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What is the price of smart solar street lighting for developing world?

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 [16]: 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 [17]. 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 [6]. 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 [18]. 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 producti