Photovoltaic Inverters: Important Features Forgotten

For photovoltaic power plants, PV modules and inverters are undoubtedly the core equipment. The  panels convert sunlight into electrical energy. The inverter turns DC into AC and can be connected to the grid.

The industry has clearly understood the energy conversion function of the inverter. It is undoubtedly the efficiency index that determines the inverter conversion quality. The industry generally has this understanding: the DC output power is determined after the component is selected, and the AC output power of the system is also determined after the inverter is selected.The inverter efficiency parameters of each manufacturer is almost the same (the highest efficiency is about 98.7%, the European efficiency is about 98.4%), then the main factor determining the system efficiency is the cells,it doesn’t matter which inverter to choose.

Is this really the case? We look at the test data of an inverter test platform built by an institution in Hainan. The installation angles and orientations of components, brackets, and components are all the same. Six inverters are selected to actually test the power generation. Some data has reached 6% difference. Is the efficiency parameter given by the inverter manufacturer such a large amount of water? Actually not, if we take the power analyzer to measure the DC input and AC output power of the inverter separately, we will find that although the inverter conversion efficiency is not necessarily claimed High, but the efficiency of the two inverters is not much different, all below 1%. Can it be explained by the difference in DC power of the panel? For example, if there is a set of panels, there is a quality problem that causes a significant drop in output power, but when we just exchange the inverter, we will find that the original power generation after switching the inverter is high. It still generates a high amount of power, which means that it is not a problem determined by the difference in the component array itself.

Where is the problem? To understand this problem, we must first review the basic characteristics of the panel and the working principle of the inverter MPPT.

From the above figure, an important working characteristic of the component can be seen: the output power of the component is determined by the working voltage relationship, that is, the maximum power point of the component output power, and the voltage deviating from the maximum power point is too low or high, which will cause the output power of the component to decrease. That is to say, if the actual operating voltage of the components in a power station system deviates from its maximum power voltage, then the output power of the PV module array will decrease, which will result in a reduction in the power generation of the power station.

Then how is the working voltage of the component determined? This is the working principle of the MPPT tracking of the inverter. The inverter can adjust its input DC voltage, and the DC input of the inverter is directly connected to the positive and negative components of the component. At this time, the inverter detects an increase or decrease of the DC input voltage by detecting a change in the output power, and is finally relatively stable near the maximum power voltage value of the component.

In the power station system, whether the PV module works in the best state and how much capacity can be exerted is not determined by itself, but by the inverter, and the working voltage has a great influence on the power output of the component. %the above. It can be seen that in addition to the energy conversion function, the inverter has a more important function: the control of the power station system. Moreover, for the power generation capacity of the power station, the inverter conversion efficiency may affect the power generation by 0.5~1%, and the control of the inverter system will affect the power generation capacity of the power plant by 5~10%, 10 times the impact of its own efficiency. .

Therefore, as the owner of the power station purchases the inverter, in addition to looking at the inverter’s own conversion efficiency, it also needs to pay more attention to the control capability of the power station system. The difference in power generation caused by the system control capability is far greater than the efficiency difference of the inverter itself. Much bigger. Among the current common inverter types, the string inverter has multi-channel MPPT characteristics, which is more precise and accurate in the control function of the power station system, and can often bring high power generation. It is the preferred inverter type for power plant owners. .

Your photovoltaic power station has less revenue, and it may be that these points are not done well!

  1. Photovoltaic panel ash

For long-running photovoltaic power generation systems, the impact of panel dust can not be underestimated. The dust on the surface of the panel has the function of reflecting, scattering and absorbing solar radiation, which can reduce the transmittance of the sun, reduce the solar radiation received by the panel, and reduce the output power. The effect is proportional to the cumulative thickness of the dust.

In addition, because the dust absorbs solar radiation, the photovoltaic panel can be heated, and the dust contains some corrosive chemical components, which also reduces the photoelectric conversion efficiency.

In the low rain period, the cell efficiency loss can reach more than 15% due to the accumulated dirt on the panel surface. Dirt and dust on the surface of the panel can reduce annual average power generation efficiency by 6%. In general, dust and dirt in the air include: dust, rain, and pollutants, and their presence causes a decrease in the output energy of the cell. Because dust particles have a large impact on the forward scattering of sunlight, the current loss of such centralized modules is usually much higher than that of decentralized ones.

At the same time, other parts of the photovoltaic panel will also be corroded by wet dust, such as joints, brackets, etc., the materials are mostly various types of metals, which may cause damage and safety after corrosion, which may be due to strong winds, earthquakes, etc. Natural factors are destroyed and the life of photovoltaic panels is reduced.

  1. Photovoltaic components are shaded

Shadow is the most taboo problem of photovoltaic power plants. Pay attention to design and installation, and pay attention to later operation and maintenance. Common shadows mainly include bird droppings, dust, shade, buildings, deciduous branches, etc…

Therefore, first of all, it is necessary to do the landmark survey work. You can choose the right location to install the PV modules. Try not to install the components in the sheltered place. In the unavoidable situation, choose a suitable component placement method to reduce the shadows and block the shadows. Impact. In the daily operation and maintenance process, it is more important to pay attention to the cleaning of photovoltaic modules and timely clean up foreign objects such as ash.

  1. Hot spot loss of photovoltaic components

Speaking of the hot spot effect, many people are puzzled… but the problems hidden in it, the adverse effects of the lack of efficiency of photovoltaic modules can not be underestimated!

What is the “hot spot effect”? Under certain conditions, a solar cell component that is shielded in a series branch will be used as a load to consume energy from other illuminated solar cell components. The shaded solar cell component will heat up at this time, which is the hot spot effect.

The hot spot effect severely destroys the solar cell itself to some extent, and part of the energy generated by the illuminated solar cell may be consumed by the shielded cell. In addition, long-term untimely cleaning has a great impact on the service life of PV modules. Serious conditions are also the source of fire. The hot spot effect of photovoltaic power plants will directly lead to a 30% reduction in the service life of PV modules, which may cause component failure in the long run.

As a photovoltaic person, since the installation of photovoltaic power station, it is essential to develop scientific operation and maintenance habits, and master the scientific operation and maintenance methods. In view of the above-mentioned common problems of photovoltaic power plants, the small box will of course let everyone know the solution!

PV module operation and maintenance knowledge

  1. Photovoltaic component dust removal:

At present, some photovoltaic power generation systems rely on natural effects such as rainfall and wind to remove the ash from photovoltaic panels. Some small photovoltaic power plants use manual cleaning methods, which are usually cleaned with a mop, rubber scraper or a soft rag.

Large and medium-sized photovoltaic power plants are difficult to clean manually, and mechanical cleaning is generally used. The high-pressure water gun is cleaned, and the water is pressurized to form a water vapor mixture. The dust on the surface of the photovoltaic panel is cleaned and the cleaning effect is good, so it is widely used in many photovoltaic power stations. In addition, there is a mechanical dust removal technology, which uses a mechanical brush combined with a water spray to wash the automatic dust removal device of the photovoltaic panel, and the dust is swept away by mechanical force.

  1. Photovoltaic components avoid shadow occlusion:

Before the construction of photovoltaic power station, it is necessary to do a good job of preliminary exploration to determine whether there will be occlusion of surrounding high-voltage lines, railings, vegetation, existing buildings (planned buildings should be expected as early), to find ways to eliminate occlusion and change the installation location. .

Some people always think about what can be done for the power station, such as installing a fence, in order to drive the bird frame to drive the bird, this is a kind and positive move, but there is a counter-effect of “drawing the snake”, and some people lack the photovoltaic operation. Dimensional knowledge, in the photovoltaic components drying clothes, vegetables and other wrong practices, these behaviors will invisibly block the power station.

  1. Photovoltaic components to avoid hot spot effects:

In order to avoid this factor, the performance of the PV module is reduced. This requires the construction project department to do the technical work before the construction, and strengthen the inspection of the project quality during the construction process. Only in this way can the situation be prevented from affecting the life of the component.

The measures in the production section of the module include: controlling the reverse current of the cell, controlling the impurities inside the cell, and using parallel diode protection for the components.

The measures on the application side include: using a cell (or component) with good performance consistency, ensuring that the components are not blocked during installation, and cleaning and cleaning in time when there is contamination, so that the photovoltaic system maintains good power output.

How to Maintain Photovoltaic Power Plant Equipment

Important equipment maintenance check

According to the current equipment maintenance, the maintenance requirements of PV modules and combiner boxes are relatively large, and daily defects are concentrated on these two types of equipment. Some common abnormalities, such as component damage, MC4 plug overheating damage, busbar communication board damage, branch circuit fuse, branch cable grounding, etc., we must be targeted technical treatment, otherwise it will develop into equipment failure, it will Seriously affect power generation efficiency and cause more accidents.

Confluence box maintenance

For the combiner box, we must first know how to judge the health of the equipment through the monitoring system and analyze whether the change of the data is within the normal interval. The warning of the system is generated after the abnormality of the fault occurs. Our maintenance work needs to be in advance to determine the possibility of error before the abnormal warning, and go to the maintenance adjustment in time.
Check the branch current and insurance status. If there is zero current, you need to check if you want to replace the insurance.
Reinforce the string MC4 plug to determine if there is any heat. If it is, in order to avoid the plug burning, you need to replace the plug.
Check whether the bypass cable is complete and clean the foreign objects around the cable. For example, if the voltage of one pole to ground is zero or a small fixed value in the open state, the grounding pole should be twisted and the damaged insulation layer should be repaired in time. .
Check whether the input and output terminals of the combiner box are blackened and blackened, and the terminal and cable head should be replaced in time for serious aging.
Clean the dust and deposits on the inner wall of the combiner box, check whether the base is hot and discolored, especially the newly put into operation, pay special attention to the heat, clean and reinforce the related heat dissipation facilities.

Component maintenance

Check and reinforce the various wiring and fixtures between the components and brackets. Inspect and clean the surface of the component for damage and hot spots.
Check all components, cables, electrical equipment and grounding, clean the outside of the insulation, replace the new cable segments with signs of aging, or seal them with insulating tape.
In the case that the corrosion degree of the support is light and does not affect the stability of the support, the rust-removed part is subjected to rust removal treatment, and the rust-proof layer is re-sprayed. If the degree of corrosion affects the stability of the installation, the patch is welded and reinforced or replaced. Inverter maintenance
Compared with the components and the combiner box, the inverter has a complicated structure, many components, complicated working principle, relatively poor reliability, and more complicated maintenance work.
Daily records closely observe operating data such as voltage and current. Most of the potential problems are intuitively feedback at the data level, and there are certain differences in the different component families that need to be considered.
For each maintenance and cleaning, pay attention to the condition of the exhaust system of the inverter facility, and clean and reinforce the interface cable of the exhaust facility. If there is abnormal exhaust, it should be dealt with immediately if there is any problem with the operation of the inverter.

Tips to solve the problem of perovskite solar cells

Thanks to new manufacturing methods, scientists have achieved more than 15% energy conversion on perovskite-type solar cells larger than one square centimeter.

Researchers report that perovskite-type batteries are more than 20% efficient and comparable to traditional silicon cells. But those high-efficiency perovskite batteries are only one-tenth of a square centimeter and are only suitable for laboratory testing, if used when solar panels are too small.

According to NitinPadture, a professor of engineering at Brown University, it is a real improvement to improve the efficiency of a battery of more than one square centimeter by 15%.

Padture says how to maintain high efficiency in larger perovskite batteries has proven to be a challenge, “The problem with perovskites is that when you try to make larger solar films with traditional methods, low efficiency defects It will be exposed.”

The previous manufacturing process of the perovskite battery was established by Zhou Yuanyuan, a graduate student at Padture Labs (not found in the original name, using transliteration, the same below). The perovskite precursor dissolved in a solvent and then precipitated on the substrate. The substrate is then immersed in a second solvent (referred to as an anti-solvent) which selectively dissolves the solvent of the precursor, leaving the ultra-smooth film produced by the perovskite crystals.

The new study, published in the Journal of Advanced Materials, Zhou Yuanyuan (transliteration) and the National Renewable Energy Laboratory postdoctoral researcher Yang Mengjin (transliteration), through a small technique to find ways to increase the size of perovskite crystals. The method is to add an excess of organic precursor, stick to small perovskite crystals, expand them by heating, and treat excess organic precursors by heat treatment.

“The solvent method ensures complete coverage and uniformity,” says Padture. “By covering, we increased the size of the crystal, which allowed us to produce films with fewer defects and higher efficiency.”

A 15% efficiency in this latest product is a good start, Padture said, but there is still room for improvement. Researchers using this or similar methods will eventually hopefully achieve a 20% to 25% efficiency for large batteries.

Causes and analysis of common phenomena in the lamination process of polycrystalline components

The following are some of the problems that are often encountered in actual production.

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1. There are fragments in the component.

2. There are bubbles in the assembly.

3. There are hair and garbage in the assembly.

4. The bus bar is bent inward.

5. The back film of the component is uneven.

problem analysis

First, there are fragments in the assembly, which may cause: 1. Since there is no welding flatness during the welding process, there is a pile of tin or tin slag, and the battery piece is crushed when vacuuming.

2, the original battery has been a dark injury, coupled with premature lamination, EVA also has a very good fluidity.

3. When the component is lifted, the gesture is unreasonable and the hands are pressed to the battery.

Second, there are bubbles in the components, the possible causes: 1, EVA has been cut, placed too long, it has absorbed moisture.

2. The EVA material itself is not pure.

3, the vacuum is too short, the pressure can not drive out the bubble.

4. The pressure of lamination is not enough.

5, the temperature of the heating plate is uneven, so that the local curing in advance.

6. The lamination time is too long or the temperature is too high, so that the organic peroxide is decomposed and oxygen is produced.

7. There is a foreign matter, and the wetting angle is greater than 90°, so that there is gas next to the foreign object.

Third, the components have hair and garbage, may cause: 1, due to EVA, DNP, small cars have static electricity, the floating hair, dust and some small garbage to the surface.

2, when stacked, the body works above the components, but not some small flying insects die in the assembly.

Fourth, the bus bar is bent inward, which may cause: 1. In the lamination, the bus bar position will gather more gas. The rubber sheet is pressed down to press the gas out of the assembly, and the part of the gap is filled by the EVA which is more fluid. This flow of EVA bends the original straight bus bar.

2. The contraction of EVA.

Fifth, the back film of the component is uneven, which may cause: 1. The excess EVA will stick to the high temperature cloth and the rubber board.

problem solved

1. There are fragments in the assembly: 1. First, the welding quality should be checked in the welding area, and some needles should be made for the employees.

Sexual training allows the weld to be formed at one time.

2. Adjust the lamination process, increase the vacuuming time, and reduce the lamination pressure (adjusted by lamination time).

3. Control all the links and optimize the gesture of the laminate personnel.

2, there are bubbles in the component: 1, control the number of EVA used every day, let each employee understand the daily production tasks.

2, the material is determined by the manufacturer, so try to choose a better material.

3. Adjust the lamination process parameters to make the vacuuming time appropriate.

4. Increase the lamination pressure. (Adjustable by lamination time or by laminating a high temperature cloth.

5, pad high temperature cloth, so that the components are evenly heated. (The maximum temperature difference is less than 4°).

6. According to the parameters provided by the manufacturer, determine the total time of lamination to avoid too long.

7, should pay attention to 6S management, especially in the lamination process, try to avoid the fall of foreign bodies.

3, the components have hair and garbage: 1, do a good 6S management, keep the surrounding working environment clean, and work laundry pants to do personal hygiene.

2. Adjust the process, optimize the operation of the lamination process, and change the single-handed material to double.

3, control channel, install mosquito killer lights, reduce the entry of small flying insects.

4. The bus bar is bent inward: 1. Adjust the lamination process parameters to lengthen the vacuuming time and reduce the lamination pressure.

2. Choose a better material.

5, the component back film unevenness: 1, buy a better rubber sheet.

2. Do a good job of cleaning the high temperature cloth every time, and clean the residual EVA on the rubber board in time.