Analysis on the string type and the reliability of the centralized inverter

Polaris solar PV net news: Editor’s Note: the long-term reliability of PV products directly impact investor returns, in a 25-year payback period, increasing generating efficiency, reduce product failure is an eternal theme. Quality long-term reliability risk heavy domestic photovoltaic power stations, of which inverter reliability has become the focus of everyone’s attention.

2014 of Munich of Intersolar Forum Shang, senior of PV practitioners persons ManfredBachler (had is global maximum of EPC manufacturers Phoenixsolar of Chief Technology Officer) proposed has with Group series type inverse variable device transformation existing of concentrated type inverse variable device of programme, to out of conclusions is 5-6 years can recovered transformation of cost, main of causes is because concentrated type inverse variable device maintenance trouble, available sex poor, just in available degrees aspects on than group series type inverse variable device poor 6 %。

Recently, the industry for string type with the centralized inverter failure rate, reliability controversial. So who is more reliable, who is stronger? Based in detail following and attract valuable comments.

1. inverter failure rate, a centralized above-string, is 3 times times

-The industry’s leading string inverter under the 25 systems reliability design with IP65 protection rating and achieve internal and external environment, keep the internal components in a dust-free and stable operating environment, greatly reducing the temperature, wind, humidity, salt spray, such as external environmental influences on device lifetime, so reliability is greatly enhanced. Also no wearing parts, no fuse, no fan needs to be replaced periodically, such as devices, maintenance of the system; the malfunction rate of less than 1%.

Centralized programs generally use conventional housing or container room, protection class IP54, but rooms generally in-line air cooling solution is actually only achieve IP44 or lower, can hold back the wind, dust and corrosive gases into the inverter. Centralized inverter protection grade IP20 only, internal circuit element easy exposure to poor working conditions. Like dust in inverse variable device within circuit board, and Terminal row, of cumulative will caused climbed electric distance reduced, eventually caused discharge, and fire, security risk; wet dust in PCB or components between easy formed leakage effect and corrosion effect, caused signal of exception or high-pressure pulled arc sparking, also has may caused grid on PE of short-circuit, caused inverse variable device exception shut machine or blew up. While the inverter fan is wearing parts, with an average service life of about 5 years or so. Centralized inverter failure rates than the industry 3%, the failure rate is a string inverter 3 times more than double. Many power stations were built in the Gobi desert in the North, which is actually typical of saline-alkali soil and dust containing large amounts of salt ions. In intermittent duty day and night mode, corrosion and much bigger leakage than conventional electrical devices.

On auxiliary power supply from the inverter, centralized auxiliary power failure rate is generally between 2~5% on the market, the main reason for its high failure rate is straight-through air cooling, dust, salt fog will affect reliability. Series inverters in series with the auxiliary power supply is circuit, working in a closed environment, the failure probability is extremely low.

History from inverters, SMA introduced in 1995 for the first inverter is-string inverter, after 7 years, was launched in 2002, the first centralized inverters. Outdoor string inverter has gone through nearly 20 years of practical tests, used in large power plants in Europe’s history longer than centralized inverters, technology is more mature.

Figure 1 figure 2 inverter room dust inside the inverter device dust

2. cooling effect on reliability: centralized is greater than the string type

Group series type inverse variable device single power hundreds of w, can achieved natural thermal design, and can meet 60 ℃ environment temperature Xia reliable run, concentrated type inverse variable device, especially 10 feet container programme, 1MW of loss up to 30-kilowatt, equivalent has 30 a 1-kilowatt of furnace silk in 10 feet container internal baking, single by several fan is hard achieved reliable thermal of, great increased has burn machine of risk.

According to the actual measurement, ground station in the West, string inverter hanging underneath the component, open airy, ambient temperature of 21 ° c internal temperature of 43.8 degrees Celsius, temperature of 22.8 degrees centigrade, and centralized in room temperature 23 ° c, Cabinet body temperatures as high as 53 degrees Celsius, temperature of 30 degrees Celsius. In the hot summer, room temperature exceeding 50 degrees is a regular thing, centralized inverter Cabinet body temperature is higher and more severe. Will be the reduced life expectancy from high temperature, Derating even blow up risk.

Sandstorm affected areas in the Northwest, inverter ash deposits result in dust-proof net congestion, poor radiator thermal performance, sharp rise in the temperature of large power devices, cause a temperature alarm, more serious will corrupt the internal IGBT devices, the device continuously restart, even burn. Since the first half of this year, almost every month because of cooling problems, and bombing incidents, such as the centralized program.

3. system availability and its effect on electricity: the loss of centralized groups a series of 17 times

-Europe’s top string inverter, can do to 350,000 hours MTBF, annual failure rate is below 1%, some factory owners can be done below 0.5%, and centralized conventional General can do 50,000 to 100,000 hours MTBF.

Centralized localization needs to manufacturers and maintenance, long processing time, affecting power generation; and string inverters can be directly processed by the site operation and maintenance personnel replaced, quick and easy, guaranteed power, then the fault analysis and maintenance. String-any inverter fails, the other inverters can keep working, without affecting the other generating capacity. Centralized program if any of the links in the system equipment failures, probably the whole square will stop working, fixed time depending on site location and spare parts to prepare the case may be, generally at least 2-3 days, up to 1 week, or a month, loss of generating capacity well beyond the expected value of the loss.

10MW power plant, for example, calculated according to the peak sunshine hours 6 hours a day on average, centralized programs with an average annual loss of generating capacity will reach 7154KWH, and string-only 420KWH, contrast, centralized loss is a string of 17 times.

4. String maintenance costs are much lower than the centralized

Centralized inverter maintenance must be carried out by professional maintenance personnel, skill requirements are high, even if it is damaged, also calls for professional operation and maintenance personnel to the site, to locate replacement, except parts replacement costs, labor costs, travel costs are high maintenance costs. Also, centralized inverter if it is the machine completely, replacing extremely troublesome, admission to the heavy machinery and equipment, inverter, remove from room is very difficult. Match software and hardware, such as the effect of centralized inverters must use original manufacturer’s spare parts, once the factory closed down, the future maintenance will be forced to shut down, owners only replacement of the product. String-just need to directly replace the machine, do not need professional maintenance personnel, 30-minute replacement is complete. 5-year maintenance period, free replacement failure outside of the warranty period of the machine, using modern logistics platform, low-cost return to Depot, only charge a small service fee, maintenance costs are much lower than centralized programmes.

Current inverter brands in the industry, and recently-some say string inverter required after 5 years a large number of claims is biased. -If the string inverter no breakthroughs in the design, and the centralized inverter, cooling fan and fuse protection class lower, that after 5 years and need a large number of centralized. However, if you select IP65, design of natural cooling and no fuse brand, these problems do not exist. For string inverter selection should give full consideration to its quality. Preferred quality, superior quality, to permanently station a good operations and large-scale application of inverter manufacturers. -The world’s top string inverter, annual failure rate is below 0.5%, far less than the centralized program. Some string brands a few years closed or does not exist, you can also replace one other brand of string inverters, replacement of lower cost, little impact on the overall capacity of the system.

In summary, centralized compared to-string inverter, both in the failure rate and operation and maintenance costs are more dominant, can guarantee the plant long-term reliable operation. In the past more than 10 years in development of inverter, 2-3 European technology leader in the global market, is a barometer for technology and market, China, the United States and Japan and other markets, basically follows the European routes, while absorbing the European experience and the lessons learned. Now represented by SMA technology manufacturers in the United States and Europe are pushing string program. More and more domestic photovoltaic power stations are also used string program. Therefore, string type is becoming a mainstream PV power station construction plan. Of course, when the select-string device manufacturers, we should also choose products of reliable quality and good reputation, to let owners of 25 real at ease the worry-free!

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