Solar and Heat Pump: The Perfect Dream Team for Affordable Heating
A heat pump consumes electricity, a photovoltaic system generates electricity -- the combination is obvious. But how well do the two technologies actually work together? The answer: better than any other pairing in the building energy sector. A well-sized PV system covers 30–50% of the heat pump's electricity demand through self-consumption. At generation costs of 8–12 cents per kWh instead of 27–36 cents for grid electricity, that saves EUR 500–1,200 per year -- and the payback of both systems accelerates each other.
However, this interplay does not happen automatically. The PV system generates most of its electricity in summer, while the heat pump needs most of its electricity in winter. To get the most out of the combination, you need to coordinate sizing, storage and controls. This article shows how to achieve this -- with concrete figures, sizing guidance and a full cost analysis.
Why PV and Heat Pump Are an Ideal Match
The Basic Principle: Three Paths to Cost Savings
The PV + heat pump combination saves money in three ways simultaneously:
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Self-consumption reduces electricity costs. Every kWh of solar electricity fed directly into the heat pump costs only 8–12 cents instead of 27 cents (heat pump tariff) or 36 cents (household electricity). That is a saving of 15–28 cents per kWh.
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The heat pump increases the PV system's self-consumption ratio. Without a heat pump, a typical PV system's self-consumption is 25–35%. With a heat pump, it rises to 40–55% because the heat pump acts as a flexible load that "absorbs" the solar electricity.
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The battery storage is used more efficiently. A battery that buffers both household and heat pump electricity has higher cycle utilisation and a shorter payback period.
The Timing Problem -- and Its Solution
The obvious problem: the PV system produces the most when the heat pump needs the least. In July, the PV system delivers 5–6 kWh per kWp of installed capacity, but the heat pump only needs electricity for hot water (2–4 kWh/day). In January, the ratio reverses: the PV delivers only 0.5–1.0 kWh per kWp, but the heat pump requires 20–40 kWh per day.
The solution lies in realistic expectations and intelligent controls:
| Month | PV yield (10 kWp) | HP consumption (5,600 kWh/a) | Direct self-consumption | Coverage rate |
|---|---|---|---|---|
| January | 280 kWh | 870 kWh | 120 kWh | 14% |
| March | 750 kWh | 650 kWh | 250 kWh | 38% |
| May | 1,200 kWh | 250 kWh | 200 kWh | 80% |
| July | 1,350 kWh | 150 kWh | 130 kWh | 87% |
| October | 550 kWh | 500 kWh | 210 kWh | 42% |
| December | 200 kWh | 950 kWh | 90 kWh | 9% |
| Total | 9,500 kWh | 5,600 kWh | 1,900 kWh | 34% |
Without a battery, the PV system covers around 34% of the heat pump's electricity directly. With a battery (8–10 kWh), the coverage rate rises to 45–50%. No economically viable PV system can fully cover the winter demand -- this is a physical constraint, not a design flaw.
Hot water as free storage: The heat pump can heat the hot water tank to 55–60 °C during the day when the PV system is generating electricity. That equates to 3–5 kWh of "stored" energy without additional hardware. Many modern heat pumps have an SG Ready interface that controls this automatically.
Sizing: How Large Should the PV System Be?
The right PV size depends on the heat pump's electricity consumption, the available roof area and the household electricity consumption. The heat pump alone should not dictate the sizing -- after all, the PV system also supplies the household and feeds surplus electricity into the grid.
Rule of Thumb
PV capacity (kWp) = (household electricity + HP electricity) x 1.2 / 950
The factor 1.2 accounts for the fact that not all electricity is consumed directly (feed-in proportion). The 950 represents the average specific yield in Germany (kWh per kWp per year).
Sizing Table
| Household electricity (kWh/a) | HP electricity (kWh/a) | Total demand | Recommended PV capacity | Required roof area |
|---|---|---|---|---|
| 3,000 | 3,000 | 6,000 kWh | 7–8 kWp | 35–40 m² |
| 4,000 | 4,000 | 8,000 kWh | 9–11 kWp | 45–55 m² |
| 4,500 | 5,600 | 10,100 kWh | 12–14 kWp | 60–70 m² |
| 5,000 | 7,000 | 12,000 kWh | 14–16 kWp | 70–80 m² |
Assumption: 5 m² roof area per kWp for roof-mounted installation, average location in Germany
Inverter Sizing
The inverter should be sized at 70–90% of the PV nominal capacity. For a 10 kWp system, an 8 kW inverter is sufficient because peak output is only reached for a few hours per year. This so-called "undersizing" is not a disadvantage -- it reduces investment costs with minimal yield loss (1–3%). More on this in the article Planning a Solar System.
Battery Storage: Worthwhile or a Luxury?
A battery increases the self-consumption ratio and thus the savings -- but it also costs EUR 5,000–12,000. The question is: does it pay off?
Self-Consumption With and Without Storage
| Configuration | Self-consumption ratio (PV -> HP) | Self-consumption ratio (PV -> total) | Self-sufficiency rate |
|---|---|---|---|
| PV 10 kWp, no storage | 34% | 30% | 35% |
| PV 10 kWp + 5 kWh storage | 42% | 45% | 50% |
| PV 10 kWp + 10 kWh storage | 48% | 55% | 60% |
| PV 10 kWp + 15 kWh storage | 51% | 60% | 65% |
The first 5 kWh of storage capacity delivers the biggest jump: +15 percentage points in self-consumption. Each additional kWh brings diminishing returns. A 10 kWh battery is the economic sweet spot for most households.
Storage Cost-Effectiveness
| Item | Without storage | With 10 kWh storage |
|---|---|---|
| Additional self-consumption | — | +2,500 kWh/a |
| Money saved (delta 17 ct/kWh) | — | EUR 425/a |
| Storage cost | — | EUR 8,000 |
| Storage payback | — | ~19 years |
| Storage + reduced feed-in | — | Net benefit ~EUR 300/a |
The pure payback of the battery takes around 19 years at current prices -- with a typical lifespan of 15–20 years, that is borderline. The battery pays off primarily when:
- The household electricity price is high (>EUR 0.35/kWh)
- Feed-in tariff payments have ended (post-EEG systems)
- Emergency power capability is desired
- A dynamic electricity tariff is used (charging at low market prices)
Storage rule of thumb: 1 kWh of storage capacity per 1,000 kWh of annual electricity consumption. A household with 4,500 kWh household electricity + 5,600 kWh HP electricity = 10,100 kWh needs a 10 kWh battery. More than 1.5 kWh per 1,000 kWh delivers barely any additional economic benefit.
Cost-Benefit Analysis: The Combination in Detail
The following calculation compares four scenarios for a renovated older building (150 m², 16,800 kWh heat demand, 4,500 kWh household electricity, air-to-water HP with SPF 3.0).
Annual Operating Costs
| Item | Gas + grid electricity | HP + grid electricity | HP + PV (10 kWp) | HP + PV + storage (10 kWh) |
|---|---|---|---|---|
| Heating energy costs | EUR 2,240 | EUR 1,512 | EUR 1,075 | EUR 910 |
| Household electricity | EUR 1,620 | EUR 1,620 | EUR 1,130 | EUR 850 |
| Feed-in tariff income | — | — | –EUR 480 | –EUR 320 |
| Heating maintenance | EUR 280 | EUR 150 | EUR 150 | EUR 150 |
| Total cost/year | EUR 4,140 | EUR 3,282 | EUR 1,875 | EUR 1,590 |
| Savings vs. gas | — | EUR 858 | EUR 2,265 | EUR 2,550 |
Investment and Total Cost Analysis (20 Years)
| Item | Gas + grid electricity | HP + grid electricity | HP + PV | HP + PV + storage |
|---|---|---|---|---|
| Heating system investment | EUR 12,000 | EUR 30,000 | EUR 30,000 | EUR 30,000 |
| PV system investment | — | — | EUR 14,000 | EUR 14,000 |
| Storage investment | — | — | — | EUR 8,000 |
| BEG subsidy (heat pump) | — | –EUR 12,000 | –EUR 12,000 | –EUR 12,000 |
| Net investment | EUR 12,000 | EUR 18,000 | EUR 32,000 | EUR 40,000 |
| Operating costs 20 yrs | EUR 99,400 | EUR 79,200 | EUR 44,400 | EUR 37,400 |
| Total cost 20 yrs | EUR 111,400 | EUR 97,200 | EUR 76,400 | EUR 77,400 |
| Savings vs. gas | — | EUR 14,200 | EUR 35,000 | EUR 34,000 |
The HP + PV combination (without storage) is the cheapest option over 20 years: EUR 35,000 less than gas + grid electricity. With storage, the savings are similar because the storage investment almost offsets the additional electricity cost savings. The battery pays off primarily for comfort and self-sufficiency reasons.
Calculation assumptions: Gas price increase 3%/a (incl. CO2 levy), electricity price increase 1.5%/a, PV degradation 0.5%/a, battery replacement after 15 years not included, feed-in tariff 8.1 ct/kWh (commissioning 2026). Excluding capital costs/interest.
SG Ready: The Intelligent Connection
Modern heat pumps and PV inverters communicate via the SG Ready interface (Smart Grid Ready). This standardised protocol enables four operating states:
| SG Ready status | Meaning | PV relationship |
|---|---|---|
| 1 -- Lock | HP locked (e.g. during grid overload) | No operation |
| 2 -- Normal | Normal operation following heating curve | Grid electricity |
| 3 -- Recommendation | Increased operation recommended (PV surplus) | Solar electricity available |
| 4 -- Start-up | Forced operation (large PV surplus) | Plenty of solar electricity |
How SG Ready Increases Self-Consumption
In status 3 and 4, the heat pump raises the hot water temperature (e.g. to 55 instead of 48 °C) or heats the buffer tank more intensively. This effectively "stores" solar electricity as heat -- without expensive battery storage. In practice, SG Ready increases the solar coverage rate of the heat pump by 5–10 percentage points.
Requirements:
- Heat pump with SG Ready interface (standard on all branded manufacturers since 2020)
- Inverter or energy manager with SG Ready output
- Connection cable (2-core) between inverter and heat pump
Setup typically takes 30 minutes and costs nothing beyond the cable. Nevertheless, SG Ready is estimated to be inactive in 60% of installed systems -- a wasted savings potential of EUR 150–300 per year.
Practical Example: The Mueller Family, Renovated Detached House
Starting Point
- Building: 160 m², year of construction 1992, facade insulated, new windows
- Occupants: 4 persons
- Previous heating: Gas condensing boiler, 22 years old
- Gas costs 2025: EUR 2,650/a (incl. hot water)
- Household electricity: 4,800 kWh/a (EUR 1,728/a at EUR 0.36/kWh)
Switching to HP + PV
- Heat pump: Air-to-water, 10 kW, SPF 3.1
- PV system: 12 kWp south-west, 30° tilt
- Battery storage: 10 kWh
- Investment: HP EUR 28,000 + PV EUR 16,000 + storage EUR 9,000 = EUR 53,000
- BEG subsidy (50%): –EUR 14,000 -> Net: EUR 39,000
Results After the First Year
| Item | Before (gas + grid electricity) | After (HP + PV + storage) |
|---|---|---|
| Heating costs | EUR 2,650 | EUR 980 |
| Household electricity | EUR 1,728 | EUR 720 |
| Feed-in tariff income | — | –EUR 420 |
| Maintenance | EUR 320 | EUR 150 |
| Total costs | EUR 4,698 | EUR 1,430 |
| Annual savings | — | EUR 3,268 |
Payback of the net investment: EUR 39,000 / EUR 3,268 = 12 years
With rising gas and electricity prices, the payback period shortens to an estimated 10 years. After that, the family saves over EUR 3,000 per year on an ongoing basis.
Common Mistakes When Combining the Systems
1. PV System Sized Too Small
Those who size their PV system only for household electricity and then add a heat pump later are leaving potential on the table. The heat pump increases electricity consumption by 3,000–6,000 kWh. Better: factor in the heat pump's demand when planning the PV system -- even if the heat pump is not installed until later.
2. SG Ready Not Activated
The connection between inverter and heat pump is forgotten during installation or not configured due to time pressure. This costs EUR 150–300 in savings per year. After installation, check whether SG Ready is active and whether the heat pump actually responds when there is PV surplus.
3. Hot Water Tank Too Small
A 200-litre tank is sufficient for a heat pump without PV. With PV, it should hold at least 300 litres, ideally 400 litres. The larger tank allows more hot water to be produced and stored at midday when the sun is shining. The additional cost of EUR 200–400 for the larger tank pays for itself within a year.
4. Battery Storage Oversized
More than 15 kWh of storage capacity provides barely any additional self-consumption in a detached house. The last 5 kWh of a 15 kWh battery are only fully used on a few days per year. Rule of thumb: maximum 1.5 kWh storage per 1,000 kWh annual consumption.
5. Activating the Immersion Heater Instead of the Heat Pump
Some installations use an electric immersion heater (COP 1.0) instead of the heat pump (COP 3–4) when there is PV surplus. This wastes 70% of the solar electricity. The heat pump should always take priority over the immersion heater -- the heater should only run for legionella cycles or as an emergency backup.
Frequently Asked Questions
Is a PV system worthwhile for a heat pump?
Yes, almost always. The PV system reduces the heat pump's electricity costs by 30–50%. With a heat pump electricity consumption of 5,000 kWh and 40% solar coverage, that saves around EUR 340 per year on heating electricity alone. Combined with saved household electricity and feed-in tariff income, the overall return on a PV system is typically 6–10% per year.
How many kWp of PV do I need for a heat pump?
As a rule of thumb: 1 kWp per 1,000 kWh of total electricity consumption (household + heat pump), multiplied by 1.2. A household with 4,500 kWh household electricity and 5,000 kWh HP electricity therefore needs around 11–12 kWp. That corresponds to a roof area of 55–60 m².
Do I need a battery storage system?
Not necessarily, but it is recommended. Without storage, self-consumption is 30–35%; with a 10 kWh battery, it is 55–60%. The cost-effectiveness of the battery depends on the electricity price: from EUR 0.30/kWh household electricity upwards, a battery generally pays off.
Does the combination work in winter too?
To a limited extent. In December and January, the PV system provides only 5–10% of the heat pump's demand. The main benefit of the combination unfolds during the transitional months (March–May, September–November), when both significant PV yields and heating demand are present. In summer, solar covers the heat pump's hot water demand almost entirely.
What is SG Ready and do I need it?
SG Ready is a standardised interface that connects the heat pump and PV inverter. When there is a PV surplus, the heat pump is instructed to heat the hot water or buffer tank more intensively. This increases self-consumption by 5–10 percentage points and saves EUR 150–300 per year. Activation is free and should be standard with every HP + PV installation.
Conclusion -- Stronger Together Than Alone
In summary: A PV system and a heat pump are each economically viable on their own -- together, they reach their full potential. The PV system reduces heat pump operating costs by 30–50%, while the heat pump increases PV self-consumption by 10–20 percentage points. The combination saves around EUR 2,000–2,500 per year compared to gas heating plus grid electricity. Over 20 years, that is EUR 35,000 less in total costs. The keys to success: correct sizing (1 kWp per 1,000 kWh consumption x 1.2), SG Ready activation and a sufficiently large hot water tank. Battery storage is not essential but improves comfort and self-sufficiency. Anyone building new or replacing their heating system should always plan PV and heat pump together -- the synergy is too significant to leave on the table.
Article Series
| No. | Article | Topic |
|---|---|---|
| 1 | Heat Pumps: The Complete Guide | Overview and introduction |
| 2 | How Does a Heat Pump Work? | Physical fundamentals |
| 3 | The Components | Heat exchangers, compressor, expansion valve |
| 4 | Key Figures and Sizing | COP, SPF, design |
| 5 | Operating Modes | Monovalent, bivalent, hybrid |
| 6 | Heat Pump Types and Solar Integration | Types & combination with PV |
| 7 | SCOP Explained | Seasonal coefficient of performance |
| 8 | Optimisation & Settings | Practical operating guide |
| 9 | Calculating Output | Sizing |
| 10 | Heat Pump Costs 2026 | Purchase, installation, operation |
| 11 | Heat Pumps in Older Buildings | Efficient use in existing buildings |
| 12 | Electricity Consumption per Year | Consumption by building type |
| 13 | Saving on Heating Costs with a Heat Pump | Cost comparison gas/oil/HP |
| 14 | Solar and Heat Pump: The Dream Team | You are here |
Further Reading
Optimising Self-Consumption · Calculating PV Yield · Planning a Solar System · Heat Pump Electricity Consumption · Heat Pump Costs 2026
Sources
- Fraunhofer ISE: Heat Pump Monitoring
- BSW Solar: Solar Electricity Costs 2025
- HTW Berlin: Independence Calculator
- BWP: SG Ready Label
- Verbraucherzentrale: PV + Heat Pump
- co2online: Increasing Self-Consumption
- BDEW: Electricity Price Analysis 2026
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