Low and medium temperature geothermal resources suitable for direct use applications are more widely available globally than geothermal resources required to generate electricity. Estimates suggest that between 4.105 and 5. 106 exajoules (EJ) stored in suitable aquifers can theoretically be used for direct geothermal heat applications.
With a recovery factor of 1% and an assumed lifetime of 30 years, the annual recoverable geothermal energy could match world final energy consumption of 363.5 EJ per year. Nevertheless, actual exploitation is estimated at 587,786 TJ per year, less than one-thousandth of the technical potential.
Increasing the use of geothermal heat applications offers significant benefits. Geothermal direct utilization boosts the development of economic activities in the areas near the resource location, thereby providing employment for local communities.
Additionally, geothermal is a renewable and indigenous energy source. Increasing its use can reduce dependency on fossil fuels, therefore improving the trade balance and protect businesses and consumers from the risk of volatile prices and energy shortage.
Geothermal energy in the agrifood sector can be used to heat greenhouses and sterilize the soil, creating growing environments suitable for food production in locations where natural conditions would not normally allow.
Additionally, protection from diseases and extreme weather conditions increases productivity and offseason availability of products. Geothermal heat can also serve for drying purposes, which helps preserve a wide range of foods.
It contributes to mitigating food waste and results in a substantial reduction in drying space and time requirements. Furthermore, food drying can maintain a high protein content of some products. The wide range of geothermal applications in the agriculture and agro-industry sector depends on varied fluid temperatures.
GEOTHERMAL HEAT APPLICATIONS IN THE AGRI-FOOD SECTOR
Aquaculture (20°C-40°C) Geothermal waters can be used to heat freshwater in heat exchangers or mixed with freshwater to obtain suitable temperatures for fish farming. This application has been reported in 21 countries worldwide and it is mainly used for aquaculture pond and raceway heating.
Cultivation of algae – mainly spirulina – is another growing use, which requires temperatures of 35°C-37°C.
Soil heating (20°C-40°C) The constant soil temperature increases the yields and makes it possible to extend the growing season. Soil heating is used, for example, to grow carrots and cabbages.
Greenhouse heating (25°C-100°C) This is one of the most common direct applications of geothermal energy reported in 31 countries worldwide. Greenhouse heating is employed to grow crops such as vegetables and fruit in addition to flowers, houseplants and tree seedlings.
Irrigation (40°C-75°C) Geothermal energy at this temperature range can be employed to heat winter crops in open field agriculture and in greenhouses.
Food/crop drying (around 60°C up to 100°C) Low to medium temperature geothermal resources can reduce energy consumption in the drying process, which consists of removing water contained in the product, thus reducing moisture quantity to below 20%. Drying vegetables, fruit and fish typically requires temperatures of 70°C-95°C.
Milk pasteurization (around 70°C up to 100°C) Geothermal hot water can be used for milk pasteurization, while geothermal steam can be used for milk drying and ultra-heat treatment (UHT)
processes.
Evaporation and distillation (around 80°C up to 120°C) This is commonly employed to separate mixtures and/or to increase the concentration of some components of the product. Examples include milk evaporation, sugar and liquor processing.
Sterilization (>105°C) Geothermal heat is used to achieve a temperature of 121°C for food sterilization in the meat and fish industry, which is a standard temperature for food sterilization. Besides, geothermal water can also be used at 105°C-120°C to sterilize food processing equipment.
Refrigeration (>120°C) Geothermal energy can be used for refrigeration by absorption technology, using an ammonia/water cycle for applications below 0°C. So far, there has been very limited use of this geothermal application.
