Mariene Gutiérrez
Tlalli Energía

Geothermal Heat's Untapped Potential

Wed, 02/22/2017 - 11:35

Mexico has abundant geothermal resources. For the past few decades the country has successfully generated electricity mainly from its high-temperature (over 200° C) geothermal resources. On the other hand, direct uses or non-electric uses of geothermal energy have remained largely overlooked in Mexico (Gutierrez-Negrin and Quijano Leon, 2005). Direct use refers to the immediate use of the energy for applications such as heating swimming pools, balneology (baths or spas), agriculture (greenhouse heating, crop drying, animal husbandry), space heating and cooling (including district heating), aquaculture (heating of fish ponds and raceways), and providing heat for industrial processes and heat pumps (for both heating and cooling). Iglesias et al (2011) reported the existence of at least 2,300 geothermal manifestations with surface temperatures over 30° C.

About 90 percent of the geothermal resources studied in 26 of Mexico’s 32 states fall in the temperature range between 50° and 150° C. The estimated energy content of just 30 percent of these resources is about 1,200 exajoules (EJ) (Iglesias et al, 2011). In contrast, by 2010 only about 164MW had been used in Mexico, mainly for recreational purposes in spas and baths (IEA-GIA, 2013). The potential for direct geothermal heat use is, thus, far greater and remains essentially untapped

The vast availability of geothermal resources of medium and low temperatures across the country and the energy potential they contain is evident, and it could be harvested in direct use applications. In 2015, the industry and building sectors such as residential, commercial and public, accounted for 50 percent of the total energy consumption in Mexico. Industry sectors related to production of food, beverages, glass, paper and other small industries require a great deal of low to medium-grade heat for their processes (IRENA, 2015), which could be partially or totally delivered by geothermal sources while reducing reliance on oil products and other fossil fuels. So far, biomass is the only renewable employed (excluding renewable power) in the industry sector’s energy mix. In the building sector, energy demand is dominated by thermal uses such as water heating and cooking, accounting for almost two thirds of demand (SENER, 2011). Space heating accounts for roughly 1 percent. Geothermal heat could potentially satisfy some or all of the hot water demand and heating requirements (IRENA, 2015).

Deploying geothermal heat in the building and industry sector implies that conventional fuels such as oil derivatives used for heat generation have to be substituted. Recent analyses by IRENA show that from all the renewable energy options, geothermal sources are among the least expensive. Substitution remains cost-competitive for geothermal heating when the deployable resources are in the proximity of manufacturing facilities. A potential of around 800MW of geothermal heat for the industry sector is considered to be feasible by 2030 (IRENA, 2015). Space cooling also represents an important energy consumption, particularly in extreme climates (de Buen, 2011). So far, the use of geothermal-based systems for space heating and cooling has received little attention in Mexico.

Geothermal Heat Pump (GHP) systems combined with underground thermal energy storage (UTES) have proven an efficient way for heating and cooling spaces. Systems can either use aquifers thermal energy storage (ATES) or borehole thermal energy storage (BTES). Furthermore, these systems rely on seasonality: heat available during the summer is stored for use during the cold season. Similarly, the cold from the winter would be stored for summertime use. GHPs in combination with UTES for heating and cooling purposes are popular in countries with moderate climates like the Netherlands, Sweden and increasingly in the US, as they lead to considerable primary energy savings and to carbon emissions reduction (Godschalk and Bakema, 2010). However, these systems and applications are practically unknown in Mexico. The overall suitability of ATES/BTES systems for heating and cooling applications is assessed with of climate, type of aquifers present and groundwater temperature in mind. Climates more favorable for UTES have a distinctive warm and cold season. A higher aquifer permeability is more favorable, as well as colder groundwater temperatures.