Heat pump in combination with photovoltaic system

Actually, one only connects a heating rod into the buffer tank of the hot water.

Actually, you only connect a heating element to the buffer tank for hot water.

Why buy an additional heating element (which then draws how many kW directly? Not fun with little sun, especially not in winter), when the heat pump can produce hot water?

The specially designed heating rods have a power output of 0–3000 kW and cost between 100 and 500 euros.

The advantage of this solution is that the excess energy is directed into a buffer – not the available energy. This is exactly the effect Musketier criticizes: during the day, the underfloor heating can overheat, while at night it cools down too much. Additionally, the hot water preparation consumes more energy than is actually available. And it is purchased at a higher cost.

However, the regulation is simple: at night, circulation and hot water preparation are deactivated. From the moment the sun shines, the buffer is charged.

Some inverters, such as those from Deye, even use weather data from [weather.com] to optimize planning.

So far, however, this is only theory for me – I myself am not yet using this solution.

From the moment the sun shines, the buffer is charged.

No buffer! You are talking about a DHW tank. That doesn't buffer much. You really need a big buffer tank. Investing in the heating element is not worth it.

The heating element that I currently have in the storage tank is completely oversized at 7kWh. Therefore, a smaller/controllable one would have to be used. On the other hand, the price per kWh for me is currently about 4 times higher than the reimbursement. So, with the current prices and an assumed COP of 4, it doesn’t make much difference whether I feed in electricity and buy electricity for the heat pump or whether I heat the water with the heating element instead of the heat pump. Since the heat pump also coincidentally operates during surplus times, the heat pump should still remain the preferred option.

The problem is also that I do not have a classic hot water buffer tank, but a stratified tank, where the hot water is heated as it flows through the heating buffer. Targeted hot water heating is therefore not possible.

How do you handle this?

The hot water heater has a heat pump. In case of surpluses, the water is heated up to 10 degrees higher. Heat pump and photovoltaic control communicate via a corresponding sinusoidal signal.