ᐅ Integration of Air-to-Water Heat Pump, Photovoltaic System, and Energy Storage

Hello everyone,

In our new build, an air-to-water heat pump will be installed as the heating system. The system will be installed by our general contractor (GC) or their heating company.

I would now like to have a photovoltaic (solar) system installed on the roof (not through the GC, but by a specialist company that I select myself), with the unused electricity being stored.

The idea behind this is, among other things, to generate part of the electricity needed for the air-to-water heat pump ourselves.

Since I wanted to inform myself a bit before talking to the heating company and the solar company, I searched online. Unfortunately, it wasn’t really helpful.

What I found out is the order in which photovoltaic electricity is used:
1) Current consumers in the house
2) Battery charging
3) Air-to-water heat pump
4) Feeding into the grid

Is this correct so far?

Then you need the technical prerequisites so that the inverter, battery, and air-to-water heat pump can communicate with each other.
Who provides these prerequisites and who usually configures this? The heating company or the solar installer? Are special devices required for this?

When the air-to-water heat pump needs electricity again, the battery should of course be used first before drawing from the public grid. Does this also work if we have a special heat pump tariff?

I would appreciate it if someone could shed some light on this!

Thanks in advance and best regards

A

Appel2000 schrieb:

What I have found out is the order in which photovoltaic electricity is consumed:
1) current household loads
2) charging the battery storage
3) air-to-water heat pump
4) feeding surplus electricity into the grid

Is this sequence correct?

I can't answer in detail since I don't have a battery storage myself. When the battery is charged depends on its management system. The air-to-water heat pump is basically just a regular consumer—so why should the battery be charged before the heat pump?

I chose this approach:
1. Heat pump powered by household electricity: no blackout periods (during sunny times?) for the heat pump, so photovoltaic usage is possible. The cheaper heat pump electricity is only marginally cost-effective for me. There are also setups with meter cascades that allow supplying the heat pump with photovoltaic power despite having a second meter.
2. No battery storage, as it’s neither economically nor ecologically sensible: due to manufacturing, charging, and storage losses during operation.
3. My heat pump is controlled independently of photovoltaic production: during the heating season, it simply runs throughout the day by increasing the heating curve with a timer. This way, I don’t miss any sunlight, and another advantage is that it’s warmer during the day, making the heat pump more efficient. At night, it doesn’t always run—depending on the outside temperature. A more intelligent control system would bring little or no improvement. Many winter days are cloudy, and I consume 100% of the electricity from the solar panels anyway. A battery storage wouldn’t help in that case either. Given the low heating costs, additional measures are difficult to justify economically.

By far the best favor you can do for yourself is to oversee and monitor the planning of the air-to-water heat pump to avoid common mistakes that can significantly reduce efficiency: appropriate sizing, designing the underfloor heating with a low flow temperature based on a room-by-room heating load calculation, and not installing a buffer tank. There are many threads on this topic online.

Hello, similar setup here with us.

Air-to-water heat pump + underfloor heating + photovoltaic system (without storage). As mentioned before, run the heat pump during the day since air temperatures are usually higher in winter during the day than at night, and the sun is shining. Your screed stores your energy/electricity.

Someone once wrote about a photovoltaic storage system: in summer you can’t empty it, and in winter you hardly manage to fill it up.

As already mentioned, push your general contractor (GC) strongly to design the underfloor heating with a maximum supply temperature of around 30°C (86°F); the lower, the better.

Specify the desired room temperature to the GC as the basis for designing the system.

Do not let them install a buffer tank or bypass valve in the system. However, it will be difficult to avoid these. If needed, you can later deactivate individual room control (IRC) if you end up having no choice.

If you want towel radiators, choose electric ones, or even better, start with just an electrical outlet and decide later if you actually want or need such a device. Also, those units are generally cheaper everywhere than through your GC.

Don’t be discouraged by claims that some rooms might become too cold (unless you need 24°C (75°F) everywhere).

To summarize:

Calculate heating loads per room and design the underfloor heating accordingly.
Provide your desired room temperatures for the heating load calculation!

Underfloor heating should have the lowest possible supply temperature and as close pipe spacing as possible.

If feasible, avoid buffer tanks, bypass valves, and individual room control (IRC).

Size the heat pump as small as possible; don’t let them sell you the biggest unit based on kW capacity—less is often more.

For towel radiators, go electric or just install an outlet for later retrofitting.

And if you can reduce or omit any of the points mentioned, don’t forget to ask for price reductions or credits—they often get forgotten by the GC.

Hello everyone,
since November 2019, we have had our photovoltaic system with battery storage.
The systems are installed and programmed so that self-consumption is prioritized first, then the battery storage is charged, followed by excess photovoltaic energy being supplied to the heat pump, and anything beyond that is sold to the grid. The battery can only be charged at a limited power rate, and the heat pump does not consume 100% of the photovoltaic output, so it is always a mix. The components are monitored and controlled via the SMA HomeManager, which keeps track of the house’s power usage, photovoltaic production, and the battery. It also communicates with the heat pump, which absorbs power by primarily increasing the hot water setpoint.

First of all, thank you for your quick and detailed responses.

Is this a system with or without a buffer tank? I assume it has one, right?

@blackm88
Who handled the installation and the communication between the devices for you? Was it a heating engineer or the photovoltaic company?

I find this sequence (air-to-water heat pump at the end) unfortunate. In winter, for example, the storage tank doesn’t really get fully charged. So the air-to-water heat pump basically runs constantly on "purchased electricity"... wouldn’t it make more sense the other way around, filling the storage tank last?

Although, if I’m not using a heat pump electricity tariff anyway, it probably doesn’t matter which device consumes the electricity...

I’m curious to see how this will turn out in the end.