Use of geothermal energy
In aquaculture, geothermal energy is mainly used to heat aquaculture ponds and raceways, but mainly in fish hatcheries. Geothermal water heats the freshwater in heat exchangers or is mixed with fresh water to obtain suitable temperatures for fish farming. There are two options for transferring the heat energy to the fish ponds, a closed system using heat exchangers and direct supply of water to the fish pond. When using a closed system, geothermal water is used for heating the fish pond via a heat exchanger. A heat exchanger allows the flow of thermal energy between two or more water streams at different temperatures. In conventional heat exchangers, one stream recovers some of the heat of the other stream and the heat transfer takes place through a separating wall. When a direct supply of geothermal water to the fish pond is used for heating, the water is also used to flush the organic matter from the pond contributing to the water quality of the pond. The water treatment facilities typically include high-pressure pumps, a chlorine injection system (or other form of disinfection) and an automatic filtration system. In direct contact, the heat is transferred between cold and hot water through direct contact between the two. After the procedure, the water is heated to the optimum temperature for the farmed aquatic species. The low water temperature (13–30 °C) provides a relatively cheap and pollution-free source of energy for direct aquaculture use.
Main countries and species
Among the leading countries are Iceland, China, USA, Italy, and Israel, yet the use of geothermal energy in fish farming is expanding rapidly in other countries, too, for example, in France, Greece, Hungary and New Zealand. In the approximately 70 Icelandic fish farms of which 15-20 use geothermal water, tilapia, Arctic char, turbot and Atlantic halibut are farmed. A number of such fish farms operate in Romania, too. In Greece, there are also some farms, where geothermal water at a temperature of 51°C and a flow of 10 kg/second is used to heat the water to 33–36 °C for spirulina cultivation. Other species raised in geothermal water aquaculture include carp, catfish, frogs, mullet, eels, salmon, sturgeon, shrimps, lobsters, crayfish, crabs, oysters, clams, scallops, alligators, mussels and abalone. For example, tilapia can be reared intensively in mono and in polyculture systems with other compatible and commercial species such as carps and mullets. They are a group of fish that can be farmed in a wide range of salinities with relatively short production cycle (6 to 8 months to market size). In USA, tilapia is raised in raceways using geothermal water at 35 °C. Genetically improved Nile tilapia (Oreochromis niloticus) is farmed in tanks situated under a greenhouse roof to protect it from weather conditions, natural predators such as birds and from pathogens. Domesticated varieties of the common carp (Cyprinus carpio) are raised in cascades that are downstream from geothermal greenhouses. Other raised species in USA include catfish, hybrid striped bass and largemouth black bass (Micropterus salmoides). Around 11 commercial facilities operate in the desert and arid region of Arizona, 12 facilities in Idaho and there are also some operations in New Mexico, Nevada and Texas. Being among the most common species grown in geothermal aquaculture, tilapia is also grown in Israel. The country has 15 commercial fish farms currently operating in the Negev Desert where tilapia common carp are the most common species, accounting for about 75% of Israeli inland aquaculture. These species in terms of popularity in Israel are followed by silver carp, grass carp, grey mullet, North African catfish and gilthead sea bream. Of five model pilot-scale farms established during the 1980s and 1990s, two were expanded to a full commercial scale of 200–400 tons/year of aquaculture production.
Prospects and opportunities of geothermal aquaculture
Compared to regular fish farming, using geothermal water in fish farming is an affordable and sustainable solution to reduce dependence on fossil fuels. As farming of freshwater or marine organisms in a controlled environment enhances the production rates by 50 to 100% thus increasing the number of harvests per year, the availability of cheap geothermal water makes breeding and production of different species of fish cheap all year round. However, unlike fossil fuels, geothermal resources are not available everywhere, so that even though geothermal energy has the potential to provide long-term and secure base-load energy for the aquaculture sector, the prospects for its use are limited to areas around the Pacific Ocean and the Pacific Plate as well as some European countries and the deserts of North America and the Middle East.
Despite access to geothermal water some countries still do not employ it in fish farming. For example, in Lithuania, the use of geothermal water in aquaculture is still under consideration. The country has access to hot underground water in its western part a kilometer below the surface, however, currently it is only used to produce energy for heating. These facilities are labour intensive and require well-trained personnel, which are often hard to justify economically, thus, growth in the geothermal aquaculture is slow. The number of small-scale ground-source heat pumps in the country is growing. The natural springs and deep wells in Albania produce geothermal water up to 65.5 oC, therefore the country is also considering using the geothermal heat for aquaculture. Albania already utilizes it in spas, bathing and swimming pools, and uses geothermal heat pumps for heating and cooling. Like Albania, Croatia also utilises geothermal energy in spas and recreation centers, and for space heating. However, the country currently does not have any plans to employ it for fish farming. This situation is similar in Poland. Although it has access to geothermal water, the country does not utilise it in aquaculture. During 2010-2014 geothermal energy was used for several purposes, mainly for heating, bathing and swimming. Over the past five year the total installed geothermal capacity and heat sales have increased, however, utilisation of geothermal water in fish farming remains to be developed.
Barriers for geothermal aquaculture development
Geothermal energy is already used in many countries, but geothermal development has been slow in most. The main constraints and challenges impeding the use of geothermal energy are policy, regulatory, technical and financial barriers. The initial high investment costs of geothermal projects reduce the appeal of geothermal water in fish farming and is one of the main barriers to geothermal energy development in resource-constrained economies. As fossil fuels are a major competitor to renewable resources, the development of geothermal aquaculture has been slow in most countries. However, numerous countries have been doing the necessary groundwork, conducting inventories and quantifying their resources in preparation for development when the economic situation is better and governments and private investors see the benefits of developing a domestic renewable energy source. Hence, financing plays an important role in geothermal programmes. Government policies and legislation are important factors in creating an enabling environment for geothermal investment and resource mobilization and in encouraging investments from the domestic and foreign private sector. However, few governments have clear policies that promote the use of geothermal energy, especially for geothermal aquaculture, and budgetary allocations to geothermal energy research and development tend to be low. Regulations aiming to preserve and improve the environment also affect the development of geothermal systems. The main EU environmental regulations affecting the geothermal sector are the regulations on water and environmental assessment. Thanks to this legislation the development of geothermal is compatible with other environment objectives.
The use of geothermal energy is slowly increasing worldwide. Some countries with access to this renewable resource employ geothermal water in many areas. Despite being a sustainable method of farming fish, geothermal water is penetrating the aquaculture sector with difficulty. Some countries in Europe with access to geothermal resources do not utilise it in aquaculture although some of them anticipate its use in fish farming in the future.
A list of sources is available at www.eurofishmagazine.com