The Brest Metropole heating tower

The challenge

Brest Metropole (the city of Brest and the surrounding municipalities) has been pursuing its energy transition since the late 1980s via a district heating network powered by household waste incineration and a biomass boiler system. However, spikes in demand at the local university were posing a real challenge to the local authorities’ efforts to break free from fossil fuels. We were tasked with finding an innovative approach to meeting our clients’ emerging needs.

The solution

Brest had untapped heating potential at its waste-to-energy facility. This led Dalkia to build what has become known as the "Energy Mirror": a tower comprising a stack of polished stainless steel rings that reflect the sky and surrounding urban landscape. The 1,000-cubic-metre storage tower houses a huge hot water tank and is installed above the district heating network near the university. The heat produced by the waste-to-energy facility and the biomass boiler system is recovered and stored as layers of hot water. The harnessed heat is then simply fed back into the system in short cycles of two to three hours during spikes in demand, such as when the university’s heating is turned back on in the morning. A smart management system designed by Dalkia helps absorb these surges in demand as close as possible to the point of use. It seems fairly straightforward, and yet it is the first of its kind in France! That’s our way of doing things. We put our bold ideas, passion and technologies into solving problems for our clients and giving them peace of mind, so that at the end of the day, they could never imagine doing things any differently!

The benefits

The storage tank provides an additional 2,500 MWh/year of recovered energy, enough to heat 400 households. Brest has secured its energy supply while also reducing fossil fuel consumption and greenhouse gas emissions.

The university was already heated by energy produced through waste recovery. But until now, we had to resort to gas to start up the heating quickly. The storage tower enables us to avoid that excess consumption.

Natalia Leclerc,

Vice-President of Université de Bretagne Occidentale, in charge of culture and sustainable development

The project in figures

1,000 m3

storage volume

12,700 tonnes

reduction in CO2 emissions over 20 years, equivalent to taking more than 6,300 cars off the road.

4,470 TOE

(tonnes of oil equivalent) replaced over 20 years


project cost

  1. April 2016

    Civil engineering work begins

  2. June–August 2016
    Erection and assembly of storage structure on site
  3. September 2016

    Building exterior and hydraulic process

  4. October 2016

    Testing and commissioning

  5. November 2016


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