The photovoltaic off-grid power generation system first meets the user load, and then stores the excess power in the battery for night and rainy days. When the battery is out of power, most inverters can also support mains input (or diesel generators). ) As a supplementary energy to supply power to the load.
We need to consider the user’s load size, daily power consumption, local climate conditions and other factors, choose different design schemes according to the actual needs of customers, and the design of photovoltaic off-grid systems. The information that needs to be understood by customers mainly includes the following aspects:
- Where is the solar power system used? What is the solar radiation situation in this place?
- What is the load power of the system?
- What is the output voltage of the system, DC or AC?
- How many hours does the system need to work every day?
- In case of rainy weather without sunlight, how many days does the system need to supply power continuously?
- What is the starting current when the load is purely resistive, capacitive or inductive?
Selection of main components
1.Inverter selection: determine the inverter power according to the size and type of user load
Off-grid inverter is one of the core components of off-grid solar power generation system, which is responsible for converting direct current into alternating current for use by alternating load. In order to improve the overall performance of the photovoltaic power generation system and ensure the long-term stable operation of the power station, the performance indicators of the inverter are very important. The inverter selection is based on the characteristics of the load (such as resistive, inductive or capacitive) and the size of the load power.
The power of the inverter should generally be selected not less than the total power of the load, but considering the service life of the inverter and subsequent expansion, it is recommended that the inverter power needs to be considered to have a certain margin, generally 1.2~1.5 of the load power In addition, if the load includes inductive loads with motors such as refrigerators, air conditioners, water pumps, range hoods, etc. (the starting power of the motor is 3~5 times the rated power), the starting power of the load needs to be taken into consideration, namely The starting power of the load should be less than the maximum impact power of the inverter. The following is the calculation formula for power selection of the inverter for reference during design.
- PV module capacity determination: Determine the module capacity according to the user’s daily electricity consumption and light intensity
Part of the electricity generated by the photovoltaic module during the day is supplied to the load, and the rest is used to charge the battery. At night or in the case of insufficient solar radiation, the electricity stored in the battery will be discharged to the load. It can be seen that when there is no utility power/or diesel engine as In the case of supplementary energy, all the power consumed by the load comes from the electricity generated by the photovoltaic module during the day. Considering that the light intensity in different regions will vary in different seasons, in order to ensure the reliable operation of the system, the capacity of the photovoltaic panel should be designed in the most light The demand can be met even in bad seasons. The following is the capacity calculation formula for photovoltaic modules:
- Determination of battery capacity: determine the battery capacity according to the power consumption at night or the backup time
The main task of the battery pack is to store energy, so as to ensure the load power consumption at night or rainy days. The number of batteries in series and in parallel can be configured according to the requirements of the system’s DC voltage level. When batteries are connected in series and parallel, they should follow the principles of the same model and specification, the same manufacturer, the same batch, and simultaneous installation and use.
For photovoltaic off-grid systems with important loads, the design of battery capacity needs to consider the longest number of local rainy days. Ordinary photovoltaic off-grid system load power supply requirements are not high, considering the cost of the system, the number of cloudy and rainy days can be ignored, as long as the use of the load is adjusted according to the actual light intensity. In addition, most photovoltaic off-grid systems use lead-acid batteries, and the discharge depth of lead-acid batteries is generally 0.5-0.7.
- solar charge and discharge controller
The solar charge and discharge controller is also called “photovoltaic controller”. Its function is to regulate and control the electric energy generated by solar cell components, charge the battery to the maximum, and protect the battery from overcharge and overdischarge. effect. In places with large temperature differences, the photovoltaic controller should have the function of temperature compensation. According to the DC voltage level of the system and the power of the solar cell module, the appropriate photovoltaic controller is configured. Common photovoltaic controllers have different voltage levels of DC12V, 24V, 48V, 110V, and 220V.
Fives. HANFY SOLAR 10KvA photovoltaic off-grid system design scheme
Project background: Design a photovoltaic off-grid system for a school in Africa to meet its daily electricity consumption.
1) Project demand survey
In the early stage of the design plan, it is necessary to conduct a survey of project requirements (load information must be accurate), as follows:
2) Selection of inverter
The customer’s load is mainly classroom lighting, classroom fans, public place 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 JDSOLAR inverter power is 10kVA.
3) Determination of photovoltaic module capacity
According to the customer demand survey table, the average daily electricity consumption of the school is about 61.5kWh, and the local light conditions are good. According to the daily sunshine time of 4.23h, the module configuration is 1.1 times the margin, and the design uses 88 270W polycrystalline photovoltaics The total power of the components is 23.76kW, and the average daily power generation is 100.5kwh. Considering the system efficiency, it is generally 0.8, and the available power is 80kwh per day.
4) Determination of battery capacity
The school’s lighting is mostly used at night. Considering the battery life, the battery capacity should be appropriately increased. The battery backup time required by the customer is 2 days, and the battery discharge depth is 0.7. This project uses 110-cell 1000AH/2V The gel batteries are connected in series, with a total capacity of 220,000VAH, and an available power of about 154kwh, which can meet the power demand of 2 days of backup time.
5) System plan diagram