Off-grid photovoltaic power generation systems are widely used in remote mountainous areas, areas without electricity, islands, communication base stations and street lights. The system is generally composed of a photovoltaic array composed of solar cell components, a solar control inverter integrated machine, a battery pack, and a load. The photovoltaic square array converts solar energy into electrical energy when there is light, and supplies power to the load through the solar control inverter integrated machine, and at the same time charges the battery pack; when there is no light, the battery supplies power to the solar control inverter integrated machine, and then supplies AC load power supply. Off-grid system topology diagram Off-grid system scheme design mainly considers the selection and calculation of components, inverter control integrated machine, and battery. Before designing, it is necessary to understand the basic information of the project: the total power of the user’s load and the nature of the load, the climatic conditions of the installation site (mainly considering the temperature), and the power consumption during the day and night. In the photovoltaic off-grid system, if there is no external mains/generator access, the generated electricity basically depends on the weather, which is not completely reliable. If there are many rainy days in a row, there is no guarantee that the power can meet the usage requirements. In the early stage of design, it is necessary to understand the actual backup power requirements and the project cost for comprehensive consideration. After the basic information of the project is clearly understood, the system design can be started.
The design of the off-grid system mainly considers three points. The first is the selection of the integrated inverter, the second is the determination of the capacity of the photovoltaic module, and the third is the calculation of the battery capacity.
Selection of inverter control integrated machine—
First, confirm the power of the inverter control integrated machine according to the load power and type of the user. Household loads are generally divided into inductive loads and resistive loads. Loads with motors such as washing machines, air conditioners, and refrigerators are inductive loads. The starting power of the motor is 3-5 times of the rated power, after normal startup, the current will gradually stabilize at around the rated current. When calculating the power of the inverter, the starting power of these loads should be taken into consideration. The output power of the inverter must be greater than the power of the load. At the same time, the power demand of single-phase/three-phase equipment also needs to be considered.
After knowing the load power, you can select the off-grid inverter. lolsolar solar inverter integrated machine (integrated controller and inverter) can be powered by solar panels alone, or can be connected to mains or diesel generators to realize solar/mains complementary and solar/generator complementary; applicable In areas with power shortage and unstable grid. lolsolar’s new SPF6000ES Plus series single-phase solar off-grid inverter control integrated machine, adopts a new generation of full digital control technology, pure sine wave output; solar controller and inverter are integrated into one, easy to use;
the product has the following features: ( 1) Control and inverter all-in-one machine: integrated solar controller and inverter, easy to connect and easy to use; (2) High efficiency, the efficiency can reach more than 93.5%, and maximize the use of solar energy; (3) Light weight: the inverter adopts High-frequency design, light weight, convenient transportation and installation; (4) Perfect protection functions: battery overcharge and overdischarge protection and advanced battery management functions to prolong battery life, overload protection, short circuit protection and other functions to protect equipment and load safety Reliable operation; (5) LCD liquid crystal screen intuitive display: photovoltaic input voltage/current, AC output voltage/current, battery capacity and other operating status parameters monitoring. (6) The energy storage system is compatible with lead-acid batteries and our own lithium batteries, providing users with a variety of options. (7) Photovoltaic charging, mains (gasoline) charging, hybrid charging and other charging methods, battery power supply, mains power supply and other power supply methods, the priority of charging and discharging can be set. (8) Support up to 6 inverters in parallel, convenient power expansion, rated output power up to 36KW, photovoltaic input power up to 48KW. (9) GPRS/WIFI monitoring mode is optional, support screen and remote APP to view parameters Model interface introduction:
Determine the capacity of photovoltaic modules—Po=(P×t×Q)/(η1×T) where:
P0—Peak power of photovoltaic modules, unit Wp;
P — load power, the unit is W;
t—the daily power consumption time of the load, unit h;
η1—the efficiency of the system, generally 80%~85%;
T — local daily average peak sunshine hours, unit is h;
Q—surplus coefficient in continuous rainy period, generally 1.2~1.5;
The design principle of the module is to meet the daily power consumption demand of the load under average weather conditions, that is to say, the annual power generation of the solar cell module must be greater than or equal to the annual power consumption of the load. Because the weather conditions are lower or higher than the average, the design of the solar cell module basically meets the needs of the season with the worst light, even in the season with the worst light, the battery can basically be fully charged every day. However, in some areas, the illuminance in the worst season is far lower than the average annual value. If the power of solar cell modules is designed according to the worst case, then the power generation at other times of the year will far exceed the actual needs. , causing waste. At this time, we can only consider appropriately increasing the design capacity of the battery, increasing the storage of electric energy, keeping the battery in a shallow discharge state, and making up for the damage to the battery caused by the lack of power generation in the worst season of sunlight. The power generation of the components cannot be completely converted into electricity consumption, and the efficiency of the controller, the loss of the machine and the loss of the battery must also be considered. The battery will also lose 10-15% during the charging and discharging process.
lolsolar off-grid case
Calculation of battery capacity – the capacity of the battery is determined according to the daily power consumption of the system, the number of days of energy storage, the depth of discharge of the battery and the efficiency of the system. The calculation formula is:
L— the daily power consumption of the system, the unit is kwh;
D—the number of days of energy storage, that is, the number of rainy days considered;
DOD—the depth of discharge of the battery, about 50%~80%;
E1—system energy conversion rate, about 80%~90%;
E2 — power transmission efficiency, about 5%.
The task of the storage battery is to ensure the normal power consumption of the system load when the solar radiation is insufficient. For important loads, to ensure the normal operation of the system within a few days, the number of consecutive rainy days should be considered. For general loads such as solar street lights, etc., it can be selected within 2 to 3 days according to experience or needs. Batteries are mainly used for energy storage to provide electrical energy to loads at night or on rainy days. The battery is an important part of the off-grid system, and its quality is directly related to the reliability of the entire system. However, the battery is the device with the shortest mean time between failures (MTBF) in the entire system. If the user can use and maintain it normally, its service life can be extended, otherwise its service life will be significantly shortened. Commonly used batteries are lead-acid batteries and lithium batteries, and their respective characteristics are shown in the table below. Compare the advantages and disadvantages of different types of batteries Note: the ambient temperature has a greater impact on the battery. Too high or too low ambient temperature will affect the service life of the battery. Therefore, the ambient temperature is generally required to be around 25°C for indoor installation. Lead-acid batteries
lithium battery
The default operating mode of the system—the photovoltaic array converts solar energy into electrical energy when there is sunlight, and supplies power to the load through the output of the inverter. When the load is not exhausted, it can charge the battery pack, and the excess power will not be sent to the grid. When there is no light, the battery supplies power to the AC load through the inverter. When there is no light and the battery is dead, you can choose to supply power to the load through the grid/oil generator (provided there is a grid/oil generator) and charge the battery. After the mains power passes through the inverter, the inverter automatically performs the mains bypass switch, and the output is used with load through the AC output port of the inverter. //