Photovoltaic street lighting is an elevated light source that is powered by solar panels usually installed in the lighting structure or integrated into the pole itself. Solar panels power a battery, which powers a fluorescent or LED lamp at night.
Features
Most photovoltaic lighting switches on and off automatically when sensing outside light using solar panel voltage. Photovoltaic poles are designed to work throughout the night. Many can stay lit for more than one night if the sun is not in the sky for an extended period of time. Older models included light bulbs that were not fluorescent or LED. Solar lights installed in windy regions are often equipped with flat panels to better handle winds.
Modern projects use wireless technology and fuzzy control theory for battery management. Light poles using this technology can operate as a network with each lamp having the ability to switch on and off the network.
Components
Solar street lights consist of four main parts:
Photovoltaic panel
The photovoltaic panel is one of the most important parts of a photovoltaic street lighting, as the solar panel can convert solar energy into electricity that the light bulbs can use. There are two types of solar panels used in solar street lighting: monocrystalline and polycrystalline. The conversion rate of monocrystalline solar panels is much higher than their polycrystalline counterparts. Solar panels also vary in power systems.
Light fixture
LEDs are generally used as the primary lighting source of modern photovoltaic street lighting, as the LED will provide much greater brightness with less energy consumption. The energy consumption of an LED luminaire is at least 50% lower than the HPS counterpart which is widely used as a lighting source in traditional street lights. The lack of warm-up time on the LEDs also allows the use of motion detectors for additional efficiency gains.
Rechargeable battery
Batteries store the electricity generated by the photovoltaic panel during the day and provide energy for the luminaire at night. Battery life cycle is very important for light life and battery capacity will affect lights backup days. There are two types of batteries used in solar powered photovoltaic street lighting - gel cell deep cycle batteries as well as lead acid batteries. Lithium-ion batteries are also popular because of their compact size.
Pole
Strong poles are needed for all street lights, especially PV poles, as there are usually components mounted on top of the pole: light fixtures, panels, and sometimes batteries. However, in some more recent projects, the photovoltaic panels and all electronic components are integrated into the pole itself. Wind resistance is also a factor.
Also, there are accessories for these types of posts, such as foundation cage and battery box.
Type
Each street light pole can have its own photovoltaic panel, independent of other light poles. Alternatively, multiple panels can be installed as a central power source in a separate location and provide power to multiple lamp posts.
All-in-one type photovoltaic street lights are gaining popularity due to their compact design that incorporates all necessary parts in a compact manner, including the battery.
Benefits
• Photovoltaic public lighting is independent from the electricity grid. Thus, operating costs are minimized.
• Requires much less maintenance compared to conventional street lights.
• As external wires are eliminated, the risk of accidents is minimized.
• Electricity produced from photovoltaic panels is non-polluting.
• Separate parts of a solar panel system can be easily transported.
• Energy costs can be saved.
Disadvantages
• The initial investment is higher compared to conventional street lighting.
• The risk of theft is greater as equipment costs are comparatively higher.
• Snow or dust, combined with moisture, can accumulate on horizontal photovoltaic panels and reduce or even stop energy production.
• Rechargeable batteries will need to be replaced several times over the lifetime of the luminaires, adding to the total lifetime cost of the light.
• Battery charge and discharge cycles are also very important considering the total cost of the project.
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