Solar Street Lighting - Smart Way to Light Up the future
Today's solar street LED lights are able to provide reliable, quality lighting both in developing and developed countries, thereby reducing light poverty and the economic and environmental costs of electric outdoor lighting. Rapid technical innovation and dramatic price reduction in the LED, PV module, and battery components, which has occurred in the last 5 years, will accelerate the penetration of solar street LED lights across the world. Applications will not be limited to countries with significant insolation only but will extend to Northern regions as well. This study provides a critical overview of a technology that will play an important role en route to global sustainability. For further resources related to this article, please visit the WIREs website.
Solar street lighting based on photovoltaic(PV) electricity accumulated in digitally con-trolled, reliable batteries and used at night to powerhighly efﬁcient light-emitting diode (LED) light sources is an advanced renewable energy technology increasingly used across the world to eradicate light poverty in developing countries and to provide inex-pensive quality lighting in afﬂuent areas of the world.
1 Dramatic cost reduction coupled with technical hardware and software advances in all main compo-nents (PV module, LED lamp, battery, and micro-controller) has increased the adoption of these stand-alone systems, resolving historic reliability problemssuch as in the case of the 450 poles installed in south-ern Sicily in 2005 that went out of work a fewmonths after installation.
2 Today’s solar street lighting is able to bring low-cost and environmentally friendly lighting to populations with no access to electricity, such as inthe case of several hundred solar streets installed in 2010 in Conakry, Guinea, for years providing the only lighting in town.
3 Contrary to expectation (see below), the technology today can also be successfully used in Northern regions, providing ﬁnancial relief to municipalities. Furthermore, glare-free LED lighting presents signiﬁcant opportunities to mitigate sky glow and the ecological impacts of light pollution. 4 This study intends to show the relevance of this critically important technology in the context of global efforts aimed to achieve a more sustainable development. Following an overview on the main technology trends, we provide economic arguments based on recent results achieved in different regions of the world with different solutions that demon-strate how solar lighting systems have evolved to become affordable, versatile, and reliable, pointing to a forthcoming boom in demand and utilization.
OWARDS INTEGRATED, SMARTSOLAR LIGHTSThe working principle of solar LED street lighting is simple. Solar cells, either on top of the pole or verti-cally integrated into the mast, generate electricity during the day. Electricity is accumulated in a battery through a charge controller, and when the sun hasset, it is used to power highly efﬁcient LED sources of white light with a small (typically 350 mA) direct current. It is emphasized here that the current output that powers the LED lamp comes from the charge controller (Scheme 1) and not from the battery so asto avoid its unsafe and undesirable deep discharge.Certain manufacturers opt for burying the bat-tery underground, whereas others leave the battery on the top or at the bottom of the pole (mast).Others, ﬁnally, elegantly insert the battery within the pole, a technical solution suitable for light, energy dense Li-ion batteries.Solar street lights were initially used in remote locations and disaster-prone areas, with the poor lumi-nous efﬁciency of incandescent or ﬂuorescent lampsforcing the industry to over-size the solar lighting sys-tem, especially the solar module and the battery, to facethe longest nights and cloudiest weather of winter.
5 This lack of balance translated into wasting 50–60% of the energy generated throughout the year, high costs due to over-sized solar modules and battery, and poor appearance, conﬁning the market for solar lighting to areas closer to the equator with the highest average levels of solar irradiation and temperatures that did not affect the performance of the incandescent or ﬂuorescent lamps.All this has changed in the last decade with the widespread diffusion of highly efﬁcient solid-state LED lights. Today’s reliable solar LED luminaires offer a documented long lifetime of at least 15 years(60,000 working hours, namely at least three times longer than conventional lighting discharge technolo-gies) and are currently used to light a broad set of outdoor environments:
-Pedestrian and bike paths
-Gardens and parks