How to calculate the module power of PV off-grid system?

The module power is confirmed according to the daily power consumption of the customer.

The design principle of the module is to meet the daily power demand of the load under average weather conditions, which means that the annual power generation of the solar module should be equal to the annual power consumption of the load. Because weather conditions are below and above average, solar modules are designed to basically meet the needs of the worst light season, that is, in the worst light season the battery can basically be fully charged every day. However, in some areas, the worst season of illumination is much lower than the average value of the year, if the worst case design solar cell module power, then in other times of the year the power generation will be far more than the actual need, resulting in waste. At this time, we can only consider appropriately increasing the design capacity of the battery to increase the electrical energy storage, so that the battery is in a shallow discharge state to make up for the damage caused by the lack of power generation in the worst light season to the battery.

The power generation of the components can not be fully converted into electricity, but also consider the efficiency of the controller and the loss of the machine and the loss of the battery, the solar controller has two types of PWM and MPPT, PWM controller efficiency of about 85%, the input voltage range is relatively narrow, but the price is relatively low, MPPT controller efficiency of about 95%, the price is relatively high. There is also a 10-15% loss in the battery during charging and discharging. Power available in PV off-grid system = total module power * average hours of solar power * controller efficiency * battery efficiency.

The off-grid system is designed to prevent the components from being too large. In some places, customers need to ensure that they can use electricity even on cloudy and rainy days, and there are more batteries, so when customers consider the solar system components, they count all the battery capacities, resulting in a large capacity. But if you include all the battery capacity, you need 12KW modules, which are only partially used most of the time, and only when the battery is fully used up and charged the next day.

For very important places, you need to consider the interval between two rainy days, the components should be equipped with more, generally recommended 3-5 days, in order to ensure their own power consumption, to fill the battery.