Summary. The Azores archipelago is located near the triple junction between the Nubian (NU), North America (NA), and Eurasia (EU) plates. It is characterized b

Renewable forms of energy are increasingly penetrating the electricity market, particularly, geothermal energy. A wide range of resource temperatures and fluid quality are converted mostly using traditional binary power plants and, recently, using Climeon modular units. Portuguese natural geothermal resources are far from precise estimations. Despite the parameter uncertainties, electric power resource estimations of two natural geothermal reservoirs are presented: a volcanic sourced heated high-enthalpy geothermal reservoir in Sete Cidades, São Miguel Island, Azores; and a low-enthalpy geothermal reservoir linked to a fractured zone in a granitic setting in Longroiva, in the northern part of the Portuguese mainland. Based on the volumetric method, we assessed the power potential of geothermal resources in Sete Cidades and Longroiva using a probabilistic methodology—Monte Carlo simulation. The average reserve estimations for Climeon module were 5.66 MWe and 0.64 MWe for Sete Cidades and Longroiva, respectively. This figure was by far higher when compared to traditional binary technology; those differences were mostly attributed to distinct conversions efficiency factors.

São Pedro do Sul Hydromineral and Geothermal Field, located in the northern interior zone of Portugal (Lafões zone), has the greatest widespread utilization of geothermal energy in Portugal mainland and is the most important thermal centre from the economical revenues point of view, obtained from direct and indirect utilization of the thermal water, mostly for wellness, health, and leisure of human beings. Recent utilization includes district and greenhouses heating and even cosmetic applications. The Hydromineral Field includes two exploitable zones: the Termas and Vau Poles. The waters are recognised for their mineral and medicinal effects, since the time of the Romans about 2000 years ago and, later on, on the 12th century, by the first King of Portugal, D. Afonso Henriques. The traditional spring and the 500 m well (AC1), located in the Termas Pole, currently supplies artesian hot water flow of about 16.9 L/s with a temperature of 67 °C. Despite the low flow rate of the actual two exploration wells drilled in the Vau Pole, the geothermal potential is high; a new deep well is planned to be drilled in this zone where is expected to obtain fluid temperature of around 75 °C. The occurrence of São Pedro do Sul mineral water, included in the sulphurous type waters, are linked to Hercynian granitoids, emplaced between 290 and 321 Myr. There is a close relationship between the placement of the main hot springs and the Verin-Chaves-Penacova fault, namely Verin (Spain), Chaves, Moledo, and S. Pedro do Sul (Portugal) hot springs. Heat flow generated at shallow crustal zones by the radiogenic host mineral of the granitic rocks, added to the deep Earth heat flow, heats the cold water inflow along fractures. Open fracture network along the main faults allows the hot fluids reach the surface, thus giving chance to the occurrence of hot springs and mineralized cold springs. Coupling between fracture opening and density difference between cold water inflow and hot water upflow is assumed to be the main driven factors that explain the occurrence of hot spring in regions with normal to slightly abnormal geothermal gradient. Actual thermal output of the captured fluid in the São Pedro do Sul Hydrothermal area is not fully used, namely in summer times. Thus the main focus for the concessionary includes the saturation of the actual Termas heat power capacity either in the SPA utilization and expansion for newer users in the district heating system. Further studies must be conducted in order to ascertain for possible source deep exploitation to refine quantitatively the São Pedro do Sul reservoir conceptual model in order to make sustainable wise management of this important natural resource, critical for the São Pedro do Sul municipality development and also contributing for the Portuguese sustainable economic growth. In this paper we give new insights for the knowledge of São Pedro do Sul Hydromineral and Geothermal Field, namely the geothermal reservoir, the concession hot water exploitation and future perspectives for upcoming sustainable developments of this valuable natural resource.