Street lighting represents about 20% of global lighting energy usage. The legacy streetlight system entirely relies on the grid for power, imposing a burden on the network during peak hours.
Simultaneously, many public areas are devoid of sufficient nighttime illumination in developing cities that lack funding for infrastructure, including that needed to meet street and area lighting requirements for visibility and safety.
Solar street lighting can solve these problems. Grid-connected solar engines can feed existing streetlights during peak nighttime hours, reducing the burden on the electrical grid. In areas where accessing the electrical network is onerous, stand-alone solar exterior LED luminaires can provide an illuminated environment that enhances visual quality and public safety.
Solar lighting basics and benefits
The primary electrical components of a solar streetlight are a photovoltaic (PV) panel, rechargeable battery unit, LED light head typically between 20 and 100W, solar controller, and built-in or separate LED driver. The PV panel produces direct current (DC) electricity during the day, while the solar controller stores the generated electrical energy in the battery unit, with a typical capacity of 0.5 to 5kWh and potentially smaller if the light is outfitted with automated controls or dimming.
When the sun sets, the PV input voltage to the solar controller falls below a preset value, triggering the solar controller to discharge the battery through the integrated or remote LED driver (DC to DC). The connected LED light circuitry then illuminates the area until sunrise. The output is comparable to a conventional product; for example, a solar light with a 30W light head and three nights of autonomy – the number of nights a solar light can operate at a specified wattage with no or minimal sunlight availability during the day – will deliver the same output as that of a grid-connected LED light for that duration.
This is the general operating principle of solar lights available in the marketplace. However, the technology is in its infancy, and different manufacturers are adopting different product designs.
A solar lighting system offers several benefits, including ease of installation, cost savings, and energy savings. The installation is comparatively straightforward for stand-alone solar lights, which are available in two different categories: an all-in-one solar light package, which includes a PV panel, battery, controller, and LED light module; and a remote solar, or split, system, which has a remote PV or controller, battery, and a light head mounted onto the fixture’s arm. Neither of these types requires a mains connection with AC input or the related electrical wiring or cabling. While the overall overhead expense is less, the unit hardware cost is higher than that of most conventional lights.
For grid-connected solar lighting systems, the benefit is limited to the cost savings of electricity from the grid. Grid-tied solar lights are wired to the grid and operate similarly as a stand-alone solar streetlight for a specified period, say nighttime peak hours, or until the battery storage drops to a set value; the system then switches to grid power. They typically do not require huge battery storage or a large PV panel, which reduces the unit cost as compared to nongrid-connected, portable solar streetlights.
Like many renewable energy systems, the energy storage device plays a key role. Recent growth in this sector has led to robust rechargeable batteries and associated battery management systems. The solar lighting industry could leverage the growth in these technologies. The cost/kWh will also decrease as the renewable energy industry grows and batteries for electric vehicles (EVs) and similar applications are more broadly available. In 2010, the cost of Li-ion batteries was $1,200/kWh; by 2021, it was down 89%, to $132/kWh.
On a related point, solar streetlights are more reliable than EVs as the primary energy source for charging – sunlight – can be abundantly available* and is free throughout the year. For example, a 30W light head with three nights' autonomy in Sydney will need approximately a 160W PV panel and 1.5kWh battery. Moving closer to the equator, the PV panel and battery size requirement will decrease due to the consistent availability of solar energy year-round. Moving away from the equator, the panel size and battery requirements will increase.
Nevertheless, the road ahead for the solar street lighting industry is rocky. Technological challenges result in gray areas from a compliance perspective. The design process is detailed and complex; for simplicity, we will touch on the best practices for solar lighting system design, reliability, compliance, and maintainability.
Best practices begin with data
In Australia, government-employed engineers or consulting engineering firms hired by the agency typically oversee public projects, while consulting firms design private projects. Independent lighting contractors might step in to design the lighting layout, but not the overall electrical and lighting system.
To develop a solar street lighting system with optimal solar energy harvesting and use of stored electrical energy to maintain light levels and avoid noncompliance infractions**, the project team must design a balanced autonomous system based on several factors: the geographical location of the intended installation, a detailed historical study of solar irradiance in the area, and a compliant light level calculation.
Designers can research solar irradiance data from the National Solar Radiation Database and the National Renewable Energy Laboratory website; in Australia, the Bureau of the Meteorology website is a good reference. The Lighting Council of Australia’s Commercial Solar Lighting Guide is another helpful nonmandated guideline. The electrical standards, wiring rules, and lighting codes are to be used for general compliance. Additional reference documents may be needed depending on the project type.
Still, things can go wrong. When minimal sunlight availability due to unforeseen events — weather, cloud coverage — is followed by the consumption of stored energy at night, the result is a lower battery storage level. Here, the intelligent aspect of the solar controller system becomes helpful. If the battery storage level goes below a preset threshold, a built-in program or battery management system will reduce energy consumption based on a smart algorithm.
Read the full article here: https://www.ledsmagazine.com/architectural-lighting/article/14288486/best-practices-for-solar-street-lighting-systems
