Due to differences in economic development levels, there are still a small number of remote areas that have not solved the basic electricity consumption problem and cannot enjoy modern civilization. Photovoltaic off-grid power generation can solve the basic electricity consumption problem of residents in areas with little or no electricity.
The household photovoltaic off-grid power generation system is mainly composed of photovoltaic components, brackets, controllers, inverters, batteries, and power distribution systems. The electrical design of the system mainly considers the selection and calculation of components, inverters (controllers) and storage batteries. Before the design, the preliminary work should be done well, because the off-grid systems are customized and there is no unified plan. You need to understand the user load type and power, the power consumption during the day and night, and the climatic conditions at the installation site. In photovoltaic off-grid systems, electricity depends on the weather and there is no 100% reliability.
The off-grid system must be equipped with batteries, and occupies 30-50% of the cost of the power generation system. Moreover, the service life of lead-acid batteries is generally 3 to 5 years, and they have to be replaced later. From the economic point of view, it is difficult to get a large-scale promotion and use, only suitable for use in places where there is a lack of electricity.
Off-grid systems are not the same as on-grid systems. Components and inverters are not configured according to a certain ratio, but are designed according to the user's load, electricity usage and local weather conditions:
1. Confirm the power of the off-grid inverter according to the user's load type and power
Household loads are generally divided into inductive loads and resistive loads. Loads with motors such as washing machines, air conditioners, refrigerators, water pumps, and range hoods are inductive loads. The starting power of the motor is 3-5 times the rated power. In calculating the inverter Power, the starting power of these loads must be taken into account. The output power of the inverter should be greater than the power of the load. But for ordinary poor families, considering that all loads cannot be turned on at the same time, in order to save costs, the sum of the load power can be multiplied by a factor of 0.7-0.9. The following list is the power of commonly used household appliances for reference in design.
2. Confirm the component power according to the user's daily power consumption
Electricity available from off-grid system = total module power * average time of solar power generation * controller efficiency * battery efficiency. The design principle of the module is to meet the daily power demand of the load under average weather conditions, that is to say, the daily power generation of the solar cell module is slightly larger than the daily power consumption of the load. Because the weather conditions are lower and higher than the average, the design of the solar cell module basically meets the needs of the worst lighting season, that is, in the worst lighting season, the battery can be basically fully charged every day. However, in some areas, the illumination in the worst season is far lower than the annual average. If the power of the solar cell module is also designed according to the worst case, then the power generation at other times of the year will far exceed the actual demand. , Causing waste. At this time, we can only consider appropriately increasing the design capacity of the battery and increasing the storage of electric energy, so that the battery is in a shallow discharge state, and make up for the damage caused by the lack of power generation in the worst season of the sun to the electricity storage. The power generated by the components cannot be completely converted into electricity, and the efficiency of the controller, the loss of the machine and the loss of the battery must also be considered.
The installation angle of the module should consider the geographical location of the user, and try to meet the requirements of summer and winter. In China, the azimuth of the solar cell is generally selected to the south direction, so as to maximize the power generation per unit capacity of the solar cell, and the optimal tilt angle It is the inclination angle to make the solar cell power generation capacity as large as possible, and the difference between the power generation capacity in winter and summer as small as possible.
For loads such as light bulbs, electric fans, and hair dryers, the power consumption is equal to power times time; loads such as air conditioners and refrigerators work intermittently. The power consumption of the air conditioner and the difference between the indoor and outdoor temperatures, the room area, and the energy efficiency of the air conditioner are It has a lot to do. A 1P air conditioner can be used for 8 hours at night and consumes 1-5 degrees of electricity.
3. Determine the battery capacity according to the user's night electricity consumption or expected standby time
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, we must consider the number of consecutive rainy days. For general loads such as solar street lights, etc. can be selected within 2 to 3 days according to experience or needs. For ordinary poor families, the main consideration is the price, and it is not necessary to consider rainy days. Use less when the sun is not good, and don't use it if there is no sun. When choosing the load, try to use energy-saving equipment, such as LED lights, inverter air conditioners. The design of the battery mainly includes the design calculation of the battery capacity and the design of the series and parallel combination of the battery pack. In the photovoltaic power generation system, most of them use lead-acid batteries. Considering the battery life, the discharge depth is generally between 0.5 and 0.7. Battery design capacity = (average daily power consumption * number of consecutive rainy days) / depth of battery discharge.
4. Design scheme of 5kVA household system
The customer's electricity needs: lighting 200 watts working 6 hours a day, refrigerator 50 watts working 24 hours a day, a horsepower inverter air conditioner working 12 hours, TV 50 watts working 10 hours a day. There are also occasional household appliances such as washing machines, desktop computers, rice cookers, electric fans, etc. The customer's installation location is in Diqing, Yunnan.
1. Count the total load power
Lighting 200 watts, refrigerator 50 watts, air conditioner 750W, TV 50 watts, washing machine count 300W, desktop computer 200W, rice cooker 1200W, electric fan 100W, a total of 2850W, choose Gurivat SPF 5000 control inverter integrated machine, output power It is 4.0KW.
2. Daily electricity consumption statistics
Lighting 1.2 degree electricity, refrigerator 1 degree, air conditioner 2 degree, TV set 0.5 degree, washing machine count 1 degree, desktop computer 0.5 degree, rice cooker 1 degree, electric fan 0.5 degree, average total 7 ．7 degrees, actually about 6-10 kWh per day on average. The lighting conditions in Diqing, Yunnan are relatively good. The average is 4.5 hours per day. The design uses 9 280W modules with a total of 2.52kW. The average daily power generation is 11.34 degrees. The efficiency of the off-grid system is low, generally about 0.8. The average available electricity is 9 degrees per day, so it can basically meet more than 99% of the electricity demand.
3. Calculate the battery
Most household appliances are used at night, and may be only about 20% during the day. In order to increase the life of the battery, the capacity of the battery can be appropriately increased. The daily charge and discharge depth is low. This project design uses 4 12V250AH colloidal lead-acid batteries The total capacity is 12000VAH, the available electricity is about 8.4 degrees, the average electricity is 6 degrees at night, and the depth of discharge is about 50%.
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