Photovoltaic off-grid power generation system does not depend on the power grid and operates independently, and is widely used in remote mountainous areas, areas without electricity, islands, communication base stations and street lights and other applications, using photovoltaic power generation to solve the needs of residents in areas without electricity, lack of electricity and unstable electricity, schools or small factories for living and working electricity, photovoltaic power generation with the advantages of economic, clean, environmental protection, no noise can partially replace or completely replace diesel The power generation function of the generator.

1 PV off-grid power generation system classification and composition
Photovoltaic off-grid power generation system is generally classified into small DC system, small and medium off-grid power generation system, and large off-grid power generation system. The small DC system is mainly to solve the most basic lighting needs in areas without electricity; the small and medium off-grid system is mainly to solve the electricity needs of families, schools and small factories; the large off-grid system is mainly to solve the electricity needs of whole villages and islands, and this system is now also in the category of micro-grid system.
Photovoltaic off-grid power generation system is generally composed of photovoltaic arrays made of solar modules, solar controllers, inverters, battery banks, loads, etc.
The PV array converts solar energy into electricity when there is light, and supplies power to the load through the solar controller and inverter (or inverse control machine), while charging the battery pack; when there is no light, the battery supplies power to the AC load through the inverter.
2 PV off-grid power generation system main equipment
01. Modules
Photovoltaic module is an important part of off-grid photovoltaic power generation system, whose role is to convert the sun’s radiation energy into DC electric energy. Irradiation characteristics and temperature characteristics are the two main elements affecting the performance of the module.
02、Inverter
Inverter is a device that converts direct current (DC) into alternating current (AC) to meet the power needs of AC loads.
According to the output waveform, inverters can be divided into square wave inverter, step wave inverter, and sine wave inverter. Sine wave inverters are characterized by high efficiency, low harmonics, can be applied to all types of loads, and have strong carrying capacity for inductive or capacitive loads.
03、Controller
The main function of the PV controller is to regulate and control the DC power emitted by the PV modules and to manage the charging and discharging of the battery intelligently. Off-grid systems need to be configured according to the system’s DC voltage level and system power capacity with the appropriate specifications of the PV controller. PV controller is divided into PWM type and MPPT type, commonly available in different voltage levels of DC12V, 24V and 48V.
04、Battery
The battery is the energy storage device of the power generation system, and its role is to store the electrical energy emitted from the PV module to supply power to the load during power consumption.
05、Monitoring
3 system design and selection details design principles: to ensure that the load needs to meet the premise of electricity, with a minimum of photovoltaic modules and battery capacity, in order to minimize investment.
01、Photovoltaic module design
Reference formula: P0 = (P × t × Q) / (η1 × T) formula: P0 – the peak power of the solar cell module, unit Wp; P – the power of the load, unit W; t – -the daily hours of electricity consumption of the load, unit H; η1 -is the efficiency of the system; T -the local average daily peak sunshine hours, unit HQ- – continuous cloudy period surplus factor (generally 1.2 to 2)
02, PV controller design
Reference formula: I = P0 / V
Where: I – PV controller control current, unit A; P0 – the peak power of the solar cell module, unit Wp; V – the rated voltage of the battery pack, unit V ★ Note: In high altitude areas, the PV controller needs to enlarge a certain margin and reduce the capacity to use.
03、Off-grid inverter
Reference formula: Pn=(P*Q)/Cosθ In the formula: Pn – the capacity of the inverter, unit VA; P – the power of the load, unit W; Cosθ – power factor of the inverter (generally 0.8); Q – the margin factor required for the inverter (generally chosen from 1 to 5). ★Note: a. Different loads (resistive, inductive, capacitive) have different start-up inrush currents and different margin factors. b. In high altitude areas, the inverter needs to enlarge a certain margin and reduce the capacity for use.
04、Lead-acid battery
Reference formula: C = P × t × T / (V × K × η2) formula: C – the capacity of the battery pack, unit Ah; P – the power of the load, unit W; t – the load daily hours of electricity consumption, unit H; V – the rated voltage of the battery pack, unit V; K – the discharge coefficient of the battery, taking into account the battery efficiency, depth of discharge, ambient temperature, and influencing factors, generally taken as 0.4 to 0.7; η2 –inverter efficiency; T – the number of consecutive cloudy days.
04、Lithium-ion battery
Reference formula: C = P × t × T / (K × η2)
Where: C – the capacity of the battery pack, unit kWh; P – the power of the load, unit W; t – the number of hours of electricity used by the load per day, unit H; K –discharge coefficient of the battery, taking into account the battery efficiency, depth of discharge, ambient temperature and influencing factors, generally taken as 0.8 to 0.9; η2 –inverter efficiency; T -number of consecutive cloudy days. Design Case
An existing customer needs to design a photovoltaic power generation system, the local average daily peak sunshine hours are considered according to 3 hours, the power of all fluorescent lamps is close to 5KW, and they are used for 4 hours per day, and the lead-acid batteries are calculated according to 2 days of continuous cloudy days. Calculate the configuration of this system.