Due to differences in the level of economic development, there are still a few remote areas that have not solved the basic power problems and cannot enjoy modern civilization. Photovoltaic off-grid power generation can solve the basic electricity problem of residents in areas without electricity.

The photovoltaic off-grid power 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 batteries. Preliminary work must be done before designing, because the off-grid system is customized and there is no unified solution. It is necessary to understand the user's load type and power, the power consumption during the day and night, and the conditions of the climate installation location. The photovoltaic off-grid system relies on weather to supply power and is not 100% reliable.

Off-grid systems must have batteries, which account for 30-50% of the cost of power generation systems. Moreover, the service life of lead-acid batteries is generally 3-5 years and must be replaced afterwards. From an economic point of view, it is difficult to get widespread promotion and use, and it is only suitable for use in places where there is no electricity.

Different from off-grid systems and grid-connected systems, components and inverters are not configured in a certain proportion, but are designed according to the user's load, power consumption and local weather conditions:

1. Determine 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, range hoods, etc. are inductive loads. The starting power of the motor is 3-5 times the rated power. The power of these loads must be considered when calculating the inverter. The output power of the inverter is greater than the power of the load. However, 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 0.7-0.9 times. The following table lists the power of common household appliances for reference during design.

2. Determine the component power according to the user's daily power consumption

Off-grid system available power = total component power * average solar power hours * controller efficiency * battery efficiency. The design principle of the module is to meet the daily power consumption of the load under average weather conditions, that is, the daily power generation of the solar module is slightly larger than the daily power consumption of the load. Due to the lower and higher than average weather conditions, the design of solar cell modules basically meets the needs of the worst season, that is, the battery can be fully charged every day in the worst season. But in some areas, the illuminance in the worst season is much lower than the annual average. If the power of the solar module is designed for the worst-case scenario, the power generation will far exceed the actual demand at other times of the year. Cause waste. At this time, we can only consider appropriately increasing the design capacity of the battery, increasing the storage of electric energy, and keeping the battery in a shallow discharge state to make up for the damage caused by insufficient power generation in the current season. The power generation of the components cannot be completely converted into electrical energy, and there is also the efficiency of the controller and the loss of the machine and the loss of the battery. Make up for losses caused by insufficient power generation in the current season. The power generation of the components cannot be completely converted into electric energy, and there is also the efficiency of the controller and the loss of the machine and the loss of the battery. Make up for losses caused by insufficient power generation in the current season. The power generation of the components cannot be completely converted into electric energy, and there is also the efficiency of the controller and the loss of the machine and the loss of the battery.

3. Determine the battery capacity according to the user's night power consumption or expected standby time

The task of the battery is to ensure the normal use of the system load when the solar radiation is insufficient. For important loads, ensure that the system operates normally within a few days, and consider the number of consecutive cloudy and rainy days. For general loads such as solar street lights, it can be selected within 2-3 days based on experience or needs. For ordinary poor families, the main consideration is price, so don't worry about it in rainy days, use it when the sun is good. Use less when the sun is bad, don't use it when there is no sun. When choosing a load, try to use energy-saving equipment such as LED lights and inverter air conditioners. The design of the battery mainly includes the design calculation of the battery capacity and the design of the series-parallel combination of battery packs. In photovoltaic power generation systems, lead-acid batteries are mostly used. Taking into account the battery life, the depth of discharge is generally between 0.5 and 0.7. Battery design capacity = (load daily average power consumption * continuous cloudy and rainy days) / battery discharge depth.