Presently, in the modern energy world, the energy storage systems of distributed photovoltaic have been taking centre stage. But, most of them wonder if distributed PV energy storage necessarily has to be grid-connected. Well, let us look further into the question, and understand various modes of the distributed PV power systems along with associated electrical design points.

To begin with, a distributed PV power generation system can be off-grid.
Distributed photovoltaic power generation systems are not necessarily connected to the grid; they can also be off-grid. Off-grid distributed photovoltaic power generation systems are mainly applied to areas where it is impossible or difficult to connect to the power grid, or where the power grid is unstable. Such systems generally include solar panels, batteries, controllers, and inverters. The solar panels convert solar energy into electricity, the battery is charged through the controller, and when electricity is needed, the electricity in the battery is converted to AC through the inverter for use by the load.
The advantage of the off-grid system is its independence and reliability. In some remote areas, such as mountainous regions and islands, off-grid PV power generation systems can provide local residents with a stable power supply without being affected by grid failures. Besides, in some special occasions, such as field operations, emergency rescue, etc., the off-grid system can also be used.
Off-grid systems have a number of disadvantages, too. First, the cost of such systems is relatively high because one needs to equip storage batteries. Second, batteries have limited service life and should be replaced periodically, which increases the maintenance cost. In addition, the capacity of off-grid systems is usually small and cannot meet large-scale electricity demand.
In contrast, a grid-connected distributed PV system connects the electricity generated from solar panels to the grid after converting it into AC through an inverter. During this process, when solar power generation is greater than electricity consumption, the surplus electricity can be delivered to the grid, while when the generated solar power is not enough for the users, they can gain it from the grid.
The advantage of a grid-connected system is that it can fully use the stability and reliability of the grid, and at the same time, it also can sell the excess power to the grid for some economic return. Besides, a grid-connected system is relatively simple and not expensive to be installed and maintained.
However, the grid-connected system also has some problems: for instance, it has to meet the requirements of accessing the grid in terms of voltage, frequency, power factor, and others. Added to this, its generation will be affected by weather conditions, like rain or snow, and there is some instability in its generation. Second, what should the electrical design include?
Whether off-grid or grid-connected distributed photovoltaic power generation system, its electrical design needs to consider the following aspects: selection and layout of solar panel. Solar panel is the core component of distributed photovoltaic power generation system, and its selection and layout directly affect the system's power generation and performance. When selecting the solar panel, factors such as power, efficiency, reliability, and life span need to be considered. Meanwhile, in view of the installation place's light condition, roof area, orientation, and other factors, it is also necessary to perform a reasonable layout to maximize the use of solar energy.
For an off-grid system, there is also a need for considering matching conditions between solar panels and batteries to fully charge the batteries under various conditions of light.
Battery selection and capacity calculation
Battery is the indispensable part in the off-grid distributed PV power generation system, its function is to store the electricity generated by the solar panel for use at night or on cloudy and rainy days. In the selection of type, it is necessary to consider factors such as the type, capacity, life, charging and discharging efficiency of the battery.
For the grid-connected systems, although the equipping of storage batteries is not necessary, but in some particular situations, like the failure of the grid, it also can consider equipping a certain capacity of storage batteries as the backup power source. Then the battery capacity has to be calculated for its capability of satisfying users' needs during emergency. Controller and inverter selection
The controller is one of the most important components in the distributed photovoltaic power generation system; it controls the output of the solar panel to prevent the battery from overcharging or over-discharging. When choosing a controller, the function of the controller, performance, reliability, and other factors should be considered.
The inverter is a device that converts the DC power generated by the solar panels into AC power, and its selection needs to consider factors such as the inverter's power, efficiency, output waveform, and reliability. For off-grid systems, it is also necessary to consider whether the output voltage and frequency of the inverter match the load.
 
Electrical wiring and protection devices
Electrical wiring is an indispensable component of the distributed PV power generation system, and its design must take into consideration such aspects as the safety, reliability, and aesthetics of the system. In wiring, attention should be paid to adhering to the relevant electrical codes and standards so that the requirements on the cross-sectional areas of wires, insulation performance, among others, are satisfied.
Protection device is the important safety guarantee in the distributed PV power generation system. When the system fails, it will cut off the power supply in time to prevent the expansion of the accident. The protective devices include circuit breakers, fuses, leakage protectors, etc., which should be reasonably configured according to the capacity and requirements of the system during selection and installation. Monitoring system design
The monitoring system is an important part of the distributed PV power generation system, which can monitor the operation status of the system in real time, including the power generation of solar panels, the battery power, the output power of the inverter, and so on. Through the monitoring system, users can understand the operation of the system in a timely manner, find problems, and deal with them in a timely manner.
It needs to consider the scale and requirement of the system, choose appropriate monitoring equipment and software, and do reasonable installation and commissioning. Third, the summary Distributed PV energy storage is not necessarily grid-connected, but also can be off-grid. Off-grid systems are applicable to those areas that cannot be connected to the grid or for which the grid is not stable, with the advantages of independence and reliability, but the cost is relatively high. A grid-connected system can utilize all the stability and reliability from the grid while selling surplus power to the grid for some economic gain.
 
During the implementation of the electrical design in a distributed photovoltaic power generation system, the following shall be taken into consideration: the selection and laying-out of the solar panel, the selection and calculation of the battery capacity, the selection of the controller and the inverter, electrical wiring and protection device design, design of monitoring system, among other aspects. Only a rational electrical design is able to ensure that distributed PV power generation systems work safely, reliably, and with high efficiency.
Along with continuous technological advancement and cost reduction, in the future, more significant roles will be played by distributed photovoltaic energy storage systems. The systems for generating distributed photovoltaic power will provide us either on-grid or off-grid with a cleaner and more reliable source of energy.