**6. Roof-top solar photovoltaic with battery energy storage system**

Considering the same RTPV installed capacity of 200 W per residential home. In addition to this, it is assumed that each home is equipped with a battery which has 600 W of dispatchable power; an overview of this connection is seen in **Figure 5**. This inclusion of BESS is limited only by its charge and discharge rate. Based on the available power generated by a 200 W RTPV source, it was then assumed that the battery would reasonably charge and discharge at less than 7 amps.

The network normal (P) is the load profile for the study. **Figure 6** shows the comparison of RTPV with and without BESS. During daylight hours 80 W of power is allowed to charge the battery while the remaining power supplies the customer or overflows onto the electrical grid. During the evening peak period, the same 80 W is dispatched from the stored energy over a period of 7.5 hours.

As demonstrated in **Figure 6**, RTPV including BESS can be seen to benefit both the Utility and Customer. The Utility benefits by the reduced voltage regulation and thermal violations which are experienced during the evening peak, and the

**Figure 5.** *RTPV with battery storage [15].*

*Battery Energy Storage Systems and Rooftop Solar-Photovoltaics in Electric Power Distribution… DOI: http://dx.doi.org/10.5772/intechopen.99248*

**Figure 6.**

*Active power of NB36 with 200 W RTPV penetration and BESS, considered for a winter weekday.*

Customer benefits by an overall reduction in power consumed. From this analysis, it is seen that the Utility loses 5.76% in revenue. While the customer's power consumption, referring to data in **Figure 4**, is reduced by 5.8%. Further investigation of **Figure 4** shows a negligible difference of power consumed if the customer has RTPV alone or including BESS.

#### **7. Varied levels of BESS**

While the results from the above analysis speak of how the Utility and Customers are affected, there still raises the fundamental concern related to the constraints experienced on NB36. At normal, when the load is peaking, it's found that the minimum Voltage is 92.7% and the network is thermally loaded to 102%. The analysis shows that if customers provide back-feeding, from their stored energy, during peak times, it will reduce the constraints on the network. Analysis has considered the back-feeding of 80 W, following the discussion above, and 250 W for each residential customer.

**Figure 7** reflects the effect of the voltage along the backbone of NB36, also showing the ability of BESS to dispatch power at 80 W and 250 W. It can be seen that with an increasing ability of the BESS to dispatch power, it alleviates the voltage constraint by <1% at 80 W, and 2.1% at 250 W.

**Figure 8** shows that the normal network condition exceeds the rating of the conductor at peak loading.

With BESS dispatching power we see that the thermal constraint is reduced from 102–94% when 80 W of power is dispatched, and improved further when 250 W is dispatched to 79.8%.

#### **Figure 7.**

*NB36 minimum voltage at peak (winter weekday – 18:30).*

**Figure 8.** *NB36 thermal rating vs. load current.*

#### **8. Power dispatched, consumed and its effect on technical losses**

**Figure 9** shows the network sending power, consumed power (including with RTPV, and RTPV+BESS). The difference between the sending power and consumed power is attributed to the technical losses resulting from transmitting power down the network.

Technical losses are calculated as a percentage of the total load of the feeder including both no-load and load losses. The results from the analysis help to obtain a view of the network losses; this can be used as a basis for historic trending and benchmarking and can be used as one of the triggers for network strengthening. Therefore, this statistic also aids the conditioning of the priority ranking criteria. DER's may have a significant effect on network losses.

*Battery Energy Storage Systems and Rooftop Solar-Photovoltaics in Electric Power Distribution… DOI: http://dx.doi.org/10.5772/intechopen.99248*

#### **Figure 9.**

*Sending active power, power consumed by customers and P losses, considered for a winter weekday.*

A generator can lower or increase losses, depending on its location and the network configuration [16].

The technical losses vary slightly between the different options analyzed:


#### **9. Conclusion**

This chapter has demonstrated the benefit of roof-top solar photovoltaic and/or including battery energy storage systems. It offers relief for constrained networks in dense and radial distribution systems. 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. The results show the following:

#### **9.1 BESS only**

This option does not benefit the customer, as the batteries require grid connection to charge and discharge, not to mention efficiency losses. If discharging the stored energy occurs during peak periods, this can benefit the utility by reducing the peak violations. Therefore, it is recommended that a tariff/time-of-use incentive is introduced to motivate customers for BESS only installations.

#### **9.2 RTPV only**

This is an excellent way for a customer to reduce his overall electrical utility bill. Unfortunately, the utility is negatively affected by the reduced sale of electricity.

#### **9.3 RTPV+BESS**

The results show that with the addition of RTPV including BESS the utility still loses revenue. However, with the addition of BESS, Utilities have the ability to reduce technical violations during peak periods. Installing BESS, in this manner, shows no benefit to the customer. Therefore, it is recommended that a tariff/timeof-use incentive is introduced to motivate customers for RTPV+BESS installations.

#### **9.4 Varied levels of BESS**

Though RTPV inclusive of BESS reduces the violations on the network; it can be seen from **Figures 7** and **8** that voltage and thermal violations persist for this specific network. Therefore, it is necessary to consider an increased installation of BESS. 250 W of dispatchable power offered the most appropriate quantity of power to alleviate the violations. The effect on technical power losses: seen in **Figure 9**, shows a constant 5.41%–5.49% of technical power losses for each of the above considerations. This demonstrates that technical losses are similarly proportioned to its source sending power when conducting analysis on the various installation types relating to RTPV/ BESS. While these amounts are typical and expected for a reticulation network – losses will defer due to topology, loading and design of networks.

For Utilities and Municipalities, the extent of challenges encountered when considering large scale installations of RTPV would be related to availability and visibility of data for adequate analysis. Current standards do not address the practical design solutions needed for all variations within customer installations and expectancy from RTPV. This can result in non-standard customer installations which will lead to undesirable impacts on the source and shared utility power systems.

Visibility and compliance of electricity supply regulations are required at the point of supply which is conditioned to be met at the point of supply and not the point of generator connection which is embedded in the customer's installation. Therefore, smart metering systems with predefined charge and discharge times/durations need to accompany RTPV installations. This requires an evaluation of currently employed metering technology, to ensure they accommodate these operational scenarios.

The cost for an electrical system, in which a customer is partially or completely off-grid, will still be attributed to the Utility to ensure the security of supply. Hence Utilities should take the lead in this segment of small-scale embedded generation to remain viable and relevant. Utilities may consider engaging suppliers to carry out maintenance and/or repairs during initial warranty periods.

Data visibility, both topological and metered data, is crucial for power system analysis, and need to be available and validated from time to time to cater for load growth. Utilities must ensure competent staffing for data acquisition and analysis. *Battery Energy Storage Systems and Rooftop Solar-Photovoltaics in Electric Power Distribution… DOI: http://dx.doi.org/10.5772/intechopen.99248*

There may be a lack of data validity for non-telemetered devices, such as unknown tap positioning of reticulation transformers, conductors or cables which has been replaced with different ratings and types. This can be challenging when configuring simulation models.

For this study analysis was given to the network classification that was predominately found with residential type loads, which has been identified as C2 TZ2 type. This study, therefore, adopted a common sending voltage regulation set point of 1.03pu applied at reticulation busses. The voltage limit allowable for a normal condition is 95.5% and for abnormal conditions are 93.5. From an operations view, the abnormal limit is the benchmark to be adhered to, while network planners work with the normal limit of 95.5%.

Continuous network changes due to rising electrification and illegal connections discredits network analysis and requires more frequent update of simulation models. Pre-existing RTPV installations may pose a problem if they do not meet compliance requirements. Utilities need to conduct surveys of pre-existing RTPV installations and update its electrical connection to the power grid.

It is recommended that during site visits, meter re-programming including 'time-of-use' tariffs and amendments to supply agreements, can be implemented. Presently, there is no information on households which has become "self-suppliers" due to lack of a registry for small-scale embedded PV plants. This will assist in ensuring that customer contributions to unbalance be limited to 1% voltage unbalance at the point-of-common coupling.
