Solar channel light system design method

The sun is a huge, long-lasting, endless source of energy. Solar energy is both primary energy and renewable energy. It is rich in resources and can be used free of charge without transportation. It has no pollution to the environment and has the advantages of energy saving, environmental protection and convenience.

According to the amount of solar radiation received, China can be roughly divided into five categories. Shenzhen is located in the subtropical zone and has a warm winter and hot summer weather. It belongs to the third category. The annual sunshine hours range from 2200 to 3000 hours, and it has favorable natural conditions for using solar energy.

There are three kinds of direct application of solar thermal conversion, photoelectric conversion, photochemical conversion, indirect and comprehensive use of more variety. Photoelectric conversion mainly includes solar panels and solar power supply systems; photothermal conversion mainly includes water heaters, water boilers, solar cookers, and dryers; photochemical conversion is mainly applied to photosynthesis and photoelectrochemistry, and is still in the experimental research stage.

I. Introduction to Solar Channel Light System

1, solar channel light system installation background

There are many overpasses in Shenzhen with a length of more than 40 meters. Due to lack of daylight, these passages are very dark during the day. Especially in the more than one hour and rainy days before the street lights are turned on and after the lights are turned off, the passages are dark. For the safety of the citizens, the passage must be lighted for 24 hours. However, the original channel light is connected to the street light power and can only be turned on at night. If the city power supply is used to power the lights in the daytime, the lines must be re-layed, the investment is large, and the construction is difficult; the use of solar photovoltaic systems requires less power and the construction is convenient.

On the other hand, the power supply in Shenzhen has been strained in recent years. The government advocates saving electricity. Therefore, it is necessary to install a solar channel light system.

2, channel conditions

The following section will discuss the composition of the system by taking Honghu Interchange southbound as an example.

The channel on the south side of Honghu Interchange is 40 meters long and 6 meters wide. The distance from the access point to the solar installation is about 15 meters. The original three sets of 250W high pressure sodium lamps have power supply at night.

3, system principle

Photovoltaic conversion of solar energy refers to the process by which the sun's radiant energy photons are converted into electrical energy through semiconductor materials. It is often called the "photovoltaic effect."

The total power of the original channel lights is 750W. The required solar battery power and battery capacity for using solar energy for power supply are relatively large, and the system cost is high. Moreover, a set of lamps is always on for 24 hours*365 days, and the lamp life will be reduced. Therefore, in order to ensure a stable lighting effect, a solar channel lighting system is additionally installed. In the evening, when the mains power supply, the original channel lights are on; at night, when the mains power fails or during the day, the solar energy-powered channel lights are turned on to ensure that the channel is always on.

Second, DC / AC load comparison and selection

If the DC load is selected, the intermediate part of the inverter can be omitted and the energy utilization efficiency can be improved. However, due to the length of the channel of 40 meters, from the battery to the end of the lamp about 40+15+5=60 meters, 24V DC voltage line loss up to 10%; In addition, DC low voltage and large current control loss, lifting voltage technology is more complex, DC energy-saving lamps Low light efficiency (45Lm/W), short life (5,000 hours), difficulty in purchasing, etc.

In contrast, although the use of AC load utilization is slightly lower, the inverter's conversion efficiency is >90%, and the loss is not very large, while the AC load is more practical and convenient, so the AC load is selected.

Third, the choice of light sources and lighting fixtures

Through the comprehensive comparison of light source efficacy, lifespan, price, and versatility, choose 5*25W high-efficiency energy-saving lamps.

Fourth, solar panels
Solar panels are the main component of solar photovoltaic conversion. The peak power Pk of a solar cell module is determined by the local average solar radiation intensity and the end-use electrical load (electricity demand).

1. Peak power selection (estimation formula):
Pk = lamp power × number of lamps × daily use time ÷ effective daily sunshine hours ÷ practical use of solar cell array power factor ÷ battery conversion efficiency ÷ inverter efficiency Pk = 25 (W) × 5 (sets) × 12 (H ) ÷5(H)÷0.7÷0.85÷0.9=560.22W
among them:
1) Since the lighting time of the mains channel lights is adjusted by the theodolite according to the seasons, the solar channel lights are lighted for 11 to 14 hours a day for 12 hours.
2) The practical power factor of the solar cell array takes into account the charging efficiency of the solar panel and the losses during the charging process, taking 0.7.
Therefore, the solar panel power is 600W (75W×8pcs)
3. The installation inclination angle is 33-35 degrees, and the direction is southward, which is not only convenient for fully absorbing solar energy, but also can use rainwater to self-clean the solar panels.

Fifth, the controller

The controller uses a PWM pulse width modulation controller. Has the following features:
1, overcharge protection: When the battery voltage exceeds 28V, stop charging;
2, over discharge protection: When the battery voltage is lower than 22V, cut off the load;
3, battery charging temperature compensation;
4, positive polarity reverse protection;
5, short circuit protection;
6, overload protection;
7, overheat protection (with heat sink);
8, lightning strike protection;
9, low-power AC supplementary charging system: When the rainy days, solar energy is insufficient, the battery voltage is lower than the DC 22V, in the evening through the high-frequency rectifier switch AC 220V mains converted into 24V DC, the battery to supplement charging;
10. Detecting electricity and switching: When there is mains power at night, the mains channel light is on, the controller turns off the solar channel light; when the mains fails or during the day, the controller detects no mains signal, and turns on the solar energy channel. light. This can ensure that the channel lights up for 24 hours more than when the switch is installed.

Six, the battery

A battery is a device that stores electrical energy. Since the input energy of the solar photovoltaic power generation system is extremely unstable, it is generally necessary to configure a battery system to work.

Due to the outdoor installation, valve-controlled maintenance-free lead-acid batteries are used. Because 12V batteries are more common, they are connected in 24V with two 12V batteries.

1, battery capacity selection:

In the controller section of the previous section, it is possible to supplement the battery with the mains electricity at night when it is rainy, and to turn on the solar channel light at night when the mains power fails. However, in the worst case, when both conditions occur at the same time, it depends on the battery alone to supply power. On the other hand, in order to ensure stable operation of the battery, it is required that the battery discharge depth be between 40% and 60%. Of course, maintenance workers will deal with mains failures in a timely manner, so it is only necessary to consider the situation where the mains failure and rainy days occur for one day at the same time.

The battery capacity is 25W×5×12h×1÷24V÷0.4÷0.85÷0.9=204.25Ah
Choose two 12V/200Ah batteries.

2. When the battery is used for the first time, it must be charged to the rated capacity before it can be overcharged or overcharged.

Seventh, inverter

The inverter converts DC power into AC power through the turning on and off of power semiconductor switching devices.

1. Comparison of three types of inverter waveforms:

The structure is simple, the manufacturing cost is low, the conversion efficiency is higher than 75%, and the inductive reactance load is poor. It is suitable for general impedance loads such as ordinary incandescent lamps.
Sine wave: See Figure 4. The conversion efficiency is as high as 95%, and the waveform is accurate and stable. It is suitable for telecommunication communication equipment and all electrical appliances, but its cost is high.
Correct sine wave: see Figure 5. Conversion efficiency> 90%, performance close to sine wave, lower cost. Therefore, the system uses a modified sine wave inverter.

2, power selection

Since the start-up current of the energy-saving lamp is 5-7 times of the rated operating current, and the load power is 125W, the power of the selected inverter is 800W/24V.

Eight, anti-theft measures

Controllers, batteries, inverters, etc. are all installed in the distribution box, placed in the gantry frame of the solar cell array at 4 meters; the wire sleeves are fully enclosed, and the lamps are installed with anti-theft cages.

Nine, other components

The solar cell square array adopts a windproof structure, the column must not be smaller than Φ140mm, and the structural parts adopt internal hot-dip galvanizing outside spray (make sure that it does not rust for 10 years).

The wire uses single-phase RVV-3*4mm2. The column grounding resistance is not more than 10 ohms. All metal shells that the human body may contact are reliably grounded.

Ten, summary

The general solar street light is charged during the day to discharge at night, and this system needs to be turned on under the condition that the mains channel light cannot be turned on due to the actual needs of the channel, but the basic principle is the same.