I’m not that keen on making my own. Even if I could get all the components locally, which is highly unlikely in Norway, they’d probably cost more overall than PBW.
I thought I'd use your post as an excuse to look up the components of PBW. Humm, in the UK (on EBay) the main component (Sodium Percarbonate) is creeping up in price ... 20Kg (can't even get 25Kg sacks no more) is £50 (small bottles of it are a ridiculous price).
What follows will be a bit below your understanding, but I'm writing here for anyone. (And perhaps anyone to correct me for anything dumb I've said!).
As this stuff gives off oxygen if it gets damp, it is potentially a fire risk (it will help sustain fire, not burst into flames itself) so there could be reluctance of governments to let you have it, store it, transport it, etc.
The (only) other active component is sodium metasilicate (30% suggested by some), a degreaser, and substitute for trisodium phosphate which is an ecological disaster (which you
can still get it in the UK, but it should have been banned ages ago). I don't bother with it, percarbonate will deal with any organic grime and I'm not in a habit of spraying WD40 over my brewing kit.
So, +1 for using just sodium percarbonate to replace PBW ... if you can get it! Bulk buy (20-25Kg) or get ripped off with smaller amounts (it does come in handy for other jobs BTW!).
This is a bit more about the stuff (commercial chatter ... or lies?):
https://stppgroup.com/understanding-sodium-percarbonate-a-powerful-cleaning-agent/
Now, the other bit that I've wanted to look up for ages ... it's "kill" ability! (Just microbes, I'm sure it'll evict any rats in your fermenter, or perhaps turn their fur white so it's easier to aim half-bricks).
Found this:
https://www.chemicalforums.com/index.php?topic=87407.0
So, 1g made up to 100ml creates a 0.325% w/v hydrogen peroxide solution? That's the same as the 10g per litre concentration I use mostly (at 40-60°C). Not really enough? From what I've seen you need x10 for that (3%) to be an effective killer? 100g in one litre, that'll strip paint! (Not kidding, it does strip paint!). Maybe 10g/L for general cleaner, 100g/L (but fraction of volume) as a cleaned surface wash as killer? Do rinse off ... don't need to be as meticulous as with a chlorine cleaner, but it will make a bad flavour (using it as "no-rinse" as some suggest is a dumb move as I see it).
