Thermal Energy Storage - TES

Thermal Energy Storage addresses a key element of the renewable energy dilemma: Solar heat is freely available in summer, but the largest heating requirement is for space heating in winter. This is why Seasonal Thermal Energy Storage has been described as the holy grail of the renewables industry. ICAX achieves TES by storing summer heat in ThermalBanks™ (see below).

More generally the term "Underground Thermal Energy Storage", or UTES, is used to describe this critical function.

This can be further divided into:
Aquifer Thermal Energy Storage - ATES - which has been used in Holland
Borehole Thermal Energy Storage - BTES - which is widely used
Cavern Thermal Energy Storage - CTES - which has been used in Sweden.

ThermalBanks™ store heat between seasons

A Thermal Bank is a bank of earth used to store heat energy collected in the summer for use in winter to heat buildings. A Thermal Bank is an integral part of an Interseasonal Heat Transfer system invented, developed and patented by ICAX to answer the need for on site renewable energy without burning fossil fuels.

Interseasonal Thermal Store

A Thermal Bank is used to store warm temperatures over a very large volume of earth for a period of months, as distinct from a standard heat store which can hold a high temperature for a short time in an insulated tank.

Heat moves slowly in the ground – Thermal Inertia

It is a characteristic of earth that heat only moves very slowly through it – as slowly as one metre a month. ICAX exploits this thermal inertia to input surplus heat into the ground over the summer months and extract that heat over the winter months for use in the space heating of buildings.

Interseasonal Heat Transfer works by capturing heat energy from the sun via a collection pipe network just beneath the surface of black tarmac roads (or car parks or school playgrounds). It then stores the energy in computer-controlled Thermal Banks in the ground under the foundation of buildings, and releases it to heat the buildings in winter via heat pumps linked to underfloor heating.

Constant temperature only if undisturbed

The temperature of the ground at a depth of seven metres in the UK will normally be very close to 10°C – the temperature will vary very little between summer and winter as heat only moves very slowly in the ground. ICAX uses this characteristic of the ground to store heat from summer to winter. Using fluid – in an array of pipes – as the transport mechanism solves the difficulty of getting the heat into the ground – and out again.

The way in which heat is absorbed and released by the ground is complex and required to be studied using complex iterative methods that have only become practical with the use of computational fluid dynamics (“CFD”). The computer models developed by ICAX have since been tested in practical installations and refined to reflect empirical results. These have been used to refine the design parameters for successful ThermalBanks to provide thermal energy storage for solar heating and cooling.

Black surfaces absorb heat

Tarmac roads 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 tarmac can often reach 15°C higher than the ambient air temperature.

Sun heats tarmac

ICAX collects heat using water circulating through an array of pipes embedded in the surface of the tarmac and deposits it in ThermalBanks constructed beneath the insulated foundation of buildings. The temperature across the ThermalBank can be increased from its natural temperature of 10°C to over 25°C in the course of the summer months.

ICAX uses a ground source heat pump to extract heat from the ThermalBank when it is needed to heat the building in winter using underfloor heating. Unlike a normal ground source heat pump which typically starts with an autumn ground temperature of 10°C the heat pump in an Interseasonal Heat Transfer system starts with a temperature of over 25°C from the ThermalBank.

IHT doubles the CoP by starting with warmth

This doubles the Coefficient of Performance of the heat pump and allows an 80% saving of carbon emissions compared to providing heat from a gas boiler.

Underground Thermal Energy Storage – UTES

A Thermalbank is also described as Underground Thermal Energy Storage – UTES, or as providing Seasonal Heat Storage.

Borehole Thermal Energy Storage – BTES

Where it is not practical to create a horizontal Thermalbank to store energy ICAX uses a vertical Thermalbank to perform the same function. A vertical Thermalbank is created by drilling a borehole field – a set of boreholes drilled to depths of 100 metres or more. This is described as Borehole Thermal Energy Storage - BTES. In BTES, a closed loop polyethylene probe is inserted after drilling, the borehole is then filled with a high conductivity grouting to provide a good thermal contact with the surrounding soil.

ICAX has used Borehole Thermal Energy storage at the Wellington Civic Centre, Suffolk One College, Merton's Acacia Intergenerational Centre and Greenfield Supermarket.

Borehole fields are also described as Heat Wells.

Geo Exchange system

The term Geo Exchange is also used for the mechanism of using the earth as a heat exchanger and a store of heat energy. Heat can be collected from the ground by circulating cold fluid through pipes in the ground. Heat can be deposited in cold ground by circulating warm fluid through pipes in summer for cooling systems.

See also: Renewable Heat

See also: Renewable Heat Incentive clean energy cashback for most of your running costs for over 20 years.

See also: Banking on IHT

“A useful technology will surely be long-term thermal storage,” according to Professor David MacKay.

Thermal Bank

A Thermal Bank is a bank of earth used to store heat between seasons. Alternative descriptions include: Heat Bank, Heat Battery, Heat Store, Heat Vault, Underground Energy Storage, Seasonal Heat Storage, Interseasonal Heat Store, Seasonal Thermal Store, Interseasonal Thermal store, Underground Thermal Energy Storage ("UTES"), seasonal soil heat accumulator.

See also: Economic Renewable Energy