I added insulation around my cylinder, saved a couple of kWh a day.
Though if you spread the showering out over that day, the HP can recharge it.
If you take the showers at about the same time, there is no need to recharge until a bit before it is needed again i.e. early morning.
Teach everyone to take shorter showers and the problems go away. I got my lodger to go from 25 minute to 4 minutes, or 275 litres to 44 litres.
She smelt the same.