Techno-economic analysis of off-grid photovoltaic LED road lighting systems: A case study for northern, central and southern regions of Turkey
Introduction
Over the past decade, there has been a strong upward trend in renewable energy investments in many sectors with reasons such as global warming, policies to reduce carbon emissions, increased environmental awareness and decline trend in renewable energy system costs. Solar energy has become one of the most promising among the other renewable energy technologies due to rapid decrease in photovoltaic (PV) module spot prices which were above 3 $/W in 2009 and vary between 0.29 and 0.25 $/W today (with an average of 0.285 $/W) [1]. In addition, the prices of other components such as inverters, charge regulators, trackers, mounting and electrical equipment have reduced in the range of 5–7% [2].
PV systems can operate both on-grid and off-grid. Off-grid systems are particularly attractive in rural regions of the world where installation of new transmission lines are required for electrification [3]. According to the World Bank data, approximately 23% of the people in rural areas lack electricity in the world by 2016 [4]. One of the sectors where off-grid systems are used is street and road lighting, and interest in these systems has started to increase in recent years, particularly in developing countries with high solar potential. For instance, Nigeria aims to increase the capacity of PV street lighting from 100 MW to 1000 MW by 2015 and to 10000 MW by 2030 [5]. In Cameroon, 3000 off-grid PV lighting systems were already installed on major streets and public sites [6]. In Malawi, which has one of the lowest grid access in South Africa (9%), 250 off-grid PV street lights were planned to be installed by a Chinese funded project. In Zimbabwe 15 million $ has been set aside for deployment of 4000 off-grid PV road lighting systems which is predicted to save about 200000 $ per month [7].
Increasing interest in the systems is not only due to declining in PV module costs but also developments occurred in light emitting diode (LED) technology in the last 10–15 years. LED luminaires have offered more cost-effective and longer-lasting lighting solutions than the conventionally used high-pressure sodium (HPS) luminaires in road lighting. In the past, roads that can be illuminated using 100–150 W HPS luminaires can now be illuminated using 40–70 W LED ones. This means previously higher PV and battery size can now be reduced and off-grid PV lighting can be achieved at lower costs. In addition, there is no need for inverters because LED luminaires can operate at DC voltage in contrary to HPS luminaires. A lighting pole can carry only a limited size of PV, thus providing the same lighting quality of HPSs at lower power consumption with LEDs makes it possible to meet lighting criteria also in higher leveled road lighting classes.
Section snippets
Literature review
Above-mentioned developments in PV and LED technology offer promising possibilities for the assessment of solar potential in roadways, and there is a growing body of research dealing with off-grid PV LED road lighting in the literature. Velaga and Kumar [8] carried out techno-economic feasibility of off-grid PV LED street lighting systems for a village in rural India which does not have street lighting and needs new transmission lines for electrification. In the study, off-grid PV LED lighting
Content and contributions
These papers regarding technical and economic feasibility analysis of off-grid PV road lighting systems have provided valuable contributions to the literature. However, it is seen that road lighting criteria are often neglected and based on assumptions. The papers are mainly concentrated on the sizing optimization of the PV and battery systems, but the total cost of the entire energy system also depends on the number of lighting poles to be built which can only be obtained after road lighting
Structure of off-grid PV LED road lighting systems
Off-grid PV LED road lighting systems consist of PV modules, battery groups, charge regulators, LED luminaires and lighting poles as shown in Fig. 2. PV panels charge the batteries throughout the day and charge regulators control the PV output voltage and current and protect the batteries from overcharging and discharging. The advantages of off-grid PV LED road lighting systems can be listed as low maintenance requirement, helping to reduce CO2 emissions, lack of transmission and distribution
Road lighting
Road lighting can be described as illumination of squares, intersections, streets, inner and outer main traffic roads and it covers the largest portion of total electricity consumption in general lighting. In Turkey, general lighting accounts for 1.8% of the total electricity consumption of 231204 GWh as of 2016 [30].
The International Commission on Illumination (CIE) and the European Union Standards (CEN) develop internationally agreed basic standards and procedures on lighting criteria [31,32
Solar energy potential in Turkey and the selection of the case regions
Turkey is situated between 36° and 42° north latitudes and 26°–45° east longitudes and has the highest solar potential in Europe after Spain. According to the study carried out by the Electricity Affairs Survey Administration (EIE), Turkey has an average annual total sunshine duration of 2741 h (daily total 7.5 h) and the average total radiation intensity in the country is 1527 kWh/m2-year (total 4.2 kWh/m2-day).
Turkey's Solar Energy Potential Atlas called GEPA is used in the selection of the
Simple payback periods under current conditions and for future scenarios
After obtaining the total NPC of the energy systems and the electricity consumption of the loads, simple payback periods of the systems were calculated for the current case and the future projections. The electricity price is taken as 0.128 $/kWh for general lighting [42]. Table 7, Table 8, Table 9, Table 10, Table 11 show the results of payback periods, respectively under current conditions and for future scenarios which are 1) 25% increase in electricity prices, 2) 25% decrease in cost of PV
System installation costs per kilometer
In this part, the total cost of system installation per km is calculated according to the results obtained in the previous two parts. At first, cost of single pole system is calculated, and then the result is multiplied with the number of poles to be installed per km. System installation costs per km for M4 and M5 road lighting classes in Antalya, Izmir, and Istanbul are given in Table 12 in detail.
Discussion and conclusions
In this study, techno-economic feasibility analysis of off-grid PV LED road lighting systems is performed under M4 and M5 road lighting in three case regions from Turkey. Since the accuracy of the load profile is related to the power consumption of the LED luminaire, and the total installation cost is dependent on the size and number of lighting poles to be installed, firstly detailed road lighting calculations were performed using DIALux software based on the international and national road
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