Hi,
last month we put a photovoltaic system without storage into operation.
Currently, we are not receiving any compensation because a bi-directional meter has not yet been installed. The current meter has a reverse current lock, so we are effectively giving away all excess electricity.
For the first 2-3 years after moving in, I had our heat pump set up to operate without an outdoor reset control and only respond to the outside temperature. Differences between day and night operation were not configured. This has been running more or less unchanged for about 7-8 years.
To avoid giving away electricity right now, I’ve been adjusting the heat pump settings over the past two weeks — shifting domestic hot water production more towards daytime and, through parallel shift, raising the heating curve during the day and lowering it at night. This initially caused it to become noticeably too warm in the evenings last week, in combination with the sun. So I lowered the curve during the day again. This morning it was a bit too cold. Nothing serious, but not as consistent as before.
How do you handle this?
last month we put a photovoltaic system without storage into operation.
Currently, we are not receiving any compensation because a bi-directional meter has not yet been installed. The current meter has a reverse current lock, so we are effectively giving away all excess electricity.
For the first 2-3 years after moving in, I had our heat pump set up to operate without an outdoor reset control and only respond to the outside temperature. Differences between day and night operation were not configured. This has been running more or less unchanged for about 7-8 years.
To avoid giving away electricity right now, I’ve been adjusting the heat pump settings over the past two weeks — shifting domestic hot water production more towards daytime and, through parallel shift, raising the heating curve during the day and lowering it at night. This initially caused it to become noticeably too warm in the evenings last week, in combination with the sun. So I lowered the curve during the day again. This morning it was a bit too cold. Nothing serious, but not as consistent as before.
How do you handle this?
N
nordanney14 Mar 2025 13:14tomtom79 schrieb:
Actually, you usually only integrate one heating element into the hot water storage tank.Why buy an additional heating element (which consumes how many kW directly? Not much fun with little sunlight, and definitely not in winter) when the heat pump can prepare the domestic hot water?The specially designed heating rods have a power output of 0–3000 kW (0–4023 hp) 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 that Musketier criticizes: during the day, underfloor heating can overheat, while at night it cools down too much. In addition, heating the domestic hot water requires more energy than is actually available, and it is more expensive to purchase.
The control system is simple: at night, the circulation and domestic hot water production 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, for me this remains theoretical—I have not yet used this solution myself.
The advantage of this solution is that the excess energy is directed into a buffer—not the available energy. This is exactly the effect that Musketier criticizes: during the day, underfloor heating can overheat, while at night it cools down too much. In addition, heating the domestic hot water requires more energy than is actually available, and it is more expensive to purchase.
The control system is simple: at night, the circulation and domestic hot water production 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, for me this remains theoretical—I have not yet used this solution myself.
N
nordanney14 Mar 2025 14:35tomtom79 schrieb:
From the moment the sun shines, the buffer is charged. No buffer! You are referring to a domestic hot water (DHW) tank. That does not store much energy. You definitely need a proper large buffer tank.
Investing in the electric heating element is not worthwhile.
The heating element I currently have in the storage tank is completely oversized at 7 kWh. A smaller or controllable one would be needed. On the other hand, my electricity price per kWh is currently about four times higher than the feed-in tariff. So, given the current prices and assuming a COP of 4, it doesn't make much difference whether I feed electricity into the grid and buy power for the heat pump or heat the hot water directly with the heating element instead of the heat pump. Since the heat pump also happens to run during times of surplus electricity, it should still remain the preferred option.
The problem is that I don’t have a traditional hot water buffer tank but a stratified tank, where the hot water is heated as it flows through the heating buffer. So, targeted hot water heating is not possible with this setup.
The problem is that I don’t have a traditional hot water buffer tank but a stratified tank, where the hot water is heated as it flows through the heating buffer. So, targeted hot water heating is not possible with this setup.
W
wiltshire14 Mar 2025 19:14Musketier schrieb:
How do you handle this?The hot water storage tank is equipped with a heat pump. In case of surplus energy, the water temperature is increased by up to 10°C (18°F). The heat pump and photovoltaic control system communicate via a corresponding sine wave signal.Similar topics