A green sweep
June 1st 2010

Tennant is currently trialling its 500ze electric street sweeper. Karel Huijser, VP international, and Alan Riach, engineering director city cleaning, recently gave the lowdown on the new green solution. Additional reporting by Gerardine Coyne

It is predicted that by 2050, 70% of the world’s population will live in cities. These city centres will need to cleaned, but at the same time we need to reduce greenhouse gas emissions. It is currently estimated that London’s poor air quality, has contributed to 1000 premature deaths and 1000 hospital emissions. A street cleaning vehicle can emit 50 tonnes of CO2 annually, which to offset would require the yearly planting of 50 trees, and EU targets mean that solutions are needed now.

Many EU countries do not confirm to set noise legislation, with studies showing that inhabitants view noise as a health risk as well as a nuisance. And 60% of European cities with a population over 100,000 are using groundwater at a faster rate than can be replenished. (source: WBCSD).

Tennant’s aim is the provision of sustainable cleaning solutions and other technologies. We have set up a centre in Falkirk, Scotland, to help providers in municipalities.

The world demands lower noise, reduced water usage and improved air quality; for street cleaning among other areas, this means a shift to electric vehicles. Currently Spain has a target of 25% electric vehicles by 2014, (though this may be affected by the economic situation).

The streets ahead

The 500ze is a lithium ion powered street sweeper. It emits no CO2, has reduced noise, no exhaust and low dust. And it performs a full day’s sweeping on one battery charge.

Alan Riach is engineering director at Tennant’s City Cleaning. He works with city cleansing departments “We embarked on the 500 ZE in 2008, and it was developments in li-ion tech batteries that finally tipped the balance,” says Riach. “Our customers’ problems were: carbon emissions, air quality and noise pollution. It took the development team in Falkirk one year from conception to put a prototype on the road.

“We felt the market pressing us with a demand for greener products,” explains Riach, “hence the fast development.” As the volume of battery and the energy needed is much higher on a working machine than on a car, there was a packaging challenge. The problem was accommodating the weight of the li-ion battery while still giving easy access. The team created a chassis structure with a battery each side. The batteries are intelligently balanced and can be changed in twenty minutes.

It’s estimated that the cost of charging the batteries for an eight hour shift is under €3. The equivalent diesel costs could be up to €80. According to internal benchmarking, 40 cars worth of CO2 is saved when compared to a diesel sweeper.

“With significantly lower noise levels, the public will enjoy a cleaner, quieter environment,” says Riach. Lower noise enables work in late night and early morning slots. “You can hear the early morning birdsong as you drive to the cleaning site,” exclaims Riach. Little noise also means that the machine is non-intrusive in pedestrian areas.

Powerful suction is suited to even coarse debris, effectively ‘eating’ litter thanks to its 3-stage cyclonic separation. The ‘Cloudmaker’ misting system provides improved dust control while minimising water consumption. The 500ze uses 70% less water than other traditional dust control techniques. According to Tennant it uses 120L for four hours’ operation. The sweeper has reduced operational costs, and fewer parts resulting in reduced servicing costs.

In terms of reliability, diesel is easy, so ensuring enough energy in the 500 ZE is crucial. The machine constantly monitors the battery charge and alerts the operator when it is running low. If the alert is ignored, the sweeping function switches off to ‘gently encourage’ the operator to return to base. Speed is also automatically slowed down.

The 500 ZE is designed, engineered and manufactured with sustainability in mind. The components; stainless steel, aluminium and polyethylene are all recyclable. Recycling aluminium for example requires less than a tenth of the energy needed for its extraction. The batteries are also recyclable. “This is a breath of clean air for cities everywhere,” ends Riach.

The Green Machines 500ze is currently in trials across Europe and will soon be seen in operation in major cities across Australia, Benelux, France, Germany, Italy, Netherlands, Spain and the UK.

www.tennantco.com