Solar market heating inverter prices are expected to go lower

The rise of emerging markets often means the birth of new opportunities. As a new energy source, solar energy provides a new stage for related companies such as battery manufacturing and power conversion. Because the current generated by the photovoltaic power generation system is DC, but the civilian power is mainly AC power supply, and the solar power generation will eventually go into grid operation, which means that solar power must be converted from DC power to AC power to drive household appliances through the inverter. load. Therefore, inverters play a decisive role in solar power systems.

The main function of the inverter is to convert the variable DC voltage input of the power supply into a non-interfering AC sine wave output, which can be used by the equipment as well as the grid. In addition to the AC/DC conversion, the inverter can perform other functions such as disconnecting the circuit to prevent the circuit from being damaged due to current surges. In addition, the inverter can also charge the battery, store the data usage and performance, and Track the maximum power point (MPPT), etc. to maximize the efficiency of power generation.

Although solar cell manufacturers have been working hard to increase the photoelectric conversion efficiency of solar cells in recent years, the solar cell of 15cm × 15cm in thickness and 200μm in thickness is only able to achieve 19.3% conversion in terms of the highest photoelectric conversion efficiency of solar cells in February 2010. effectiveness. Since the solar panel's photoelectric conversion efficiency is relatively low (about 15% on average), the task of obtaining as much output power from solar panels as possible falls on the inverter.

The performance improvement of solar inverters is more dependent on power switching devices. In order to obtain high-efficiency AC output voltage and current, it is necessary to properly select power devices. At present, China mainly develops medium- and high-power solar power generation systems. The Interim Measures for the Administration of Financial Aid Funds for Golden Sun Demonstration Project stipulates that the installed capacity of individual projects shall not be less than 300 kWp. With the increase of single-machine power, solar inverters are limited by technology and devices, and the circuit form is relatively single, mainly three-phase inverter bridges. The important task of improving energy efficiency falls on power devices, and the performance of the devices themselves. Design use is the key.

Many companies in the low- and medium-power solar inverters have their own patented circuit structures. The new generation of power devices has made these circuits even more powerful. Efficiency and reliability have all been greatly improved. Infineon has developed a series of products for solar applications, such as the high-power three-level module Easy and Econo4 series, product range 50A ~ 300A650V; high-speed IGBT and SiC diode PrimePACK module, specification 600A1200V. These power devices help to boost the efficiency of solar inverters above 100KW to a higher level. In addition, Infineon's trench termination technology, FieldStop IGBT, CoolMOS, and silicon carbide diode SiC, also perform well in high-efficiency solar inverters.

IR is also a pioneer in solar technology. Alberto Guerra explained that as early as the early 60s, IR's solar cells were used on the first satellite and even used to drive the first solar-powered electric vehicle. Today, IR provides a diversified power management product for the solar industry, especially string inverters for home, commercial, and utility-class applications. IRMOSFET and IGBT technology have advanced performance and can be used in different solar inverter topologies, such as single-phase and three-phase designs, to help the system reduce power dissipation. IR's IGBT products can fully take care of the above-mentioned various Puro's performance requirements. The power range covers 5KW to 30KW and above, and the voltage range is 600V to 1200V.

For engineers familiar with power management, what are the points for designing inverters for solar power generation systems that require additional attention? First, in terms of the use of inverters in existing photovoltaic systems, they can generally only be used for 5 to 10 years. With a lifetime of up to 25 years for photovoltaic panels, inverters are the least reliable components in photovoltaic systems.

IR's Alberto Guerra suggested that designers must consider the lifetime of photovoltaic system inverters. Solar inverter technology industry has high expectation for product life, generally can guarantee the use period of 20 to 25 years, so special emphasis on the reliability of each component. Although semiconductor components typically achieve this level of reliability, it can be a challenge for passive components, especially capacitors. Alberto Guerra further pointed out that the solution to overcome this challenge is to adopt circuit topology solutions (soft-switch vs. hard-switch) that can reduce the stress experienced by these components to a certain extent and meet the special needs of the solar industry relative to traditional power management applications. need. He also pointed out that designers need to pay special attention to semiconductor characteristics when selecting devices, including voltage range or switching speed. Second, solar power is constrained by high construction costs and slow development. From the economic point of view, the total cost of generating electricity is also not environmentally friendly. Efficiency is the most important indicator. Increasing the efficiency of solar inverters can save the energy lost in current conversion, which in turn reduces the production cost of solar power. To improve efficiency, the design of the device is also very critical. How to make use of the advantages of IGBT modules is also closely related to the design of the system design engineer. For example, efforts should be made to reduce the parasitic inductance of the power circuit in the design and to drive the IGBT to be stable and faster, which will directly affect the system efficiency. To this end, Infineon offers integrated power unit design solutions for wind power and solar power, such as PrimeStack and MODStack products, which can be used for tens of kW to 8 MW inverters.

At present, the inverter efficiency can reach 97.2%, and the space for further improvement is also extremely limited. Some companies try to improve the efficiency of solar power generation in other ways, among which the "micro-inverter" and the "power optimizer" of NS, which are introduced by TI, are the most representative.

The structure in which a conventional inverter is connected in series with a plurality of solar battery modules has drawbacks that the output efficiency is lowered due to uneven sunlight, uneven battery performance, and the like, and the overall output power is greatly reduced. In order to solve this problem, there have emerged a new architecture in which each solar cell module is equipped with an inverter and a converter function, namely, a "micro-inverter" and a "micro-converter." Dave Freeman, responsible for solar cell-related business at Texas Instruments, pointed out that the output power of each module can be optimized to maximize the overall output power.

In addition, in combination with the communication function, it can also be used to monitor the status of each module and detect failed modules. In short, micro-inverters are all equipped with existing inverter functions on each module. That is, the optimization from output power to DC-AC conversion is performed by the module. The power output from the module is AC and can be directly incorporated into the grid. IR also has special products that meet the needs of micro-inverters and DC-DC solutions, and these devices represent a destructive technology that can affect the solar energy inverter. Compared with the use environment of general electronic equipment, the environment of the solar photovoltaic system is much worse. The general panel is installed in the field. Partial shadows, different tilt angles and orientation, dirt, different aging, small cracks, and different temperatures of different photovoltaic panels can easily cause system mismatch if the voltage between the photovoltaic panels and Current mismatch will cause mismatch problems throughout the solar system. In addition, the longer the solar system is used, the less power is generated and the return on investment has fallen sharply.

The traditional solar energy system has its structural defects, so that the system performance can not be fully exerted, and the longer the system is used, the lower the efficiency will be. These disadvantages limit the market development of the solar energy system and make the solar energy system unable to be popularized. Zhang Yaoqiang, director of business development for National Semiconductor's core market in the Asia-Pacific region, pointed out that the biggest challenge for solar systems is to optimize inverter performance.

SolarMagic, the power optimizer formally supplied by National Semiconductor in 2009, can use distributed circuits to increase the amount of power generated by each module, and can also adjust the voltage and current of each row of photovoltaic panels until all are balanced to avoid systems. Mismatched.

In addition, each module has a monitoring function, which not only provides additional protection for the system, reduces system maintenance costs, but also improves system performance and ensures that the system operation is more stable and reliable. Even if some panels are affected by shadows, dust cover, etc., the SolarMagic Power Optimizer can still track the best local MPP (Maximum Power Point) to recover more than 57% of lost power. At the same time, the SolarMagic power optimizer converts the input voltage/current to different output voltages/currents to maximize the energy transfer in the system. The power optimizer will communicate with each other in an indirect way, detecting its own current and voltage environment and self-adjusting until the entire row of panels in series can achieve the optimum value while achieving a local optimization point at the panel level. SolarMagic Power Optimizer has actively solved the inherent problems of centralized MPPT, thus successfully reducing the panel mismatch issue.

In 2009, the global economy experienced a painful experience. With the arrival of 2010, the semiconductor industry ushered in the dawn of recovery. According to iSuppli's previous forecast, the installed capacity of global photovoltaic systems will increase by 68% in 2010 to 8.6 GW. IR's Alberto Guerra predicts that in the next few years, the solar engineering market's annual growth rate will reach 20% to 30%. Correspondingly, the price of solar inverters will also drop. Because the cost of the inverter accounts for 15% to 20% of the total solar energy system cost, because there is greater market demand and get price support, he believes that the decline in semiconductor prices will not cause pressure on the industry.

“Despite the unpredictability of the future, in every industrialized country, people’s attitude towards renewable energy policies has changed a lot. This situation will continue, it will extend to a broader range, and efforts will increase. "Alberto Guerra is optimistic about the future. He believes that the PV market will maintain its growth momentum, and the solar inverter industry's demand for power products will continue."