City noise sensor

Quiet! Solar Owl is monitoring you

The Solar Owl is a simple unit that is maintenance free.
The Solar Owl is a simple unit that is maintenance free.

What: Solar Owl
Where: Warwick University

Scientists remain obsessed with the idea of mapping our cities in ways that go far beyond physical geography. Organisations founded in academia, such as UCL’s Centre for Advanced Spatial Analysis, have found potential revenue streams by interpreting urban meta-data visually; their virtual models of carbon monoxide generation, urban heat sinks or people movements are becoming part of the broader understanding of how a city functions.

Solar Owl is part of this bigger-picture thinking. Now undergoing prototype testing, it is the brainchild of PV firm Polysolar, the University of Warwick and Cambridge-based specialist technology consultancy Sentec. The aim is to make it the first commercially viable noise pollution sensor that provides real-time data on outdoor noise levels without requiring maintenance.

With a projected cost of less than $20 (£13) per unit, and without the need for an external power source, Solar Owl has the potential to provide very detailed information on noise levels over an extended period, allowing us to build a definitive aural map of our cities.

  • The campus at Warwick University where Solar Owl prototypes are still undergoing testing ahead of full scale production.
    The campus at Warwick University where Solar Owl prototypes are still undergoing testing ahead of full scale production.

The unit consists of a photovoltaic unit, a sound sensor with a range of up to 200m, and a transmitter. The innovation, says Polysolar chief technology officer Joanna Slota-Newson, is the way the energy management system stores solar power, allowing it to optimise readouts according to the amount of power available, giving it an almost intuitive flexibility.

‘If the energy sensor picks up a reduction in available power it can either decrease the number of readings it sends out by spacing out the time periods it transmits in or it can store the readings over the same period and transmit them at a later time when more power is available,’ says Slota-Newson, arguing that this consistency gives the Solar Owl unit its accuracy.

The algorithms controlling the power management, data collection and transmission were developed to keep the system foolproof and maintenance free for at least 10 years. After final testing the team plans to roll them out to the Greater London Authority to monitor sound levels in the capital. To do this on a scale where the information can be useful, units need to be fitted at sufficient density, hence the cost limit. Sentec is now seeking large-scale manufacturers who’ll be able to make and supply Solar Owls at the requisite volume and price.

Solar Owl technical spec

  • 3.5V Organic photovoltaic
  • PV size 45mm by 55 mm
  • AIMD-based power management algorithm
  • Data send interval 40 seconds
  • Energy level evaluated every 24 hours: cautious increase in send rate vs aggressive decrease in send rate at low energy levels
  • 30F super-capacitator for energy storage
  • $20 (£13) per module

A 2011 World Health Organisation report ‘Burden of disease from environmental noise – Quantification of healthy life years lost in Europe’ – claims that long-term exposure to noise may account for 3% of deaths associated with heart disease and stress. The argument is that noise keeps our bodies alert, continually producing stress hormones even when we are sleeping, a factor that can contribute to heart attacks and strokes. At the most quantifiable level noise levels can be linked to broken concentration and reduced academic achievement. ‘The point of the smart cities movement is to inform governments and guide future policy and the Solar Owl is part of that thinking,’ explains Joanna Slota-Newson. But how invasive is the technology? Does it merely measure sound or record it? This is always an issue that comes up, she says: ‘The system isn’t designed to pick up voices but measure levels of sound in timed bursts. That said, it could be activated by extremes of sound, such as a gunshot, which might have a relevance in future criminal investigations.’