FAQ

1. Temperature characteristics of photovoltaic modules

PV modules generally have 3 temperature coefficients: open circuit voltage, short circuit current, and peak power. When the temperature rises, the output power of PV module will drop. The market mainstream crystalline silicon photovoltaic module peak temperature coefficient is about -0.38 ~ 0.44% / ℃, that is, the temperature increases, the PV module power generation decreases, theoretically is the temperature increases per degree, power generation is reduced by about 0.38%.

Simulated data for reference only: the current, voltage and power output curve of the same crystalline silicon solar cell at 5-85°C]

It is worth noting that as the temperature rises, the short-circuit current is almost unchanged, while the open-circuit voltage is reduced, indicating that the ambient temperature will directly affect the output voltage of the PV module.

The above graph shows the results of the simulated data. It is obvious that when the operating temperature is at 85°C, the efficiency is reduced by 22% compared to the standard temperature of 25°C. It shows that it is especially important to reduce the ambient temperature and increase the module ventilation and heat dissipation in the actual use.

2. Aging decay

In long-term practical application, the modules will show slow power decay. As can be seen from the following two graphs, the maximum value of attenuation in the first year is about 3%, and the rate of attenuation in the next 24 years is about 0.7% per year. From this calculation, the actual power of the PV module after 25 years can still reach about 80% of the initial power.

And aging decay mainly due to two categories.

1) The attenuation caused by the aging of the cell itself, mainly affected by the cell type and cell production process.

2) Decay caused by aging of the packaging material, mainly affected by the module production process, packaging materials and the use of the environment. UV irradiation is an important reason for the degradation of the main material. Long-term UV irradiation makes EVA and backsheet (TPE structure) aging and yellowing phenomenon, leading to module transmittance decline, thus causing power decline. In addition, cracking, hot spot, sand wear and tear are common factors that accelerate module power degradation.

This requires module manufacturers to strictly control the selection of EVA and backsheet to reduce the module power attenuation caused by the aging of auxiliary materials. As one of the first companies in the industry to solve the problems of photovoltaic attenuation, photovoltaic high temperature attenuation and potential induced attenuation, Hanwha New Energy has won wide recognition from customers mainly by virtue of its Q.ANTUM technology of anti-PID, anti-LID and anti-LeTID, hot spot protection, quality tracking Tra.QTM, which is a fourfold power generation guarantee.

3.Module initial photovoltaic attenuation

The initial photovoltaic attenuation of the module, i.e., the output power of the PV module decreases substantially in the first few days of use, but then stabilizes, and the degree of photovoltaic attenuation varies among different types of cells.

In P-type (boron-doped) crystalline silicon (mono/polycrystalline) wafers, light or current injection leads to the formation of boron-oxygen complexes in the wafers, which reduces the oligon lifetime and thus makes some photogenerated carriers compound, reducing the cell efficiency and causing photogenic attenuation.

And amorphous silicon solar cells in the initial use of half a year, the photoelectric conversion efficiency will drop significantly, and eventually stabilize at about 70% to 85% of the initial conversion efficiency.

4. Dust shading

Large photovoltaic power plants are generally built in the Gobi region, sandy winds, less precipitation, while the frequency of cleaning will not be too high, after long use, can cause efficiency loss of about 8%.

5. Component series mismatch

The mismatch of components in series can be explained by the image of the barrel effect. The water capacity of the barrel is limited by the shortest board; and the PV module output current is limited by the lowest current in the series-connected components. In fact, there is a certain power deviation between modules, so the mismatch of modules will cause a certain power loss.

What is the relationship between module power and what equipment and how should it be designed? In the PV grid-connected system, the power of the module and the inverter are related, and the power matching of the module and inverter is not a fixed ratio of 1:1, but needs to be considered in conjunction with the specific conditions of the project. The main influencing factors are irradiance, system loss, inverter efficiency, inverter life, inverter voltage range, module installation angle and other aspects.

1, component installation tilt angle and orientation angle

When the plane of the object and the light is completely perpendicular, the power received is the maximum. If the object is placed at an angle, the plane of the object and the light are at a certain angle, the power received will be discounted, and the power received will be much less for the same area, and the power is maximum when the angle of the module and the sun are perpendicular.

2、Irradiance of the installation area

The output power of the module and irradiance related. Solar energy resources in good areas, due to clear days with few clouds, good air quality, high atmospheric transparency, the sun's radiation reaching the surface of the module is much higher than the average value of poor resources.

3, installation altitude

The higher the altitude, the thinner the air, the weaker the atmosphere on the solar radiation, the stronger the solar radiation reaching the ground. For example, the Qinghai-Tibet Plateau is the strongest area of solar radiation in China. And the thinner the air is, the worse the inverter heat dissipation is, and the altitude exceeds a certain height, the inverter should be derated to run.

4、DC side system efficiency

Photovoltaic system, energy from solar radiation to photovoltaic modules, through the DC cable, converter box, DC distribution to reach the inverter, in which each link has losses,. Different design solutions, such as the use of centralized, string, decentralized and other programs, DC-side losses are very different.

5、Inverter cooling conditions

The inverter should generally be installed in a well-ventilated place to avoid direct sunlight, which is conducive to heat dissipation. If, due to site constraints, the inverter has to be installed in a closed place that is not conducive to heat dissipation, we should consider the derating problem of the inverter and allocate fewer components.

6, component factors

Power positive tolerance: in order to meet the PV module attenuation of 25 years not more than 20%, many component factories have 0-5% positive tolerance for components just leaving the factory, such as 265W components, just leaving the factory the actual power may have 270W.

Negative temperature coefficient: The power temperature system of the module is about -0.41%/°C. The power of the module will rise when the temperature of the module drops. A 250W module, without considering the equipment loss, in the best sunny areas of China, such as northern Ningxia, northern Gansu, southern Xinjiang, etc., it is possible that the maximum output power may exceed 250W.

Double-sided modules: Double-sided modules can not only receive the radiation power of sunlight on the front side, but also receive the reflected radiation power of sunlight on the back side. Different objects, in different spectral bands, have different reflectivity of sunlight. Snow, wetland, wheat, desert, different features in the same band its reflectivity is different, the same feature in different bands reflectivity is also different

7、Inverter factor

Inverter efficiency: the efficiency of the inverter is not a constant value, there are power switching device losses and magnetic losses, at low power, the efficiency is relatively low, in 40% to 60% power, the efficiency is the highest, more than 60%, the efficiency gradually decreases. Therefore, the total power of PV power should be controlled between 40% and 60% of the inverter power to obtain the best efficiency.

Inverter life: PV inverter is an electronic product, its reliability and inverter operating temperature has a lot to do with it, where capacitors, fans, relays and other components temperature increase by 10 ℃, the failure rate can be increased by more than 50%. And the operating temperature is related to the power, according to statistics, the inverter long-term work in power 80-100% than power 40-60%, life expectancy is about 20% lower.

The best operating voltage range of the inverter: working voltage around the rated operating voltage of the inverter, the highest efficiency, single-phase 220V inverter, the inverter input rated voltage of 360V, three-phase 380V inverter, the inverter input rated voltage of 650V.

Conclusion

In some places, the PV system is based on the capacity of the module to calculate the system capacity, this time according to the actual maximum power output of the module to select the inverter, so as to avoid inverter current limit, according to the actual situation, the module and inverter can be 0.9:1 to 1.4:1 to configure. However, in some places, the system capacity is calculated according to the inverter AC output power. If the selling price of electricity is high and the module price is quite cheap, the power of the module can be increased in order to increase the power generation as much as possible. Modules and inverters can be configured from 1.4:4 to 1.8:1, depending on how many modules the inverter can connect.

Photovoltaic modules have polycrystalline silicon, monocrystalline silicon, thin film three technical routes, various technologies have advantages and disadvantages, under the same conditions, the efficiency of the photovoltaic system is only related to the nominal power of the components, and the efficiency of the components are not directly related, the components technology is mature, domestic first- and second-tier brands of component manufacturers are more reliable quality. PV modules have 60 cells and 72 cells, distributed PV is generally small-scale, difficult to install, so it is recommended to use 60 cells components, small size and light weight easy to install.

Monocrystalline and polycrystalline power generation, in recent years the debate is very intense, but for the average user, the significance is not significant, the current level of PV system efficiency between 75% and 90%, and the difference between single polycrystalline power generation within 2%, less than the error of detection, many manufacturers are doing both monocrystalline and polycrystalline, choose the right manufacturer than choose the right single polycrystalline more important, users need to choose from reliable channels to buy, there are also many second-hand components on the market, pay special attention.

If the customer wants to install a larger capacity, it is recommended to choose monocrystalline high-efficiency modules, because the technical route is different, the same area, monocrystalline modules will generally be 5-10W higher than polycrystalline modules.

Budget certain, customers who wish to install more power generation, it is recommended to choose polycrystalline low efficiency components, this low efficiency components, not low power generation efficiency, may be the high efficiency components in earlier years were not sold, but the quality is still very good, if it is the manufacturer to clear the inventory, the price will be lower than normal components, but these components will not affect the power generation.

If the owner's roof does not carry enough load, it is recommended to install CIGS flexible thin film modules, which are light in weight and easy to install.

If it is a sunroom and needs light transmission, it is recommended to install CdTe CdTe thin film modules, which can be selected according to the actual situation with different light transmission performance.

The battery capacity is determined according to the user's power consumption or desired standby time.

The task of the battery is to ensure the normal power consumption of the system load when the amount of solar radiation is insufficient. For important loads, to be able to ensure the normal operation of the system within a few days, the number of consecutive cloudy days should be considered. For general loads such as solar street lights can be selected within 2 to 3 days based on experience or need. Important loads such as communication, navigation, hospital rescue, etc. are selected within 3 to 7 days. Also consider the installation location of photovoltaic power generation system, if in a remote location, the battery capacity should be designed to be larger, because it takes a long time for maintenance personnel to reach the site. In practice, some mobile communication base stations due to high mountains and far away, it is very inconvenient to go once, in addition to the configuration of the normal battery pack, but also equipped with a set of backup battery pack, for the general poor families, the main consideration price, then do not have to consider the rainy days, the sun is good when more use. When the sun is bad less use, no sun is not used. When choosing the load, try to use energy-saving equipment, such as LED lights, inverter air conditioners. The design of battery mainly includes the design calculation of battery capacity and the design of series-parallel combination of battery pack.

In the photovoltaic power generation system, most of the batteries used are lead-acid batteries, taking into account the life of the battery, generally take the depth of discharge is between 0.5-0.7. Battery design capacity = (load average daily power consumption * number of consecutive cloudy days) / battery discharge depth.

Battery charging current is generally 0.1C-0.2C, the maximum does not exceed 0.3C, for example, 1 lead-acid battery 12V200AH, charging current is generally between 20A and 40A, the maximum can not exceed 60A; battery discharge current is generally 0.2C-0.5C, the maximum does not exceed 1C, 1 12V200AH lead-acid battery, the maximum output power does not exceed 2400W, different manufacturers, different models, the specific value is not the same, the design should ask the manufacturer for instructions.

Different application scenarios have different battery design ideas. There are three main common normal application scenarios: self-generation (higher electricity costs or no subsidies), peak and valley tariffs, and backup power (grid instability or important loads).

Self-generation: choose to select the capacity of the battery based on the average daily household electricity consumption (kWh) (default PV system is energy sufficient)

Peak and Valley Tariff: Calculate the maximum demand value of the battery capacity based on the total electricity consumption during the peak period. Then find an optimal battery capacity within that interval based on the capacity of the PV system and the benefits of the investment.

Standby power: where the total power used when off-grid and the expected time off-grid are the most critical parameters. Based on the maximum power and electricity consumption of the power-using load during the longest continuous power outage hours throughout the day, the battery capacity needed is finally determined.

PV+Storage Application Scenario

Photovoltaic + energy storage has become a very common way of utilization in foreign countries, and there are many kinds of application scenarios, the following describes several application scenarios of energy storage.

1. Microgrid

Small-scale power generation and distribution system consisting of distributed power supply, energy storage device, energy conversion device, load, monitoring and protection device, etc. is the main application of energy storage system in China at present.

2.New Energy Vehicle Charging Station

The development of new energy vehicles is inseparable from the construction of charging infrastructure, and setting up supporting energy storage facilities is conducive to improving the quality of local power grid and increasing the selectivity of charging station sites.

3. Diesel-powered areas

Energy storage technology can replace diesel generators, reduce the cost of power generation, and at the same time reduce the air and noise pollution caused by diesel generators.

4.Trading with renewable energy plants

Energy storage systems participate in the paid peaking auxiliary service of electricity, thus helping to make up for the shortage of power supply peaking capacity.

The warm days of spring have come, for PV users, the peak of power generation is also coming, today small benefit would like to talk with you about some general knowledge of the installation, operation and maintenance of PV systems.

1. photovoltaic modules on the shadow of the house, leaves and even bird droppings will have an impact on the power generation system?

A: The shaded photovoltaic cells will be consumed as a load, the energy generated by other unshaded cells, when the shaded cells will be hot, easy to form the hot spot effect. This reduces the power generation of the PV system, and even burns the PV module in serious cases.

2. In rainy or foggy weather, will the PV module still work? Will there be insufficient power or power failure?

A: The sun irradiance is low on rainy or hazy days, but the PV module still generates electricity under low light. As long as the working condition of the PV module reaches the start condition of the inverter, the PV power system will work normally. When the distributed grid-connected PV system is not working, the load is automatically powered by the grid, so there is no problem of power shortage and power failure.

3. winter when it is cold will not be insufficient power?

A: The factors that directly affect the power generation is the irradiation intensity, sunshine duration and the working temperature of the PV module, the irradiation intensity will be weaker in winter, the sunshine duration will be shorter, so the power generation will be reduced compared with the summer. But the distributed photovoltaic power generation system will be connected to the grid, as long as the grid has electricity, the household load will not have a power shortage and power outages.

4. Do I need to disconnect the PV system during a thunderstorm?

A: Distributed photovoltaic power generation systems are equipped with lightning protection devices, so no need to disconnect. For safety and insurance, it is recommended that you can choose to disconnect the circuit breaker switch of the sink box to cut off the circuit connection with the PV module, so as to avoid the lightning protection module cannot remove the harm caused by direct lightning. Operations and maintenance personnel should promptly test the performance of the lightning protection module to avoid the harm caused by the failure of the lightning protection module.

5. home installation system lightning protection only module bezel grounding lightning protection?

A: DC side of the module bezel grounded, in the case of a higher installation to join the DC surge protector, in addition, the AC side is also required to add AC surge protector.

6. how to clean photovoltaic modules?

A: Rainwater can be cleaned, no special maintenance is required. If you encounter adhering dirt, you can simply wipe with a soft cloth and water. It is recommended to use a soft brush and clean and mild water to clean the glass surface of the PV module, and to use less force when cleaning to avoid damaging the glass surface.

7. Is there any danger of electric shock when wiping with water?

A: There is no danger when wiping with water, the PV power system and the modules are protected by insulation and grounding. However, in order to avoid electric shock and possible damage to the modules when wiping them under high temperature and strong light, it is recommended to do the module cleaning in the morning or late afternoon.

8. Do I need to clean the PV modules after snow? How to clean?

A: When heavy snow accumulates on the module after snow, it needs to be cleaned manually. You can use soft objects to push the snow down, and be careful not to scratch the glass.

9. Can I step on top of the module to clean it?

A: The modules have a certain load capacity, but you cannot step on them to clean them, as it will cause hidden cracks and damage to the modules and affect their power generation and service life.

In general, strictly comply with the manual of each component of the system, and regular inspection and cleaning maintenance of the PV system, power generation will rise!