A heat pump makes use of the higher temperatures underground (between 8°C and 13°C) to heat from water in pipes which are then be circulated through a heating system.
As the fluid passes through the house it looses some of its heat and so is re-circulated back through the ground where it will absorb more heat before being passed through the heat pump again.
Heat pumps do not generate electricity; they can however provide heating and can be operated in reverse to provide cooling. They do require electricity to operate, but ground source heat pumps are very energy efficient, producing up to five times the amount of heat energy for every unit of electrical energy needed to power it. These systems are particularly green if this electricity can be provided by renewable means such as wind turbines or solar photovoltaic panels.
When installing heat pumps households will require a different cylinder to those traditionally used in the home (see Storage).