How to calculate off-grid solar photovoltaic power generation system capacity?

The calculation of solar photovoltaic power generation system capacity requires the following basic data.

① Determine all load power and continuous working time. The names of all loads, rated working voltage, power consumption, power consumption time, whether there are any special requirements, etc.

② Determine the geographical location of solar cell module installation: longitude, latitude and altitude.

③ Determine the meteorological data of the installation site: annual (or monthly) total solar radiation or annual (or monthly) average sunshine hours; Annual average and extreme temperatures; The longest continuous rainy days; Special climate data such as maximum wind speed and ice electricity.

The output power Wp of the solar cell is the output power of the solar cell under standard solar illumination conditions (i.e. 101 standard defined by the European Commission, radiation intensity 1000 W/m2, air quality AM1.5, cell temperature 25 °C). This condition is similar to the sunlight conditions around noon on a sunny day at ordinary times (it can only be close to this value in the lower reaches of the Yangtze River). That is to say, the output power of the solar cell is random. At different times and places, the same solar cell The output power is different.

One of the main principles of solar cell module design is to meet the daily power demand of the load under average climate conditions. Because the weather conditions are lower than and higher than the average, it is necessary to ensure that the solar cell module and the battery work coordinately under different weather conditions. Under harsh weather conditions, the state of charge (SOC) of the battery will be greatly reduced. In the design of the output power of the solar cell module, do not consider fully charging the battery as quickly as possible. If so, a large solar module will be required, making the system cost too high, and for most of the year, the power generation of the solar module will be far greater than the load usage, resulting in unnecessary waste of solar modules. The main function of the battery is to supply power to the load when the solar radiation is lower than the average. When the solar radiation is higher than the average, the output power of the solar cell module is greater than the part required by the load, which will automatically charge the battery.

When designing solar cell modules, the first consideration is that the output power of the designed solar cell modules should be equal to the average load demand power throughout the year. In this case, the solar module will provide all the energy required by the load. But this also means that the battery is out of power nearly half of the time every year. If the battery is in a state of power loss for a long time, the plates of the battery will be sulfated. A backup power supply is installed in the off-grid solar photovoltaic power generation system to recharge the battery in bad weather, so that the service life and performance of the battery will be greatly affected, and the operating cost of the whole system will also be greatly increased.

In the design of solar cell modules, a better method is to make the solar cell modules meet the load needs in the worst light seasons, that is, to ensure that the battery can be completely fully charged in the worst light conditions, so that the battery can be fully charged throughout the year, which can prolong the service life of the battery and reduce maintenance costs. If the illumination intensity is much lower than the average in the worst season of the year, and the solar cell module is still designed according to the worst case, then the power output of the designed solar cell module at other times of the year will exceed the actual need, thus increasing the system cost. Therefore, the key to designing off-grid solar photovoltaic power generation system is to choose the most cost-effective solution.

There are many factors that affect the power generation capacity of solar cell modules, such as temperature, sunshine intensity, shadow, crystal structure and load impedance. For the simplicity of calculation, the following simple methods can be used to estimate

The method of converting the amount of radiation into the daily peak sunshine hours is that if the unit of the amount of radiation is cal/cm2, then the number of peak sunshine hours = the amount of radiation × 0. 0116 [0.0116 is the conversion factor of the amount of radiation (cal/cm2) to the number of peak sunshine hours]. If the unit of the amount of radiation is MJ/m2, then the number of peak sunshine hours = the amount of radiation ÷ 3. 6 (3.6 is the conversion factor of the amount of radiation (MJ/m2) to the number of peak sunshine hours).