Street lighting design:
Street lights that are installed on streets and highways need constant energy sources so that they can stay lit throughout the night. The cost of energy production, transmission, conversion and distribution along a long highway is very high. Therefore, the use of renewable energies such as solar and wind energy to provide the required power for street lighting is a cost-effective alternative.
Suppose 2000 light poles are installed for street lighting in a 100 km long highway. Because of their long distance, the street lights will have a high cost of cabling. The transformers that are installed in this way, in addition to the high cost, will also bring voltage conversion losses. So, if energy is produced and consumed in a scattered manner, it can bring more efficiency and lower cost for the whole project.
A solar system for street lighting consists of 4 main components. The solar panel is responsible for generating energy during the day. Solar charge controller that stores the energy produced by the panels in the battery. The battery is responsible for storing energy for night use. If the street lighting equipment is AC, we need an inverter to convert the energy.
Stay with us to learn how to design a solar system for street lighting.
First step: Designing street lights
Before designing the solar system, the design of street lights must be done. After the design is done and the street lighting equipment is determined, write down the power consumption of the lights in watts.
Note that the power consumption only indicates the amount of energy consumed by the lamp to produce light. Higher power does not necessarily mean more light. Rather, lumen is a unit of light measurement, and the more it is, the more light you will have. For example, you need 2000 lumens for indoor lighting. For this purpose, you can use 6 watt LED lights or 15 watt fluorescent lights. Both lights produce equal light, but the energy consumption of LED lights is almost one third of fluorescent lights.
توان مصرفی بیشتر همیشه معادل تولید انرژی بیشتر نیست.
You can also use lights with high efficiency and less energy consumption in the design of the passageway lighting to reduce your energy production and storage costs. In this article, we assume that we want to use a 200 watt street light base.
Second step: designing solar panels for street lights
The solar panel should generate all the required energy that the street lights use at night and store it in the battery during the day. For this reason, we first calculate the total energy consumption of a lamp at night. A light consumes 200 watts of energy per hour, and assuming it is left on for 10 hours a night, consumes 2,000 watt hours or 2 kilowatt hours of energy per day.
On average, in Iran, each solar panel has 5 hours of useful production during the day. Of course, this amount is around 4 hours in the northern provinces and around 6 hours in the provinces. So, to supply 2 kilowatt hours of energy every day, it is enough to divide 2000 by 5. So we need at least 400 watts of solar panels in this project.
Considering the losses of dust, heat, ohmic, etc., it is better to consider the solar panel up to 30% more. It means to use 520 watt panel in this project.
As you can see in the above picture, the open circuit voltage of this panel is about 49 volts and its short circuit current is about 14 amps. Considering these two parameters, we design other solar system equipment for street lighting.
The third step: battery design for street lights
To calculate the battery, we have to divide the daily consumption of the street lights by the battery capacity. The daily consumption of street lighting in this example was 2 kilowatt hours. We also assume that we want to use 12 volt and 100 amp hour batteries that are very common in Iran. The capacity of these batteries is 1200 watt hours. Of course, in the design, we do not allow the battery to be empty, because its life will decrease.
Therefore, we consider only 80% of its capacity, that is, the capacity of each battery to provide energy for road lighting is 960 watt hours. By dividing 2000 watt-hours by 1080 watt-hours and then randing it, we find that in this example we need 2 12-volt 100 amp-hour batteries.
Considering the 49-volt voltage of the panels, it is better to reduce the voltage difference between the panel and the batteries. For this purpose, we connect two batteries in series with each other.
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Fourth step: design of charge controller and inverter
The charge controller is a DC to DC converter with the aim of increasing power efficiency. This device adjusts the output voltage to the required voltage of the battery. When designing the charge controller, we must know the allowed input and output current and choose the appropriate product. The input current to the charge controller is the same as the current of the panel, i.e. 14 amps. The output current is equal to the power of the panel divided by the voltage of the batteries. That is, we have to divide 520 by 24, which is 21 amps.
If the street lighting is DC or direct current, we don’t need an inverter and the cost is zero. But if we use AC street lights, we have to put 50% more than the power of inverter lights. That means we should consider a 300 watt inverter.
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