The time for 1500 V PV systems has come

With global non-renewable resources becoming increasingly scarce, renewable energy is being called upon in all major electricity markets.

The International Energy Agency (IEA) forecasts that the share of renewable energy in global power generation is expected to be over 30% before 2030, solar PV power generation accounting for 10% of it. By 2040 it will be over 50% (solar PV: 20%) and grow to over 80% (solar PV: 60%) at the end of this century. Meanwhile, global solar power capacity is growing sharply and could reach 540 gigawatts (GW) by 2020, according to a study by SolarPower Europe (SPE).

As a cost-competitive, reliable and sustainable electricity source, solar PV is currently blossoming. Europe is the biggest solar market at 157 GW, with the fastest growth in the UK. China is the fastest growing market globally, which is expected to add 86 GW until 2020. The Indian market is predicted to rank in third place with 54 GW, followed by Japan and the United States.

Up until now, the comparably high cost of power generation has been the main barrier to mass deployment of PV markets. Therefore, more attention is paid to how to reduce the cost and how to improve the efficiency. Statistics show that the Chinese market price for PV modules has dropped from ¥36/W to the present ¥3.5–3.8; for grid-connected PV systems from ¥60/W to ¥7–8; and for inverters from ¥4/W to ¥0.3 from 2007 to 2015.

Beyond China, other markets’ prices reduce too. The global average inverter prices will be reduced by 9% per year, dropping from US$0.17/W in 2013 to US$0.11 in the next five years. And the global price of crystalline silicon PV modules on average declines slightly by 5% in 2015, compared with 13% in 2013 and 11% in 2014. Such cost reduction trends are likely to continue, but price pressure is expected to be maintained, though the demand for PV in China, Japan and other emerging markets continues to grow and global inverters could reach around 70 GW (AC grid-connection) in 2018. Achieving PV grid parity is a matter of time. With the realisation of grid parity, it will greatly reduce the cost of power generation. On one hand, increase the generation capacity of the system; on the other hand, reduce the costs of initial investment and maintenance.

Advantages of 1500 V systems

What is a 1500 V system? It simply defines that the withstand voltage of cables, converters, inverters and other components used in PV systems increases from 1000 to 1500 V. An advantage of this is that it costs less but is more efficient than 1000 V systems.

Boosting voltage to reduce line losses is an effective measure for design cost reduction. Higher voltages of input reduce wire losses on the AC side and DC side, as well as winding losses in the low-voltage side of the transformer, and improve the power plant system’s efficiency by 1.5–2%. Calculated by P = UI, given that the power is constant, the current will drop to 1/1.5 when the voltage increases 1.5 times. Similarly, assuming the length and diameter of the cables are confirmed and the resistance R is constant, the cable loss will be 1/2.25 when the current lowers 1.5 times, as in Ohm’s Law P=I2R. To sum up, equipment loss will reduce and power generation increases when DC-side voltage rises from 1000 to 1500 V.

A complete PV power generation system design should have a PV array, a combiner, a DC cabinet, an inverter and a step-up transformer. Compared with traditional 1000 VDC voltage systems, 1500 V systems have fewer connections between the sting arrays and inverter. The PV arrays are constructed in the form of strings and then connect with the combiners in parallel, DC cabinet, inverter and power grid in sequence.

Another measure for design cost reduction comes from fewer components. 1500 V systems expand the number of single-string components from 22 to 32, reducing the quantities of strings, inverters, combiners and DC-side cables. A lower volume of equipment due to higher power density is also beneficial to reducing the costs of transportation and maintenance. For example, in a 10 MW PV power plant, a 1500 V system could reduce 568 strings and 38 PV combiners, with a cost reduction of US$77,390. Due to less equipment, the costs of post-operation and maintenance will be reduced accordingly.

	1000 V system	1500 V system
Number of strings (blocks/strings)	22	32
Power per string (W/string)	5500	8000
Number of connected strings	1818	1250
Power per array (W/array)	110,000	160,000
Number of arrays	91	63

 Design comparison between 1000 and 1500 V systems.

Challenges of 1500 V systems

Although changing voltage from 1000 to 1500 V benefits the system a lot, it is challenged by three aspects: PV module and related components technology, raw material and certification. Therefore, a benign collaboration across the industry and new standards meeting the requirements of 1500 V systems are needed.

PV module and related components technology

Seen from the PV module itself, the main challenges are electrical safety and potential performance degradation. Seen from the system design, it causes a stricter product selection, better-matched components and higher risk of potential induced degradation (PID).

Raw material

The insulation and the electric clearance count most when the voltage rises to 1500 V, for higher voltage may cause disruptive discharge. So, it will have higher requirements for the reliability of raw materials in terms of the layout of backboard, electrical connectors and electrical insulation. This technology requires the cooperation of other circuit breakers, fuses, lightning protection devices and switching power supplies, owing to higher requirements of withstand voltage and reliability than 1000 V systems.

Certification

1500 V systems require a full range of certification standards for production components. Since 2013, multiple component groups have been certified with TUV for 1500 V, but very few for special devices, such as high-voltage power supply and others, meet the standard.

The 1500 V system solution

A PV power system usually takes power from either AC grid power or a high-voltage DC battery. The former needs a long wire to connect the AC power because it is usually installed in a sunny position in remote areas, which greatly increases the costs. Therefore, taking power from a high-voltage DC battery is more popular.

As a PV combiner and PV inverter are key components of PV systems, the power solution has been challenged with 1500 VDC voltage. Most manufacturers directly use power products on the market because there are lots of difficulties when converting 1000 VDC high-voltage into 24 V low-voltage, and some choose to self-design a power solution to save costs. It cannot be denied that there are certain advantages to self-design; however, solutions provided by professional power manufacturers are far superior in terms of reliability and performance (eg, high temperature, life, altitude, etc).

Besides, using a power module greatly simplifies the system design and avoids the risks of system failure caused by supply. Moreover, certification is the greatest challenge for power products. 1500 VDC high voltage should meet the relevant standards for higher safety distance and creepage distance, which self-designed solutions find difficult to meet. High altitude also exacerbates the technical difficulty for PV module design.

High-voltage PV modules from professional manufacturers could solve the abovementioned problems and provide a more reliable and longer life-cycle power solution, which usually has CE certification meeting different requirements for PV modules in different countries.

To address the need for 1500 V systems, MORNSUN has released 15/40 W 1500 VDC input PV15/PV40-29Bxx. Featuring 200–1500 VDC ultrawide input voltage, CE/CSA approval and built-in input undervoltage protection, the system is suitable for high-altitude applications (up to 5000 m).

Summary

The gradual large-scale popularity of PV energy is the rational development trend of global energy. MORNSUN actively participates in the development of green energy technology and developed the 1500 V high-voltage PV power module PVxx-29Bxx series to address the needs of control monitoring units in 1500 VDC PV power systems. PV power simplifies circuit solutions, reduces the cost of building and maintenance and comprehensively enhances the stability, security and reliability of the system.

Written by MORNSUN.

MORNSUN products are distributed in ANZ by DLPC and in Victoria by Fairmont Marketing.

Top image credit: ©stock.adobe.com/au/Ingo Bartussek