues regarding the technical performance of the network at both the transmission and distribution (T and D) levels must be ascertained. These include voltage regulation, voltage fluctuations, rapid voltage rise, electrical loses, distribution plant loading and utilization, fault level, generation stability, harmonics, phase balancing, system security, and supply availability [1]. The approach of Power Utilities to address any constraints or violations, experienced within medium voltage networks, would be based on extensive technical evaluation. While overvoltage is a concern if roof-top solar-photovoltaic (RTPV) penetration is not regulated [2], this study shows the benefit of RTPV and/or including battery energy storage systems (BESS), as this offers relief for constrained networks.

### **2. Network model selection and appraisal**

Real-time power system analysis deals with two critical criteria, from the network appraisal, this being Voltage and Thermal constraints/violations. From the analysis, a network was identified which has both voltage and thermal violations. This study explores the technical influence that RTPV has on MV networks. From the appraisal analysis, a most fitting network type was identified which is found most common amongst the feeders that were analyzed. The predominate network classification is found to be a C2, TZ2 type network [3, 4]. In-line with the investigative violations (voltage and thermal) these networks have a tolerable minimum voltage of 95.5% during normal conditions, and 93.5% during abnormal conditions.

The thermal limit defined in **Table 1** indicates this to be alarming above 90% of its rated capacity.

The MV network selected for this study is Madadeni NB36. **Table 2** shows the appraisal results of Madadeni NB36; this network has been selected due to having both voltage and thermal violations. This study goes on to showcase how RTPV and/ or BESS influences the violations identified on NB36.

As stated in **Table 2**, NB36 peaks during a winter's weekday at 18:30. Annual statistical metering data was analyzed and using statistical analysis methods, data has been fashioned into four, twenty-four hours, thirty-minute intervals; seasonal profiles, based on the four weather seasons. The load profile for a winter's weekday demonstrates the peak loading period and is used throughout this chapter to demonstrate the effective influence of RTPV and/or BESS.

**Figure 1** shows a typically generated PV profile which have been defined to represent each season [7, 8]. The duration of sunlight hours differs between each season. To be consistent with the network analysis, the winter PV profile was selected to match the network breakers winters statistical load profile.

When considering RTPV, some configurations should be considered to decide on the most cost-effective or technically beneficial solution for both the Utility and Customer. This chapter considers the following configurations:


Power simulation has been conducted in Power Factory, the results have been extracted, analyzed and stated in the legends field within the applicable figures.


**Table 1.** *Network characteristics for calculating customer number limits [5].* *Battery Energy Storage Systems and Rooftop Solar-Photovoltaics in Electric Power Distribution… DOI: http://dx.doi.org/10.5772/intechopen.99248*


#### **Table 2.**

*Madadeni NB36 appraisal data [6].*

**Figure 1.** *Typical p.u. generated seasonal PV output profile.*

#### **3. Installed RTPV system**

The scope of this study relates to RTPV installations connected to every customer connected to an MV network, this is defined as the high penetration of RTPV. The equipment type used in this study is found to be commonly available in South Africa.

While some studies consider large PV installation's sizes to show benefits to customers [9], this study utilizes an average solar panel output of a single 200 W panel installed at every connected customer [10], this is a very conservative approach taking into account that panel outputs degrade over time due to aging and associated output reduction [11], the build-up of dirt/residue and orientation.

Further to this the battery technology assumed in the assessments, also commonly available, are lead-acid type batteries. These batteries have a depth of discharge rate (DOD) and while it is common to find a DOD of 80%, for the purposes of this study it is assumed that a 100-ampere hour battery with a DOD or 50% is utilized offering 600 W of power. Inverter capabilities [12] have been assumed to operate at 7 amps due to low household breaker sizing and inverter costings. This simulation design, though very conservative, leads to defining the required design for households. The criteria of the PV, battery and inverter that have been utilized in this study are considered as a base design which can be improved upon implementation.
