How to calculate photovoltaic off-grid system

Confirm the power of the module according to the user's daily power consumption.

Confirm the power of the module according to the user's daily power consumption.

The design principle of photovoltaic modules is to meet the daily power consumption demand of the load under average weather conditions, that is to say, the annual power generation capacity of solar cell modules should be equal to the annual power consumption of the load. Because the weather conditions are lower and higher than the average, the solar cell modules are designed to basically meet the needs of the worst seasons, even in the worst seasons, the battery can basically be fully charged every day. However, in some regions, the illuminance in the worst season is much lower than the annual average. If the power of the solar cell module is also designed according to the worst case, the power generation at other times of the year will far exceed the actual demand. , Resulting in waste. At this time, we can only consider appropriately increasing the design capacity of the battery, increasing the storage of electric energy, so that the battery is in a shallow discharge state, and making up for the damage to the battery caused by the insufficient power generation in the worst season.

The power generation of photovoltaic modules cannot be completely converted into electricity, and the efficiency of the controller and the loss of the machine and the loss of the battery must be considered. There are two types of solar controllers: PWM and MPPT. The efficiency of the PWM controller is about 85%, and the input voltage The range is relatively narrow, but the price is relatively low, the efficiency of the MPPT controller is about 95%, and the price is relatively high. In the process of charging and discharging the battery, there will be 10-15% loss. The power available for off-grid systems = total component power * average solar power generation hours * controller efficiency * battery efficiency.

In order to prevent the module design from being too large for the off-grid system, in some places, customers need to ensure that they can use electricity even in rainy and rainy days. There are more batteries. When customers consider solar modules, they include all the battery capacity. The result is a large capacity, such as one The daily power consumption is 10KWH system, the customer requires 2 rainy days, normal design, 4KW components are enough, but if all the battery capacity is included, 12KW components are needed, and these components are only used most of the time Only when the battery is completely used up, it can be used when it is charged the next day.

For very important places, you need to consider the interval between two cloudy and rainy days. More components should be equipped. Generally, 3-5 days are recommended. The battery should be fully charged under the condition of ensuring its own power consumption.