Watertight Solar Collector

A Watertight Solar Collector provides an alternative means of collecting solar energy for Interseasonal Heat Transfer from flat roofs: it allows solar energy to be collected efficiently and economically from flat roofs in the centre of cities.

Flat roof solar collector – Solar Roof

A Watertight Solar Collector collects solar heat energy from the surface of flat roofs for storage in thermal banks and use for space heating in winter. A Watertight Solar Collector provides the dual functions of providing complete waterproofing for flat roofs and solar thermal collection.

The design of the Watertight Solar Collector follows the ICAX philosophy of providing a second function to existing building fabric. In this case the second function of solar thermal collection has been added to the primary function of a flat roof covering – to ensure a waterproof seal.

A Watertight Solar Collector, like an Asphalt Solar Collector, is an efficient means of collecting a large amount of warmth to raise the temperature of a ThermalBank from the natural temperature of the ground up to over 25°C for use in Interseasonal Heat Transfer.

Black roads – and black roofs – tend to absorb the heat of the sun up to the point when they radiate heat as quickly as they are absorbing it: the surface temperature of roads in direct sunshine can often reach 15°C higher than the ambient air temperature. ICAX collects heat using fluid circulating through an array of pipes embedded in the surface of the road and deposits it in ThermalBanks constructed beneath the insulated foundation of buildings. The temperature across a large ThermalBank can be increased from its natural temperature of 10°C to over 25°C in the course of the summer months.

A second function for existing building fabric

ICAX gives a second function (heat collection) to standard building fabric (roads, school playgrounds or flat roofs) that will need to be built in any event. The marginal extra cost of adding solar collection to a planned road – or roof – is much less than the cost of buying dedicated solar thermal panels. There is no visual impact.

ICAX places a ThermalBank beneath the foundation of a new building. This gives a second function (heat storage) to standard building fabric (the insulated foundation of a new building). There is no visual impact.

ICAX uses a heat pump to recover warmth from the ThermalBank in winter and deliver heat via underfloor heating into buildings to provide heat without burning fossil fuels. There is no visual impact, no noise and no emissions of carbon dioxide on site.

Successful Trial

TRL reports on the successful trial of Asphalt Solar Collectors and Solar Road Systems for the Highways Agency in Toddington Results.


Asphalt Solar Collector

Cost of solar collectors

The marginal cost of adding solar collection to a flat roof that is going to be needed anyway is £90 a square metre fully installed. The equivalent flat plate collectors can be £600 a square metre, before the installation costs of mounting and plumbing.

Solar collectors and planning permission

A Watertight Solar Collector raises no planning issues – from a distance it looks like any other flat roof.


See Renewable Heat.


ICAX Projects: Toddington | Howe Dell | Hiroshima | Garth | Merton | Suffolk One | Wellington | Tesco Greenfield

See Ground Source Heating      Ground Source Cooling     Ground Source Energy