Cooling geothermal power plants is necessary in order to condense the vapour feeding 
the turbine, lower the heat rejection temperature, raise power output and increase 
heat to power conversion efficiency. Three main cooling options are used: a) surface 
water (once-through systems), b) wet type cooling towers, and c) dry type cooling 
towers. Cooling with surface water yields the lowest condensing pressure and 
temperature and the highest conversion efficiency, followed by wet cooling towers, 
and then by dry cooling towers. Regarding the need for cold water supply, the order 
is reversed. Typical values are 970 t/h, 30 t/h and zero t/h respectively per MWe of 
installed power. In terms of costs, once through cooling may require both high 
capital costs and electricity consumption for transporting water. Dry cooling is the 
most expensive option due to the much higher heat capacity and heat transfer 
coefficient of water compared with ambient air. A dry cooling tower for a binary 
power plant of high conversion efficiency may cost 10 times more than its wet 
counterpart, which may result in raising overall power plant costs by 50%. In flash 
plants, where there is plenty of steam condensate to use as make up water, the 
standard technology adopted almost exclusively is cost effective direct contact 
condensers coupled with wet cooling towers. In binary plants, where the more 
expensive shell-and-tube or plate heat exchangers are used as surface condensers, 
the selection of the cooling system type is governed by water availability, local 
water use regulations and economics.


CRES profile
The Centre for Renewable Energy Sources (CRES) is the Greek National Centre for 
Renewable Energy Sources (RES) and Rational Use of Energy (RUE) (Law 2244/94 and Law 
2702/99). CRES is a public entity, supervised by the Ministry of Development, 
General Secretariat of Research, and Technology. CRES has participated in more than 
500 European, national and international projects including applied research and 
development, demonstration, commercial applications, energy policy, energy 
information and modelling systems, feasibility studies, environmental impact 
assessment, market research and promotion. CRES has a notable experience in all 
aspects of geothermal energy, including research, design, financing, works 
supervision, construction, testing and monitoring of innovative geothermal 
applications, geothermal resource assessment, geothermal exploration, policy making, 
legislation and others.

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