Geothermal Energy for Melrose?

As the age of carbon fuels draws to a close, one often finds oneself in conversations about new energy sources and words fly around like –  “solar thermal”, “PV”, “wind”, “nuclear”, “hydroelectric”, ”biomass,” etc. One occasionally hears whispers of “geothermal energy”, which will either “save the world” or be a “huge waste of money”. Googling the word “geothermal” produces conflicting information and one is left with enduring questions – “What is Geothermal Energy?” and “Can it help resolve our energy crisis?”. In this series of blog posts we seek answers to such questions.

To understand “What is Geothermal Energy?”, one must realize that a tremendous amount of energy was stored inside the Earth’s core when the solar system was formed 4.5 billion years ago. As outer space is very poor conductor of heat, most of this energy remains trapped inside the earth even today.

Human energy consumption today is zillions of times smaller than this stored energy inside the earth. If some way could be found to take this energy out of the earth and turn it into something that humans can use instead of coal, oil or natural gas, then GHG (Greenhouse Gas) emissions could be reduced.

There are two main methods of exploiting Geothermal Energy (and they are confusingly referred to as “Geothermal” in public discussions):

1)      Geothermal Power – a process by which a large temperature difference (about 300 F) between the surface temperature and subterranean temperature is used to generate electricity. This approach works best in places where the crust is thin (ex. Iceland, Kenya, and New Zealand). In order to access this large temperature difference very deep holes (several miles deep) have to be dug. This kind of power generation comes with significant costs for prospecting, well digging and maintenance. The power output of these plants is typically in the 1-100 Megawatt scale and they can provide uninterrupted electric supply to a grid.

2)      Geothermal Heating & Cooling – a process by which small temperature difference (about 20 F) between surface temperature and subterranean temperature is accessed to provide local heating and cooling. The actual exchange of heat is done via a Ground Source Heat Pump (GSHP). In order to access this temperature difference we dig much shallower holes (6-300 feet) and the holes can be dug almost anywhere. The expenses associated with this form of energy are much lower than Geothermal Power. The heat energy transfer using GSHPs is more efficient than alternatives like Air Source Heat Pumps. GSHPs provide HVAC options for residential, commercial and municipal applications. Typical power output of these Geothermal HVAC  setups is in the 1 kilowatt – 1 Megawatt range.

The Geothermal Heating and Cooling idea is of particular interest to us in Melrose. As the energy required to run the ground source heat pump can be obtained from other renewable sources, one can use geothermal heating and cooling as a way to get to Passiv Haus or Net Zero buildings. Geothermal HVAC can help Melrose reach any emissions reduction goals it sets for itself. 

Sunil Sainis

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