Typical design of photovoltaic off-grid system
There are still a large number of people in the world living in a world without electricity or electricity. They live in poverty or remote areas, away from power plants and the public power grid. Because there is no electricity, they cannot enjoy the information that modern civilization brings to life. And convenience. Photovoltaic off-grid power generation system is an independent and self-sufficient renewable new energy supply system that can solve their basic electricity problems.
The typical photovoltaic off-grid power generation system is mainly composed of solar components, brackets, solar controllers, off-grid inverters, storage batteries, distribution boxes, etc. After the solar modules are connected to the solar controller, the user load is first used, and then The excess power is stored in the battery for night and rainy days. When the battery is dead, most inverters can also support the mains input (or diesel generator) as a supplementary energy source for the load.
The design of the PV off-grid system is different from the grid-connected power generation system. It needs to consider the user's load size, daily power consumption, local climatic conditions and other factors, and select different design schemes according to the actual needs of customers, which is relatively complicated, in order to ensure off-grid. The system can work reliably, and it is very necessary to do a preliminary survey of customer needs. The design of the photovoltaic off-grid system mainly includes the selection of the inverter, the design of the component capacity and the design of the battery capacity:
One. Inverter selection: determine inverter power based on user load size and type
The choice of inverter power size is generally not less than the total load power, but considering the service life of the inverter and subsequent expansion, it is recommended to consider the inverter power to leave a certain margin, generally 1.2~1.5 of the load power. In addition, if the load contains an inductive load with a motor similar to a refrigerator, air conditioner, water pump, range hood, etc. (the starting power of the motor is 3 to 5 times the rated power), the starting power of the load needs to be taken into account, ie The starting power of the load is less than the maximum impact power of the inverter. The following is the calculation formula for the power selection of the inverter, which is used for design reference.
two. Component capacity determination: component capacity is determined based on user daily electricity consumption and light intensity
Part of the electricity generated by the PV modules during the day is supplied to the load, and the rest is used to charge the battery. At night or when the solar radiation is insufficient, the electricity stored in the battery will be discharged to the load. It can be seen that there is no mains or diesel engine. In the case of supplementary energy, all the electricity consumed by the load comes from the electricity generated by the photovoltaic modules during the day. Considering different seasons, the light intensity of different regions will be different. In order to ensure the reliable operation of the system, the capacity design of the photovoltaic panels should be the most in the light. The poor season can also meet the demand, the following is the calculation formula of the capacity of photovoltaic panels:
three. Battery capacity determination: determine battery capacity based on night power consumption or backup time
The battery of the photovoltaic off-grid system is mainly used for energy storage to ensure that the load can work normally when the solar radiation is insufficient. For photovoltaic off-grid systems with significant loads, battery capacity design requires consideration of the longest rainy days in the area. Ordinary photovoltaic off-grid system load power requirements are not high, considering the system cost reasons, you can not consider the number of rainy days, as long as the actual use of light intensity to adjust the use of the load. In addition, most of the photovoltaic off-grid systems use lead-acid batteries, and the discharge depth of lead-acid batteries is generally 0.5-0.7. The design of battery capacity can refer to the following formula:
four. Typical design scheme of 10kVA photovoltaic off-grid system
Project Background: Design a photovoltaic off-grid system for a school in the Congolese capital to meet its daily electricity use.
1) Project demand survey
In the early stage of the design plan, you need to do a good customer demand survey (load information should be accurate), as follows:
2) Inverter selection
The customer's load is mainly classroom lighting, classroom fans, public places lighting, wall lighting and broadcasting systems, etc. The total load power is 6.84kw, the inverter power selection is not less than 9.8kVA, and the Jingfuyuan ESS10K reverse control integrated machine can be selected. The output power is 10kVA.
3) Component capacity determination
According to the customer demand questionnaire, the average daily electricity consumption of the school is about 61.5kWh, and the local lighting conditions are good. According to the daily sunshine time of 4.23h, the component configuration is 1.1 times margin, and the design uses 88 270W polycrystalline photovoltaic. The total power of the module is 23.76kW, and the average power generation is 100.5kwh per day. Considering the system efficiency, it is generally 0.8, and the available electricity is 80kwh per day.
4) Battery capacity determination
Most of the school's lighting is used at night. Considering the battery life, the battery capacity should be increased appropriately. The battery backup time required by the customer is 2 days, and the battery discharge depth is 0.7. The project uses 110 AAA/2V. The colloidal battery is connected in series, the total capacity is 220,000VAH, and the available power is about 154kwh, which can meet the power demand of 2 days of backup time.
5) System plan
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