Precautions for paralleling Bluesun off-grid inverters

Calculation method of photovoltaic power station power generation, theoretical annual power generation = annual average total solar radiation * total battery area * photoelectric conversion efficiency. However, due to the influence of various factors, the actual power generation of photovoltaic power stations is not that much. Actual annual power generation = theoretical annual power generation * actual power generation efficiency. So what factors affect the power generation of photovoltaic power plants?