Using Solar Power as an Alternative Source of

Using Solar Power as an Alternative Source of Electrical Energy for Street Lighting in Ghana 1

Solomon Nunoo, 2Joseph C. Attachie and 3Charles K. Abraham Department of Electrical and Electronic Engineering, University of Mines and Technology, Tarkwa, Ghana 3 Electricity Company of Ghana, Tarkwa District, Western Region, Ghana 1 [email protected], [email protected], [email protected]

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Hence, to overcome and improve the problem of street lighting in Ghana, there is the need to explore the use of alternative lamps and alternative sources of electrical power for lighting them. One of such lamps and energy source is the light emitting diode (LED) lamp and solar energy respectively.

Abstract—Streetlights in Ghana receive electrical energy from the national grid. To pay for the energy consumed, residential consumers on the grid are levied 0.0001 of their total monthly consumption. Unfortunately, these levies are inadequate to defray the cost. There is therefore the need to look at other alternative sources of electrical power, which do not depend on the national grid to light the streetlights. The findings show that most streetlights in Ghana are not metered, thus making it impossible to bill the respective District Assemblies. Again, the socio-political climate in the country complicates the design process by not allowing for ample time for a thorough design work to be done before incorporating streetlights onto the national grid. This paper discusses the use of solar power as an alternative source of electrical energy for street lighting in Ghana. It proposes the use of LED-based lighting systems that receive energy from lead-acid batteries, charged by the solar panels. The design has an auto turn-on and turn-off for the streetlights and for charging the back-up batteries. The expectation is that changing to the LED-based street lighting system will lead to an increased initial installation cost but the savings made due to the reduced maintenance cost is enormous.

This paper presents the various benefits that LED lamps have to offer instead of the existing discharge lamps used for street lighting in Ghana and using solar energy as the source of electrical power. Cost-benefit analysis to ascertain the viability of implementing such a project is also discussed.

2. OVERVIEW OF STREET LIGHTING Types of Street Lighting Lamps Street lighting is the artificial illumination of streets and pathways when available natural light (sunlight) drops below a predetermined level. It dates back to pre-electricity era when oil lamps were used to provide illumination for pathways at night as well as providing security. Some benefits of street lighting are; it allows the safe movement of motorists or pedestrians; it enhances the amenity of an area; and it assists with property protection by acting as a deterrent to criminals.

1. INTRODUCTION In Ghana, electricity consumption has been increasing at a rate of 10-15 percent per annum for the last two decades. It is projected that the average demand growth over the next decade will be about six percent per year. As a result, frequent blackouts have occurred and could continue as energy demand increases and energy generation fails to keep up [1].

There are several types of lamps used for street lighting depending on their photopic illumination for the least consumption of electricity [2]. Such lamps include incandescent, fluorescent, high intensity discharge and LED lamps. Incandescent Lamps Incandescent lamps are among the first and least efficient light sources used in street lighting. Incandescent lighting was a popular option for street lighting until the 1950s, when other lamps proved to be more efficient and lower maintenance.

The issue of street lighting is almost non-existing in many localities in Ghana. The few existing ones use discharge lamps which come with their own disadvantages such as; high power consumption, low efficiencies, very fragile and low rated life (hours). One major environmental concern is their contribution to global warming, because of their associated greenhouse gas emissions when in operation. Besides, most of these streetlights are unmetered because they are mostly installed without authorization from the service providers.

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Fluorescent Lamps Fluorescent lamps gained popularity for street lighting applications in the 1950s. These lamps were more efficient than their incandescent counterparts were, and required less maintenance. The lamps were primarily used in downtown

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application was for indicator lights, which had efficacy of only 0.01 lumen/watt.

areas and parking lots. They were good for any place requiring a lot of light over a large area. The popularity of these lamps was relatively short lived, as more efficient, compact and lower maintenance high intensity discharge lamp technology was advanced.

Recently, LEDs are used in multitude of applications and are available in several colors and packages. LEDs for street lighting applications package a number of LED chips onto a coated printed circuit board and enclose them in housing suitable for the outdoor environment.

High Intensity Discharge Lamps High Intensity Discharge (HID) lamps in general require an external ballast to operate. These lamps usually take between 1 and 5 minutes to reach full brightness, and if there is a dip in electricity, these lamps will shut off. The lamps must cool sufficiently to restrike, which usually takes from 1 to 10 minutes.

Current State of Street Lighting in Ghana The street lighting system employed in Ghana is the cobrahead type, which employs the use of mercury vapor lamps for its illumination. The operating voltage is 240V and typical lamps used have wattages ranging from 120W to 400W but the 250W mercury lamps are mostly used as is the case in the Western Region (see Table 1). Hence, the issue of high power consumption with lumen depreciation associated with mercury vapor lamps poses a challenge in trying to conserve electrical power.

Streetlights using these lamps have been labeled on the bottom of the fixture since the late 1970s. A number on the bottom multiplied by 10 yields the wattage rating of the fixture. For example, “10” means 100 watts, and “25” means 250 W. The only exception is 1000-W fixtures, which are labeled as “X1”. Mercury vapor lamp has a blue label, metal halide has a red label and both types of sodium lamps have yellow or gold labels. There are three main types of high intensity discharge lamps namely, mercury vapor lamp, metal halide lamp, and high pressure sodium lamp.

Under the tariff system of Ghana, streetlights are categorized as non-residential facilities so the Public Utilities Regulatory Commission (PURC) approved tariff rates for a non-residential user, effective June 1, 2010, is used to calculate the cost of energy consumed per hour. The total power consumed per month in Table 1 was calculated with the assumption that streetlights are used for 12 hours each day for 30 days every month and there is one energy meter per district.

LED Lamps Today, because of the advancement in technological research LED lamps for street lighting are available. Even though, the technology is in its early years of streetlights application compared to the traditional streetlights, and it promises great deal of success in this 21st century street lighting technology.

The total monthly charges (TMC) is calculated using the relation,

TMC = (U × kWh) + (L × kWh) + Tax + SC

LEDs are semiconductor devices that convert electricity to light. LED lighting is also called solid-state lighting, because the light is emitted from a semiconductor material rather than from a vacuum or gas tube. LED technology has existed since the 1960s. The early LED technology

(1)

where U is unit charge based on PURC approved tariff rates, kWh is the total power consumed per month, L is the applicable levies which is made up of government levy and streetlight levy, Tax is the applicable tax for non-residential consumers and it comprises of VAT and National Health

Table 1 – Number of Unmetered Street Lamps in the Western Region of Ghana Number of Lamps Total Power Total Power Total Monthly Charges Per Month District Per Hour 120-W 150-W 250-W 400-W (GH¢) (kWh) (kWh) Lamp Lamp Lamp Lamp Juaboso 729 291.60 104976.00 54,238.70 Enchi 105 74 20 39.10 14076.00 7,170.68 Bibiani 34 75 38.50 13860.00 7,058.83 Takoradi 870 217.50 78300.00 40,425.87 Bogoso 79 13 91 51.50 18540.00 9,482.14 Setwi Wiaso 42 113 55.70 20052.00 10,265.05 Axim 150 84 56 65.90 23724.00 12,166.41 Sekondi 2 696 360 318.24 114566.40 59,204.61 Asankraguah Agona Nkwanta 7 393 158.95 57222.00 29,511.68 Tarkwa 430 74 137.10 49356.00 25,438.66 Half Assin 209 354 17 126.65 45594.00 23,490.70 Total 107 438 2604 1928 1500.74 540266.40 278,453.32

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electricity. Energy is stored in the battery during daytime and consumed at night. The LED lamp (LED streetlight) is driven to operate by the LED lamp driver – this controller monitors the system and manages the light on and light-off in day and night time.

Insurance Levy (NHIL) at a combined rate of 15 percent and SC is the service charge at a rate of GH¢2.50 per month. To pay for the energy consumed, residential consumers on the national grid are levied 0.0001 of their total monthly consumption. Unfortunately, most of the streetlights are unmetered so the service provider is unable to charge the respective district assemblies for the usage.

The solar LED streetlight controller not only controls solar energy storage to the battery, but it also manages the power consumption to the LED lamp.

3. PERFORMANCE OF LED LAMPS

There are installations that can effectively radiate 85% of light output from the LED lamps to hit the road surface [4]. Figure 2 [5] show a typical solar street lighting system.

Lamp performance is measured by a variety of metrics, but the most significant metric is lamp efficacy (lumens generated per watt of energy consumed). Table 2 [3] shows the performance of LED lamp against high-pressure sodium and mercury vapor lamp.

Table 2 – Performance of Various Types of Lamps for Street Lighting Type of Lamp Parameters LED Lamp High Pressure Sodium Lamp Mercury Vapor Lamp Flux (lm) 3,325 5,510 4,340 Power Consumption (W) 67 90 138 System Efficacy (lm/W) 50 61 31 Average Lux 14 19 14 Utilization Factor 0.0042 0.0034 0.0032 Lux/W 0.21 0.21 0.10 Min/Avg Lux Ratio 0.40 0.32 0.23 Lifetime (hours) 60,000 20,000 – 30,000 6,000 – 10,000

4. DESIGN OF LED-BASED STREETLIGHT The solar LED streetlight described in this paper is designed to achieve an 85W solar energy battery charger and a 25 W LED lamp driver. During the daytime the controller preserves the electricity energy gathered by the solar module (PV module), then stores it in the battery. In the evening, the controller uses the battery energy to power the LED streetlight.

Figure 2 – A Typical Solar Street Lighting System Streetlight Control System A simplified block diagram of the solar-LED streetlight controller is shown in Figure 3. It consists of the power supply, battery charger, LED lamp driver, and protection circuits.

Figure 1 – Block Diagram of Solar LED Streetlight System The system block diagram is illustrated in Figure 1. The sunlight delivers rays of photons (solar energy) which hit the solar panel (photovoltaic or PV module). The PV absorbs the photons and electrons are released. The electrons flow along the metal contact of the PV and form

The power supply is from the battery and it is regulated to 12 V DC. The battery charger is a DC/DC converter using buck topology. It converts solar energy to electricity and

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stores the electricity in the battery. The LED lamp driver is also a DC/DC converter using flyback topology in order to drive the LED lamp and provide even illumination. Again, the system must have overvoltage, under voltage and over current protection circuits and reverse-connection protection for the battery and the LED lamp.

lighting system is 2.44 years. This result shows the solarpowered LED streetlight is economically feasible.

5. CONCLUSIONS Streetlights in Ghana receive electrical energy from the national grid and residential consumers are levied 0.0001 of their monthly consumption. Most of the streetlights use 250 W mercury vapor lamp but this paper suggests the use of solar-powered LED streetlight due to its numerous advantages. The use of LED technology can help relieve the government’s ever-present budgetary and environmental challenges as well as improve streetlight quality through features like reduced glare and better color rendering. The findings of this research show that, the total initial installation cost of a solar-powered LED streetlight is GH¢1,423,750.00 (US$1,002,640.85) and that of the gridpowered mercury lamp streetlight is GH¢969,485.00 (US$682,735.92). The payback period for LED system is 2.44 years and the lifetime maintenance savings given that the system has a 20-year lifespan is GH¢2,350,037.00 (US$1,654,955.63). Hence it is economically feasible.

Figure 3 – Simplified System Block Diagram of the Solarpowered LED Streetlight Controller In sophisticated architectures, a microcontroller unit (MCU), which includes human machine interfaces (HMI), DIP switch for the selection of the operating time schedule and the indicators of debugging status, is incorporated. The software routines for the protection circuit are then implemented in the MCU.

ACKNOWLEDGEMENT The writers will like to acknowledge the help of Eco-Solar and Construction Limited for availing data on costs related to solar-powered street lighting installation in Ghana.

Economic Analysis of the Proposed System

REFERENCES

There are 5077 unmetered streetlights in the Western Region of Ghana [6] as shown in Table 1 and several others in the remaining nine regions. Thus, Electricity Company of Ghana (ECG) losses GH¢3,341,439.84 (US$2,353,126.65) annually in Western Region only?

[1] J. A. Aboagye, “An Alternative Street Lighting for UMaT Campus using LED (Light Emitting Diode) Lamps”, BSc Project Work, University of Mines and Technology, Tarkwa, May 2010.

The analysis presented in this paper considers a solarpowered streetlight system using high-power LED lamp (100 W) for 10 km of single lane highway because most highways in Ghana are single lane. The fixtures are installed on one side of the road with a pole distance of 30 m (amounting to 335 fixtures).

[2] Anon., “Types of Lamps Used in Streetlights”, retrieved on February 10, 2010 from http://www.eskimo.com/~jrterry/ lamps.html. [3] Philips, “White Paper: Street Lighting”, retrieved on July 6, 2010 from http://www.philipslumileds.com/pdfs/WP14 .pdf.

Table 3 shows an economic comparison of solar-powered LED streetlight and grid-powered mercury vapor lamp streetlight. Each unit of the solar-powered lighting system includes a 100 Wp PV module, a 100 Ah-12 V battery, and 100W LED lighting fixture. It shows that the total initial installation cost is GH¢1,423,750.00 (US$1,002,640.85) and that of the grid-powered mercury lamp streetlight is GH¢969,485.00 (US$682,735.92).

[4] M. S. Wu, H. H. Huang, B. J. Huang, C. W. Tang and C. W. Cheng, “Economic Feasibility of Solar-powered LED Roadway Lighting,” ISESCO Science and Technology Vision, Volume 4, Number 6, 43-47, November 2008. [5] Energy Efficiency, “Activity: Is Solar Energy Suitable for Hong Kong?”, retrieved on March 31, 2010 from http://www.hk-hy.org/energy/alternate/act_solar_cell_e.html.

The maintenance cost for a solar-powered LED streetlight system over a 20-year period is also shown in Table 4. The payback period for the excess investment of LED street

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[6] Electricity Company of Ghana (ECG), “Unmetered Street Lighting Report”, Western Region, Ghana, 2010. Table 3 – Initial Installation Cost for Solar-powered LED Streetlight System Solar-Powered LED Lamp Mercury Vapor Lamp Streetlight Streetlight ITEM UNIT PRICE SUBTOTAL UNIT PRICE SUBTOTAL (GH¢) (GH¢) (GH¢) (GH¢) Lamp 1,000.00 335,000.00 10.00 3,350.00 Lamp Pole 300.00 100,500.00 300.00 100,500.00 Solar PV Module 800.00 268,000.00 Deep Cycle Battery 400.00 134,000.00 Controller 500.00 167,500.00 Power Line Cost 100,000.00 400,000.00 PVC Pipe Cost 30,000.00 150,000.00 Transformer Station Cost 60,000.00 Civil Construction and 500.00 167,500.00 500.00 167,500.00 Installation Subtotal (GH¢) 1,302,500.00 881,350.00 Miscellaneous (10%) 130,250.00 88,135.00 Total Initial Installation Cost (GH¢) 1,423,750.00 969,485.00 Table 4 – Maintenance Cost for Solar-powered LED Streetlight System Over a 20-year Period Solar-Powered LED Lamp Mercury Vapor Lamp ITEM Streetlight Streetlight Lighting power per lamp (W) 100 250 Total power consumed per hour (kWh) 33.5 83.75 Initial Installation Cost (GH¢) 1,423,750.00 969,485.00 Maintenance and Item Replacement Times Lamp Replacement Time (years) 10 2 Deep Cycle Battery (years) 6 Controller (years) 5 Solar PV Module (years) 20 Lifetime Lamp Replacement Cost (GH¢) 335,000.00 33,500.00 Lifetime Battery Replacement Cost (GH¢) 402,000.00 Lifetime Controller Replacement Cost (GH¢) 502,500.00 Lifetime Total Maintenance Cost (GH¢) 1,368,475.00 33,500.00 Overall Savings Power Savings per day (kWh) 603 Monthly Energy Charges (GH¢) 15,493.80 Yearly Total Energy Savings (kWh/year) 217080 Yearly Total Energy Savings (GH¢/year) 185,925.60 Lifetime Energy Savings (GH¢) 3,718,512.00 Lifetime Maintenance Savings (GH¢/year) 2,350,037.00 Additional Investment for LED (GH¢) 454,265.00 Payback Period (years) 2.44 -

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