Street lighting is a public good benefit that enhances safety, comfort, commercial prosperity, and socialization. Lower solar panel prices opened new chapter in solar street lighting industry.
Safety and security increase not only because criminal activities are easily detected and prevented but also because traffic accidents decrease. Commercial prosperity occurs as a consequence of higher productivity and extension of marketplace hours. Socialization will also increase with street lighting because an illuminated village invites people to the streets and contributes to a decrease of rural exodus.
There are 3 main objectives to achieve with street lighting:
1. To allow all street users to proceed safely (motorized traffic vehicles, slow moving vehicles, cyclists, pedestrians and animal drawn vehicles) 2. To allow pedestrians to see hazards, orientate themselves, recognize other pedestrians and give them a sense of security 3. To improve day and night time appearance of the environment Usually, street lighting is supported by a public entity (government, municipality, or other) that should purchase the equipment. Users have the responsibility of using it properly and report operational issues to the contractor. In some countries, street lighting is a public responsibility while in others all the taxpayers contribute to street lighting, and finally in others just some of them pay for it. For example, in Portugal, municipalities have to pay for street lighting, in Ghana urban communities and companies contribute with some extra payments or taxes for street lighting (as well as rural electrification projects) , and in Sudan the group of families in the vicinity of each light are supposed to cover their cost (if not, the light is moved) .
Street lighting systems consumes 43.9 billion kWh of electricity every year all over the world. For example, Peninsular Malaysia used 876.3 GWh of power for public lighting during 2006 (which corresponds to 1.07% of Peninsular Malaysia electric demand). Regardless of who pays for street light, a bet in energy efficiency is essential because energy efficient technologies and designs can reduce street lighting costs substantially. This may help municipalities to expand their services by providing lighting in low income and other undeserved areas.
Some recommendations related to street light strategies should help to accomplish optimal lighting solutions . These recommendations are divided in recommendations for energy savings and recommendations resulting from user needs.
The first group of recommendations are : 1. Prior to reconstruction of street lighting a choice between an upgrade and redesign should be made. 2. Special attention should be paid to the determination of the street lighting class. 3. Measurements for determining the road surface reflection properties are recommended. 4. If high-pressure sodium (HPS) lamps are applied, they should be used with improved photometric and technical characteristics. 5. Luminaires which are efficient, easy to handle, and with the degree of protection of at least IP652 are recommended. 6. It is very important to use the correct value of maintenance factor in the design process. 7. Luminaires characterized by a power factor of at least 0.95 are recommended. 8. The use of dimming system is recommended.
Recommendations resulting from user needs are: 1. Places where people gather and places with intensive pedestrian activity should be illuminated by white light sources characterized by excellent colour rendering. 2. Dark areas should be avoided. 3. The effects of obtrusive light should be minimized. 4. Position, size and design of the pole and luminaire should not stand out from the environment. 5. Full galvanized steel poles should be used instead of painted ones. In all street lighting systems (SLSs) the lamp is the main component. Different light sources can be used in SLS, that can be divided into 4 groups : incandescent, fluorescent, high-intensity discharge (HID) and light emitting diode (LED) lamps. In street lighting HID (which includes HPS), induction and LED lamps are the most commonly used . In the next subchapter an introduction to HID and LED lamps will be presented. The type of connection and energy source is also an important aspect. SLSs can be on-grid or off-grid. The first one is the most commonly used in the world (mainly in developed countries). Off-grid or stand-alone street lighting appears to fulfil and be the best solution to rural or remote areas needs. In these places, a grid connection does not exist, grid extension cost is exorbitant, and inaccessibility is a huge problem. A World Bank study proves that on rural electrification programs the average cost of grid extension varies between US$5,000 and US$10,000 per km in "normal" terrains and between US$19,000 and US$22,000 per km in difficult terrains . This is obviously a huge contribution to street lighting investment costs in remote areas. In addition to this cost in developing countries the majority of SLSs are assembled with poor quality components, and no lighting requirements are taken into account. This usually results in oversizing, no maintenance, vandalism and poor lighting. These facts, combined with unstable and limited diesel powered grids, high environmental temperatures and low electrification levels, offer several challenges to this market . Different energy sources are used to power street lighting. In grid connected systems, the energy used comes from the grid. In stand-alone systems, photovoltaic, wind and diesel generators are the most commonly used energy sources. Each one of these sources may be used alone or in a combination that includes two or three sources. Models based on renewable energy sources are the ideal ones because they contribute to the sustainability lowering the running costs and being environmentally friendlier. In these regions it is especially important that running costs (like fuel) are minimized, or even eliminated, if one expects any kind of maintenance to be done. The main drawbacks of these systems are: the fact that renewable energy sources always present a variability; the correct choice of the best solution in a given place must be accessed through a careful analysis of local conditions3 ; and also the fact that energy production will not be in general synchronized with demand and thus a battery bank is always necessary for energy storage.
2.1 Types of Light Sources As mentioned above, different types of light sources are available on the market. For street lighting applications the most commonly used are HID and LED. These two types of light sources will know be briefly presented. High-intensity discharge light sources can be divided in four types: metal halide, high-pressure sodium, low-pressure sodium and mercury vapour. The light production technique is similar to
he one used in fluorescent lamps but here visible light is produced, and so there is no need for the phosphor coating. The bulb is made from a quartz or ceramic glass envelope (Figure 3). This envelope provides a stable thermal environment for the arc tube, and the atmosphere inside it prevents the electrodes oxidation, and also reduces the amount of UV radiation emitted by the lamp.
HID bulbs produce light when an electric arc passes between the electrodes in the pressurized arc tube, causing metallic additives to vaporize. Arc tube contains a mixture of argon, mercury, and metal halide salts. A high voltage pulse is applied to the electrodes to ionize the gas. When the gas is fully ionized, an arc is created and current (limited by the ballast) flows across the tube. As the pressure and temperature inside the tube increase, the materials within the arc tube vaporize, and light is emitted in the form of visible light (and UV). Because HID lamps require a high voltage for ignition, a current limitation during warm-up, and a constant power while running, the existence of electronic ballast is needed. Ignition time ranges between 1 and 15 microseconds. After ignition the lamp voltage drops quickly due to low lamp impedance after discharge starting, whilst the current increases to a significant value (ballast avoids a short circuit occurrence). During the period of lamp warming up (the warm up time ranges between 1 and 4 minutes for pulse-start technology and 2 and 15 for probe-start), the current decreases and the voltage increases. This second effect is bigger than the first one resulting in a power increase during this period. Eventually lamp voltage reaches its nominal value and the power is regulated to a constant level.
These HID lamps have long lifetime and are extremely energy efficient, but they do not produce pleasing light colors (exception for metal halides). They are most commonly used for outdoor security and area lighting.
Light Emitting Diodes (LED) as well as organic light-emitting diode (OLED) and polymer light-emitting diode (PLED) belong to the group of solid-state lighting (SSL). SSL systems produce light when current is passed through a pn junction, causing electrons and holes to recombine and generate the emission of photons. The radiation emitted in this process in a given
pn junction is essentially monochromatic, presenting a colour that depends on the energy gap through which the electron-hole recombination process occurs. LEDs are commonly made from aluminium-gallium-arsenide (AlGaAs) based pn junctions , , . White LED light can be obtained in two different ways: by a combination of phosphor excited by blue or UV LED emission, or by a mixture of multi-colour LEDs (RGB4 ). The last option has a lower efficiency due to the power loss in the down conversion process . A single light LED bulb is a combination of different LEDs . In the present work, LEDs will be used mainly because they are the most energy efficient light source, and because these light sources are easily controlled through dimming. LEDs are on the streets since the early 90s, when cities throughout Europe and USA started replacing incandescent-based traffic lights by LEDS. The market share of LEDs has continued to grow in the field of street lighting, and it is expected that this type of light source will dominate in the future, at the expense of high intensity discharge street lamps . If properly used, LEDs present lifetimes of 10 to 15 years, which is equivalent to more or less 60,000 working hours (that is at least 3 times higher than current technologies), offer energy savings that can achieve 50%, and have a low environmental impact (it is a RoHS5 compliant product).
They also reduce light pollution (better light distribution by the ability to precisely control light direction through optical optimization), have better colour rendering and colour temperature, and lower power consumption (higher efficacy (in lm/W), more lux per Watt). Moreover, LEDs have a lower operating and maintenance cost (O&M) mainly because they offer a reduction in energy use as well as a higher lifetime. Thus, the return on investment (ROI) for new equipment based on this technology will be faster, even with higher initial cost as still happens today. It is important to stress that accomplishing the standard regulations for luminance level and uniformity is easier to achieve using LED street lamps than with conventional lamps. LEDs have also a dimming option that allows an adjustment of power using intelligent systems, which will reduce, even further, energy consumption and light pollution, as well as a quick turn on/off (because the problem with hot ignition is eliminated) . With respect to nocturnal insects, LEDs have also a big advantage: LEDs emit light in a small peak in a blue range and smaller than conventional light sources in the green range; since insects are attracted to the emission of UV-blue and green light they will be less attracted by a LED light source. In addition, as LED can reduce power consumption in lighting, cooper wire of transmission lines can also be reduced. Nevertheless, LEDs also have some disadvantages, namely, high investment cost, the need for a driver and for a heat sink. These needs appear because LEDs are greatly influenced by electric failures and temperature. Furthermore, failures have been identified in at least one of four functional aspects of luminaire design and manufacturing using this type of light sources: power management, thermal management, optical management and luminaire assembly integrity. Power management should ensure that the power delivered to the LED is appropriately sized and filtered. Thermal management should guarantee that heat generated by 1the LED is removed in order to keep the pn junction temperature within the acceptable range. Optical management should ensure that light output is correctly shaped and directed through the desired surface. Assembly integrity should ensure that luminaire housing design and materials must provide sufficient protection for the LEDs according to the anticipated working environments .
Street lighting, as a public good service, will increase the quality of life of people by increasingsafety, comfort, commercial prosperity, and socialization. The products were developed takinginto account EN13201. The "worst month" method was used to size the stand-alone product,while for on-grid system a typical daily failure of 3 hours was considered. Performance analysisacross Africa demonstrate that the system can be installed everywhere, although battery lifetimedecreases as distance from equator increases. Developed products' initial investment is highercompared to conventional grid power system.In both systems storage capacity requires special attention since it is essential to know batterybehaviour while it is charging and discharging, as well as temperature effect. Monitoring batterycharge state could be important, since with this information one can in each moment forecast theenergy that is available and adjust the lamp diming to fulfil the lighting time still required. Forthis it would be better to measure the battery current rather than the voltage, because the resultwill be much more accurate and independent of the type of the used battery. The most availablebattery type in the market was used (VRLA), although in the future a different type should beused.In the stand-alone model, generation and consumption always occur at non overlapping timeintervals and in most part of the year this system remains underused. This means that, using theinstalled PV power, other uses for the generated electricity could in principle be done after thebattery is fully charge. However, in a decentralized solution the energy surplus cannot beenough to suppress other energy needs. A local mini-grid for street lighting with centralizedstorage could be interesting in this context, namely because these other uses for the energy (likecell phone charging for instance) could lead to a lower payback time, and also because of alower theft risk and probably less expensive maintenance. Therefore, centralized solutions canbe an area for further investigation.Regarding monitoring, if remote monitoring is useless, a charge controller with automaticdetection of day and night can be used in the stand-alone system and Arduino is unnecessary. Inaddition, the Zener diode can be replaced by an optocoupler, which will isolate power circuitfrom signal circuit. If we pretend to include monitoring, a new concept needs to be defined.Adafruit Data Logger Shield should be replaced by Arduino GSM Shield, meaning that SD cardis not necessary and a SIM card should be used. The Arduino GSM Shield allows an Arduinoboard to connect to the internet using the GPRS wireless coverage (requiring at least anavailable second-generation wireless telephone technology).One other important consideration is that, in the near future, the outsourced items should belocally assembled. This would not only contribute to local economy growth but also to a lowercost and probably a faster delivery time. This should be considered in marketing strategydefinition in the future.Developed prototype has been working in accordance with our expectation. Grid connectedsystem has not been tested, although it has a high potential to overcome the problem ofunreliable grid despite entailing a highest investment than the one corresponding to theluminaire alone. Concerning the marketing plan, an extrapolation from Bambadinca was done.According to this study, the number of poles per person and per household (based on populationdensity and street distribution of Bambadinca) ranges between 0.18 and 0.26, while the numberof poles per household ranges between 1.14 and 1.64. If we considered a market share of 5% inGuinea-Bissau, Uganda and Mozambique, as well as a market share of 2% in Kenya and Tanzania, the total number of poles will be between 754.6 and 1,084.2 thousand poles (482.3for the first three countries and 272.3 for the last ones for the lowest option, and 693.0 plus391.2 for the most expensive option).
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