1500Vdc application in the photovoltaic system
Reducing costs and increasing efficiency has always been the direction of electric people’s efforts
1500VDC trend and inevitable choice of parity system
Reducing costs and increasing efficiency has always been the direction of Electric people’s efforts. Among them, the role of technological innovation is key. In 2019, with China’s accelerated subsidies, 1500Vdc has high hopes.
According to IHS data from the research and analysis organization, the 1500Vdc system was first proposed in 2012, and FirstSolar invested the first 1500Vdc photovoltaic power plant in the world in 2014. In January 2016, the first domestic 1500Vdc demonstration project Golmud Sunshine Qiheng New Energy Golmud 30MW Photovoltaic Power Generation Project was officially connected to the grid for power generation, marking that the domestic 1500Vdc application in the photovoltaic system has truly entered the stage of large-scale practical demonstration applications. Two years later, in 2018, 1500Vdc technology has been applied on a large scale internationally and domestically. Among the third batch of domestic leading projects that started construction in 2018, the Golmud project with the lowest bid price (0.31 yuan / kWh), as well as the GCL Delingha and Chint Baicheng projects have all adopted 1500Vdc technology. Compared with the traditional 1000Vdc photovoltaic system, the 11500Vdc application in the photovoltaic system has been widely used recently. Then we can easily have such questions:
Why increase the voltage from 1000Vdc to 1500Vdc?
Except for the inverter, can other electrical equipment withstand the high voltage of 1500Vdc?
How effective is the 1500Vdc system after use?
1. Technical advantages and disadvantages of 1500Vdc application in the photovoltaic system
1) Reduce the amount of junction box and DC cable
In “Code for Design of Photovoltaic Power Plants (GB 50797-2012)”, the matching of photovoltaic modules and inverters should comply with the following formula: According to the above formula and the relevant parameters of the components, each string of the 1000Vdc system is generally 22 components, while each string of the 1500Vdc system can allow 32 components.
Taking a 285W module 2.5MW power generation unit and string inverter as an example, 1000Vdc system:
408 photovoltaic strings, 816 pairs of pile foundation
34 sets of 75kW string inverter
280 photovoltaic groups string
700 pairs of pile foundations
14 sets of 75kW string inverters
as the number of strings is reduced, the amount of DC cables connected between the components and the AC cables between strings and inverters will be reduced.
2) Reduce DC line loss
∵ P = I R I = P / U
∴ U increases by 1.5 times → I becomes (1 / 1.5) → P becomes 1 / 2.25
∵ R = ρL / S DC cable L becomes 0.67, 0.5 times the original
∴ R (1500Vdc) <0.67 R (1000Vdc)
In summary, the 1500VdcP of the DC part is about 0.3 times the 1000VdcP.
3) Reduce a certain amount of engineering and failure rate
Due to the reduction in the number of DC cables and junction boxes, the number of cable joints and junction box wiring installed during construction will be reduced, and these two points are prone to failure. Therefore, 1500Vdc may reduce a certain failure rate.
4) Reduce investment
Increasing the number of single-string components can reduce the cost of a single watt. The main differences are the number of pile foundations, the length of the cable after DC convergence, and the number of junction boxes (centralized).
Relative to the 22-string scheme of the 1000Vdc system, the 32-string scheme of the 1500Vdc system can save about 3.2 points / W for cables and pile foundations.
1) Increased equipment requirements
Compared with the 1000Vdc system, the voltage increased to 1500Vdc has a significant impact on circuit breakers, fuses, lightning protection devices and switching power supplies, and put forward higher requirements for withstand voltage and reliability, and the unit price of equipment will be relatively increased.
2) Higher safety requirements
After the voltage is increased to 1500Vdc, the risk of an electrical breakdown is increased, thereby improving insulation protection and electrical clearance. In addition, once an accident occurs on the DC side, it will face more serious DC arc extinction problems. Therefore, the 1500Vdc system increases the system’s safety protection requirements.
3) Increase the possibility of PID effect
After the photovoltaic modules are connected in series, the leakage current formed between the cells of the high-voltage module and the ground is an important cause of the PID effect. After the voltage is increased from 1000Vdc to 1500Vdc, it is obvious that the voltage difference between the cell and the ground will increase, which will increase the possibility of the PID effect.
4) Increase matching loss
There is a certain loss of matching between photovoltaic strings, mainly caused by the following reasons:
- The factory power of different photovoltaic modules will have a deviation of 0 ~ 3%. The cracks formed during transportation and installation will cause a power deviation.
- Uneven attenuation and uneven blocking after installation will also cause a power deviation.
- In view of the above factors, increasing each string from 22 components to 32 components will obviously increase the matching loss.
- In response to the above problems of 1500V, after nearly two years of research and exploration, equipment companies have also made some improvements.
Second, the 1500Vdc photovoltaic system core equipment
1. Photovoltaic module
First Solar, Artus, Tianhe, Yingli, and other companies took the lead in launching 1500Vdc photovoltaic modules.
Since the world’s first 1500Vdc photovoltaic power plant was completed in 2014, the application volume of 1500V systems has continued to expand. Driven by this situation, the IEC standard began to incorporate 1500V related specifications into the implementation of the new standard. In 2016, IEC 61215 (for C-Si), IEC 61646 (for thin films), and IEC61730 are component safety standards below 1500V. These three standards complement the performance testing and safety test requirements of the 1500V component system and break the last obstacle of the 1500V requirements, which greatly promotes the compliance of the 1500V power station standards.
At present, China’s domestic first-line manufacturers have launched mature 1500V products, including single-sided components, double-sided components, double-glass components, and have obtained IEC related certification.
In response to the PID problem of 1500V products, the current mainstream manufacturers take the following two measures to ensure that the PID performance of 1500V components and conventional 1000V components remain at the same level.
1) By upgrading the junction box and optimizing the component layout design to meet the 1500V creepage distance and clearance requirements;
2) The thickness of the backplane material is increased by 40% to enhance insulation and ensure the safety of components;
For the PID effect, each manufacturer guarantees that under the 1500V system, the component still guarantees that the PID attenuation is less than 5%, ensuring that the PID performance of the conventional component remains at the same level.
Overseas manufacturers such as SMA / GE / PE / INGETEAM / TEMIC generally launched 1500V inverter solutions around 2015. Many domestic first-tier manufacturers have launched inverter products based on the 1500V series, such as Sungrow SG3125, Huawei’s SUN2000HA series, etc., and are the first to be released in the US market.
NB/T 32004: 2013 is a standard that domestic inverter products must meet when they are marketed. The applicable scope of the revised standard is a photovoltaic grid-connected inverter connected to a PV source circuit with a voltage not exceeding 1500V DC and an AC output voltage not exceeding 1000V. The standard itself already includes the DC 1500V range and gives test requirements for PV circuit overvoltage, electrical clearance, creepage distance, power frequency withstand voltage, and other tests.
3. Combiner box
The standards for the combiner box and each key device are ready, and 1500Vdc has entered the combiner box certification standard CGC / GF 037: 2014 “Photovoltaic combiner equipment technical specifications”.
At present, the 1500V standard for photovoltaic cables has also been introduced.
5. Switch and lightning protection
In the photovoltaic industry in the 1100Vdc era, the output voltage of the inverter is up to 500Vac. You can borrow the 690Vac distribution switch standard system and supporting products; from 380Vac voltage to 500Vac voltage, there is no switch matching problem. However, in the early period of 2015, the entire photovoltaic and power distribution industry did not have 800Vac / 1000Vac power distribution switches and other specifications, resulting in difficulties in supporting the entire product and high supporting costs.
The 1500Vdc photovoltaic system has been widely used overseas and is already a mature application technology worldwide.
Therefore, the main equipment of the photovoltaic system has achieved mass production, and the price has fallen sharply compared to the demonstration stage in 2016.
1500Vdc application in the photovoltaic system
As mentioned above, the 1500Vdc photovoltaic system has been applied abroad as early as 2014 due to its low overall cost and high power generation.
Global 1500Vdc application in the photovoltaic system exploration case
The first solar announced in May 2014 that the first 1500Vdc power plant built in Deming, New Mexico was put into use. The total capacity of the power station is 52MW, 34 arrays adopt 1000Vdc structure, and the remaining arrays adopt 1500Vdc structure.
SMA announced in July 2014 that its 3.2MW photovoltaic power plant built in Sandershauser Berg industrial park in Niestetal, Kassel, northern Germany has been put into use, and the power plant uses a 1500Vdc system.
1500Vdc has been widely used in low-cost projects
At present, LSP has successfully developed T1+T2 Class B+C, Class I+II PV surge protective device SPD 1500Vdc, 1200Vdc, 1000Vdc, 600Vdc are widely used in solar photovoltaic power generation.
Large-scale 1500Vdc application in the photovoltaic system
For the first time, the 257 MW photovoltaic power generation project of Fu An Hua Hui in Vietnam was successfully connected to the grid. All the 1500V container-type inverter step-up integrated solutions were used to successfully achieve the acceptance from design, construction to grid connection. The project is located in Huahui Town, Fuhua County, Phu An Province, Vietnam, and it belongs to the central and southern coastal areas. Taking into account the local geographical environment and the economics of the project, the project customer finally chose the 1500V container-type inverter boost integrated solution.
In the demonstration photovoltaic power station project, customers have strict requirements for construction and product quality. The installation capacity of the project on the DC side of the project is 257 MW, which is made up of 1032 sets of 1500V DC combiner boxes, 86 sets of 1500Vdc 2.5MW centralized inverters, 43 sets of 5MVA medium voltage transformers and containerized integrated solutions for ring network cabinets, making it easy Installation and commissioning can shorten the construction cycle and reduce system cost.
1500V solution brings together “big technology”
The 1500V container-type inverter boost integrated solution has the characteristics of 1500V, large square array, high capacity ratio, high-power inverter, integrated inverter boost, etc., which reduces the cost of equipment such as cables and junction boxes. Reduced initial investment costs. In particular, the high capacity ratio design effectively improves the overall boost line utilization rate and sets a reasonable capacity ratio through active over-provisioning to make the system LCOE optimal.
The 1500VDC solution is used in photovoltaic projects of more than 900MW in Vietnam. Vietnam Fu An Hua Hui 257MW photovoltaic project is the largest single photovoltaic power station project. As the first batch of new energy demonstration projects in Vietnam, after the project is put into operation, it will optimize the power structure of Vietnam, ease the power shortage problem in southern Vietnam, and promote economic and social development in Vietnam Of great significance.
Is the 1500Vdc application in the photovoltaic system still far from large-scale?
Compared with the 1000Vdc photovoltaic system widely used in photovoltaic power stations, the research of 1500Vdc application in the photovoltaic system led by inverter manufacturers has recently become an industry technology hot spot.
It’s easy to have questions like this:
Why raise the voltage from 1000Vdc to 1500Vdc?
Except for the inverter, can other electrical equipment withstand the high voltage of 1500Vdc?
Is anyone using the 1500Vdc system now? How’s the effect?
Technical Advantages and Disadvantages of 1500Vdc application in the photovoltaic system
1. Advantage Analysis
1) Reduce the use of combiner boxes and DC cables. Each string of a 1000Vdc system is generally 22 components, while each string of a 1500VDC system can allow 32 components. Take a 265W module 1MW power generation unit as an example,
1000Vdc system: 176 photovoltaic strings and 12 combiner boxes;
1500Vdc system: 118 photovoltaic strings and 8 combiner boxes;
Therefore, the amount of DC cables from photovoltaic modules to the combiner box is about 0.67 times, and the amount of DC cables from the combiner box to the inverter is about 0.5 times.
2) Reduce DC line loss ∵P loss = I2R cable I = P / U
∴U increases by 1.5 times → I becomes (1 / 1.5) → P loss becomes 1 / 2.25
In addition, the R cable = ρL / S, the L of the DC cable becomes 0.67, 0.5 times of the original
∴R cable (1500Vdc) <0.67R cable (1000Vdc)
In summary, the 1500VdcP loss of the DC part is about 0.3 times of the 1000VdcP loss.
3) Reduce a certain amount of engineering and failure rate
As the number of DC cables and combiner boxes is reduced, the number of cable joints and combiner box wiring installed during construction will be reduced, and these two points are prone to failure. Therefore, 1500Vdc may reduce a certain failure rate.
2. disadvantage analysis
1) Increase in equipment requirements Compared with a 1000Vdc system, increasing the voltage to 1500Vdc has a significant impact on circuit breakers, fuses, lightning arresters, and switching power supplies, and puts forward higher voltage and reliability requirements. improve.
2) Higher safety requirements After the voltage is increased to 1500Vdc, the danger of electrical breakdown and discharge is increased so that insulation protection and electrical clearance should be improved. In addition, if an accident occurs on the DC side, it will face a more serious DC arc extinguishing problem. Therefore, the 1500Vdc system raises the system’s requirements for safety protection.
3) Increasing the possible PID effect After the PV modules are connected in series, the leakage current formed between the high-voltage modules’ cells and the ground is an important reason for the PID effect (for a detailed explanation, please reply to “103” in the background). After the voltage is increased from 1000Vdc to 1500Vdc, it is clear that the voltage difference between the battery chip and the ground will increase, which will increase the possibility of the PID effect.
4) Increasing matching loss There is a certain matching loss between photovoltaic strings, which is mainly caused by the following reasons:
The factory power of different photovoltaic modules will have a deviation of 0 ~ 3%.
Hidden cracks formed during transportation and installation will cause power deviation
Uneven attenuation and uneven shielding after installation will also cause a power deviation.
In view of the above factors, increasing each string from 22 components to 32 components will obviously increase the matching loss.
3. Comprehensive analysis In the above analysis, how much 1500Vdc can be compared with 1000Vdc can improve the cost performance, and further calculations are needed.
Introduction: Compared with the 1000Vdc photovoltaic system widely used in photovoltaic power plants, the research of 1500Vdc application in the photovoltaic system led by inverter manufacturers has become an industry technology hotspot recently. Then we can easily have such questions.
Second, the core equipment of the photovoltaic system at 1500Vdc
1) Photovoltaic modules At present, FirstSolar, Artes, Trina, Yingli, and other companies have launched 1500Vdc photovoltaic modules, including conventional modules and double glass modules.
2) Inverter At present, mainstream manufacturers have launched 1500Vdc inverters with a capacity of 1MVA ~ 4MVA, which have been applied in demonstration power stations. The voltage level of 1500Vdc has been covered by the relevant IEC standards.
3) Standards for combiner boxes and other key components Combiner boxes and key components have been prepared, and 1500Vdc has entered the combiner box certification standard CGC / GF037: 2014 “Technical Specifications for Photovoltaic Combined Equipment”; 1500Vdc has been clarified by most IEC standards as belonging to the category of low voltage directives, such as circuit breaker standards IEC61439-1 and IEC60439-1, photovoltaic special fuses IEC60269-6, and photovoltaic special lightning protection devices EN50539-11 / -12.
However, since the 1500Vdc photovoltaic system is still in the demonstration stage and the market demand is limited, the above-mentioned equipment has not yet started mass production.
1500Vdc application in the photovoltaic system
1. Macho Springs Solar Power Station
Firstsolar announced in May 2014 that the first 1500Vdc power station completed in Deming, NewMexico was put into use. The total capacity of the power station is 52MW, 34 arrays use 1000Vdc structure, and the remaining arrays use 1500Vdc structure.
SMA announced in July 2014 that its 3.2MW photovoltaic power plant in Sandershauser Bergindustrialpark, an industrial park in Niestetal, Kassel, northern Germany, has been put into use. The power plant uses a 1500Vdc system.
2. Application cases in China
Golmud Sunshine Qiheng New Energy Golmud 30MW Photovoltaic Project
In January 2016, the first domestic 1500Vdc photovoltaic power generation system demonstration project, Golmud Sunshine Qiheng New Energy Golmud 30MW photovoltaic grid-connected power generation project, was officially connected to the grid for power generation, marking that the domestic 1500Vdc photovoltaic system has actually entered the actual demonstration application stage.
Photovoltaic components and electrical equipment in current solar photovoltaic systems are designed and manufactured based on the DC voltage requirements of 1000V. In order to achieve a better yield of photovoltaic systems, a breakthrough is urgently needed in the case of the reduction of photovoltaic subsidies for its power generation costs and efficiency. Therefore, the development of 1500V related photovoltaic products has become a trend. 1500V high-voltage components and supporting electrical equipment means lower system costs and higher power generation efficiency. Introducing this new equipment and technology can make the photovoltaic industry gradually get rid of dependence on subsidies and achieve parity on-line access at an early date. 1500V requirements for solar photovoltaic modules, inverters, cables, combiner boxes, and system optimization ”
The relevant core equipment of the 1500V system is shown above. The requirements of 1500V for each device have also changed accordingly:
• The layout of components is changed, which requires higher creepage distance of components;
• Component material changes, increasing material and testing requirements for the backplane;
• Increased test requirements for component insulation, voltage resistance, wet leakage, and pulse;
• The component cost is basically flat and the performance is improved;
• There are currently IEC standards for 1500Vdc system components. Such as IEC 61215 / IEC 61730;
• 1500Vdc system components of mainstream manufacturers have passed relevant certifications and PID performance tests.
1500V DC cable
• There are differences in insulation, sheath thickness, ellipticity, insulation resistance, thermal extension, salt spray, and smoke resistance test, and beam burning test.
1500V combiner box
• Test requirements for electrical clearance and creepage distance, power frequency voltage and impulse withstand voltage and insulation resistance;
• There are differences in lightning arresters, circuit breakers, fuses, wires, self-powered sources, anti-reverse diodes, and connectors;
• Standards for combiner boxes and key components are in place.
• Lightning arresters, circuit breakers, fuses, and switching power supplies are different;
• Insulation, electrical clearance, and breakdown discharge caused by voltage rise;
• 1500V voltage level has been covered by relevant IEC standards.
In the design of 1500V system strings, the components of each string of the 1000V system used to be 18-22, and now the 1500V system will greatly increase the number of components in series to 32-34, making multiple strings less and becoming a reality.
Current photovoltaic power generation system, DC-side voltage 450-1000V, AC-side voltage 270-360V; 1500V system, the number of single string components increased by 50%, DC-side voltage 900-1500V, AC-side 400-1000V, not only the DC side line loss decreases The line loss on the AC side has dropped significantly. 1500V requirements for components, inverters, cables, combiner boxes, and system optimization ”
In terms of inverters, 1MW centralized inverters were used in the past, and now they can be expanded to 2.5MW inverters after using a 1500V system; and the rated voltage of the AC side is increased. Inverters of the same power and AC side The reduced output current helps reduce the cost of the inverter.
Through comprehensive calculations, after the technical improvement of the 1500V system, the overall system cost can be reduced by about 2 cents, and the system efficiency can be improved by 2%. So the application of the 1500V system is of great help to reduce the system cost.
By using a 1500V system, the number of components in series increases, the number of parallel connections decreases, the number of cables decreases, and the number of combiners and inverters decreases. The voltage is increased, the loss is reduced, and the efficiency is improved. Reduced installation and maintenance workload also reduces installation and maintenance costs. This can reduce the cost of electricity LCOE value.
The big trend! 1500V photovoltaic system accelerates the advent of the parity era
In 2019, with the changes in photovoltaic policies, the industry is bidding to reduce the cost of electricity, and it is an inevitable trend to move towards affordable Internet access. Therefore, technological innovation is the breakthrough, reducing the cost of electricity and reducing the dependence on subsidies has become a new direction for the healthy development of the photovoltaic industry. At the same time, China, as the world’s leading manufacturer of the photovoltaic industry, has helped most countries to achieve parity on the Internet, but it is still some distance away from parity on the Internet for various reasons.
The main reason why the overseas photovoltaic market can achieve parity is that in addition to China’s advantages in terms of financing, land, access, lighting, electricity prices, etc., the more important and lessons learned point is that they are relatively China is more advanced. For example, a photovoltaic system with a voltage of 1500V. At present, 1500V voltage-level related products have become the mainstream solution for the overseas photovoltaic market. Therefore, domestic photovoltaics should also focus on system-level innovation, accelerate the application of 1500V and other advanced technologies, realize cost reduction, efficiency, and quality improvement of power stations, and comprehensively promote the photovoltaic industry to move towards the parity era.
1500V wave has swept the world
According to the IHS report, the first proposed use of the 1500V system dates back to 2012. By 2014, FirstSolar invested in the first 1500V photovoltaic power plant. According to the calculation of FirstSolar: 1500V photovoltaic power station reduces the number of parallel circuits by increasing the number of series photovoltaic modules; reduces the number of junction boxes and cables; at the same time, when the voltage is increased, the cable loss is further reduced, and the power generation efficiency of the system is improved.
In 2015, China’s leading inverter manufacturer Sunshine Power took the lead in promoting system solutions based on the 1500V inverter design in the industry, but because other supporting components have not formed a complete industrial chain in China, and investment companies have limited awareness of this, Rather than giving priority to overseas expansion after large-scale domestic promotion, it first “conquered” the world and then returned to the Chinese market.
From the perspective of the global market, the 1500V system has become a necessary condition for large photovoltaic projects to reduce costs and increase efficiency. In countries with low electricity prices such as India and Latin America, large-scale ground photovoltaic power stations are almost all adopting 1500V bidding schemes; countries with developed power markets in Europe and the United States have switched DC voltage from 1000V photovoltaic systems to 1500V; emerging markets such as Vietnam and the Middle East have directly entered 1500V systems. It is worth noting that the 1500-volt GW-level photovoltaic project is used worldwide and has repeatedly set a global record with ultra-low on-grid electricity prices.
In the United States, the installed capacity of 1500Vdc equipment in 2016 accounted for 30.5%. By 2017, it had doubled to 64.4%. It is expected that this number will reach 84.20% in 2019. According to the local EPC company: “Each new 7GW ground power station every year uses 1500V. For example, the first large-scale ground photovoltaic power station in Wyoming, which has just been connected to the grid, uses a sunlight power 1500V centralized inverter solution.
According to estimates, compared with a 1000V system, the cost reduction and efficiency increase of 1500V are mainly reflected in:
1) The number of components connected in series has been increased from 24 blocks/string to 34 blocks/string, reducing the number of strings. Correspondingly, the consumption of photovoltaic cables has decreased by 48%, and the cost of equipment such as combiner boxes has also been reduced by about 1/3, and the cost has been reduced by about 0.05 yuan / Wp;
2) The increase in the number of components in series reduces the system cost of support, pile foundation, construction, and installation by about 0.05 yuan / Wp;
3) The AC grid-connected voltage of the 1500V system is increased from 540V to 800V, the grid-connected points are reduced, and the AC and DC side system losses can be reduced by 1 ~ 2%.
4) According to the mature case of the overseas market, the optimal capacity of a single sub-array can be designed to be 6.25MW in 1500V systems, and even up to 12.5MW in some areas. By increasing the capacity of a single sub-array, the cost of AC equipment such as transformers can be reduced.
Therefore, compared with the traditional 1000V system, the 1500V system can reduce the cost by 0.05 ~ 0.1 yuan / Wp, and the actual power generation can increase by 1 ~ 2%.
Multiplying by “potential” 1500Vdc system domestic market
Compared with the international market, in the early years of the Chinese photovoltaic industry, due to the immature supply chain of the technology industry, the 1500V system started late and its development was slow. Only a few leading companies such as Sunshine Power have completed R & D and certification. But with the rise of the 1500V system on a global scale, the domestic market has taken advantage of it, and has achieved good results in the development and innovation of 1500V systems and applications:
- In July 2015, the first 1500V centralized inverter developed and manufactured by Sunshine Power in China successfully completed the grid connection test and opened the prelude to the 1500V technology in the domestic market.
- In January 2016, the first domestic 1500V photovoltaic power generation system demonstration project was connected to the grid for power generation.
- In June 2016, in the first domestic Datong leader project, 1500V centralized inverters were applied in batches.
- In August 2016, Sunshine Power took the lead in launching the world’s first 1500V string inverter, further enhancing the international competitiveness of domestic photovoltaic inverters.
In the same year, China’s first 1500V photovoltaic system benchmarking project was formally connected to the grid for power generation in Golmud, Qinghai, marking that the domestic 1500Vdc photovoltaic system has begun to enter the field of practical application. The total installed capacity of the power station is 30MW. Sunshine Power provides a complete set of solutions for this project, reducing the cable investment cost by 20%, the cost of 0.1 yuan / Wp, and greatly reducing the AC and DC side line losses and the transformer low voltage side winding losses.
1500V has become the mainstream of the global market
The 1500V system, which has both cost reduction and efficiency, has gradually become the first choice for large ground power stations. Regarding the future development of 1500V systems, IHS predicts that the share of 1500V inverters will continue to increase to 74% in 2019 and will soar to 84% in 2020, becoming the mainstream of the industry.
From the perspective of 1500V installed capacity, it was only 2GW in 2016 and exceeded 30GW in 2018. It has achieved a growth of more than 14 times in just two years, and it is expected to maintain a sustained high-speed growth trend. It is expected that cumulative shipments in 2019 and 2020 will be The amount will exceed 100GW. For Chinese enterprises, Sunshine Power has installed more than 5GW of 1500V inverters worldwide and has plans to launch more advanced 1500V series strings and centralized inverters in 2019 to meet the rapidly growing market installed demand.
Increasing the DC voltage to 1500V is an important change in reducing costs and increasing efficiency, and has now become the mainstream solution for international photovoltaic development. With the era of subsidy decline and parity in China, the 1500V system will also be used more and more widely in China, accelerating the arrival of China’s comprehensive parity era
From 2018, no matter abroad or domestic, the application proportion of 1500V system is getting larger and larger. According to IHS statistics, the application volume of 1500V for large foreign ground power stations in foreign countries exceeded 50% in 2018; according to preliminary statistics, among the third batch of front runners in 2018, the proportion of 1500V applications was between 15% and 20%.
Can the 1500V system effectively reduce the cost of electricity for the project? This paper makes a comparative analysis of the economics of the two voltage levels through theoretical calculations and actual case data.
I. Basic design scheme
In order to analyze the cost level of the 1500Vdc application in the photovoltaic system, a conventional design scheme is used to compare the project cost with the traditional 1000V system cost.
1. calculation premise
1) The ground power station, flat terrain, installed capacity is not limited by land area;
2) Extreme temperature and extremely low temperature of the project site shall be considered according to 40 ℃ and -20 ℃.
3) The key parameters of selected components and inverters are shown in the table below.
2. Basic design scheme
1) 1000V series design scheme
22 310W double-sided photovoltaic modules form a 6.82kW branch, 2 branches form a square array, 240 branches total 120 square arrays, and enters into 20 75kW inverters (1.09 times over-distribution at the DC side, gain on the backside) Considering 15%, it is 1.25 times over-provisioning) to form a 1.6368MW power generation unit.
The component is installed horizontally in accordance with 4 * 11, and the front and rear double-post fixed brackets.
2) 1500V series design scheme
34 310W double-sided photovoltaic modules form a 10.54kW branch, 2 branches form a square matrix, 324 branches have a total of 162 square arrays, and 18 175kW inverters are installed (1.08 times over-distribution at the DC side, gain on the back Considering 15%, it is 1.25 times over-provisioning) to form a 3.415MW power generation unit.
The component is installed horizontally in accordance with 4*17, and the front and rear double-post fixed brackets.
Second, the impact of 1500V on the initial investment
According to the design scheme above, a comparative analysis of the engineering quantity and cost of the 1500V system and the traditional 1000V system is as follows.
Table 3: Investment composition of 1000V system
Table 4: Investment composition of 1500V system
Through comparative analysis, it is found that compared with the traditional 1000V system, the 1500V system saves about 0.1 yuan / W of the system cost.
Third, the impact of 1500V on power generation
Using the same components, there will be no difference in power generation due to differences in components; assuming flat terrain, there will be no shadow occlusion due to terrain changes;
The difference in power generation is mainly based on two factors: mismatch loss between components and strings, DC line loss, and AC line loss.
1. mismatch loss between components and strings
The number of series components of a single branch has been increased from 22 to 34. Due to the power deviation of ± 3W between different components, the power loss between 1500V system components will increase, but it cannot be quantitatively calculated.
The number of access paths of a single inverter has been increased from 12 to 18, but the number of MPPT tracking paths of the inverter has been increased from 6 to 9 to ensure that 2 branches correspond to 1 MPPT. The MPPT loss does not increase.
2. DC and AC line loss
Calculation formula of line loss
Q loss = I2R = (P / U) 2R = ρ (P / U) 2 (L / S)
1) Calculation of DC line loss
Table: DC line loss ratio of a single branch
Through the above theoretical calculations, it is found that the DC line loss of the 1500V system is 0.765 times that of the 1000V system, which is equivalent to reducing the DC line loss by 23.5%.
2) Calculation of AC line loss
Table: AC line loss ratio of a single inverter
According to the above theoretical calculations, it is found that the DC line loss of the 1500V system is 0.263 times that of the 1000V system, which is equivalent to reducing the AC line loss by 73.7%.
3) Actual case data
Since the mismatch loss between components cannot be calculated quantitatively, and the actual environment is more responsible, the actual case will be used for further explanation.
This article uses the actual power generation data of the third batch of a front runner project. The data collection time is from May to June 2019, a total of 2 months of data.
Table: Comparison of power generation between 1000V and 1500V systems
From the table above, it can be found that at the same project site, using the same components, inverter manufacturers’ products, and the same bracket installation method, during May to June 2019, the power generation hours of the 1500V system were 1.55% higher than the 1000V system.
It can be seen that although the increase in the number of single string components will increase the mismatch loss between components because it can reduce the DC line loss by about 23.5% and the AC line loss by about 73.7%, the 1500V system can increase the power generation of the project.
Fourth, a comprehensive analysis
Through the analysis above, we can find that compared with the traditional 1000V system, the 1500V system,
1) Can save about 0.1 yuan / W system cost;
2) Although the increase in the number of single string components will increase the mismatch loss between the components, but because it can reduce the DC line loss by about 23.5% and the AC line loss by about 73.7%, the 1500V system will increase the power generation of the project.
Therefore, 1500Vdc application in the photovoltaic system the cost of power can be reduced to a certain extent.
According to Dong Xiaoqing, president of Hebei Energy Engineering Institute, more than 50% of the ground photovoltaic project design schemes completed by the institute selected 1500V; it is expected that the national 1500V share of ground power stations in 2019 will reach about 35%; it will be further increased in 2020.
IHS Markit, a well-known international consulting agency, gave a more optimistic forecast. In their 1500V global photovoltaic market analysis report, they pointed out that the global 1500V photovoltaic power plant scale would exceed 100GW in the next two years.
Figure: Forecast of the proportion of 1500V in global ground power stations
Without a doubt, as the global photovoltaic industry’s de-subsidization process accelerates, and the ultimate pursuit of cost of electricity, 1500V, as a technical solution that can reduce the cost of electricity, will be increasingly used.