Step 3: How to Model Co-Products

In this video, you’ll learn how to model multiple products within a single system using co-product functionality in XYCLE. When a product you produce is sold (rather than discarded), it must be treated differently within an LCA. This tutorial walks you through identifying co-products, completing allocation, and optionally using system expansion to handle impacts appropriately.

What You’ll Learn

• What defines a co-product in LCA

• How to add a co-product to your model in XYCLE

• Why allocation is required and how to complete it

• When to use mass-based, economic, or system expansion methods

• How XYCLE applies impact subtraction through system expansion

Step-by-Step: Modelling Co-Products

1. Add a Co-Product

   • In your flow diagram, click “New Outbound Item” at the bottom of the unit process.

   • You’ll see the diagram split, representing multiple products within the same system.

   • A co-product is defined as something you sell — not something that is discarded.

2. Differentiate from Waste

   • If the secondary product is not sold, it should be treated as waste instead.

   • Waste items should be handled using standard inventory entries and characterisation factors for waste treatment.

3. Complete Allocation

   • Once you add a co-product, XYCLE will require you to allocate impacts before proceeding.

   • Allocation determines how shared impacts are divided between your main product and co-product(s).

   • XYCLE supports three allocation methods:

     • Mass-based Allocation – divides impact according to mass.

     • Economic Allocation – divides impact based on economic value (e.g. sale price).

     • System Expansion – subtracts the impact of the co-product based on reference data.

4. Using System Expansion

   • Choose system expansion if you have robust data to describe the co-product’s downstream lifecycle.

   • Use XYCLE’s background database to define the co-product’s inventory.

   • The system will subtract the environmental impact of that co-product from your total, based on the same methodology used for other inputs.

   • This is often the preferred approach when accurate substitution data is available.

Expert Tip

Co-product handling is one of the most complex parts of LCA modelling. If you're unsure which allocation method is best for your case, Minviro’s team is available to help guide your approach to ensure scientific rigour and compliance with LCA standards.