Application of Pultruded Beam Slab in Wind Power and its Future Development Direction

 

Industry Prospects

According to data released by the National Energy Administration, as of the end of June 2021, the installed capacity of renewable energy power generation in China reached 971 million kilowatts, of which hydropower installed capacity was 378 million kilowatts, wind power installed capacity was 292 million kilowatts, photovoltaic power generation installed capacity was 268 million kilowatts, and biomass power generation installed capacity was 33.19 million kilowatts.

 

From January to June 2021, the country’s new grid-connected wind power installed capacity was 10.84 million kilowatts, of which 8.694 million kilowatts were added on land and 2.146 million kilowatts were added at sea. As of the end of June 2021, the country’s cumulative installed capacity of wind power was 292 million kilowatts, of which 281 million kilowatts were installed on land and 11.134 million kilowatts were installed at sea.

 

Judging from the data, the overall momentum of wind power development is good. In 2021, wind power entered the era of parity. Many people expected that wind power would decline overall this year, but after a buffer in the first half of the year, wind power development is now gradually recovering.

 

 

Of course, we should not only see the positive development trend of wind power, but also the challenges that the era of wind power parity brings to the development of the industry. With the advent of the era of parity, we should learn from the development of other new energy sources such as photovoltaics.

 

At present, the cost of photovoltaics is lower than that of wind power. Therefore, from the perspective of the cost reduction model, we should work on both the numerator (including the price of input and material components) and the denominator (i.e., power generation) to improve efficiency and thus reduce overall costs. A relatively effective means of cost reduction is the large-scale unit.

 

Large-capacity units can significantly reduce the number of units, reduce the costs of raw materials, hoisting and land allocated to unit capacity, and reduce the cost of later operation and maintenance and management. Considering the improvement of efficiency from the denominator end, the means of increasing revenue is also the large-scale unit.

 

Large-capacity units have a larger peak sweeping area and a higher hub height, the wind speed of the unit is lower, and the utilization hours per unit capacity are higher.

 

 

 

The Picture Shows the Cost Reduction Model

With the advent of the era of parity, large-scale units have become the only choice to reduce the cost of wind power. Large-scale units mean further lengthening of the blade length, and the requirements for the beam are also increased accordingly. Pultrusion beams have become a new process option for large-scale blades, but this option is not the only one.

 

In order to improve the modulus of the beam, the best way is to replace the raw materials. By selecting different raw materials, the modulus of the beam can be improved. The use of carbon fiber can effectively improve the performance of the beam. Regarding the economic forecast of using carbon fiber, the first thing to note is that all economic forecasts are relative. When glass fiber cannot meet the performance requirements, carbon fiber may become the only choice. It cannot be considered that carbon fiber has no future just because the economic efficiency of carbon fiber is not superior now.

 

Process Introduction

 

The production process of the beam plate mainly has 4 steps: pultrusion of the plate, packaging and transportation of the plate, post-processing and infusion of the blade. The performance of the plate is mainly obtained during the pultrusion process. Post-processing mainly involves some processing of some slopes, left and right chamfers, laying length, and tearing off the mold cloth. The last step is infusion molding.

 

It should be noted that infusion is related to pultrusion. In the process of designing the pultrusion process, attention should also be paid to the infusion link, such as the tearing of the demoulding cloth or the straightness of the plate, which will affect the performance of the final infusion.

 

There are two common forms of pultrusion, one is open, which has a long history; the second is injection.

 

Both processes are currently used in pultruded beams. Each has its own advantages and disadvantages, and does not have an absolute advantage. For example, the open-type has a longer impregnation time and a lower probability of impregnation defects.

 

For the injection type, its fiber straightness and new and old glue are less, but the impregnation time is shorter, and it is easy to produce impregnation defects. The impact pressure may also have some effect on the distribution of fibers.

 

These all need to be continuously improved and experienced in the actual application process. There is no absolute substitution relationship between the two forms.

 

 

 

The upper device in the figure is open, and the lower one is injection type

 

Performance Requirements

The performance requirements are mainly divided into five parts: dimensional appearance, physical properties, mechanical properties of the body, mechanical properties of the components and fatigue.

 

Dimensional Appearance

The dimensional appearance mainly includes appearance, width, thickness, thickness of the demoulding cloth, straightness, roughness, and flatness in the width direction. What needs to be paid attention to is straightness and size.

 

Straightness involves the splicing seam after splicing into a beam in the future. The size of the splicing gap between the two plates, the wider the gap, actually has some effect on the transverse tensile strength.

 

And this effect may be related to the chamfer of the final product, such as with a slope, or without a slope, or an arc chamfer, the performance of the final splicing seam is different.

 

Another very important thing is that if there is some filling in the splicing seam, the performance will be greatly improved. Another is the thickness and width of the demoulding cloth, which determines the weight of the beam after the blade is spliced ​​in the future, or the weight of the blade. If the size is out of tolerance or unstable, the possibility of blade overweight will increase.

 

Another is the roughness, which is related to the release cloth. As long as the release cloth is selected correctly, or the release cloth is bonded correctly, there will be no problem.

 

Physical Properties

Mainly fiber volume content, resin mass content and TG density. I think the key indicators are TG density and resin mass content. The curing and bonding degree of epoxy resin, as the ambient temperature changes, the TG density will also fluctuate. Especially for pultrusion open glue slot.

 

If it is injection type, this problem will be smaller. In areas with high humidity in summer, TG will be unstable. The resin mass content affects the final longitudinal tensile modulus and strength. Therefore, it is necessary to control the stability of the resin mass content as much as possible, reduce fluctuations, and thus achieve longitudinal performance.

 

Mechanical Properties of the Body

The mechanical properties of the body are mainly some tension, compression, bending, shearing and V-shaped shearing. I think the key mechanical properties of the body are the zero-degree tensile modulus and the 90-degree tensile strength. The blade itself is more critical to these two performance requirements.

 

Mechanical Properties of Components

There are two main concepts for the mechanical properties of assemblies, one is surface bonding and the other is transverse bonding.

 

The main meaning is the interlayer bonding between the sheets and the transverse joints between the sheets. In terms of the final quality of the infusion, the bonding between different resins and different sheets should also be considered.

 

Another thing we should pay attention to is that when the surface is pasted, the release cloth should be used as soon as possible after it is torn off. Because our release cloth is a process of immediate use and immediate connection, it is best to reduce the sluggish time. If the sluggish time is long, the surface bonding performance may be reduced.

 

Fatigue Performance

It is mainly tension, tension and compression, and compression. The main parameters of concern are M value and residual strength. The fatigue characteristics of the same fiber and the same resin in similar curing processes are theoretically close.

 

We have also studied fatigue with different porosity, mainly for tension. Under high load and low load conditions, the effect of porosity on tension fatigue is not particularly prominent. Therefore, the most important factors are still the material and resin content, which determine the final fatigue properties.