Planning a successful outdoor solar lighting installation.

This document was written to assist lighting, asset and project manager professionals achieve successful lighting outcomes for their outdoor solar street, path, car park and area projects, please feel free to share as you see fit.

Introduction
Solar lighting is a reliable, compliant, and in many cases a more cost-effective lighting solution. The improvement of technology and methodologies over the past 10 years has been significant, however there are still inexperienced manufacturers/suppliers, therefore it is up to the customer to invest in education at the beginning of the process to ensure an optimum outcome. The following factors need to be assessed (and are often inadvertently overlooked) when selecting solar lights. Awareness of these factors preceding the decision to purchase will certainly avoid possible system failure, costly replacement and servicing costs.
Qualify the manufacturer/supplier
Find out how long the solar lighting product, supplier or manufacturer has been in the business, to ensure they have the necessary experience and can demonstrate a robust track record. Ensure they provide numerous references on relevant jobs. If necessary, go out and inspect their lights at night.
Quality components
Ensure all the components have the credentials and have been in the market for a sufficiently long time to have proven themselves. Also find out if spare parts are readily available and what warranties are provided.
Quality Lighting outcome
For mission critical and compliant lighting, a professional lighting design should be conducted to ensure the optimum optic is utilised so the least number of lights are used, whilst the light is compliant, safe, compliant to relevant different standards, and caters for the following points: In most instances, natural and warm white colour temperatures are the most desirable (4500k or less), research now shows that cool and blue white colour temperatures are detrimental for humans (and animals) affecting natural circadian rhythms. No glare to the user. Dark sky compliant and no light pollution (into neighbouring properties or up light). IMPORTANT NOTE: To comply with world-wide pathway lighting standards, the light levels must be based on the LOWEST level the light runs on all night. (This pertains particularly to lights that use sensors to dim and boost the lights). If the lowest/dimmest light level throughout the night is less that required by the particular sub-category, it does not comply.
Sufficient solar panel and battery
This is one of the biggest issues, some manufacturers/ suppliers do not understand system sizing well, and supply a battery and/or solar panel that is too small. This ends up being a big cost to the end customer as it causes unreliable light, and the battery life plummets with the frequent deep discharges. A quality and properly sized battery (with a correctly sized solar panel) should last 5 – 10 years. Batteries are the largest and most expensive consumable in a solar lighting system so it is important to get this right. To calculate this amount of battery back-up, a lead acid cannot discharge more than 70% and the average daily depth of discharge should not exceed 50%. A lithium phosphate Ion (LiFePO4) should not be discharged more than 80%. It is important to note that solar panel ration is CRITICAL, a LiFePO4 battery at 80% of discharge is going to take a lot more solar panel to recharge than an acid battery at 50% discharge. The battery size calculation then needs further derating applied to allow for performance drop in extreme temperatures, degradation over time and voltage drop. The solar panel needs a de-rate to allow for high temperatures, dirt on the solar panel or PV tube, voltage drop and degradation over time.
Planning for shading
Many proposed lighting locations will have shading from neighbouring buildings and trees. Solar lights perform properly with the solar panels unobstructed from shade all day, all year around. Performance plummets with shade and most solar lights are designed to perform with no shade ever on the solar panel or PV tube. The most challenging time of year for solar lighting is winter, when the night times are longest, the days are shortest, and the sun is tracking very low to the North, therefore the shadows are the longest. The exception to this is tropical northern locations, summer monsoon months are the most challenging times for solar lighting. The supplier/installer of the solar lighting project needs to carefully assess the shade and if necessary allow for buffers or lower power settings on the solar lights to allow for any shade at site. Alternatively, the light pole can be powered by a solar ‘slave’ pole, which has the solar panel and battery, located in a shade free location, with a low voltage cable trenched and cabled to the light pole in the shade. We recommend a highly experienced solar lighting company conduct the shade assessment and any slave pole planning.