In the field of new energy, the solar photovoltaic (PV) market continues to attract many investors in the past 10 years with an annual growth rate of over 30%. In fact, the basic technology for the development of solar photovoltaics has been available as early as 50 years ago, but it has not made much progress. Because of this, photovoltaic modules and inverter technology on the market currently seem to have failed to meet user requirements in terms of cost-effectiveness and return. They have not been widely used and rely on government subsidies. However, since the industry introduced distributed technologies such as DC/DC power optimizers and DC/AC micro-inverters, the solar photovoltaic industry has begun a new round of technological changes.
The dilemma of solar photovoltaic technology
Solar photovoltaic systems and integrated circuits began to develop about 50 years ago. During the period, integrated circuits continued to make new breakthroughs in terms of process and patented technologies, and their costs were also significantly reduced. However, solar energy technology only improved in terms of efficiency and stability. Solar power plants are still made up of arrays of solar photovoltaic modules that convert sunlight into DC power and convert the DC power to AC power from a centralized inverter and then to the grid.
Although the entire industry has been working hard to increase the amount of power generated, the technology research and development work in this area has been mainly to improve the efficiency of solar cells, or to concentrate on the development of advanced production processes that help increase power generation. However, if the cost of solar energy generation is reduced to a level comparable to that of a traditional grid, the above R&D direction is not expected to achieve satisfactory results because the costs involved are often high but the efficiency is low. For example, although the crystalline silicon photovoltaic module has a certain increase in efficiency (about 0.5% per year), other aspects of performance are basically the same as 20 years ago.
In the past 10 years, although the unit cost of power generation for thin film photovoltaic modules has dropped significantly, the long-term stability of this technology has not yet been proven. At the same time, because the U.S. government has provided substantial subsidies for photovoltaic solar energy users, the market penetration rate of solar energy systems has soared in the past 10 years, and the total power generation capacity of new systems has reached more than 10 GW. The total installed capacity of newly installed solar photovoltaic systems in 2010 was as high as 15 to 17 GW. Some countries, such as Germany, have provided solar energy users with a high amount of government-based electricity repurchasing (Feed-in Tariff, FIT) for a long time, which has greatly stimulated the market demand for solar photovoltaics. The challenge faced by the solar PV industry is how to understand the actual market environment of the existing solar energy system and related technical issues in order to ensure that once the government stops providing subsidies, the market can continue to develop rapidly.
Shadows and mismatch problems
Shadows and mismatches have led many well-known companies and emerging companies to develop new technologies to solve these problems. In a solar photovoltaic array, a problem with one module will affect other modules in the series, and any one set of series will affect the other series on the array. To be precise, if there is an imbalance in voltage and current in the photovoltaic system, there will be a mismatch problem. There are many reasons for this, such as local shadows, moving clouds, reflections from nearby objects, different angles and arrangements of photovoltaic modules, dirt, varying degrees of aging, subtle cracks, and temperature differences between solar arrays. All solar systems have more or less the problem of mismatch, but in many cases the energy loss due to mismatch will be ignored or underestimated. Many independent studies have shown that even if only 10% of photovoltaic modules are shaded, the overall system power consumption will be as high as 50%.
Current solar systems are trying to solve this mismatch problem using a special algorithm of the central inverter. This special algorithm called Maximum Power Point Tracking (MPPT) technology can adjust the voltage on the PV system's DC line to capture as much energy as possible. The limitation of this method is that the inverter cannot deeply “see†the modules and strings on the PV array, so only slow and limited adjustments can be made.
Power Optimizer Solution
In 2008, National Semiconductor introduced the power optimization technology or "power optimizer" to the market for the first time. It is characterized by the use of core analog circuit technology and power management chips on photovoltaic modules to increase the output efficiency of solar photovoltaic systems.
Over the past year, integrated circuit and solar photovoltaic module suppliers have further strengthened their cooperation with each other. For example, National Semiconductor, which provides distributed integrated circuits and power optimizers for solar systems, has announced a partnership with Suntech, the world's largest provider of crystalline silicon photovoltaic modules.
For solar systems, the introduction of integrated circuits will add value, because the main purpose of the power optimizer is to restore the energy lost due to a damaged module, and ensure that the efficiency of each photovoltaic module is improved at any time. The main function of the power optimizer is to provide DC/DC optimization through MPPT technology. Research shows that the power optimizer can increase energy harvesting by 25% over a 25-year life cycle of the solar system.
There are several different DC/DC power supply optimizer solutions on the market. We must study the differences in depth because different architectures have different effects. For example, when adjusting the MPPT of a module in a damaged string, the voltage of some modules needs to be adjusted downwards, and the other part needs to be adjusted upwards. The advantage of this buck/buck architecture is that it can increase the amount of energy collected and provide the most effective design method. Some optimizers only provide the buck function. Although this design can exert high efficiency from the perspective of power conversion efficiency, the amount of energy collected may not be able to increase accordingly. In addition, part of the optimizer only provides a boost function. Its advantage is that the voltage of the module can be increased to the same level as the DC line voltage, but the disadvantage is that the current is higher and the input voltage range is smaller, so it is more difficult to shadow the situation. Give full play to the performance of the system.
Although all new technologies will need to be accepted and optimized by the industry after some time, because the power optimizer is not only reliable, but the chip maker also provides warranty service comparable to solar module manufacturers, so its market demand continues to grow, and Strong. Module manufacturers all understand that if the product has a good market, not only must ensure the process, but also to ensure stable and reliable performance. The introduction of DC/DC power optimization technology can increase the energy harvesting of the solar energy system over the entire life cycle. In addition to its 25-year maintenance guarantee, the large-scale system installation company and the design, procurement and construction (EPC) contractors all have Willing to adopt this product. From a technical point of view, higher peak efficiency (up to 99.5%), safety, and compatibility with various types of inverters will help attract more system installers and general contractors to home and business users. Power optimization techniques are strongly recommended.
System Balanced Cost (BOS) is an important measurement factor for system installation companies and general contractors. In general, they will submit an estimate of the total cost of the system and guarantee the performance of the system during the warranty period. On the surface, installing a power optimizer increases costs, but in fact, the rest of the system can save more costs, making the total cost lower than the initial valuation. With optimizer-based modules, system users can install centralized inverters instead of string inverters.
Because the module can be installed on the entire Roof or within a certain range, there is no need to avoid obstructions and shadows, so the construction cost is low, and the rack and cable usage can be saved because the same area can accommodate more photovoltaic modules, and the series The number is no longer a problem.
Micro-inverter solution
The use of micro-inverters is another solution. This solution also has the above mentioned installation and performance issues. If the PV system uses a micro-inverter, there is no need to install a centralized inverter because the micro-inverter can directly convert the DC output from each module to AC. It is mainly for the home solar photovoltaic market, and its market share has been steadily rising. The main reason is that it is easy to install and more flexible. For example, the number of concatenations depends on the needs of the user. Another advantage of using the micro-inverter solution is that the installer may not use high voltage DC cables to avoid arcing.
Judging from the current selling prices of micro-inverters and power optimizers, it is still unclear when these new solutions will become mainstream solutions. According to the forecast of some reports, 10 to 15% of newly installed solar energy systems will use power optimizers in the next three years, and their market share may reach as high as 25% of the solar energy system market in the next 5 years. When these two solutions were introduced to the market in 2008, the unit cost of power generation was approximately $0.80 to $1.00/W. In 2010, the cost of these two solutions began to drop significantly and have a competitive advantage.
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