Geothermal energy provides heat at a temperature range from 100 – 200°C. In many
installations, this heat is used either for power production or for heat supply.
Cogeneration (Combined Heat and Power CHP) improves the overall efficiency as well as
the economics of a geothermal installation. Since the temperature of the heat source
might be sufficient for cold production in absorption chillers, trigeneration would
be an option, too.
Trigeneration, as the name implies, refers to the simultaneous production of three
useful energies, and is defined as the simultaneous production of heat and power,
just like cogeneration, except trigeneration takes cogeneration one step further by
also producing chilled water for air conditioning or process use with the addition of
absorption chillers that take the heat to make chilled water for cooling a building.
The main components of these systems would be a power plant, (direct steam or
binary), a chiller and heat exchangers of a district heating system. The design of
geothermal CHP and trigeneration systems differs from the design of conventional CHP
and trigeneration systems.
The limited temperature and capacity of the heat source calls for careful
consideration of the necessary minimum temperature of each component. Moreover,
parallel or serial coupling of the components is an important issue. The talk gives
an overview of the possible options including efficiency calculations. The pros and
cons of different alternatives as well the differences to conventional trigeneration
systems are discussed.

BRGM
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45060 Orléans cedex 02
France