Stocking up for winter

UK trials of a solar-powered under-road heating system that could be used to de-ice roads and heat buildings are due to begin later this month.

Due to last for two years, the trials are being managed by transport research group TRL on behalf of the Highways Agency, and will be carried out on a 100m stretch of private access road near the Toddington services area of the M1.

If successful and cost-effective, the heating technology could be used on stretches of the UK’s road network prone to problems during severe weather.

Its developer, London-based heat transfer specialist Icax, is also in discussion with an airport operator over possible use of the technology on runways.

The Icax system hinges on a relatively simple process that collects solar energy from the asphalt, stores it below ground and releases it when required.

It is based on the premise that dark road surfaces readily absorb solar radiation. At the height of the summer Tarmac surfaces can reach temperatures as high as 60°C. Beneath the top layer of asphalt a network of plastic pipes, through which water is pumped, collect this heat and return it to a pumphouse sited above ground. This heated water is then pumped through an additional layer of deeper pipes that lie under a polystyrene insulation layer.

As the heated water flows through these pipes it warms the ground, which acts as the system’s heat storage system. When the heat stored in the ground is required, the pumphouse can be used to divert the water to the upper layer of pipes to help prevent icing of the road surface, or to divert the warm water to nearby buildings, such as motorway service stations, where it can be used to provide heating. According to Icax, the system is capable of saving 300kW/m2 per year.

TRL project manager Derek Carder said that while it is simpler to install the system at the construction stage of a new road it could also be retrofitted to existing ones. Both approaches are being evaluated on the trial road which has been divided into two sections: one has been completely dug up, whereas the other simply had the upper layer of asphalt removed.

To evaluate the potential of the technology for heating buildings, the trials will also see the system hooked up to a simulated building, where condensers and a range of other devices will ‘waste’ heat just like an actual building does. Carder said that the trials will also investigate the use of the heat differential between a building and the stored energy to provide a cooling effect during the summer.

He said it will be some time before the trials provide conclusive results, and explained that part of the purpose of the study is to investigate how efficient the system would be and how much it would cost. ‘You need a full annual cycle, because you’re collecting heat and using it in the winter,’ he said. But he pointed to the use of similar systems in the Netherlands and Japan as evidence that such a technique is feasible.

The HA’s Les Hawker, who is working with Carder on the project, added that although there are no figures on how much it would cost to install the system over, for instance, a 10-mile stretch of road, the research project will cost around £500,000.

He said that while the technique is better suited to new road projects, there could be a case for installing it on particularly troublesome areas of the existing network. ‘It could have real benefits on particular parts of the network that have an icing problem — we’re very keen on looking at that.’

He added that the project forms part of a wider HA investigation into the use of renewable energy, pointing to last year’s introduction of solar panels at Junction 9 of the M27 in Hampshire.