With the increasing shortage of energy, environmental pollution and environmental protection more and more attention, the full development and utilization of solar energy has become one of the focuses of the current community. As a typical application of new energy sources, solar street lamps have corresponding application examples in many areas of China. Solar street lights have the advantages of no need to pay for electricity after installation, no need to set up transmission lines or cable laying, clean and environmental protection, low maintenance costs, etc., and have been favored by relevant parties. Solar street lights appearing in trial or demonstration form can be seen in many cities and villages. . However, there are still many problems in the application of solar street lamps. With the increase of practical applications, there are more and more problems in receiving complaints and repairs from users.
1 Problems in the composition and use of solar street lighting systemsSolar lighting systems can be divided into three main types, including stand-alone systems, grid-connected systems, and hybrid systems. Stand-alone systems are commonly found in residential streetlights, parking lot sign lights, and grid public lighting systems. They typically require batteries and have high storage repair and maintenance costs.
The solar independent street light system can be divided into AC type and DC type according to the load, as shown in the figure. At present, because mainstream lamps are all AC lamps, there are many types of solar lighting systems (such as solar low-voltage energy-saving lamps). The second type of solar lighting system is not used due to the current light efficiency, cost and other factors, but with the future technological innovation, its use will be more and more. The system consists of an induction lamp solar street light.
In the case of ensuring that the luminaire is in the specified working conditions, the system configuration depends mainly on the matching between the solar module, the street lamp controller and the battery. According to the current problems of solar street lights and the current technical level, there are two main problems:
(1) After a period of use, the street lamp does not work for a few days; (2) the service life of the designed battery is about 2 to 5 years, and the actual battery usage is often lower than the design life, or even less than 1 year.
2 problem analysisMany manufacturers do not pay attention to the specific differences of sunshine in various regions when configuring street lamps. They only choose PV modules empirically. Sometimes, in order to meet the low cost requirements of customers, they are equipped with low-cost solar modules, or only consider the power consumption and consumption per day. Electrical matching, without considering battery charging issues.
(1) After a period of use, the street lamp does not work for a few days.
The main reason for this problem is that the component configuration is too low, and there are cases where the battery configuration is too high, but it is mainly the former. After several days of rainy weather, the battery of the street lamp system will be over-discharged, and the controller will have over-discharge protection. At this time, if the solar power generation is less, the battery voltage will not reach the recovery discharge voltage of the controller, and the controller and the load will be powered off. If the component capacity is too small or the rainy weather is too long, it will inevitably lead to no discharge for a long time. Therefore, in the calculation of component capacity, it is necessary to consider the charging time of the battery, and it is full for 2 to 3 days.
(2) Design battery life is about 2 to 5 years, the actual battery usage is often lower than the design life, or even less than 1 year.
The main reason for this problem is the battery configuration or improper operation. For example, the battery capacity is relatively small compared to the number of consecutive rainy days, or the battery is always in a deep cycle when it is working. The second one is the main reason.
Some manufacturers, in order to reduce the above problems, often set the controller to restore the discharge voltage is too small, resulting in the battery is often less charged and then in a discharge state, not well used battery, reducing its service life.
Therefore, a reasonable choice is needed in the voltage setting of the controller to resume discharge.
3 system optimization configuration stepsThe following solutions and optimization methods are proposed for the configuration and the above problems.
Take the 24W 40W induction lamp as an example, according to the daily use hours of 8h, continuous rainy days for 4 days, in Zhenjiang application, combined with local lighting (as shown in Table 1), the specific configuration steps are as follows:
(1) First determine the battery capacity.
When configuring the battery, consider the discharge depth 0175, charge and discharge efficiency 0185, safety factor 111, etc., and estimate the battery capacity according to the load:
111 &TImes;40 &TImes;8 &TImes;4 ÷0185 ÷0175 ÷24 = 9211Ah At this time, actually use 2 12V / 100Ah batteries in series.
(2) Initial configuration of solar modules.
When configuring the components, refer to the local sunshine radiation quantity and select the appropriate tilt angle. Unlike the grid-connected power generation, the solar street light should ensure that the minimum sunshine duration is as large as possible, as shown in Table 1. At this time, the inclination angle is 30°, and the lowest radiation is in October, only 4113kWh / m2 / d, which is 4113h /d when converted to the standard sunshine intensity of 1kW / m2.
Considering that the amount of power generation is affected by azimuth, dust, local sunlight, the photoelectric conversion efficiency of the module, and other efficiency losses of the system, the average power generation efficiency during the system design life is 78%, and the efficiency of the battery system is considered.
PV module capacity = 40 &TImes; 8 × 111 ÷ 0185 ÷ 4113 ÷ 0178 = 12816Wp. At this time, if the component 130Wp is enough, it is likely that the street lamp does not work for several consecutive days.
(3) Optimize component configuration
Considering that the street lamp needs to work continuously for 4 days, in order to ensure that the work can be resumed as soon as possible after 4 consecutive days of discharge, the component capacity needs to be increased, and the full charge time is shortened. If there are more days in the local area for 4 consecutive days, the charging time is required. Control within 2 days.
Take the 160Wp component as an example to estimate the charging time. The charging efficiency is between 019 and 0195, taking 019.
Average battery charging time = 2 × 100 × 12 × 0175 / (019 × 0178 × 160 × 4145 ) = 316 days, the time is too long. Select 190Wp, and the charging time is about 3 days. The 240Wp component also needs to be charged for 214 days. The 190Wp component is actually selected considering factors such as cost.
It can be seen that when configuring components, you can't just look at the power consumption of a single day, but also combine the battery capacity to optimize the configuration.
(4) Street lamp controller selection and optimization
Because the street lamp working voltage is 24V, the battery serial output rated voltage is also 24V, so the controller should also choose 24V rated working voltage, and its photovoltaic module's rated output voltage is 34V. Most controllers on the market today have a maximum input voltage that is twice the rated operating voltage. Therefore, for a system with a total capacity of 190 Wp, two ZXM095W18V-12502 components (monocrystalline silicon solar cells) can be connected in series, and the parameters are shown in the table. If the maximum power operating voltage of a single 190Wp component is 30~34V, it can also be used.
At this time, the series operating voltage = 3414V, the maximum output open circuit voltage = 4214V, and the short circuit current = 5199A. Therefore, the rated charging current of the controller is 10A.
When the controller is selected, it is also necessary to pay attention to overcharge protection, recovery charging, overdischarge protection, and recovery discharge voltage, as shown in FIG. Especially for the recovery discharge voltage, the current 24V controllers on the market are mainly set at 25V or more, and some even 26V. As the first question analyzed earlier, it is very likely that solar street lights will not light for several days.
If the system configuration is unreasonable, it is likely that it will not work for a long time, and the user may think that the street lamp is broken, and the reputation of the company will be affected. Therefore, the recovery discharge voltage cannot be set too high.
But in the same way, if the recovery discharge voltage is set too low, even lower than 23V, in order to reduce the chance of such problems, as the second problem of the previous analysis, it is likely that the service life will be shortened, especially for the battery. This is especially true.
For these two problems with the controller, in order to balance the balance, multiple recovery conditions can be set instead of fixed values.
The working principle of solar street lamps is to convert solar energy into electric energy to realize illumination. The top of the street lamp is solar panel, also known as photovoltaic module. During the day, the photovoltaic components made of polysilicon convert solar energy into electric energy and store it in the battery, so that the solar street lamp is intelligently controlled. Under the control of the device, the solar panel is irradiated by sunlight, absorbs solar light and is converted into electric energy, and the solar cell module charges the battery pack during the day. In the evening, power is supplied to the light source through the control of the controller to illuminate people at night. At night, the battery pack provides power to supply power to the LED light source to achieve lighting functions.
Solar streetlights use solar energy to generate electricity, so there are no cables and no leakage or other accidents. The DC controller ensures that the battery pack is not damaged by overcharging or overdischarging, and has functions such as light control, time control, temperature compensation, lightning protection, and reverse polarity protection. No need to lay cables, no AC power supply, no electricity bills.
The low-carbon, environmentally-friendly, safe and reliable advantages of solar street lamps have been recognized by customers and have been greatly promoted. Therefore, it can be widely used in urban main and secondary roads, communities, factories, tourist attractions, parking lots and other places.
5 ConclusionSolar streetlights are a major area of ​​domestic solar power applications, especially in some areas as demonstration projects for solar energy utilization. The actual application of the quality will greatly affect the future promotion and use of photovoltaic systems in China. Therefore, as a member of the photovoltaic industry, we need to strengthen the experience of the actual application system, comprehensive consideration of the user's cost and system stability.
With the innovation of industrial technology, the conversion efficiency of new materials, solar cells, the cost performance of batteries, and the improvement of intermediate control conversion, the cost will inevitably be greatly reduced.
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