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Potential of Sea and Lake Water for Green Climatisation of Buildings

GeniLac is an innovative 100% renewable energy network in Geneva, Switzerland harnessing thermal energy from Lake Leman to heat and cool buildings. With significant energy efficiency and reduction of emissions, the project highlights the untapped potential for sea and lake-source water for green climatization of our built environment.

Initiated by Services Industriels de Genève (SIG) to address the “climate emergency,” GeniLac uses cold water from the lake and 100% renewable energy to heat and cool buildings connected to its 30-kilometer-long underground network.

Water is extracted from the lake at a depth of 47 metres and 1 km from shore, where the water remains at a constant 7 degrees Celsius year-round. The water is piped into an underground reservoir on land. Replacing conventional air-conditioning and heat boiler systems, the lake water passes through a heat exchanger, which transfers its thermal energy to the water circulating in the building's cooling systems via a network of pipes to cool buildings, while heat pumps are employed in the winter. Once the lake water has transferred its thermal energy, it is released back into the lake at a depth of 10-12 meters, where the water temperature is warmer to minimize changes to the lake’s average temperature.

GeniLac reduces the amount of energy used to cool buildings connected to it by 80%, replacing traditional air conditioning units and addressing refrigerant gas emissions, water consumption, and water pollution. As most Swiss homes are currently heated through the burning of either heating oil, gas, or wood, the lake-source heating model reduces fine particulate matter released into the atmosphere, while taking advantage of the enhanced energy efficiencies of heat pumps. The system provides locally sourced renewable energy, alleviating the reliance on imported fossil fuels, and reducing CO2 emissions.

The project currently serves 70 buildings in the city and continues to expand, with a new phase under construction to connect Geneva Airport to the network by 2026. This connection is expected to save 2 million litres of fuel oil per year once in operation.

By 2035, GeniLac aims to provide heating and cooling for 40% of Geneva’s buildings and reduce CO2 emissions by 70,000 tonnes per year.

While the upfront capital costs of lake and seawater source thermal energy systems are intensive, the networks are designed to last from 75 to 100 years. Energy savings result from increased efficiency in the method of heating and cooling production, in addition to the benefits of scale with collective infrastructure shared by many buildings. The district model also frees up space in each building for other uses.

Although using lake and seawater for thermal energy is not a new concept, GeniLac is one of the largest networks of its kind to incorporate both heating and cooling. Successful projects have been installed in Toronto, Canada, Cornell University, New York, and Stockholm, Sweden, but the harnessing of thermal energy in lakes and seas is still vastly untapped. A 2014 study calculated the thermal potential of Swiss lakes alone to be 97 TWh/a, with only 5 TWh/a currently being harnessed.

The scope and potential for seawater cooling systems are similarly vast, with a 2015 study by Japan’s New Energy and Industrial Technology Development Organization (NEDO) identifying more than 100 cities in 20 countries, mostly small island nations, as suitable locations for such systems. The report cites specifically Southen Pacific islands of Palau, New Caledonia, Fiji, Tahiti, Samoa, Kiribati, Marshall Islands and Cook Islands.

Energy Efficiency journal reported that just 1m3 of seawater in a thermal energy plant can provide cooling energy equivalent to a solar power plant the size of 68 football fields or 21 wind turbines.

While Europe still has higher demand for heating than cooling, as the planet warms, the global demand for cooling is expected to grow exponentially. The principles of GeniLac’s technology can be implemented in many regions of the world where a sufficient cold-water resource is in proximity to a dense climatization load to provide a clean, energy-efficient solution to combat climate change.

-article published in Tati's Journal Papua New Guinea and the Fiji Sun.
-images courtesy of, New Energy Industrial Technology Development Organisation (NEDO), and the author

Story Information:

Country: Other

Topic: Innovative Solutions

Photo or video credit: -images courtesy of, NEDO, and the author

Text Credit: Ruben C

Date : 6 July 2023

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