Solar Streetlights - Green and Economic Way to Brighten and Secure Community

Streetlights evoke romance and drama. Old black and white movies had everyone from Gene Kelly to Raj Kapoor sang and danced around ornate streetlight poles. Even modern cinema dramatized images of poor kids having to study under the streetlight, and rock music told stories of street Romeos serenading under streetlights. Well, cut to reality (Nepali style) – our streets have no shortages of poles and have even more wires swaying in between, but alas, well-lit street lights themselves are seldom to be found, making our cities a land of dark streets. The reasons are many – first, there is load-shedding, then the utter disregard on the government’s part for any public infrastructure, the list goes on.

However, there is an alternative – Solar Street Lights!

Double Lamp Solar Street Light

With the recent advances in solar photovoltaic (PV) technology and the dropping prices of solar panels and LED lights, solar streetlights have become a practical, economic, and a very green option for street lighting. Solar street lights are completely autonomous, i.e. we basically stick a pole in the ground, it has everything it needs to power itself, can turn itself on and off automatically, and more importantly, there is no need to install any wiring between the poles. Very much like point-and-click, we can choose any lighting location to our liking and install a solar street light pole instantly.

Case Study: Druk Amitabha Mountain Monastery in Sitapaila, Kathmandu

Druk Amitabha Mountain monastery is located atop Sitapaila hill, about 4 km northwest of Swayambhunath. You can only get there using 4-wheel vehicles that take you up the bumpy, dusty (and steep) gravel road. Once up there, the monastery is a 200-ropani (25 acre) span with some of the most majestic structures we’ve ever seen.

In March 2010, the monastery hired Gham Power to installing solar PV-powered outdoor security street lights to light up the compound (which used to be completely dark during nights, a concerning security issue).

4 KW Solar Street Light System at Druk Amitabha Monastery

The system installed by Gham Power is a hybrid solar PV system to provide outdoor security street lighting from dusk till dawn at the monastery compounds. Each streetlight operates independently and lights up automatically from dusk till dawn. The street lighting system has 4 Kilowatt of solar PV generating ~30 units (kilowatt-hours) of electricity per day. This system powers up 25 security streetlights using 65 watt CFL bulbs each. In terms of carbon footprint, this system will prevent 11 tons of carbon emissions per year.

In total, the PV system uses twenty 185-watt solar panels from Solar Power Inc, 3 Steca Tarom 245 charge controllers, 3 Steca XPC 2-kilowatt inverters, and 22 Exide 200-Ah deep cycle tubular solar batteries. The lighting system consists of 10 lamps (65-watt CFL) installed along the top of the monastery’s Naro conference hall, and 15 lamps mounted on eight 20-foot poles. There is approximately 800 meters of 4-core armored cable (16 sq.mm.) that connects the street light poles together, and each pole is equipped with photo-cell device that manages the automatic switching on the lights during dusk to dawn. The solar panels carry a 25-year warranty, and the rest of the system carry a 5-year warranty, except the CFL light bulbs which carry a 1-year warranty. Gham Power began work at site on March 9, 2010 and completed its work in less than a month on April 7, 2010, just in time for Annual Drukpa Council conference, where visitors from all across the world saw (and praised) how the monastery practices what it preaches about being environmentally responsible.

How does it work?

Although Druk Amitabha monastery chose to install the solar panels centrally and ran wires along their compound, a more economic way of installing solar street lights is to have all system components within the pole itself so that there is no need to run wires between the poles.

Solar Street Light Component Configuration

As in the adjacent figure, a solar street light has the solar panel installed on top of the pole, with a battery box installed right underneath the panel (and close to the lamp). This way, the system minimizes the length of cables between panel, battery, and the load, which in turn greatly minimizes electricity loss, a common problem in DC-based solar PV systems. This compact design also helps to install solar street light atop existing unlit poles.

The street light lamp itself is an LED lamp, which is the most energy efficient lighting source on the planet today. For example, a 30-watt LED street light provides the equivalent light of a 300-watt halogen street light. Also, LED lights usually provide a warranty of 50,000 hours, the longest lifetime in lighting solutions.

Furthermore, the battery used in these systems is a 3-year maintenance-free Gel or VRLA battery, which makes it relatively lightweight and easy to hoist up the pole.  Also, the system automatically turns the light on and off at dusk and dawn (you can also optionally put a timer if you only want the street lights to be on during certain night hours). So essentially, the beauty of these systems is that you stick the pole in the ground, and there is literally no maintenance to be done for at least 3 years (except for occasional panel cleanup).

Panel on Top of LED Street Lamp

20-Foot Solar Street Light Poles Approx. 100 Feet Apart

Parting Thoughts

There is no reason our street lights should abandon any hopes of romance. A financial analysis of installing solar street light versus regular utility-powered streetlight shows that the advantages of solar are quite obvious. First, solar street light will reliably light up each night, utility-powered will not because of load-shedding. Second, you save quite a bit by not having to install any cabling between the light poles.  The payback period for the solar street light is 5 years, whereas the warranty on the solar panel is 25 years. So, you pay for the light in 5 years, and then get your street lights more or less for free for the next 20 years.

This is a perfect solution for housing complexes, and any building with large parking lots and compounds such as banks, hospitals, shopping malls, etc. And we hope that as architects, builders and developers adopt this practice and start lighting up our streets wherever we can, perhaps our government will learn something from the people it is supposedly representing and start implementing similar solar street lights for our public roads. After all, it is the right thing to do.

Note: This article appears in July-August edition of SPACES magazine.