Abstract: The comparably high cost has been the main barrier to mass deployment of PV markets. How to reduce the cost and improve the efficiency becomes what counts most. 1500V PV power system takes the place of 1000V lowering the cost from design. This paper will show advantages and challenges of 1500V PV power system from three aspects and introduce a solution from MORNSUN with 1500V input PVxx-29Bxx series power supply. The power supply takes power directly from the 1500V high voltage end for monitoring the PV system circuit, simplifying the design of PV system circuit to reduce costs of system manufacturing and maintenance when compared with AC power or battery power and enhance comprehensive benefits of PV power generation system itself. This power supply also provides multiple protection functions that improve system safety when a breakdown occurs and further enhance the safety of power supply and its load safety.
Keywords: PV system, PV combiner, PV inverter, MORNSUN, PV
With global non-renewable resources are increasingly scarce, the renewable energy (RE) is called upon to increase in all major electricity markets. International Energy Agency (IEA) forecasts the share of renewable energy in global power generation is expected to 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 Solar Power Europe (SPE). As a cost-competitive, reliable and sustainable electricity source, Solar PV blossoms in the world. Europe is the biggest solar market with a sum of 157GW (reference: 89GW), in which UK was the fastest growing one. China is the fastest growing market globally, which is expected to add 86 GW (reference: 28GW) until 2020. India market is predicted to rank in third place with 54GW (reference: 3GW), followed by Japan and the United States, with 59GW (reference: Japan 23GW, the United States 19GW), respectively.
Up to 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 of PV module has dropped from RMB 36 per watt to the present RMB 3.5-3.8, grid-connected PV system from RMB 60 per watt to RMB 7-8 and the inverter from RMB 4 per watt to RMB 0.3 from 2007 to 2015.
Beyond China, other markets price reduce, too. The global average inverter prices will be reduced by 9% per year, dropping from 0.17 US dollars/watt in 2013 to 0.11 US dollars in the next five years. And 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 demands for PV in China, Japan and other emerging markets continues to grow and global inverter could reach around 70 GW (AC Grid-connection) in 2018. Achieving PV grid parity is a matter of time. With the realization 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.
I. Advantages of 1500V System
What’s 1500V system? It simply defines that the withstand voltages of cables, converters, inverters and other components used in PV systems increases from 1000V to 1500V. An outstanding advantage of it is less costs but higher efficiency than 1000V system.
Boosting voltage to reduce line losses is an effective measure for design cost reduction. Higher voltages of input reduce wire losses of AC-side and DC-side as well as winding losses in low-voltage side of transformer and improve by 1.5-2% of the power plant system’s efficiency. 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 Ohm's Law P=I2R. To sum up, equipment loss will reduce and power generation increases when DC-side voltage rises from 1000V to 1500V.
A complete PV power generation system design should have PV array, combiner, DC cabinet, inverter and step-up transformer as shown in diagram 1. Compared with traditional 1000V DC voltage system, 1500V system has less connections between 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.
Diagram 1: PV Power Generation System
Another measure for design cost reduction comes from less components. 1500V system expands single-string components from 22 to 32, superior to 1000V system, reducing the quantities of strings and inverter, combiners and DC-side cables. Besides, less volumes of equipment such as inverter or transformer due to higher power density is also beneficial to reducing the costs of transportation and maintenance. Take 10MW PV power plant as an example, 1500V system could reduce 568 strings and 38 PV combiners, with cost reduction of US$77,390. Due to less equipment, costs of post-operation and maintenance will be reduced accordingly.
Table 1: Design Comparison between 1000V System and 1500VSystem
II. Challenges of 1500V System
Although voltage from 1000V to 1500V benefits the system a lot, but it is challenged from 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 1500V system are needed.
a) 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).
b) Raw material. The insulation and the electric clearance count most when the voltage rises to 1500V, 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 overcomes and needs cooperation of other circuit breakers, fuses, lightning protection devices and switching power supply owing to higher requirements of withstand voltage and the reliability than 1000V system.
c) Certification. 1500V system requires a full range of certification standards for production components. Since 2013, multiple component groups have been certified with TUV for 1500V but very few ones for special devices such as high-voltage power supply and others meet the standard.
III. 1500V System Solution
The PV power system usually takes power from either AC grid power or high-voltage DC battery. The former needs to 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 high-voltage DC battery is more popular.
As PV combiner and PV inverter are key components of PV system, the power solution have been challenged with 1500VDC voltage. Most manufacturers directly use power products on the market because there’re lots of difficulties when converting the 1000V DC high-voltage into 24V low-voltage, and certain ones choose to self-design power solution to save costs. It cannot denied that there are certain advantages for self-design, however, solutions provided by professional power manufacturers are far superior to it in terms of reliability and performance (e.g.: high temperature, life, altitude, etc.).
Besides, using power module greatly simplify the system design and avoid the risks of system failure caused by supply. Moreover, certification is the greatest challenge for power products. 1500VDC high voltage should meet the relevant standards for higher safety distance and creepage distance (see Table 2), which self-design solution is difficult to meet. High altitude also exacerbate the technical difficulty for PV module design.
In a word, high-voltage PV module from professional manufacturers could solve the above mentioned problems and provide a more reliable and longer life-cycle power solution, which usually has CE certification meeting different requirements for PV module in different countries.
Table 2. Minimum creepage distances
IV. MORNSUN Solution for 1500V System
To address the need of 1500V system, MORNSUN released 15W/40W 1500VDC input PV15/PV40-29Bxx. There are four main features as follows.
1) 200-1500VDC ultra-wide input voltage
A trend of PV industry is that 1500VDC system will be in place of nowadays standard 1000VDC system, which enables 50% longer strings and lowers the costs with fewer combiner boxes, less wiring and trenching, and less labor.
2) CE/CSA approval
The PV series with 1500VDC input voltage pass EN62109 standards, which greatly improve the reliability of the converter itself and the system.
3) Built-in input under-voltage protection ensuring system stability
A PV system converts the sun's radiation into usable electricity and also powers itself. As the unstable sunlight intensity, voltage to the control system is also various and may lead to system restarts frequently. PV15/PV40-29Bxx series are designed with input under-voltage protection which protect system stability from frequent restart.
4) Suitable for high-altitude applications (up to 5000 meters)
Most of the PV systems are installed in harsh environments or at high altitude fields. PV15/PV40-29Bxx are designed to meet the application requirement to ensure the systems’ reliability and safety, taking the customer environment and altitude into account and passing reliability tests. They are suitable for high altitude applications up to 5000m, safe and reliable.
a. Ultra-wide input voltage: 200-1500VDC
b. Operating temperature: -40℃ to +70℃
c. Isolation: 4000VAC
d. High efficiency, low ripple & noise
e. UL 1741/CSA-C22.2 No.107.1, EN62109 approval
f. Suitable for high-altitude applications (up to 5000 meters)
g. Protections: UVP, RVP, SCP, OCP, OVP
Application 1: Monitoring Unit of PV Combiner Box
Application 2: Monitoring Unit of PV Inverter
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 develops 1500V high-voltage PV power module PVxx-29Bxx series to address the needs of control monitoring units in 1500VDC PV power system. PV power itself does simplify the circuit solutions, reduce the cost of building and maintenance and comprehensively enhance the stability, security and reliability of the system.
Please refer to the technical manual for specific product parameters: PV15/PV40-29Bxx
1. Power Solution for 1500VDC PV Power System
2. Power Solution for High-voltage Static VAR Generator (SVG)
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