Do you know all these little secrets in photovoltaic systems?
Time: 2020-10-10

Photovoltaic system, also known as solar system. Its development history can be seen in just a few pages. After the component honeymoon period in 2006-2010, we had to reposition the industry pattern. It is understandable to develop domestic demand, so the photovoltaic system is finally belatedly and officially married in by China. However, due to various reasons, our basic knowledge of system application is still in a relatively chaotic stage.  

The ancients said that there is no way to go a long way without taking steps. At present, attention to details determines success or failure. These all confirm the importance of basic details. This article is not to teach you to complain about the policy, but to suggest a down-to-earth improvement of your basic knowledge. Come take a look at these little details, do you know how much?

       1. The photovoltaic cell is a high-resistance current source, and the battery is a low-resistance voltage source. This directly explains that we can short-circuit components but never short-circuit the battery.

       2. When the battery is covered, it will become an objective large resistance, if it is not drained, it will quickly heat up. This is also the fundamental principle of component and bypass diode activation switching.

       3. The 25 degrees Celsius defined by the STC standard state of the component is the working temperature of the component and not the ambient temperature. So when you calculate the influence of temperature on the minimum operating voltage, you need to add an additional 25 degrees to the room temperature to increase the temperature of the battery panel. However, when calculating the influence of temperature on the maximum open circuit voltage, the operating temperature rise of 25 readings cannot be added. This 25 degrees is a very considerable error for the calculation of projects above 3kW.

       4. The difference between STC and NOCT, in addition to the numerical difference in several established parameters, NOCT introduces a wind speed parameter of 1m/s, the purpose of which is to better fit the output power of the assembly during actual work.

       5. The same size and the same material (single crystal/polycrystalline) and the same rated power components, if the conversion efficiency is not the same, it is deceiving. This is also a law, without exception. The reason is simple and I won't repeat it.

       6. The working voltage of the module's maximum power point and the module's open circuit voltage have a constant relationship of 0.8, which is very close. This relationship is very important and convenient for preliminary estimation of the rationality of inverter and system structure. At the same time, it is of great significance to the algorithm design of MPPT.

       7. For the current components, the system is connected in parallel with more than 3 Strings, and must be protected by an overcurrent fuse. A large number of system fires are due to this error! This is determined by the maximum series fuse rating parameter.

       8. The impact of floating dust or evenly distributed sand dust on the system efficiency is not as terrible as imagined. It is basically within 5%, and in reality it is almost 2%.

       9. In cloudy or drizzly days without the sun, the output power of the system is very small. In fact, the open circuit voltage or working voltage of the module is still very high, even full load! In Australia, many installation workers who replaced inverters indoors were electrocuted. Please keep in mind that on cloudy days, the module may not output power, but it does not mean that it is dead. This is a common sense that is often overlooked.

       10. The east-west system can be connected in parallel if the number of components is the same, and there is no serious voltage dislocation. Basically, as long as the light intensity is above 50W/m^2, the module can work and output voltage. This explains that the inverter starts early, but the real output power lags for a while.

       Hundreds of kilowatts or megawatts of projects are dazzling and attractive, but they are also made up of hundreds of watts. Without accumulating steps, you can reach thousands of miles. This old motto that any industry must follow, I hope, can also be the motto for promoting the development of photovoltaic systems.

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