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

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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.
smart solar street lights
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


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


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


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 [16], [17], [21]. 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 [22]. A single light LED bulb is a

combination of different LEDs [16]. 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 [23]. 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) [24]. 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


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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Solar poles for versatile solutions