From the surface of the Earth, solar is an intermittent power source – but that doesn’t stop it being used to supply streetlights. Photovoltaic panels can harvest energy from the sun’s rays during the day and batteries can store that energy for use by streetlights at night.
"People are either not very aware of the benefits that solar could bring to them, or are just afraid of the new technology and its complexity"
Modern solar streetlighting also needs controls that monitor input to and output from the batteries, adjusts those flows according to the season and ensures streetlights do not go out in winter months.
The system can be on grid or off grid. Obviously off-grid systems are best suited to regions such as southern Europe, the Middle East and Africa where there is no power grid or where hooking the streetlights up to it could be expensive.
According to Adrian Dennis, managing director of Zeta Specialist Lighting: ‘An off-grid system should pay for itself in the savings on installation alone.’ After that, the savings continue. The system uses zero power and, with the right components, should not have any maintenance costs until the batteries have to be replaced after about seven years.
Going on grid
In northern Europe, on-grid systems are more popular. There are well-developed power networks that are easily and cheaply accessed (with only small exceptions such as in the national parks in the UK). On-grid solar streetlighting systems feed energy into the grid during the day, then take back what they need at night.
There is a third way: hybrid systems use batteries like the first option but, like the second, they can feed excess energy into the grid during times of plenty. They are used where there is a grid, but it is unstable.
Interest in solar LED streetlighting is on the rise. Philips’ global business manager for solar lighting is China-based Steven Kang and he’s noticed a ‘significant drop’ in the price of photovoltaic panels over the past few years. ‘It’s still going down and so the adoption of solar will definitely accelerate.’
Information, however, is still at a premium. ‘People are either not very aware of the benefits that solar could bring to them, or are just afraid of the new technology and its complexity. A user-friendly system design is crucial to its adoption: it must be simple to use and include plug-and-play features.’
Where the sun don’t shine
Zeta’s managing director Adrian Dennis is confident that solar systems are becoming viable in places where bright sunshine is much rarer. ‘Systems without intelligent control technology will not work in the UK during the winter months.’
However, 2015 will be a year of ‘groundbreaking solutions that should see the uptake of solar lighting solutions grow significantly’. Specifically, there will be control systems that can regulate – and optimise – lighting from dusk until dawn.
Previously, says Dennis, there were ‘a significant number of unreliable systems imported into the UK that simply would not work in a northern European climate; this hit customer confidence’.
Technological advances will soon drive up adoption, says Gorm Teichert, chief executive of Scotia from Denmark, which has been designing and supplying grid-tied and standalone systems since 2008.
The firm has recently completed projects in Saudi Arabia and the UAE, where its vertically integrated solar panels ‘turn a passive structure [a streetlight] into an energy-producing structure without disturbing anything’.
‘The conversion doesn’t require any extra real estate and that can make solar more appealing than, say, wind power.’
Zeta’s Monopole technology could have much wider applications. ‘The usual horizontal panels you see on solar farms in the Middle East need a lot of cleaning. On vertically mounted panels, the sand just falls off,’ says Dennis. Around the world, dust, bird droppings and snow can all accumulate on horizontal panels in the same way, but not on vertical ones.
This is another running-cost advantage of the latest solar streetlighting technology, but it might soon gain a significant social advantage too. Scotia is about to start a pilot project in a part of Africa where there is neither electricity nor streetlighting.
By combining solar-gathering LED streetlights into a mini grid, they could supply the energy to run not just lamps but also, for example, electric stoves – which would replace dangerous kerosene-fuelled stoves.
A different dimension
‘This would really add a different dimension to solar streetlighting,’ says Teichert, who also suggests that government subsidies to lift the price paid for electricity returned to national grids would increase the appeal of grid-tiered systems.
As Philips’ Kang points out, there is wide scope for solar LED lighting to improve lives around the world. ‘Currently 1.3 billion people suffer from light poverty and a further billion are connected to unstable grids and suffer regular power outages.
As transformation efficiency (over the entire spectrum of the sunlight) improves continuously, solar power should become the most easy to access, clean and cheap energy.’
On top of ever-greater financial advantages and the environmental perks, such a vast social benefit would make solar LEDs truly sustainable for streetlighting. It would also make them impossible to ignore.