Analysis of technical difficulties in concentrated photovoltaic power generation system

　　I. Introduction

　　The price of solar power systems has remained high! The main reason is because of the low density of solar energy! The average light intensity of the sun shining on the ground is 1 kilowatt/square meter; the conversion rate of monocrystalline silicon can reach 23%, polycrystalline can reach 16%, and thin film can only reach 8%. The highest conversion efficiency of gallium arsenide cells can reach over 35%, but the overall conversion efficiency of solar power generation systems made of gallium arsenide is only about 25%.

　　Therefore, in order to reduce the price of solar power generation systems, increasing the intensity of sunlight is a good solution. To increase the intensity of light, you need to use a convex lens or a Fresnel lens or a reflector to focus the light; this can greatly reduce the amount of silicon and arsenic The usage of gallium is reduced, thereby reducing the price of solar power generation systems; this is the origin of CPV (concentrated photovoltaic power generation system).

　　2. Technical Difficulties of CPV System

　　The principle of CPV solar power generation system is relatively simple. Why are there so few companies in the world that have made a particularly stable and cheap power generation system? In principle, in the CPV field, the higher the concentration multiple, the cheaper the cost. However, the following problems will arise when using concentrated light.

　　1. Allow single crystal silicon to withstand higher concentration of light

　　Although gallium arsenide can withstand 1,000 times the light intensity, gallium arsenide is currently expensive and the arsenic in gallium arsenide is a highly toxic substance. It is impossible to significantly reduce manufacturing costs. In addition, in the international environment with the theme of environmental protection It is impossible to use it in large quantities, and in the end it can only be monocrystalline silicon; but monocrystalline silicon can generally only withstand 3 to 5 times of light intensity. In the CPV field, 3 to 5 times of light concentration can hardly reduce costs. If you want to To significantly reduce costs, it must reach about 10. In order to achieve 10 times the concentration of light, special single crystal silicon must be used.

　　2. Heat dissipation:

　　The temperature of ordinary silicon photovoltaic panels can reach over 75 degrees at noon in summer. Ordinary silicon photovoltaic panels will blister over time under twice the sunlight intensity, and will blister in 10 minutes under 5 times the sunlight intensity. Blistering will occur in 5 minutes under 10 times the sunlight intensity. After bubbling, the solar cells will be oxidized and the efficiency will be greatly reduced in a short period of time. In addition, due to uneven heating after bubbling, the Some batteries have exploded, rendering the system completely unusable.

　　If the solar panel uses aluminum or copper heat sinks for natural heat dissipation, a large number of heat sinks are required, which is very expensive, even more expensive than silicon light wafers; if forced air cooling is used, a large amount of electricity will be used, which is not worth the gain. , and the life and reliability of the fan are not high. To achieve high reliability, error checking and redundancy settings must be implemented, which will increase the cost several times. If the fan breaks down at noon in the summer, the entire silicon photovoltaic panel may be damaged. Completely burned. If water cooling is used, in addition to using electricity, the cost is not cheap. Water cooling has many pipelines and connection points, and it also requires a water pump. There are bound to be many fault points, and the reliability is not as good as air cooling. Of course, the efficiency of water cooling is higher than that of air cooling. But it is not available in solar systems where the failure rate determines the veto system.

　　3. Reflective board:

　　For ordinary mirrors and plastic reflectors, due to the difference in thermal expansion and contraction coefficients between the reflective layer and the skeleton layer (such as glass), the reflective surface will fall off in 2-4 years outdoors. In places with high temperatures in deserts, it may become completely unusable in a few months. , and the reflectivity will slowly decrease.

　　In addition, there are also thin aluminum plates with high reflectivity at home and abroad. However, this aluminum plate cannot withstand hail and cannot be scrubbed. If scrubbed, it will cause permanent damage. The service life of this aluminum plate is about 8 years, and the reflectivity decreases year by year. 8 years The reflectivity is basically only 40%, which is far from the 25 years required for solar systems. There are protective films on aluminum panels, but the protective films are expensive and not hail-proof, so they cannot solve all problems. In addition, in order to reduce costs, aluminum plates are generally about 0.3 mm, which is particularly difficult to process and the processing cost is extremely high.

　　4. Tracker:

　　Photovoltaic cells can only work at the focus of the concentrator. Because the earth's sun is rotating all the time, a tracker must be used to ensure that the photovoltaic cells are at the focus of the concentrator. The tracker is one of the main systems of the CPV system. The system cannot operate without a tracker. In addition to ensuring that the system can operate, the tracker also uses an average of 30-40% more power than a system without tracking. However, the tracker is a mechanical structure. It will malfunction and wear out after years of operation. If the tracker fails, the system will not be able to operate (no power will be generated). If there is wear and tear, the tracking accuracy will decrease. Since the CPV system has a negative impact on tracking, There are requirements for accuracy. If the accuracy is reduced, the power generation system will not be able to operate normally.

　　3. Solution

　　In order to solve the problems of the CPV solution system and master the core technology of the CPV system, General Manager Chen Pingjian of Beijing Anxin Hi-Tech led his R&D team starting in March 2008. After more than 2 years of research, he invested millions of funds in After countless failures, we have finally successfully solved the core technology of monocrystalline silicon's 10x light concentration, and have obtained or are applying for eight patents.

　　1. Allow single crystal silicon to withstand higher concentration of light

　　After many improvements, we finally created a monocrystalline silicon photovoltaic cell that can withstand 15 times the light intensity, and is 15% more powerful than similar cells, far exceeding similar products in the world.

　　2. Heat dissipation:

　　After dozens of designs, 10 trials and modifications, we finally designed a unique and cheap radiator. The radiator does not require any power, does not have any moving parts, and is very stable; at an outside temperature of 45 degrees, 13 It can ensure that the temperature of the photovoltaic cell is within the specified range when concentrating the light twice. No power and no moving parts means maintenance-free, high stability, and performance will not change over time. It is the radiator with the lowest heat dissipation/price ratio among similar products.

　　3. Reflective board:

　　The design and production of the reflector was relatively smooth. After more than half a year of thinking, it was successfully produced in one go. The luminous rate of this reflector is about 77%, the service life will not be less than 25 years, and the reflectivity will not decrease year by year. It can It can withstand hail and can be scrubbed, and the price is about 200 yuan per square meter. In addition, we have designed a unique processing method, which is extremely simple to process. Completely solves all problems with other reflectors.

　　4. Tracker:

　　After more than 10 improvements, a full-motion tracker was designed, that is, the whole tracker is on a large plate, and the east-west direction rotates as a whole, and the north-south direction also performs unified pitch through the coupling, which greatly improves the stability of the system and greatly improves the stability of the system. The cost is reduced, the wind resistance is reduced, and a special set of bushings is designed, which is not afraid of water or sand, and has a service life of 100,000 times (the full life of our entire system is 18,000 times). In addition, the intelligent control system can The concentrator can always be pointed at the sun even when it is blocked by clouds. As soon as the sun comes out, the system can generate electricity immediately, completely solving the shortcomings of existing trackers.

　　4. System price

　　Since our CPV system solves almost all problems, the cost has been greatly reduced compared with existing solar power generation systems. A 500 kilowatt system can achieve 0.8 yuan/kWh; 1 MW can achieve 0.7 yuan/kWh; 2 MW can achieve 0.6 yuan/kWh; 10 MW can achieve 0.5 yuan/kWh; national The Energy Bureau has determined that only solar power generation of 0.8 yuan/kWh can be subsidized by the country, and our CPV system can fully meet the requirements.

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