Thread by @TimMLatimer

1/Emissions calculations for different techs have major impact on legislation, regulation, and customer perception, especially for geothermal, but are often not well understood. So today, a THREAD on operational and life cycle emissions, technologies, and how it impacts policy.

2/Some definitions. When we think about emissions for technologies, two common categories are operational emissions, just the emissions released at the source during operations, and life cycle analysis (LCA) emissions, which are all of the emissions in the entire process.

3/This graphic for cars is useful. The operational emissions are what come out of the tailpipe, but the LCA emissions are everything. Mining, manufacturing, fuels, recycling, land use, etc.

4/Each analysis is useful. For local pollution and health effects, operational emissions are the most impactful. But from a climate standpoint, we need to understand ALL emissions across the LCA since every ton of Greenhouse Gases makes a difference.

5/For geothermal electricity, there is actually a wide range of both operational and LCA emissions. Geothermal comes in three types: dry, flash, and binary cycle. From the recent Geovision study from the DOE:

6/In dry and flash, the steam produced from the ground powers a turbine and enters a cooler, so whatever gases are in the subsurface can be released. Operational emissions vary widely depending on the resource, from close to zero to as much as half of an equivalent nat gas plant.

7/By contrast, binary cycle plants use a closed loop heat exchanger to heat a working fluid for power generation. The reservoir fluid is run through a closed cooler and then reinjected, so there are zero operational emissions.

8/As a result, there is a large difference in emissions between binary and the other types of geothermal. Flash geothermal is higher, and with a really wide range, while binary cycle is much, much lower, with a much tighter range.
nrel.gov/docs/fy17osti/…

9/You can see from this IPCC chart a comparison on life cycle emissions by technology. Unsurprisingly, fossil fuel resources suck.

For geothermal, even accounting for operational emissions, it scores pretty well, a little better than solar PV actually. ipcc.ch/site/assets/up…

10/So why does this matter? Well customers and policy makers make decisions based on perception of emissions. I can’t tell you how many times I’ve been told over the years “well, geothermal isn’t actually clean energy”, and that has real effects.

11/For example, that perception is part of why geothermal energy got left out of the ITC/PTC extension in the US. It’s also why it’s sometimes not included in RPS targets around the world.

12/Recently, I learned of a CCA in California that initially categorized geothermal as “dirty” because of this perception, and to be able to buy geothermal, they had to go all the way back to amend their Charter. And this is actually pretty common.

13/But what the climate cares about is LCA emissions, and geothermal really shines there. Additionally, the vast majority of new geothermal in the US is binary cycle technology, which has NO operational emissions. We need to update our thinking here.

14/So now you know. Geothermal, especially binary cycle geothermal, is a rock star from an emissions standpoint. Help us make sure policy makers, utilities, and other stakeholders have the latest details, because it is vital to getting more clean energy on the grid. END.

PS: inspiration for this thread came from an interesting conversation from @AkshatRathi and @umairfan, where Umair also noted the CarbFix project in Iceland, that captures CO2 at a geothermal plant and permanently mineralizes it in basalt.