Ask HN: Is Geothermal Electricity Green?
Hi HN,

I always considered geothermal energy a vast, emission-free green energy source. That is, if you happen to live in the right place. That also seems to be the sentiment on HN.

I live in Italy, in the "right place" (a seismically active area). There are a few “binary” geothermal plants in the area, with many new ones planned over the coming years, mainly due to the EU energy crisis.

To my surprise, many people here vehemently oppose these projects. So, I did some research and I would like to tap the wisdom of the HN crowd to understand if I got anything wrong and gain additional perspectives.

Findings:
Geothermal refers to two different technologies.

The first uses geothermal heat for heating houses. Water is injected into the ground in a closed loop, heated, and used as a heat source. The underground temperature needed for this system is not high. This seems to be a clean and sustainable system. The only problem is that it is only possible to transport the hot water a short distance before the water in the pipes cools down. It is, therefore, limited in its utility and economic value.

The second uses geothermal heat to drive a turbine. Electricity is then transported via the grid. The problem is that a much higher water temperature is required to turn water into steam. Also, much energy is lost in the conversion process from heat to electricity. To overcome these difficulties, fracking is used. Not just one time but periodically since the underground water temperature drops over time.

This is problematic for several reasons:

1. Fracking has been shown to trigger earthquakes [1], and since geothermal is viable mainly in areas that are already seismically active, such as where I live, it seems to be a bad match.

2. Since geothermal activity has started in the area, the level of Arsenic, other toxic minerals, and heavy metals in the groundwater has risen. In some places, arsenic is now at twice the WHO recommendation and over the legal limit [2].

3. Since geothermal activity has started in the area, the water level in the aquifer has dropped by 200 to 300 meters. In addition, the flow rate of many rivers has decreased significantly or even ceased completely. This seems to be related to the fracking activity, and since this area provides water to several cities in central Italy, it seems to be a big problem [3].

Even more surprisingly, according to my calculations, Solar seems to be a more economical option. The last plant built here has a 40mw capacity, and the construction cost around 130 million euros [4]. An equivalent solar installation only costs 30 million euros [5]. In addition, the running costs for solar plants seem to be lower than those of geothermal ones. Solar does require more land, about 100 hectares for a 40mw plant, but land is abundant around here.

Another important fact is that the Italian government incentivizes energy companies since geothermal electricity is considered green. For each MWh produced, a plant receives an incentive of 99 euros. Considering that it produces 300 gigawatt-hours annually, the incentive is 29.7 million euros. Incentives are given for a 25-year period, so overall, 742.5 million euros [6].

Am I getting anything fundamentally wrong in my reasoning? If not, should we consider geothermal electricity green? Any advice is appreciated.

[1] https://www.science.org/doi/10.1126/science.aag2583
[2] https://www.ars.toscana.it/2-articoli/4707-geotermia-e-salute-in-toscana-presentato-il-rapporto-2021-di-ars.html# (Italian)
[3] https://www.intechopen.com/chapters/79332
[4] https://www.ilgiunco.net/2016/07/25/bagnore-4-ecco-la-centrale-costata-130-milioni-produrra-310-milioni-di-kilowattora-allanno/ (Italian)
[5] https://www.pfnexus.com/blog/starting-a-solar-farm
[6] https://www.internazionale.it/reportage/stefano-liberti/2020/07/24/italia-energia-alto-rischio (Italian)