Distributed off-grid pv system is mainly composed of pv module, bracket, controller, inverter, storage battery and power distribution system. It is mainly used in power-free or power-deficient areas to solve the basic needs of daily
life. There is no standard scheme for Pv off-grid system, but there are many kinds of off-grid devices, which can be combined into different schemes to meet different user requirements. Off-grid power generation system schematic
diagram, pictures, pre-research, off-grid system design, pre-work needs to be done. One is to count the types of electric load and the sum of the power used by users, such as electric appliances such as air conditioners, washing
fans, water pumps, refrigerators, etc. . There are electric motors inside, which are inductive loads, with large starting power, electric lamps, televisions, induction cookers, computers and other electrical appliances, it is resistive
load; second, the statistics of daily average electricity consumption, peak electricity consumption, day and night electricity consumption, etc. . Third, the first to understand the weather conditions of the user's installation
site, the average peak hours of sunshine data, the number of consecutive cloudy and rainy days in a year, etc. The fourth is to know whether there is electricity, or oil-fired generators; the fifth is to know clearly the user's
budget and economic situation, the degree of emergency power. Once you understand these things, you can begin to design the solution to the problem. Picture, scheme design, off-grid system design, the main is based on previous
research data, to confirm the system inverter, components and storage capacity, this design method and grid-connected system is completely different, can not be copied. The three equipment design selection based on different, but
also need to cooperate with each other. The power of off-grid inverter should be confirmed according to user's load type and power. The output power of the INVERTER is greater than the starting power of the actual load. Washing
machine, air conditioning, refrigerator, water pump, exhaust hood with motor load is inductive load, motor starting power is rated power 5-7 times, in the calculation of inverter power, the starting power of these loads has to
be taken into account. For users with a high budget and a high demand for electricity, the output power is calculated as the sum of all the loads; for users with a low budget, considering that all the loads can not be turned on
at the same time, in order to save the initial cost, the output power can be multiplied by a factor of 0.7-0.9 over the sum of the load power. The power of the component is determined based on the user's Daily consumption of electricity.
Photovoltaic is a renewable energy source, available on a daily basis, so the modules generate on average more electricity per day than the user uses. How much depends on the weather conditions on the ground and the user's budget
and demand for electricity. General weather conditions are below and above average, with light in most areas being worse in winter than in summer, and in some areas more than double the difference. For users with a high budget
and a high demand for electricity, the power design of the modules is basically designed to meet the needs of the worst lighting season, even in the worst lighting season the batteries can be charged almost every day. Low-budget
users who design the power of solar panels for the worst-case scenario will generate more power than is actually needed at other times of the year, resulting in waste, when the power of the modules is illuminated on an annual average
basis, the design capacity of the battery can be increased properly, and the electric energy can be stored, so that the battery is in the state of shallow discharge to make up for the shortage of power generation in the worst season.
The capacity of a battery is determined by the amount of electricity consumed by the user. In the absence of photovoltaic, the battery provides power to the system load. For heavy loads, have an adequate budget, take into account
the number of consecutive rainy days, and for general loads such as solar street light can be selected within 2 to 3 days depending on experience or need, important loads such as communications, navigation, and hospital care are
selected within 3 to 7 days to ensure the normal operation of the system within a few days. For Poor families, price is the main consideration, but rainy days are not, when the sun is good, use more; when the sun is bad, use less,
no sun is not used. Pictures, pictures, equipment selection, off-grid user needs are diverse, according to user requirements design photovoltaic system. At this time need to be flexible, do not stick to a fixed formula. When selecting
inverters, it is necessary to look at the situation of use. If it is only a simple lighting application, it is recommended to select a PWM controller and a modified wave inverter, which can save the initial cost, it is suggested
that MPPT controller and power frequency inverter should be used, which has strong load capacity. If it is a comprehensive load, it is recommended to choose high-frequency INVERTER, taking into account both cost and load capacity.
Photo: Small pv off-grid Power Station, limited investment, you can consider using lead-acid Gel battery; small and medium Pv off-grid power station, limited investment, but hope long life, you can consider using lead-carbon battery;
large and medium Pv off-grid power station, with a budget and a high return on investment, consider lithium-ion batteries. In the city electricity supplement place, may also according to the actual situation, the choice different
priority pattern. In places where the voltage is stable and the price is cheap, but the time of power supply is short, it is suggested that the preferred mode of power consumption should be the power grid; in places where the price
of electricity for the market is high and the power supply is often cut off, the demand for power consumption is not particularly high among users, it is recommended to choose the battery-first mode; the market price is not very
high, frequent power outages, on high demand for electricity users, it is recommended to choose photovoltaic-first mode.
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