Factors Affecting the Performance of Solar Power Systems

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As mentioned in previous chapters, shading is a major problem with solar power system performance. In particular, if these obstacles are not carefully calculated, they will greatly affect the electricity output of solar power EPC general contractor projects .

That means, if you have “shade” due to, for example, a distant building shading a large area of ​​the panel array, the output voltage of the entire string will DECREASE SIGNIFICANTLY, similar to a cloudy day.

Therefore, the unit implementing the solar power project needs to survey the area where the solar power system is installed to come up with a solution to this problem, helping to optimize the system’s performance.

So first, let’s learn about common types of obstacles in solar power projects

Obstacles affect solar power system performance

Obstacles that affect solar power system performance can be divided into two types: shade and hidden shade.

  • Shadows are caused by obstacles that are relatively far away. Shadows are scattered or diffuse, reducing the amount of light reaching the photovoltaic cells. Tree shade is often considered shade.
  • A shade is an obstacle that completely covers or prevents sunlight from reaching the photovoltaic cell. Birds, fallen leaves, and tree branches falling on the glass panel are considered shadows.

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If the solar panel system  is in the shade , you will see a clear decrease in power output, the entire panel array only produces the same level of power as on a cloudy day.

If the solar panel system is covered by shade , the area output of the entire panel array will decrease to the extent that the photovoltaic cells are covered; If these cells are completely shaded, you may see a drastic reduction in electrical capacity, or even almost zero (depending on the level of shade tolerance of the panels). If the cells are only partially shielded, power output will be noticeably reduced.

Pay attention when designing to avoid obstacles that affect the performance of the solar power system

If solar system shading cannot be avoided , the solution would be to design the system with an acceptable shading tolerance. In other words, you must design the system in such a way that the effect of shading on any part of the system is minimal on the entire panel array.

Designing panel arrays with shading tolerances is a complex job, requiring a high level of expertise. However, it is possible to design a basic solar system with a reasonable level of shading without requiring in-depth knowledge.

Loss of power generation efficiency of solar power system when shaded for one hour during the main time (9-15 hours) every day 

Shaded period

Loss in winter (%)Losses in summer (%)

9 – 10 am 


10 – 11 am 


11 – 12 noon 



12 noon – 1pm 27


13 – 14 pm 15


14 – 15 pm 



If you design a system capable of continuous and stable operation in partially shaded conditions, here are a few options:

Keep an eye on shading

First of all, you should not design a system with some parts covered by shadows. Solar panels are installed so that they are not under trees, making it easy to check and clean, and remove hidden shadows, if any. If there are permanent obstructions that can create shadows, you should not install solar panels in those locations.

If there is shade, you need to know how much of the day this shade takes up. Remember, even shade on a small area can have a big impact. In general, the time when the solar power system reaches its maximum capacity during the summer is from 9 am to 3 pm (15 hours). If there is shade before or after this time, you will lose about 20% of your electricity output during the summer, and up to 40% if there is shade both before and after this time.

In winter, the decline will not be as great. Because the sun is slightly lower in the sky and its intensity is also reduced, almost all the electricity is generated during the prime time period (9 a.m. to 3 p.m.). If there is shade before 9 a.m. or after 3 p.m. during the winter months, electricity loss is only about 5 – 10%.

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However, if there is shade during the main period, the system’s power generation efficiency will decrease significantly. The degree of performance degradation of a solar energy system depends on the location, the severity of shading, and the type of solar panel used. The generation efficiency loss during one hour of shade, during the prime time period (9 a.m. to 3 p.m.) is listed in Appendix Table A.

The values ​​stated in this Table are for reference only, exact values ​​depend on geographical area, weather and climate conditions…

From the data in the Table, it can be seen that the level of performance loss due to shading in the range of 9-15 hours is quite large. This explains why shade around noon is the number one reason for reducing the power output of a solar energy system.

However, because it is very difficult to influence or reduce shading (trees, surrounding buildings, etc.), you can apply a few other measures to reduce the effect of shading.

Increase the number of solar batteries

This option is almost obvious. If you have enough space, you can increase the number of solar panels to increase power output during shade periods.

But this measure is not always feasible, due to lack of space, or simply insufficient funding, and is not necessarily the most effective solution.

Orientation of solar batteries

If shading is only effective during certain times of the day, you may consider rotating or orienting the panels away from the obstruction. This will increase performance during the hours when the panel is not covered by obstructions, and reduce or eliminate the impact of obstructions in previous locations. The reduction in power output due to orienting panels away from true south is usually less than the impact of shading, if the shading problem can be completely eliminated.

Choose the appropriate solar battery type

The next solution is to choose amorphous (thin film) solar panels. Panels and shapes do not appear. The photovoltaic cell’s shape is reversed in the same way as a provincial panel, so it can withstand peeling better.

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Due to the low efficiency level of amorphous solar panels, you are likely to need twice as much space for installation as compared to crystalline panels. If you have a large space, using amorphous panels is the simplest and most economical solution for independent solar power systems.

Currently, Sharp, Mitsubishi, Solar Frontier, and Sanyo are manufacturing high quality and highly reliable amorphous solar panels.

Use microinverters

If your system is grid-connected, perhaps the best solution is to use microinverters, each panel has its own inverter and can be considered a complete solar power system.

With the microinverter system, each panel will operate completely independently of each other. If a shadow affects one panel, the other panels will not be affected.

Using microinverters also means you can rotate the solar panels to different sides. For example, if installing panels on a roof with many different slopes and angles, you can choose to install the panel array on several L sections of the roof, using a microinverter system.

This method offers a relatively high degree of flexibility in terms of orientation and location choices, and may even allow you to avoid shadows altogether.

Parallel solar cell array design

By wiring panels in parallel instead of in series, you can reduce the effect of shading on some parts of the panel array. In a parallel system, when one solar panel is in the shade, the capacity of the remaining panels is completely unaffected.

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If you design a grid-connected solar system and want high voltage, this can be achieved with a parallel panel array by using specialized high-voltage solar panels connected to the electrolytic grid. coordinate. Currently, many manufacturers have provided panels of this type, even one panel with a voltage of over 100V. Other commonly used panels have output voltages of 24V or 48V, which may be suitable for independent solar power systems that require voltages higher than 12V.

Design of multi-branch solar panel array

Instead of designing a system consisting of just one set of panels connected in series, you can design a system consisting of two or more panel branches connected in series, and these branches are connected in parallel with each other. There are controllers and inverters available that allow you to have multiple solar panel branches, or you can have a controller or inverter for each individual branch.

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This means you have two or more small solar power systems, instead of one large system; You can rotate the panel arrays to face different angles, creating the opportunity to install them in completely different positions, depending on the specific conditions.

In that situation, you can design the system so that shading only affects one of the panel branches, instead of the entire solar membrane. Similar to the system using inverters, this method can help you completely solve the shading problem.

Options for installation

In reality there are other options, but the design is relatively complex and belongs to a highly specialized field. If you are designing your solar system with shading tolerances and the above options do not work for you, you may need to turn to experts in the field.

Except for shading problems that are relatively complex and difficult to solve, using one of the above options or a combination of them can still help you deal with the problem effectively.


Obstructions are a big problem with solar energy systems – especially if using crystalline panels. Even very little shading can have a big impact on the performance of a solar power system. In cases where it is difficult to solve the shading problem, you can ask experts or have to find other solutions instead of solar energy.