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.
A typical photovoltaic off-grid power generation system is mainly composed of a solar module, a bracket, a solar controller, an off-grid inverter, a battery, a distribution box, etc. After the solar module is connected to the solar controller, the user load is first used, and then Store excess power 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 supplemental 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 electricity consumption, local climatic conditions and other factors. According to the actual needs of customers, different design schemes are selected, which is relatively complicated, in order to ensure off-grid. The system can work reliably, it is very necessary to do a good customer demand survey. The design of the PV off-grid system mainly includes the selection of the inverter, the design of the component capacity and the design of the battery capacity:
I. Inverter selection: Determine inverter power according to user load size and type
The power selection of the inverter is generally not less than the total power of the load. However, considering the service life of the inverter and subsequent expansion, it is recommended that the power of the inverter be considered 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.
2. Component capacity determination: Determine component capacity 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 the photovoltaic panel:
3. Battery capacity determination: Determine battery capacity according to 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 important loads, the design of the battery capacity needs to consider the longest rainy days in the local area. Off-grid system load power supply requirements are not high, considering the system cost reasons, you can not adjust 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 system uses lead-acid batteries, generally lead acid The discharge depth of the battery is 0.5-0.7. The design of the battery capacity can refer to the following formula:
4. 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 consumption.
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 fan, public place lighting, wall lighting and broadcasting system, 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 school's average daily electricity consumption 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, and the battery backup time required by the customer is 2 days, and the battery discharge depth is 0.7. The project uses 110 volts 1000AH/2V. The colloidal battery is connected in series, the total capacity is 220,000VAH, and the available electricity is about 154kwh, which can meet the power demand of 2 days of backup time.
5) System plan
