Heat pump in combination with photovoltaic system

We have a heat pump and photovoltaic system with storage. We try to shift the consumption to daytime. Night setback by 3 degrees, hot water overheated to 60 degrees at 4 p.m., otherwise automatic operation. However, our house only loses about 1 degree overnight. Whether I input, for example, 10 kWh of heating power during the day or at night has no effect. The underfloor heating is too sluggish for that.

what kind of insulation does your house have that it loses 1 degree at night?

Why additionally buy a heating element (which then draws how many kW directly?

With the temperature increase in the hot water storage tank from, for example, 50 to 60 degrees, the heat pump no longer has major advantages. The heating element avoids additional switching operations of the heat pump. It's not entirely stupid.

what kind of insulation does your house have that it loses 1 degree at night?

better than KfW 40, but only valid down to 0 degrees, at -10 to -20 degrees the heat pump runs with 0.7 to 1.5 kWh electricity consumption continuously and easily drains the battery, e.g. today with 0 degrees at night and we are on vacation