Hi Joe,
another great resource for what Zero Carbon / Zero emissions can mean comes out of Norway:
https://www.zeb.no/index.php/en/news-and-events/256-a-norwegian-zeb-definition-guideline
I am visualizing building emissions along the life-cyle phases and right now it feels to me somewhat feasible to cut off the tally at 2050 as we are trying to avoid imminent emissions to avoid climate change feedbacks. Something like the diagram attached. Depending of where the “Zero” definition is coming from there might be different life-cycle stages included or totally ignored…
After passively optimizing your envelope you can find out what your building is emitting in regards to operational carbon buy running an energy model via a tool like PHPP, WUFI, EnergyPlus, Sefaira etc. Typically these tools have the electricity grid factors (gCO2e/kWh) for different locations built-in and can convert from energy use intensify to carbon intensity. Be aware to include the PV array in your LCA as this can have quite high emissions by itself.
To estimate the electricity offset from a certain size panel array you can use a tool like PVWatts. https://pvwatts.nrel.gov/.
This article (https://www.lowtechmagazine.com/2015/04/how-sustainable-is-pv-solar-power.html) seems to suggest that assuming China as the manufacturing origin for the PV the life-cycle carbon for solar electricity is around 70gCO2e/kWh assuming optimum yield. If your PV array’s latitude, orientation and angle is not perfect this might up to double.
Do you know the electricity grid emissions for your buildings location already?
From this (https://circularecology.com/solar-pv-embodied-carbon.html) and other sources I found the embodied carbon for crystalline PV arrays to be in the range of 2200 to 2600 kgCO2e/kWp installed. (equals ca. 6.5m²)
There is another active thread on PV and solar hot water impacts on this forum: Upfront Embodied Carbon of PV and Solar Hot Water Systems
I hope this helps,
Jens
