At this stage, PV projects must rely on subsidies to achieve profitability. The reason for this is that due to the relatively high cost in the early stage, it is currently about 8,000 yuan/kWh, which is higher than the cost of thermal power 4,000 yuan/kW; and the second is that due to the low number of full-time hours, depending on the resources, around the country Between 1000 and 1800 hours, it is much lower than the utilization hours of the national thermal power average of 4706 hours in 2014. Although the initial investment is high and the number of hours of power generation is low, the low operating cost is the biggest advantage of PV compared to thermal power.
Photovoltaic development for so many years, photovoltaic people are eager to achieve, is to make photovoltaic power to achieve "cheap Internet." Let photovoltaic power gradually move from expensive high-subsidy electricity prices to popularized electricity prices. To achieve parity Internet access, we can only proceed from the above perspectives of “investing in early-stage investments†and “increasing hours of power generationâ€.
First, the reduction of investment costs in the previous period
From 2007 onwards, the pre-investment costs of photovoltaic projects have been significantly reduced, mainly from two approaches: technological upgrading and scale.
1 Key Equipment Technology Improvement
The most critical equipment for photovoltaic power plants is PV modules and inverters. Since 2007, I have been deeply impressed by the technological advancement of these two core devices.
1) Improvement of conversion efficiency of photovoltaic modules
From the above table, we can see that in 6 years, the conversion efficiency of PV modules has increased from 14.1% to 15.9%, and the number of PV arrays in 1MW power generation units can be reduced by approximately 12%. Concomitantly, the amount of auxiliary equipment such as combiner boxes, DC cables, brackets, and foundations will decrease, and the BOS cost of photovoltaic power plants (costs of equipment other than photovoltaic modules within the area of ​​photovoltaic power plants) will decrease by approximately 4%.
In early 2015, the leader of the Energy Administration proposed that the conversion efficiency of monocrystalline silicon modules was over 17%, and the conversion efficiency of polycrystalline silicon modules was over 16.5%. TRW also launched a polycrystalline silicon module with a conversion efficiency of 19.83% and a monocrystalline silicon module with 20.48%. Although it is currently in the sample stage, the whole industry can expect the reduction in the cost of photovoltaic power plants due to the increase in the efficiency of photovoltaic modules.
2) Improvements in Photovoltaic Module Process
In addition to improving the conversion efficiency of silicon wafers, many manufacturers also use their brains in manufacturing processes. At this year's SNEC meeting, we saw that many component manufacturers have introduced high efficiency batteries with 4 gate lines and 5 gate lines. Due to the more uniform shielding of the solar cells by the silver grid lines, the output power of the entire photovoltaic module is increased under the same conditions of the silicon wafers. In addition to multi-gate batteries, some manufacturers have also introduced back-electrode batteries.
4 The gate line, the 5 gate line and the back electrode battery, through the improvement of the assembly process, realizes a substantial increase in the efficiency of the module when the efficiency of the wafer is unchanged. Its significance for the cost reduction of photovoltaic projects is comparable to that of silicon wafers.
3) The size of the single inverter becomes larger
Since 2007, the single inverter of the inverter has continuously grown in size. From the earliest 250 kW to 500 kW dominated; later, many manufacturers introduced 1 MW container-type inverters; at the SNEC meeting, even 3.2 MW power distribution cabinets, inverters, and box-integrated containers appeared.
The single machine power is big, the direct benefit is low cost per watt, small footprint, low installation cost. With the appearance of container-type inverters, the overall cost remains the same as that of the inversion houses, but it saves the construction period of inverting houses and greatly saves the construction period, thereby reducing the construction cost of the project.
4) The increase of the maximum open circuit voltage of the inverter
In 2007, the maximum open circuit voltage of the inverter was 880V. Therefore, if 60 pieces of photovoltaic modules are used, the most commonly used design scheme is 20 modules per string. Now, the maximum open circuit voltage of the inverter is 1000V. The common design scheme is 22 blocks per string. The direct change brought about by this improvement is that the string output voltage rises and the line loss decreases; the number of components in each string is more than 10%, and the number of photovoltaic power plant strings on the same scale will be reduced by 10%. The amount of DC cables can also be reduced by about 10%, and the investment cost can be reduced.
At the SNEC show, some manufacturers even demonstrated photovoltaic inverters with a 1500V DC input, and the AC output could be increased to 540V. However, experts in the industry believe that because the voltage is increased, the current at the same power is reduced, so the stand-alone power density and stand-alone efficiency can be improved, and the cost per tile can be reduced. However, the high voltage requirements for other equipment in the system are relatively high. Components with a withstand voltage of 1500V, photovoltaic cables, connectors, and DC switches are equivalent to the entire system. The cost does not decrease, but the risk increases. First, safety, 1500V DC more than doubled the risk of 1000V system; Second, the component failure risk, the total power of the components in series is determined by the smallest one, the higher the consistency of the components. Therefore, 1000V may be a more suitable voltage level at this stage.
2 Scale production of equipment
In 2007, the newly installed photovoltaic capacity in the country was only 20MW; in 2013, it was 12918MW, and in 2014 it was 10600MW, which was 650 times and 530 times of 2007 respectively. The planning for 2015 is 20GW, which will reach 1000 times in 2007!
With the increase in the annual installed capacity, a large number of related manufacturers have entered this field. Photovoltaic equipment has been rapidly reduced due to economies of scale and full competition.
3 improvement of design level
1) Basic changes
When I was just designing a photovoltaic power plant, the foundations for the foundations were all based on an extended basis, which was time-consuming, expensive, and costly. Nowadays, everyone adopts cement cast-in-place piles and spiral steel piles, which greatly reduces the cost of the foundation.
2) Proportioning of Photovoltaic Module Inverters
The first photovoltaic power station I made was mainly in Qinghai. At that time, everyone was discussing whether 500 kW PV modules should be connected to 630 kW inverters, because the inverters in the plateau region should be used at reduced capacity. The first time I did a review of the photovoltaic power plant project in Inner Mongolia, because I designed to connect 1.08MW of PV modules to two 500kW inverters, I explained to the assessment experts for a long time and made a lot of data calculations. Finally, Reluctantly agree.
Since last year, the industry has already accepted the "PV module capacity: inverter capacity" between 1.2 and 1.4. The reason is simple, because the chance of reaching 1000W/m2 of irradiance is very small, and the efficiency of the photovoltaic system is about 80%. In a 1:1 ratio, the time for the inverter to operate at full power is negligible. Photovoltaic modules are more equipped, and the utilization of inverters will be higher.
If the PV modules and inverters are installed in a ratio of 1.2, it is equivalent to the PV power plant starting from the inverter and the investment in electrical equipment is saved by 20%.
To sum up, due to the improvement of key equipment technology, the effect of scale, and the continuous improvement of the design level, the cost of photovoltaic power plants has continuously declined. The following table shows the changes in the cost of photovoltaic power plants from 2007 to 2014.
Second, the increase in full-time hours
Since the full-scale hours of photovoltaic power plants are determined by both solar energy resources and system efficiency, solar energy resources cannot be changed, and we can only continue to improve system efficiency.
1 The technological revolution of the inverter
Between 2007 and 2012, in the large-scale photovoltaic power plants, the inverters are absolutely centralized, and investors have no other choice.
After 2012, Huawei was born with a string inverter. The precise tracking of the multi-channel MPPT of the string inverter allows the photovoltaic power stations with the same installed capacity to generate 3% to 8% more power. Although the cost is slightly increased, the cost of electricity is reduced to some extent.
Beginning in 2014, distributed inverters began to emerge. The distributed inverter can provide multi-channel MPPT accurate tracking and ensure the power quality by providing integrated solutions. At the same time, the voltage in the controller (conflux box) side greatly reduces the maximum number of PV power stations. The line loss of the DC cable. Multi-channel MPPT precision tracking, DC line loss reduction, investment and centralized are basically the same. Therefore, as compared to the initial centralized type, the investment in the distributed inverter-based inverters will increase, and the investment will not be substantial, and the cost of power consumption will certainly be greatly reduced.
2 changes in stent form
Early photovoltaic power plants were basically stationary. In the first phase of the 2009 concession tender for the Gansu Jiuquan Power Station, single-axis tracking was used, but so far the track-type support has remained mainly in the demonstration stage. The reason for this is as follows. First, China's large-scale power plants are mainly located in the northwestern region where wind and sand are large. The harsh natural environment has caused great damage to the tracking system's transmission equipment, and has become a frequent failure component. Second, with the decline in the cost of photovoltaic systems, tracking systems have been used. The percentage increase in investment has increased from 3% to 6% in 2009 to the current 10% to 20%. Under the condition that theoretical power generation increases by 15 to 25%, the gains from adding some investments are not significant. In another form, fixed adjustable brackets are widely used.
Although the fixed adjustable bracket can only increase the power generation by 3 to 5%, it is not favored by increasing investment because of its good reliability, and it has been favored by more and more investors.
3 layout of photovoltaic modules
The earliest design of a photovoltaic power plant was based on a cat-painted tiger. The PV modules were horizontally arranged. However, in later engineering practice, it was found that the vertical layout was very easy to install and that it could save a bracket beam. So, from the end of 2009, all my plans were designed according to the vertical arrangement of photovoltaic modules. After researching the internal structure of photovoltaic modules in 2013, the firm began to implement a plan for the lateral arrangement of photovoltaic modules.
Although the horizontal layout scheme is cumbersome to install and adds a small amount of investment, the amount of power generation generated by the power station can be increased by reducing the loss of power generation caused by shadowing in the morning and at night. Overall, it is still very cost-effective.
4 Increase of operation and maintenance level
With the increase in the installed capacity, the operation and maintenance of photovoltaic power stations has received increasing attention. I am from two aspects of intelligent monitoring and power plant cleaning, the most direct experience to improve the level of operation and maintenance.
The earliest power plant cleaning was basically based on labor; now, mechanical cleaning has gradually replaced manual cleaning, and robot cleaning is not new. In the western part of the sandstorm, cleaning can bring about 5% increase in power generation in a timely manner.
A post-assessment of a power station was done some time ago. From the monitoring system of the power station, I can see the current of each branch of the combiner box, can accurately calculate the mismatch between the strings, and can also find out which string has problems at a glance.
In the past, we intelligently read the accumulated data of about 100 strings from the inverter. All the problems are black boxes. We can't judge whether there are problems or where the problems lie. Intelligent monitoring enables more accurate operation and maintenance of the power station, so that it can accurately locate and quickly solve problems, reduce the loss of power generation, and improve the system efficiency of the power plant.
Third, the process of photovoltaic subsidies
First use a map to explain the process of China's subsidies for the photovoltaic industry.
By the end of 2014, the cumulative amount of subsidies for all PV projects during the life cycle totaled 54.78 billion yuan.
According to national plans, 20GW of photovoltaic projects will be added each year from 2015 to 2020. If you consider 10GW per distributed, ground station. The annual subsidy amount is:
The number of full-scale hours for distributed projects is estimated at 1200h and subsidy of 0.42 yuan/kWh. Approximately 5 billion yuan/year of subsidies are needed; the number of full-scale hours for ground-based power stations is 1500 hours, and the subsidy is 0.6 yuan/kWh. It takes about 9 billion yuan/year. Subsidies; accumulated annual subsidies amounted to 14 billion yuan/year.
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