Brightway2 - Get LCA scores of immediate exchanges

Question

I\'m having some problems regarding the post-processing analysis of my LCA results from brightway2. After running a LCA calculation, if, for example, I type top_activities() I g

Answer 1

I've found the best way to get aggregated results for your foreground model in brightway is using the bw2analyzer.traverse_tagged_databases() function rather than top_activities(). Details in the docs are here.

It's designed to calculate upstream impacts of the elements of your foreground model and then aggregate the impacts based on a tag it finds in the activity. e.g. if you add 'tag':'use phase' or 'tag':'processing' to your activities you can aggregate impact results by life cycle stage.

BUT you can change the default label it looks for, so instead of tag you can tell it to look for name - that'll give you the aggregated upstream impact of each of the activities in your foreground model. It returns a dictionary with the names of your tags as keys, and impacts as values. It also returns a graph of your foreground system which you can use to create some cool tree/bullseye charts - see the docs for the format.

Here's the function you need:

results, graph = recurse_tagged_databases(functional_unit, method, label='name')

Here are a couple of examples of the kinds of visualisations you can make using the data recurse_tagged_databases gives you:

Waterfall chart example from the results dictionary

Bullseye chart example from the tagged graph

Answer 2

It is pretty easy to traverse the supply chain manually, and everyone wants to do this a slightly different way, so it isn't built in to Brightway yet. Here is a simple example:

from brightway2 import *

func_unit = Database("ecoinvent 3.4 cutoff").random()

lca = LCA({func_unit: 1}, methods.random())
lca.lci()
lca.lcia()

print(func_unit)

for exc in func_unit.technosphere():
    lca.redo_lcia({exc.input: exc['amount']})
    print(exc.input, exc['amount'], lca.score)