ᐅ Smart Grid Configuration: Using Photovoltaic Surplus for a Heat Pump

Hi,

I have a question regarding photovoltaic surplus. I have a 16.4 kWp system on the roof. I am running a SmartGrid heat pump. The SmartGrid is activated on the heat pump via the potential-free contact on the inverter. Now I need to coordinate several values:

• Photovoltaic production level to close the contact → start SmartGrid
• Photovoltaic production level to open the contact → end SmartGrid
• Kelvin increase for the domestic hot water temperature
• Kelvin increase for the temperature in the heating water buffer tank
• Kelvin increase for the room temperature

The heat pump modulates between 1.5 and 4 kW, but this depends only on demand, not on the available photovoltaic energy.

At what values would you set the potential-free contact to close/open, and by how many kelvin would you raise the temperatures?

A balance needs to be struck between

• using photovoltaic electricity during the day to avoid heating needs at night
• avoiding values that are too high, so that on cloudy days the heat pump does not draw power from the grid during the day

What are your thoughts?

How did you envision the technical implementation, and what data do you have available in which format? At first, you mention "photovoltaic surplus," but later it sounds more like a simple timer switch.

I read the feed-in meter and send the data to the bus (KNX). If the feed-in is > x, then ON; if < y, then OFF. In the heat pump, I can set target values for normal operation and SG+ mode. The latter is the highest hot water temperature achievable through the compressor. Additionally, I have a hot water lockout until 1 p.m. to ensure that there is something to store during the best sun hours (to avoid the 70% throttling). Since I also have a battery, it is charged first, either fully or with a reserve for midday, depending on the forecast.

The inverter has a potential-free output used to control SG+ on the heat pump. Currently, SG turns on at 3.5 kW (3.5 kW) inverter output and turns off again at 2.5 kW (2.5 kW). I know that my house consumes about 0.5 kW (0.5 kW).

The heat pump has a timer switch: night setback for the heating circuit and night shutdown for the hot water. When SG+ is active, the domestic hot water temperature is increased by 5 Kelvin (5 K), and the heating water buffer is also raised by 5 K.

Well, first of all, I think the difference between 3.5 kW and 2.5 kW is too small to switch meaningfully (a few clouds could then cause on-off-on-off cycling, which heat pumps usually dislike due to minimum run times, switching delays, etc.). Secondly, a 16 kWp system should practically deliver more than 3.5 kW throughout most of the day, so you basically only have a day/night switching. And last but not least, this has nothing to do with surplus, because when larger consumers are running, you might not have any surplus even at 3.5 kW.

PS: I also think that a 5 K (9°F) increase for hot water is too small to produce a significant effect. I operate from 42°C to 56°C (108°F to 133°F), although due to the hot water lock until 1 pm after the morning shower, the actual temperature is even lower. But this also depends on the tank size, habits, and so on.

Hi,

thank you for your input. Now we are in the discussion/support phase that I need.

I have measured: the house has a base load of about 400 W. When a larger appliance is added, the consumption increases accordingly. These are cooking/baking, washing machine/dryer. Both usually happen in the afternoon, so by then the heat pump should be finished. Possibly cooking in the morning, hence the 3.5 kW limit.

The smart meter must be installed in the consumption line so that the inverter knows how much surplus it is currently producing. The surplus energy goes to the car (when the heating is running, less goes to the car accordingly).