Heat Pump with Photovoltaics: Tips, Costs and Smart Strategies

Combining a heat pump with photovoltaics sounds absolutely logical at first. The heat pump needs electricity, and the solar system on the roof supplies it. But does this really work in practice? And is the solar power enough for heating in winter?

Demand for the combination of photovoltaics and heat pump is growing. Rising energy prices, falling feed-in tariffs and the goal of becoming more independent all play a central role. At the same time, there is a lot of uncertainty. Above all, people often ask whether a building can be heated with solar power while also producing domestic hot water. There is no very simple answer to that.

Because heating and hot water differ significantly. While hot water is needed in similar quantities all year round, the heating energy demand varies greatly between the summer and winter half-years. Especially in the winter months, when heating is needed most, the photovoltaic system often supplies only manageable amounts of electricity. The electricity from the roof alone is therefore not necessarily always enough for heating.

In this article, you will find out how well solar power can be used for heating and hot water, when the combination pays off, which technology makes sense and which strategies help increase self-consumption of PV electricity. You will also get an overview of typical pitfalls, sensible storage solutions and current funding options.

Why is the combination worthwhile? Here are the 5 advantages:

• Lower heating costs through self-consumption of PV electricity: The heat pump uses electricity, and that costs money. Anyone who runs it with their own solar power saves real money. Especially in the summer half-year, the heat pump for domestic hot water production can be operated sensibly. The surplus electricity from the roof then does not end up in the grid, but in the hot water storage tank.
• More independence from the electricity supplier: The combination of heat pump and photovoltaic system increases self-consumption, reduces the consumption of fossil energy and also reduces the purchase of electricity from the grid. Especially in times of rising energy prices, this provides additional planning security.
• Eco-friendly heating with free environmental heat: A heat pump extracts energy from the air, from the ground or even from groundwater. And it does so completely without fossil fuels. Combined with photovoltaics, it creates a system that uses renewable energy sources efficiently and relieves the power grid. Emissions fall, and the carbon footprint improves noticeably.
• Future-proof through intelligent energy management: Modern controls detect when the PV system is supplying electricity and automatically direct it to the heat pump. Systems with an SG Ready interface communicate with the smart grid. This not only ensures efficiency, but also makes the technology ready for future grid requirements.
• Increasing self-consumption from 30 to up to 80 percent is possible: The higher the self-consumption of electricity, the more economical my photovoltaic system is. Without battery storage and a heat pump, self-consumption from photovoltaics is often around 30 percent. If a storage system is also integrated and the heat pump is controlled intelligently, this share can be increased significantly. In well-coordinated systems, self-consumption rates of 70 to 80 percent are realistic.

What you need for an efficient heat pump photovoltaic system

An efficient heat pump photovoltaic system starts with choosing the right technology. Depending on the plot, building condition and heating demand, different heat pump types may be suitable.

Air-to-water heat pumps are considered the standard solution for existing buildings because they do not require earthworks. Ground-source and groundwater heat pumps work more efficiently, but are significantly more expensive due to ground probes and well drilling.

For domestic hot water production, compact domestic hot water heat pumps are also suitable. These extract heat from the basement air, which is used to heat the domestic hot water. Especially in summer, this is a simple way to use PV electricity directly. A heat pump for hot water is often more sensible in this context than many people think, especially if no complete heating system conversion is planned or if heating is to be provided via air conditioning units.

Properly sizing and orienting photovoltaics

The photovoltaic system itself must also be well coordinated. Correct sizing is crucial. If it is chosen too small, the electricity in winter is often not even enough for household consumption. If it is too large, you give away potential self-supply in summer. However, the roofs of single-family homes are practically never so large that oversizing becomes an issue. Therefore, in most cases: Use every suitable roof area that can be used for photovoltaics.

While surpluses often arise in the summer half-year, yield drops significantly in winter. Anyone who wants to heat their house to a significant extent with PV electricity therefore needs a large system. Until a few years ago, south-facing orientations were mainly preferred in order to feed in as much electricity as possible. That made sense because the feed-in tariff was still significantly higher.

Today, the feed-in tariff only plays a secondary role. That is why optimization today is more focused on self-consumption of electricity. This means that, in addition to south-facing roofs, east- and west-facing roofs are more or less equivalent and, where available, are all used. Anyone who also wants to supply a battery storage system and a heat pump with the solar system should therefore by no means plan too small.

The combination of heat pump with photovoltaics and battery storage not only increases self-consumption, but creates real benefit. Intelligent controls with SG Ready function also ensure that the heat pump automatically draws more power when solar radiation is high. Anyone relying on a combination of photovoltaics and battery storage benefits in several ways.

Heating with solar power? What really works and what doesn’t

Hot water and space heating place very different demands on a solar heating concept. Hot water involves a comparatively small amount of energy that is needed consistently throughout the year.

That is why this demand can often be covered well with PV electricity, especially in summer when the sun reliably supplies energy. The situation is different for space heating in winter. Here, the peak load occurs exactly when the electricity yield from the roof is at its lowest.

The idea of running a heat pump exclusively with photovoltaic electricity all year round therefore sounds tempting. In practice, however, this usually fails because of the relationship between electricity demand and supply. In summer, the PV system often produces more electricity than is needed in the household, but the heating is off.

In winter, the relationship is reversed. Then the heat pump needs the most energy, but the sun supplies very little.

This means that complete self-sufficiency is hardly achievable even under optimal conditions. Even with a generously sized PV system, the heat demand of an average single-family home cannot be covered. A large battery storage system also cannot compensate for these seasonal fluctuations between winter and summer. At best, it bridges one to two days.

A certain amount of grid electricity in winter is therefore completely normal and must be planned for. This is not a disadvantage, but simply physical reality. What matters is optimizing the coverage rate over the course of the year. And that can be achieved through a smart combination of system size, thermal insulation, buffer storage tanks and intelligent control.

Because the more solar power you can use yourself for hot water and heating, the more your dependence on the electricity supplier decreases, and that ultimately also makes itself felt financially.

How to combine photovoltaics and heat pump correctly: 6 practical tips

• Do not plan the PV system too small: A PV system that only just covers household electricity is hardly enough in combination with a heating heat pump. Certainly not in winter, when heating is needed. Anyone who wants to benefit properly should use as much of the suitable roof area as possible.
• Heat pumps do not have to be large: It does not always have to be a complete immediate switch to a heat pump. Even a small heat pump can enormously reduce oil and gas consumption. A gentle transition with air conditioning units, known as air-to-air heat pumps, is therefore an inexpensive and simple way to optimize the share of self-generated electricity.
• Plan for hot water production: Self-consumption can also be significantly increased through hot water production with a heat pump. Special hot water heat pumps are usually the simplest and cheapest solution for this.
• Produce hot water during the day: Hot water production should primarily take place when the sun is shining. A domestic hot water heat pump can then use the electricity from the roof directly. With suitable control, operation can be shifted into the sunshine hours.
• Carry electricity surpluses from the day into the night: By using a battery storage system, an electricity surplus from the day can also be used at night, additionally increasing self-consumption of electricity.
• Use SG Ready if available: Heat pumps with an SG Ready interface can be controlled intelligently. When a lot of PV electricity is available at midday, the heat pump can start automatically and, for example, charge the buffer storage tank. This allows the share of self-generated electricity to be increased in a targeted way.

When does a heat pump with photovoltaics pay off?

Whether the combination of heat pump, photovoltaics and battery storage pays off economically depends very much on the individual circumstances. However, since a shift toward electric systems, especially heat pump systems, is emerging in the heating sector anyway, every opportunity should be used to tackle this conversion in your own home as well. Anyone who starts too late could pay dearly, as the prices for fossil fuels will rise disproportionately in the coming years.

Anyone who wants to heat with photovoltaics and organize their hot water production can never build their system too small; especially in the summer half-year, hardly any grid electricity is then needed. In combination with a suitable storage system, the system can supply your house with PV electricity all day long in the summer half-year.

In these cases, self-consumption rises significantly, and the degree of self-sufficiency is often 50 percent or more. If the heat pump also produces hot water and the control system intelligently links PV yield and consumption, the self-consumption share can additionally be optimized toward 80 percent.

In old buildings with high heat demand, solar power is often nowhere near enough to operate the heat pump continuously. In the cold months, a remaining demand persists that must be drawn from the grid. But here too, a significant portion of the demand can be covered by photovoltaics, especially in the transitional season.

Hybrid systems, in which two heating systems work together (for example gas boiler + heat pump), can also make sense in existing buildings with high energy consumption in order to cover peak loads on the coldest days. This allows smaller heat pumps to be used, which reduces investment costs.

How you save real money with subsidies and self-consumption

The costs for a complete system consisting of PV, battery storage and a central heat pump can range between 30,000 and 50,000 euros, depending on the technology. Anyone who uses air conditioning units instead of central heat pumps can significantly reduce the costs. Subsidies from BEG or KfW noticeably lower the costs. Individual federal states also offer additional programs.

Anyone who not only feeds PV electricity into the grid, but mainly uses it themselves, has the greatest advantage. In the medium to long term, the combination of photovoltaics and heat pump is always worthwhile. Anyone building new today or renovating anyway should definitely include the heat pump installation directly in the PV planning.

Conclusion: Your next steps toward the optimal combination

If you are planning a heat pump or already use one, it is definitely worth looking at combining it with photovoltaics and battery storage. Before you invest, these three questions will help you assess the situation:

• Do you want to move away from oil and gas?
• Would you like to become more independent from your energy supplier in the long term?
• Do you have enough suitable space for photovoltaics on your roof?

If you can answer these points with “yes”, the PV heat pump combination is the right path for you.

If you decide in favor of the PV and heat pump combination presented here, we recommend that you first take advantage of individual subsidy advice. This way, you secure all grants and can optimally prepare and plan your project.

Image sources:

1. Featured image: Heat pump with photovoltaics (Adobe Stock)
2. Single-family home with PV system and heat pump (Carsten Herbert)
3. Terraced house with PV modules and outdoor heat pump units (Adobe Stock)
4. Schematic representation: Self-consumption of electricity with PV, heat pump and storage (Carsten Herbert)
5. Graphic: Self-generated electricity share with heat pump and PV over the course of the year (Carsten Herbert)