Add waste-to-energy (WtE) plants to consume non-recycled plastics

[fneum]

(x - yd - ze below)

I've already added this in a test, but the effect is small. WtE plants are expensive and only built if waste is forced to be used. The model chooses unabated WtE over WtE with carbon capture. Could argue this is outside system boundary and continue assuming all carbon in primary plastics lands in the atmosphere.

quote @nworbmot

What about process emissions from recycling plastics? In the current model setup, this is taken care of in that all carbon in primary production lands in the atmosphere. Suppose x+y+z carbon units of plastics are produced in a year, x primary, y mechanical and z chemical. Feedstocks required: x(1+c) primary (feedstock: naphtha), y(1+d) mechanical (feedstock: waste plastics), z(1+e) chemical (feedstock: waste plastics). There are process emissions of xc for primary production, yd for mechanical recycling and ze for chemical recycling. Of the x+y+z units in produced plastics, y(1+d)+z(1+e) are recycled for next year and x - yd - ze are burned in waste-to-energy plants. Thus total emissions are xc + yd + ze + (x - yd - ze) = x(1+c). The model currently allows the xc process emissions to be captured and the x goes into the atmosphere, correctly taking account of everything. We could allow process emissions from mechanical and chemical recycling to be captured.

quote @nworbmot

xref PyPSA/pypsa-eur-sec#166