**4. Indoor and outdoor DC-lighting experience**

• Electrolytic capacitor: It levels the pulsating rectified voltage signal. In DC, they can suppress voltage dips of the energy source but most lighting applications may consider accept-

24 Light-Emitting Diode - An Outlook On the Empirical Features and Its Recent Technological Advancements

The LED driver can be housed in an external case or in the device itself (which is much cheaper and significantly simplifies the luminaire configuration). Eliminating the AC/DC components

able to pass them and allow short flickers on the LEDs.

**Figure 7.** Typical topology of a common AC lamp driver compared to a DC counterpart.

**Figure 8.** Efficiency versus load curve of commercial AC/CC switch-mode converter drivers.

Nowadays, the US is the country that is adapting more DC-lighting installation in a context where, according to the 2016 calculation of its Energy Information Administration (EIA), this country used 15% of all its consumed energy for lighting purposes [12]. This is a significant reduction from the 22% calculated in 2009 due to the massive installation of LED equipment and efficiency initiatives as the AC to DC residential and commercial indoor grid translations. On account of this, these two sectors figure as very significant with 7% of the total electricity consumed (approx. 279 billion kWh) [13].

If all general purpose lighting equipment in the world were converted to LED light sources (agreeing an average 40% saving at each point), their energy consumption could be decreased by around 1000 TW h/year, reducing 200 million tons of greenhouse gas emission [7]. Any additional development that allows higher efficiencies, as the elimination of the AC losses, has also significant relevance due to the large amount of energy involved.

### **4.1. Indoor direct current indoor led lighting: trends and applications**

On average, 80% of the energy used in modern buildings power DC loads. Low-power devices (≤50 W), like most indoor LED lamps, are responsible for 35–50% of this use, and all of them work with small power-wasting converters. LEDs and DC power distribution in buildings can notably enhance the efficiency of this significant amount of energy.

As it is considerably difficult to eliminate all the AC loads and the general distribution grid, the basic consensus is to replace all the many AC/DC converters placed on each luminaire with a common centralized frontend to provide high-efficiency conversion and protection and then conduct the electric power in DC to the LED fixtures.

### *4.1.1. Development of systems*

LED matrixes may work from just 3.3 VDC. Over this voltage, many possible solutions can be implemented using different serial/parallel LED configurations. It is important to select the most appropriate solution to achieve the highest energy efficiency and the safest operation conditions. The main problem is that these two concepts are here antagonists. A significant number of DC distribution systems have emerged over the years, and, at present, it seems yet far to achieve a unique standard. Special focus has been put over several specific supply voltage levels along with the type of cable and connections to be used. The most developed proposals are presented in **Table 1**. The most significant aspects that are important to consider choosing one of these systems for a specific installation are described in the subsequent text.

consumption within PV power generation capability, especially when combined with control

According to the nature of LEDs, PV panels, and batteries, it is easy to use LVDC with this type of integrations as they allow a more flexible PV panel configuration and reduce voltage

Cable losses are determined by their length, diameter, and the conducting material. A copper

an energy loss of 3%. If this length increases to 50 m, energy loss becomes 16% and for 100 m raises to 32% (which erases all the efficiency advantages of DC lighting). Cable losses also

has 16% energy losses in a 1-m cable and 47% in 3 m. Working with higher voltages, even still within VLDC, reduces these losses by a square factor of the voltage variation. Moving from

The spatial layout is very important to limit this distribution problem. Large buildings will require several energy AC/DC converters placed in different powering sectors. Another way to reduce cable losses is to set up several independent power supply units (PV panels and batteries) in these sectors. Although this strategy implies the use of extra solar charge controllers,

Protection systems are among the main challenges in the design and operation of DC lighting. DC power distribution, as well as AC, becomes more dangerous as its voltage level increases but, in all cases, fast-speed fault protection, including coordination and interruption, is the

The primary protection in DC lighting grids is the circuit disconnection by overcurrent detection devices: circuit breaker or fuses. They have to be specifically designed as in DC there is no zero crossing in the waveform and they have to break the full fault current. However, they are becoming more common as more DC installations are generated. On the other hand, as total power is reduced and the most extended standards work in VLDC, grid-lighting protection is usually incorporated inside the driver modules with solid-state circuit breakers, and there is

Several significant experimental research installations involving DC lighting with published

Worldwide, outdoor public lighting means, on average, a reduced amount of the total energy usage (3% of the total energy consumed) compared with that used for indoor installations

cross section, distributing 100 W at 12 VDC over a 10-m distance, generates

copper wire, 1-kW LED projector

DC Network Indoor and Outdoor LED Lighting http://dx.doi.org/10.5772/intechopen.74974 27

systems that are able to regulate energy consumption to avoid deep discharges.

limit the use of high power luminaires. In a 12VDC 10-mm2

12 to 48VDC improves cable transmission efficiency by a factor of 16.

this might be the most efficient way to illuminate large buildings.

essential requirement to be protected against failures as short circuits.

conversions.

*4.1.1.2. Cable losses*

wire with a 10-mm2

*4.1.1.3. Protections*

no need of adding it externally.

*4.1.2. Research installation experiences*

results are presented in **Table 2** [18].

**4.2. DC outdoor led lighting: trends and applications**

#### *4.1.1.1. Solar energy*

These renewable sources are not yet the perfect solutions but match significantly well with LED lighting. In fact, DC LED lighting was first developed to be powered off-grid exclusively with solar energy as LED-lighting technology is efficient enough as to reduce its required


**Table 1.** Common voltage levels for DC indoor lighting: characteristics and standards.

consumption within PV power generation capability, especially when combined with control systems that are able to regulate energy consumption to avoid deep discharges.

According to the nature of LEDs, PV panels, and batteries, it is easy to use LVDC with this type of integrations as they allow a more flexible PV panel configuration and reduce voltage conversions.

### *4.1.1.2. Cable losses*

most appropriate solution to achieve the highest energy efficiency and the safest operation conditions. The main problem is that these two concepts are here antagonists. A significant number of DC distribution systems have emerged over the years, and, at present, it seems yet far to achieve a unique standard. Special focus has been put over several specific supply voltage levels along with the type of cable and connections to be used. The most developed proposals are presented in **Table 1**. The most significant aspects that are important to consider choosing one of these systems for a specific installation are described in the subsequent text.

26 Light-Emitting Diode - An Outlook On the Empirical Features and Its Recent Technological Advancements

These renewable sources are not yet the perfect solutions but match significantly well with LED lighting. In fact, DC LED lighting was first developed to be powered off-grid exclusively with solar energy as LED-lighting technology is efficient enough as to reduce its required

for Solar Home Systems) [14] <75 VDC Council

trucks, motor homes, caravans, and boats

inside the DC lamps

combines power and

Maximum allowed: 100 W at 60 V

230 VAC (needs equal insulation properties). Generates only about one-third of the losses in converters and cables

• - Minimum cable losses TBINK-LVDC working group

48 Allows working with higher power devices

emergealliance.org • No protection against direct

control.

[17]

at DKE/VDE DISADVANTAGES

24 Intermediate solution UL 2108

UL 1838 & UTSFfSHS (Universal Technical Standard

Emerge Alliance (US) www.

IEC 60364–7-715:2011 EDISON project (EU) http:// www.project-edison.eu/ [13]

PoE (Power over Ethernet) Lighting systems [15, 16]

IEC SG 4 Group "LVDC distribution systems up to

1500VDC"

**Range Characteristics VDC Details Standards**

• No grounding needed Low voltage conversions

DISADVANTAGES 60 Ethernet cabling

VLDC ADVANTAGES 12 Most used in cars,

• Safe from electric shock and

• Many commercially available devices

contact is required

generators and batteries

• - Relatively high cable losses (depends on the length)

• - Complex security systems

• - Arcing appears when a load is unplugged Internal arcing chambers. Voltage broken protection Standard IEC 60947–2 -3

are required

DC <1500 VDC ADVANTAGES 380 Similar DC voltage than

**Table 1.** Common voltage levels for DC indoor lighting: characteristics and standards.

<60 VDC • Simple adaptation of PV

fire hazard

*4.1.1.1. Solar energy*

Directive 73/23/

EEC

NFPA 70 National Electrical Code

Low Voltage Directive (LVD) 2006/95/EC

Cable losses are determined by their length, diameter, and the conducting material. A copper wire with a 10-mm2 cross section, distributing 100 W at 12 VDC over a 10-m distance, generates an energy loss of 3%. If this length increases to 50 m, energy loss becomes 16% and for 100 m raises to 32% (which erases all the efficiency advantages of DC lighting). Cable losses also limit the use of high power luminaires. In a 12VDC 10-mm2 copper wire, 1-kW LED projector has 16% energy losses in a 1-m cable and 47% in 3 m. Working with higher voltages, even still within VLDC, reduces these losses by a square factor of the voltage variation. Moving from 12 to 48VDC improves cable transmission efficiency by a factor of 16.

The spatial layout is very important to limit this distribution problem. Large buildings will require several energy AC/DC converters placed in different powering sectors. Another way to reduce cable losses is to set up several independent power supply units (PV panels and batteries) in these sectors. Although this strategy implies the use of extra solar charge controllers, this might be the most efficient way to illuminate large buildings.

#### *4.1.1.3. Protections*

Protection systems are among the main challenges in the design and operation of DC lighting. DC power distribution, as well as AC, becomes more dangerous as its voltage level increases but, in all cases, fast-speed fault protection, including coordination and interruption, is the essential requirement to be protected against failures as short circuits.

The primary protection in DC lighting grids is the circuit disconnection by overcurrent detection devices: circuit breaker or fuses. They have to be specifically designed as in DC there is no zero crossing in the waveform and they have to break the full fault current. However, they are becoming more common as more DC installations are generated. On the other hand, as total power is reduced and the most extended standards work in VLDC, grid-lighting protection is usually incorporated inside the driver modules with solid-state circuit breakers, and there is no need of adding it externally.

### *4.1.2. Research installation experiences*

Several significant experimental research installations involving DC lighting with published results are presented in **Table 2** [18].

### **4.2. DC outdoor led lighting: trends and applications**

Worldwide, outdoor public lighting means, on average, a reduced amount of the total energy usage (3% of the total energy consumed) compared with that used for indoor installations


**Table 2.** DC indoor-lighting experimental research installations.

(17%) [1]. However, this is still a major market where efficiency improvements can make significant advances in sustainability.

However, there are still uncertainties about the technical capability of this type of equipment in order to match their performance to their AC grid equivalents in lighting installations with large regulatory requirements: high-density traffic roads. We present a technical evaluation of the capability of present equipment to achieve these requirements in different global locations based on energy generation capability of solar panels, efficiency of DC LED luminaires, and

DC Network Indoor and Outdoor LED Lighting http://dx.doi.org/10.5772/intechopen.74974 29

The DIALux software has been used to size the requirements of the luminaires to fulfill the requirements of the ME2 and ME3 roads with geometric aspects as presented in **Table 3**. We simulate these specifications with different high-class DC LED street luminaires by three manufacturers (Philips, Solitec, and Schreder Socelec), and the results are compared with the normative classification assigned. The power and luminance requirements for each manufacturer

**Road parameters Road Type A Road Type B**

Placement setup Unilateral Bilateral face to face

**Luminaires manufacturer/model Luminous flux/power Luminous flux/power** Solitec/Navia G 8805 lm/80 W 12,101 lm/110 W Philips/UniStreet 7654 lm/76 W 11,050 lm/110 W Schreder/Ampera 9905 lm/87 W 11,972 lm/105 W

Road classification ME3a ME2 Number of lanes 2 4 Road width 7 m 14 m Interdistance 30 m 35 m Height of light point 9 m 12 m

**Table 3.** Geometric data and luminaires selection for the ME2 and ME3 roads under study.

capacity and long-term reliability of batteries.

*4.2.1. Dimensioning of an autonomous led-lighting installation*

**Figure 9.** Solar autonomous public streetlight installation in Cuimba, Angola, 2017.

Planning a similar approach than those presented in indoor lighting, one of the first studies generated to compare DC versus AC grids in outdoor LED lighting was realized in 2013. The results of a 220 VDC centralized street-lighting system over conventional 230 VAC power system showed that the efficiency can be improved by 13 (full loads) and 17% (dimmed loads) [23].

However, and independently of this trend that is still under a very early stage of development, the first and most consolidated architecture used to develop DC LED streetlight is the autonomous solar-powered equipment. Modern PV DC luminaires have become the most extended element by virtue of its simplicity, function, and robustness of its components: battery, LED luminaire, and PV panels. This technical evolution and the growth of emerging countries with underdeveloped electrification infrastructures have boosted the market of lighting installations powered only by locally produced energy from the sun [24].

Park et al. [25] remark that the development and installation costs of a micro-distributed ESSbased smart LED streetlight system have been reduced by 33% in just a few years. Moreover, Loomba and Asgotraa [26] claim that DC solar microgrids are 25–30% more efficient than their AC counterparts. The global energy efficiency benefits may vary a lot depending on the location. According to information from the World Bank, the average electric transmission losses are only 4% in Germany and the Netherlands but raise slightly, 6%, in the USA and China and much more, between 15 and 20%, in Turkey and India.

Solar low-power equipment is widespread and participates already in many in-use installations. As an example, we have participated in a public-lighting renewal project developed with 1365 autonomous 50 W LED lighting poles in the city of Cuimba (Angola), as illustrated in **Figure 9**. The equipment used is designed to store enough energy to work three nights with no solar energy input. Development installation costs were reduced in more than 35% compared to renew and bury the AC grid existing already.

**Figure 9.** Solar autonomous public streetlight installation in Cuimba, Angola, 2017.

However, there are still uncertainties about the technical capability of this type of equipment in order to match their performance to their AC grid equivalents in lighting installations with large regulatory requirements: high-density traffic roads. We present a technical evaluation of the capability of present equipment to achieve these requirements in different global locations based on energy generation capability of solar panels, efficiency of DC LED luminaires, and capacity and long-term reliability of batteries.

#### *4.2.1. Dimensioning of an autonomous led-lighting installation*

(17%) [1]. However, this is still a major market where efficiency improvements can make sig-

)

DC energy demand 2.24% lower than the

The DC system demonstrated electricity savings ranging from 2.7 to 5.5% over an

DC microgrid with bidirectional inverter and battery storage. Static payback period

/100Lux of AC

/100Lux of the

AC equivalence

VEEI: 1.80 WAC/m2

equivalent AC system

5.5 years (\$0.887/W)

380 VDC LEDs

fluorescents Vs 0.87 WDC/m2

**Project VDC Details Results and conclusions**

28 Light-Emitting Diode - An Outlook On the Empirical Features and Its Recent Technological Advancements

380 2 kWpk photovoltaic (PV) 54 LED downlights (37 W) 3 power grids of 100 m length (3 × 2.5 mm2

24 Bosch DC microgrid: 15 kW PV array. 44 DC lights. Direct power from 100 kW lithium-ion battery system

> DC office building with lighting and a 24 V DC grid for electronic loads. Batteries back-up storage

150 kWp solar panels. 20 kW LED lighting:14 W tube lights as T5 fluorescent tubes retrofits

Planning a similar approach than those presented in indoor lighting, one of the first studies generated to compare DC versus AC grids in outdoor LED lighting was realized in 2013. The results of a 220 VDC centralized street-lighting system over conventional 230 VAC power system showed that the efficiency can be improved by 13 (full loads) and 17% (dimmed loads) [23]. However, and independently of this trend that is still under a very early stage of development, the first and most consolidated architecture used to develop DC LED streetlight is the autonomous solar-powered equipment. Modern PV DC luminaires have become the most extended element by virtue of its simplicity, function, and robustness of its components: battery, LED luminaire, and PV panels. This technical evolution and the growth of emerging countries with underdeveloped electrification infrastructures have boosted the market of

lighting installations powered only by locally produced energy from the sun [24].

China and much more, between 15 and 20%, in Turkey and India.

compared to renew and bury the AC grid existing already.

Park et al. [25] remark that the development and installation costs of a micro-distributed ESSbased smart LED streetlight system have been reduced by 33% in just a few years. Moreover, Loomba and Asgotraa [26] claim that DC solar microgrids are 25–30% more efficient than their AC counterparts. The global energy efficiency benefits may vary a lot depending on the location. According to information from the World Bank, the average electric transmission losses are only 4% in Germany and the Netherlands but raise slightly, 6%, in the USA and

Solar low-power equipment is widespread and participates already in many in-use installations. As an example, we have participated in a public-lighting renewal project developed with 1365 autonomous 50 W LED lighting poles in the city of Cuimba (Angola), as illustrated in **Figure 9**. The equipment used is designed to store enough energy to work three nights with no solar energy input. Development installation costs were reduced in more than 35%

nificant advances in sustainability.

380 & 24

380 & 24

**Table 2.** DC indoor-lighting experimental research installations.

Philips Research Eindhoven (NL) [19]

Fort Bragg, North Carolina (US) [20]

Fraunhofer Institute in Erlangen (GR) [21]

Xiamen University, Xiamen (PRC) [22]

> The DIALux software has been used to size the requirements of the luminaires to fulfill the requirements of the ME2 and ME3 roads with geometric aspects as presented in **Table 3**. We simulate these specifications with different high-class DC LED street luminaires by three manufacturers (Philips, Solitec, and Schreder Socelec), and the results are compared with the normative classification assigned. The power and luminance requirements for each manufacturer


**Table 3.** Geometric data and luminaires selection for the ME2 and ME3 roads under study.

to achieve the objectives established are also presented in **Table 3**. All three results are very similar, and for the rest of the study, we use the average power in each road case. Dimming during the night is included as energy efficiency regulations advice for this possibility. This leads to a total energy consumption of 75% of the nominal value calculated previously. Moreover, the battery storage system has to accumulate at least double of the energy to bright as programmed for one night.

There are two power distribution possibilities: autonomous poles with PV panels and storage systems integrated with each luminaire (simplest installation) or an independent renewable generation system that powers a smart micro-grid with several luminaries (more complex and expensive due to wiring canalization). The first option is limited by the amount of PV surface that is mechanically adaptable in a single pole. The availability of each solution depends on the amount of energy that is possible to generate depending on the geographical latitude. This value conditions the functional elements of the facilities, the simplicity and cost of the installation, the protection requirements, and maintenance and operation cost. Several representative locations have been chosen between or close to the Tropics of Cancer and Capricorn as these are the regions that receive the greatest amount of solar radiation. The PV energy generation capability on the main cities of this portion of the world is shown in **Figure 10**. For calculation purposes, the extreme representative possibilities are found in the following:

• Rabat, Morocco (2770 Wh/m2 per day). Latitude 34°00′47"N. Its radiations present considerable differences along the year, and it has long nights in winter.

PV luminaire poles to fulfill ME2 and ME3 requirements in Rabat, this is not possible with

• UOC: Open circuit voltage [V]

• : Energy consumption [Wh/day] • \_: Standard radiation, 1000 W/m2 • (,): Incident radiation in the panel [Wh/m2

• KT: Battery and regulator efficiency [%]

• Qd: Nominal daily capacity [Ah/day]

• PDMAX: Maximum discharge depth of the battery • \_con: Battery and regulator performance

• Un: Rated voltage of the photovoltaic generator [V]

• Tmin: Historical minimum temperature (°C)

• IG,SC: Short-circuit current of the generator [A]

Equipment SunPower SPR-X21–345 2 x HIT-235 Surface 1.60 m2 2.52 m2 Weight 18.6 kg 30.0 kg

Cn C10,14 = 95.88 Ah C10,13 = 263.60 Ah Equipment Move MPA 110–12 Move MPA 245-6XL

Weight 33.3 kg 39.0 kg Number 4 4 Voltage 12 V 6 V

Weight 0.8 kg 0.5 kg Uoc ≤100 V ≤60 V I 45 A 20 A

Energy regulatory system Equipment Steca Tarom 4545–48 Steca Solarix 2020-x2

**Table 5.** Component requirements for a solar LED luminaire at worst case: city of Rabat.

• UOC (TMIN): Rated voltage of the photovoltaic generator [V]

• A: Days of autonomy

integrate them on top of a single lighting pole due to mechanical limitations.

**Type of road A (ME3) B (ME2)** Photovoltaic generator PG-min design 340.5 W 468.2 W

**Table 4.** Equations for the dimensioning of LED luminaires powered by photovoltaic panels.

of 30 kg PV panels are required, which makes it impossible to


DC Network Indoor and Outdoor LED Lighting http://dx.doi.org/10.5772/intechopen.74974 31

ME2 roads as, at least, 2.52 m2

**Minimum power required by the photovoltaic generator**

*PG*−*min* <sup>=</sup> *Wd* \_\_\_\_\_\_\_\_ <sup>∙</sup> *GCEM G*(*α*,*β*) ∙ *KT*

*CN* <sup>=</sup> *Qd* <sup>∙</sup> *<sup>A</sup>* \_\_\_\_\_\_\_\_\_\_ *PDMAX* ∙ *ηCon*

**Regulation system**

*I <sup>R</sup>* = 1, 25 ∙ *I*

*UOC*(*Tmin*) = *UOC* + *β* ∙ (*Tmin* − 25)

*G*,*sc*

Energy accumulation and regulation system

**Energy accumulation system**

• Brasilia, Brazil (4523 Wh/m2 per day). Latitude 15°46′46″S. On the other hand, it receives very constant solar radiations, and the night duration is similar all year long.

The equations used to define the power generation capability by PV panels in these two locations are presented in **Table 4**. **Table 5** shows the components required to light both classes of roads under study on the worst scenario (design day in winter in the city of Rabat), and **Figure 11** explains that while in Brasilia, it is possible to install fully integrated autonomous

**Figure 10.** Solar energy input and design requirements of the streetlighting equipment for capital cities close to the tropics.


**Table 4.** Equations for the dimensioning of LED luminaires powered by photovoltaic panels.

to achieve the objectives established are also presented in **Table 3**. All three results are very similar, and for the rest of the study, we use the average power in each road case. Dimming during the night is included as energy efficiency regulations advice for this possibility. This leads to a total energy consumption of 75% of the nominal value calculated previously. Moreover, the battery storage system has to accumulate at least double of the energy to bright

30 Light-Emitting Diode - An Outlook On the Empirical Features and Its Recent Technological Advancements

There are two power distribution possibilities: autonomous poles with PV panels and storage systems integrated with each luminaire (simplest installation) or an independent renewable generation system that powers a smart micro-grid with several luminaries (more complex and expensive due to wiring canalization). The first option is limited by the amount of PV surface that is mechanically adaptable in a single pole. The availability of each solution depends on the amount of energy that is possible to generate depending on the geographical latitude. This value conditions the functional elements of the facilities, the simplicity and cost of the installation, the protection requirements, and maintenance and operation cost. Several representative locations have been chosen between or close to the Tropics of Cancer and Capricorn as these are the regions that receive the greatest amount of solar radiation. The PV energy generation capability on the main cities of this portion of the world is shown in **Figure 10**. For calculation purposes, the extreme representative pos-

per day). Latitude 34°00′47"N. Its radiations present consid-

per day). Latitude 15°46′46″S. On the other hand, it receives

as programmed for one night.

sibilities are found in the following:

erable differences along the year, and it has long nights in winter.

very constant solar radiations, and the night duration is similar all year long.

The equations used to define the power generation capability by PV panels in these two locations are presented in **Table 4**. **Table 5** shows the components required to light both classes of roads under study on the worst scenario (design day in winter in the city of Rabat), and **Figure 11** explains that while in Brasilia, it is possible to install fully integrated autonomous

**Figure 10.** Solar energy input and design requirements of the streetlighting equipment for capital cities close to the

• Rabat, Morocco (2770 Wh/m2

• Brasilia, Brazil (4523 Wh/m2

tropics.

PV luminaire poles to fulfill ME2 and ME3 requirements in Rabat, this is not possible with ME2 roads as, at least, 2.52 m2 of 30 kg PV panels are required, which makes it impossible to integrate them on top of a single lighting pole due to mechanical limitations.


**Table 5.** Component requirements for a solar LED luminaire at worst case: city of Rabat.

procedures and voltage levels for LED-lighting DC grids that will allow mass production of

Considering the relationship between LEDs and PV energy generation, the direct interconnection possibility and the advance in efficiency of the new light emitters have renewed the interest in autonomous applications, both stand-alone and with a backup energy grid. Thus, the number of solar-powered LED equipment installed is increasing exponentially. However, a further step in the evolution of these two technologies is still expected to improve the inte-

We would like to acknowledge Alfonso C. Gago-Bohórquez for the deep critical reading, Tiara L. Orejón-Sánchez for her useful recommendations, and the Solitec Foundation (Spain)

and Manolo J. Hermoso-Orzáez2

DC Network Indoor and Outdoor LED Lighting http://dx.doi.org/10.5772/intechopen.74974 33

\*, Rami D. Orejón-Sánchez<sup>1</sup>

dings. 2017;**140**:50-60. DOI: 10.1016/j.enbuild.2017.01.028

FL (USA): CRC Press; 2016. 161p. ISBN: 9781420076622

1 Department of Graphic Expression, Design and Projects, Universidad de Málaga, Spain 2 Department of Graphic Expression, Design and Projects, Universidad de Jaen, Spain

[1] Montoya F-G, Peña-García A, Juaidi A, Manzano-Agugliaro F. Indoor lighting techniques: An overview of evolution and new trends for energy saving. Energy and Buil-

[2] Held G. Introduction to Light Emitting Diode Technology and Applications. Boca Raton,

[3] Jhunjhunwala A, Vasudevan K, Kaur P, Ramamurthi B, Bitra S, Uppal K. Energy efficiency in lighting: AC vs DC LED lights. In: International Conference on Sustainable

[4] Ciriminna R, Meneguzzo F, Albanese L, Pagliaro M. Solar street lighting: A key technology en route to sustainability. Wiley Interdisciplinary Reviews: Energy and Environment.

[5] Willems S, Aerts W. Study and Simulation of a DC Micro Grid with focus on Efficiency, Use of Materials and Economic Constraints. Leuven, Belgium: University of Leuven;

Green Buildings and Communities (SGBC); December 2016. IEEE. pp. 1-4

devices that may work anywhere as well as their AC equivalents.

gration capability and the autonomy in high-latitude locations.

for its support in contributing with technical resources.

\*Address all correspondence to: agago@uma.es

2017;**6**(2). DOI: 10.1002/wene.218

**Acknowledgements**

**Author details**

**References**

2014

Alfonso Gago-Calderón<sup>1</sup>

**Figure 11.** Basic configurations and available integrations for ME3 (Type A) and ME2 (Type B) road regulation accomplishment in the cities of Rabat and Brasilia.

Nowadays and according to these results, this technology has still a further step to evolve before autonomous pole luminaries can be used on high-density traffic roads worldwide with autonomy assurance. However, many demonstration projects are already being constructed. For example, autonomous PV luminaires have been installed in the A−62 motorway (ME3 road), in Salamanca, Spain. In this case, promoters also appraise the quick installation process (only 3 days) that avoids large dangerous installation process along traffic conditions.

## **5. Conclusions**

Many Scientifics and technicians consider that the conversion of the lighting sector toward a full DC environment is its natural evolution trend as LED technology has become the basic engine of almost any new equipment developed for both indoor and outdoor applications.

Better energy efficiencies and larger lifetime expectations are the basic economic forces that are conducting this process that, nevertheless, is still facing considerable challenges in this primitive stage of development.

The unavailability of DC infrastructures and the lack of training/educations are the main drawbacks that are being overcome as universities and private research centers have considered this a priority research line. However, some other concerns are still far to be solved such as the consolidations of worldwide regulations and standards that ensure acceptable energy savings and total human safety. The first parameter varies significantly in each experimental installations ranging from 3 to 30% [18]. This will also lead to establish common safety procedures and voltage levels for LED-lighting DC grids that will allow mass production of devices that may work anywhere as well as their AC equivalents.

Considering the relationship between LEDs and PV energy generation, the direct interconnection possibility and the advance in efficiency of the new light emitters have renewed the interest in autonomous applications, both stand-alone and with a backup energy grid. Thus, the number of solar-powered LED equipment installed is increasing exponentially. However, a further step in the evolution of these two technologies is still expected to improve the integration capability and the autonomy in high-latitude locations.
