What type of Item ar your totals? It is important.
I’d do the maths in Quantities (with units) rather than Numbers.
What it comes down to is that you’ve described your total-holding variable as a Number (without units) but your variables to be added are nasty hybrid types - declared as Number but with units given.
The rules interpreter doesn’t really know what you mean by all this, I think what really goes wrong is where kW gets involved, with its k multiplier, instead of a “root” unit W.
If you get all your input states as Quantity types, the maths works and takes account of any conversions needed. And returns a Quantity type as the sum, ready to post to a Quantity type Item.