Adaptation requirements of new high-power components to inverters

As global semiconductor technology and hot topics continue to heat up, the domestic semiconductor industry has increased its focus on the industry's top technologies.

The latest generation of semiconductor technology represented by 12-inch wafers continues to overflow from the chip industry to other semiconductor fields. The photovoltaic industry, as a field closely related to the semiconductor industry and industrial production, has benefited from the iteration of technology and the need to reduce costs. It has also officially started a new round of technological upgrades, leaping from traditional 6-inch wafers to 12-inch wafers.

As a direct representative of technology upgrades, Trina Solar, a Tier 1 brand, recently launched large-size modules with 12-inch 210mm silicon wafers, which has led to a new round of improvements in module power density, improving power generation and efficiency without significantly increasing size and weight. However, this has also brought new changes and challenges to the entire photovoltaic industry.

According to the electrical performance parameter specification table of Trina's 156mm silicon wafer modules and 210mm silicon wafer modules (under standard test conditions), as the module power increases, the output current at the maximum power point also increases. As shown in the figure below, the output current at the maximum power point of the 156mm silicon wafer 415Wp module (hereinafter referred to as Impp) is 10.15A.

The Impp value of the 210mm silicon wafer 600Wp module has increased to 17.34A. If the backside power generation gain of the bifacial module is taken into account, the Impp value will increase slightly.

Another Tier 1 series brand module manufacturer, Risen Energy, also recently launched a 600Wp+ module based on 210mm silicon wafers, with an Impp value of around 18A.

The matching between modules and inverters is mainly reflected in the matching between the inverter and the input voltage and current of the strings. However, as the module power increases, the corresponding voltage and current are also expanding. Is there a suitable inverter that can match the current module development needs without technical adjustments and does not increase the system BOS cost? This has become an urgent concern for photovoltaic project owners and EPCs.

The inverter, as the core component of the photovoltaic system, is responsible for converting the DC power of the photovoltaic module into AC power that is fed into the power grid.

The requirements of different components for inverters are mainly reflected in the three parameters of maximum system voltage, maximum power point operating current Impp, and short-circuit current Isc. The maximum system voltage determines the maximum voltage range in which the component/inverter can operate. Currently, there are mainly 1000V (1100V) system and 1500V system1); the maximum power point operating current Impp represents the maximum current corresponding to the maximum power tracking of the component/inverter; the short-circuit current Isc represents the limit current that the inverter string input can reach. The larger the component power, the larger the Impp and Isc will be, and the higher the input capacity requirements of the inverter will be.

As a global technology leader in the field of inverters in the photovoltaic industry, SMA Solar Technology AG has continued to track the development of the world's top technologies, and in 2020 released the latest version of the Sunny Tripower CORE2 string inverter based on multi-channel MPPT technology to meet the diversified technical needs of global customers. At the same time, it will meet the new round of technological upgrades in the global photovoltaic industry in the future. It is the inverter product that can best match the 12-inch 210mm large silicon wafer modules in the industry's current low-voltage grid-connected solutions.

210mm large-size silicon wafer modules have large output power and current due to their large silicon wafer surface area. The operating current of traditional 156mm half-cell modules is close to 11A, while the operating current of modules using 210mm large silicon wafer technology is often more than 17A. Combined with the current situation that the input current of each MPPT of the common string inverter in the industry is often only 26A, it is easy to find that it is almost difficult for ordinary grid-connected string inverters to access 210mm large-size modules at full power.

The following compares the access capabilities of the SMA Sunny Tripower CORE2 string inverter and other brands of string inverters under different power components.

Table 1 Comparison of the access capabilities of different inverters for large-size silicon wafer modules

The open circuit voltage Voc of the 415Wp module of 156mm silicon wafer is 49.6V. Considering the negative temperature coefficient of the module, 18 modules are connected to each string in the 1000V system. Due to its small Impp current, the DC side access capacity of mainstream inverters can be fully connected. However, in the era of 600Wp modules of 210mm large silicon wafers, due to the sharp increase in module output power, the maximum power point operating current Impp far exceeds 13A2), so traditional inverters can only connect to one string per MPPT, which leads to the problem of insufficient access capacity of traditional inverters. Under the same system capacity, the number of inverters needs to be increased, resulting in an increase in the BOS cost of the entire system.

As shown in Table 1, a 100KW inverter model A has 9 MPPT channels, and each MPPT channel has two strings. However, under 600Wp modules, since the Impp of a single string module has exceeded 17A, each MPPT channel of the 100KW model inverter can only connect to 1 string, for a total of 9 MPPT channels, so a maximum of 9 strings can be connected. Considering the negative temperature coefficient of the module, each string can connect to a maximum of 20 modules, and its maximum access capacity is 600Wp * 20 modules/string * 1 string * 9 channels = 108KW, while the maximum output power of the inverter is designed to be 110KW, which means that under 210mm modules, its utilization rate is only 98%;

Similarly, the maximum access capacity of a 125KW inverter model B is 600Wp * 20 blocks/string * 1 string * 10 channels = 120KW, and the utilization rate is only 87% under 210mm modules.

SMA's new 110KW Sunny Tripower CORE2 inverter has a super high DC/AC capacity ratio (12-channel MPPT), with a maximum access capacity of 600Wp * 20 blocks/string * 1 string * 12 channels = 144KW, and a utilization rate of 131% under 210mm modules. Further, considering the back power generation gain of 210mm bifacial modules, as shown in the figure below, at a back power generation gain of 10%, its Impp value is 18.5A, and the Sunny Tripower CORE2 inverter can still access 12 strings of modules, and its maximum access capacity can reach 642Wp * 20 blocks/string * 1 string * 12 channels = 154.1KW!

It can be seen that the SMA Sunny Tripower CORE2 inverter can really perfectly match the 210mm large silicon wafer module

3) Achieve the best balance of investment returns.

In fact, not only the Sunny Tripower CORE2 inverter, but the design concept of the entire SMA series inverters all adhere to the ultra-high DC/AC capacity ratio, which enables the SMA inverter to support higher component over-matching and is the only choice for adapting to the large-size components of the new era.

for example:

The 50KW Sunny Tripower CORE1 inverter has 6 MPPTs and 12 string inputs. With the aforementioned 210mm bifacial module 642Wp (considering 10% backside power generation gain), its maximum access capacity can reach 642Wp * 20 pieces/string * 1 string * 6 inputs = 77KW, and the maximum DC:AC capacity ratio is 1.54. The Sunny Central series centralized inverter with a rated power of 2.5MW ~ 4.6MW can even have a maximum DC:AC capacity ratio of 2.5!

For photovoltaic systems with a maximum voltage of 1500V, you can use the SMA 150KW power model Sunny Highpower PEAK3 string inverter or the Sunny Central series centralized inverter.

For centralized inverters, since the current will first be combined through the DC combiner box at the output end of the component, they are generally better than string inverters in adaptability to large-size components. It is still recommended to adapt centralized inverters when using large-size components in large ground power stations.

Notes:

1) Household and industrial and commercial projects mainly use 1000V photovoltaic systems, and large ground power stations mainly use 1500V photovoltaic systems.

2) With the M10 182mm large silicon wafer size, the Impp value of the bifacial module will also exceed 13A due to the back-side power generation gain.

3) Since the Impp value of 210mm modules is larger than that of 182mm modules, the inverter adapted to 210mm modules is backward compatible with modules of 182mm and smaller sizes.