In a recent inverter user survey, IHS gathered the preferences and opinions of more than 300 installers, distributors, and general contractors who use PV inverters for their PV inverter purchases. According to the survey, 80% of the 200+ customers who had purchased string inverters indicated that they would likely consider string inverters for PV systems larger than 100kW. Nearly half of all customers who participated in the survey said they might consider using string inverters in systems larger than 1MW. This is a significant increase compared to last year's (2013) survey. Last year, only 17% of the customers who participated in the survey said they might consider using string inverters in systems of 1MW and above.
"The survey shows increasing acceptance of string inverters for large commercial PV systems (IHS note: system sizes 1MW-5MW) over the past year, validating IHS' expectation that string inverters will increase in several major PV market shares." Gilligan, Senior PV Analyst at IHS, said, "String inverters are being selected more often for large commercial PV systems because of their more flexible system design, lower losses in the event of a failure, and lower lifecycle maintenance costs."
In response to the study, Shielden summarized the following two reasons, which should be the most common reasons for choosing string inverters today, in the hope that it can give some advice to potential users who are debating whether to choose centralized or string inverters.
Reason 1: String inverter adopts modular design, each PV string corresponds to an inverter, DC end has the maximum power tracking function, AC end is connected to the grid in parallel, the advantage is not subject to the module differences between the strings, and the influence of shadow shading, and at the same time to reduce the PV module best operating point and inverter mismatch, maximize the increase in power generation.
First, the barrel effect of centralized inverter power plants is avoided. In the centralized grid-connected inverter system, the module square array reaches the inverter after two convergences, and the maximum power tracking function (MPPT) of the inverter can't monitor the operation of each module, so it's impossible to make each module at the optimal working point, and when one module fails or is blocked by the shadow, it will affect the power generation efficiency of the whole system. Therefore, when the battery module is shaded, the centralized power plant will be more affected, and the string-type power plant will only be affected by the MPPT of the corresponding string that is shaded. Under normal circumstances, the installation spacing between the components, installation angle varies, a certain time of the day will inevitably produce local shading, especially in the morning and evening when the sun's altitude angle is low, or there are some vegetation shading some of the cells. If a 500KW square array of panels is tracked by MPPT, a certain amount of power generation will be lost. The same situation applies when the battery module is dirty, shaded, aging, warming, hot spots.
Secondly, power plants using string inverters can use modules with different orientations in the same project. Like in mountain projects, due to the complex terrain of the region, there is little flat land to do land leveling, and the terrain facing due south is limited, so in order to ensure the capacity must make full use of the southeast and southwest slopes, as well as the east and west slopes. At this time, the installation of battery panels can not be completely south-facing arrangement. If a 500KW square array of panels is tracked with one MPPT, a certain amount of power generation will be lost.
Thirdly, power plants using string inverters can use different types of modules in the same project, which cannot be realized in traditional centralized inverter power plants.
Reason 2: String inverters also have the advantages of low self-consumption of electricity, low impact of faults, and easy replacement and maintenance. The centralized inverter itself consumes a lot of power as well as the ventilation and heat dissipation in the machine room, and the system maintenance is relatively complicated. When there is a failure, the whole power station will be paralyzed, but when there is a failure of the string inverter, only one string of components will stop generating electricity, and the whole power station can operate as usual, thus reducing the loss to a large extent. In addition, string grid-connected inverters are small in size and light in weight, and are very convenient to carry and install. They do not require specialized tools and equipment, nor do they need a special distribution room, which can simplify the construction and reduce the footprint in all kinds of applications, and the DC line connection does not require DC convergence boxes and DC distribution cabinets. This means that the repair time cycle of string inverters is shorter than that of centralized inverters.
The above two reasons should be the most common reasons for choosing string inverters, but the advantages are not limited to this, for example: the flexible Internet monitoring program allows power plants using string inverters to accurately monitor each group of panels, make it easier to find out the problematic components and control the detailed information and history of each group of panels in real time, and so on. As the technology matures and the market changes, string inverters will have more advantages and string power plants will be widely used around the world.
