One side of solar panels in Australia is the use of solar power for outdoor street lighting. Orca Solar Lighting director John Warren writes an introduction to this side of the industry.

Solar lighting is a reliable, compliant and in many cases a more cost-effective lighting solution, utilised by some of Australia’s most well-known organisations, and incorporated into very large infrastructure projects.

The improvement of technology and methodologies over the past decade has been significant, however there are still inexperienced manufacturers or suppliers out there, therefore it’s 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 Australian 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).

It’s important to note that, to comply with Australian pathway lighting standards (AS/NZS 1158 3.1 2020 PP sub categories), 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, or 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 and suppliers don’t understand system sizing well, and supply a battery and/or solar panel that’s 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 five-to-ten years. Batteries are the largest and most expensive consumable in a solar lighting system, so it is important to get this right.

Here is a general rule of thumb. For most of mainland Australia, a solar lighting system requires four full nights of battery back-up, allowing for the LONGEST winter nights. For example, Melbourne has 14.39-hour long nights, therefore the battery should run the light at 100% illumination for 57.56 hours with no input from the solar panel. This example is used only to give an indication of battery back-up requirements, for example in the tropics such as Darwin or Cairns, the monsoon season requires over five nights battery back-up, however being the summer season, the night times are a lot shorter.

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’s also 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, voltage drop and degradation over time. AS/NZS 4509.2 Stand-alone power systems – system design states a minimum of 30% extra solar panel allowance.

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.

For most of mainland Australia, 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.

Compliance

Compliance pertains to larger solar lighting systems, ones with a battery capacity higher than 1,000Wh, therefore, larger than 76AH 12V capacity.

Ensure the proposed solar lighting system conforms to the relevant Australian standards AS/NZS 4509.2 Standalone power systems – system design which refers to and requires compliance to AS/NZS 3000, the Wiring Rules.

The limitations of integrated/all in one solar lights

Integrated solar lights have their place, however the fundamental nature of their design severely limits their suitability in southern latitudes (in the southern hemisphere), where the sun tracks very low to the north in winter, causing the direct sunlight to hit the solar panel on a very shallow angel.

These solar lights tend to have a very shallow solar panel angle to the horizontal. This panel angle is more suitable in equatorial latitudes where the sun does not stray far off straight overhead, therefore the solar panel operates effectively.

The Lighting Council of Australia published both the ‘Solar Lighting Guide’ and ‘Fit for purpose – the limitations of integrated solar lights’ with deeper explanation on the topic. Orca Solar Lighting also has a technical paper in Solar collection methods for solar lighting applications which can be found on its website.

This shallow solar panel angle issue does not necessarily apply to solar lighting bollards, which run at low wattage output and generally installed closer together, where-as integrated solar lights are generally run at high wattage output to compete with proper solar lighting systems that have a completely independent swivelling and angle adjustable solar panel.

In summary, solar lighting can be a very reliable, compliant, low maintenance and cost-effective solution, however requires a bit more planning up front, and due diligence into product selection.

If these points are addressed, maximum safety, product life and minimal maintenance amounts to considerable long-term savings.