Most people cut their lawn with a gas mower. Even electric requires an a mount of energy that is taking it from the grid, which unless it’s totally clean already is increasing dirty energy.
I’ve literally never even seen, or even heard of, a gas mower. Almost all of them are electric (and our electricity mix isn’t perfect, but is better than a lot of places) with the odd one being petrol for especially large gardens, but that’s increasingly rare.
Why the fuck would anyone use gas? That would be awful. Do you mean natural gas from the mains? Hydrogen? Bottled Calor gas? I’ve absolutely no idea what a gas mower could even be and searching is giving zero results that make sense.
Maybe they’re American and so mow their ten acre lawns with a sit on mower.
UK gardens are about 3 meters long and you can just plug the mower in.
