20 Nov 2020

The Earth itself could provide carbon-free heat for buildings

Please note that this article and any associated images were originally published by Vox Media, here.   The heat stored in the Earth’s crust, known as geothermal energy, is carbon-free and effectively inexhaustible. There’s enough of it to run all of civilization for generations, if it could be cost-effectively tapped.  

Tapping it turns out to be no small feat, but efforts have ramped up recently due to new urgency by the climate crisis and the search for low-carbon alternatives to fossil fuels.


The cutting edge technological developments in the field (including, yes, lasers) are devoted to drilling deeper and deeper, into hotter and hotter rock. Heat anywhere from 302°F (150°C) up to 703°F (373°C), where water enters its “supercritical” phase and above, can be used to profitably generate electricity.


But electricity is only half of the geothermal story. Well before humans generated electricity with it, they used geothermal heat directly, to bathe, cook, and heat buildings, among other things. Geothermal direct heat is still used today in industry, agriculture, and for buildings, but only a tiny fraction of its potential has been unlocked.


When it comes to direct use of heat, geothermal resources don’t need to be quite so hot. It doesn’t require 300°F to heat the air in your home to 68°F. Just about anything 50°F or above (which is available just 10 feet down or so) can be used for something, whether drying grain, running a greenhouse, melting ice on airport runways, or heating commercial buildings.

Geothermal heat is accessible almost everywhere and useful in a wide range of applications. The US Department of Energy has a research program devoted to these “low-temperature and co-produced resources.”


But the most important application, in my mind, is the use of low-temperature geothermal resources for large-scale heating and cooling of buildings.


Heating and cooling buildings isn’t as sexy as electricity in the energy world these days, but it is important, representing just over 12 percent of US greenhouse gas emissions and a larger proportion of emissions in cities, many of which have aggressive decarbonization goals. To achieve those goals, they need to figure out carbon-free heating, and geothermal is one of the best (out of very few) options.


It’s hot, or at least warm, stuff!


Decarbonization means an improved competitive landscape for geothermal heat.


Cities across the world are setting aggressive decarbonization goals, pledging to zero out their direct carbon emissions by 2050. The first three challenges facing a decarbonizing city are electricity supply, transportation, and heating and cooling of buildings. The pathways to decarbonization of electricity and transportation, while extremely challenging, are at least fairly well understood: renewable energy, electric vehicles, and good urban design that minimizes the need for cars.


For most cities, though, heat is a big unanswered question.


Oil and natural gas furnaces will need to be phased out, which means cities will need an extraordinary amount of low-carbon heat to compensate. And low-carbon options are much more limited in heat than in electricity.


Some furnaces can run on biomethane, other biofuels, hydrogen, or hydrogen-derived fuels, but in a mostly electrified world, low-carbon liquid fuels are likely to be used for high-value applications in industry and transportation — not heating your living room.


That leaves geothermal district heating or, at an individual building level, electrical options like electric resistance heating or heat pumps. In heat pumps, it’s either air-source (exchanging heat with the outside air) or ground-source (exchanging heat with the earth). The latter is far more efficient. And geothermal district heating is the most efficient of all.


In a decarbonizing world, it is these — the other low-carbon heating options — that will eventually comprise the competitors in the heating and cooling space. It’s a competition some decarbonizing cities, like Boston, are already grappling with. Boston will have trouble building lots of new electrical infrastructure to heat buildings with electricity, so it is leaning toward geothermal. A detailed analysis of the benefits and challenges of implementing these technologies is available in the original article published by Vox Media, here.

Related topics