Solar Thermal vs. Heat Pump — Which Fits Better?
Costs, efficiency, and subsidies compared side by side — and when each technology is the better choice.
⚡ Two Technologies, One Goal
Solar thermal and heat pumps both use renewable energy sources to provide heat for heating and hot water. But the approach could hardly be more different: solar thermal converts sunlight directly into heat, while a heat pump raises environmental heat from air, ground, or groundwater to a usable temperature level using electricity.
Which technology is right for your building depends on numerous factors: building condition, existing heating system, roof orientation, budget, and long-term goals. This comparison helps you make an informed decision.
How Solar Thermal Works
Solar thermal collectors on the roof absorb sunlight and heat a transfer fluid, which passes its energy via a heat exchanger to the hot water tank. The principle is remarkably simple: the sun shines, water gets warm.
Two Collector Types
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Flat Plate Collectors
More affordable, proven, and sufficient for hot water preparation. Efficiency approx. 60–80%. Typical for single-family homes.
- 🔭
Vacuum Tube Collectors
Higher efficiency (up to 95%), effective even in diffuse light and low temperatures. More expensive, but ideal for heating support.
💡 Fact: A solar thermal system covers 50–70% of annual hot water demand in a typical single-family home. For heating support, larger collector areas and a buffer tank are required.
How the Heat Pump Works
The heat pump extracts heat from the environment — from air, ground, or groundwater — and raises it to a higher temperature level using a compressor. This requires electricity, but it delivers a multiple of heat in return: with a seasonal performance factor (SPF) of 3.5, 1 kWh of electricity produces 3.5 kWh of heat.
The decisive advantage: the heat pump works year-round and covers both heating and hot water completely — regardless of the weather. Combined with a photovoltaic system, a large share of the required electricity can be self-generated.
Heat Sources Compared
- AirCOP 2,8–4,5
Simplest installation, most affordable option
- Ground (Brine)COP 4,0–5,5
Consistently high efficiency, drilling or ground collector needed
- GroundwaterCOP 5,0+
Highest efficiency, complex permitting required
Cost Comparison
Investment costs differ significantly — as does the scope of what each system delivers:
Solar Thermal
- Hot Water Only4.000–6.000 €
- Incl. Heating Support8.000–12.000 €
- BEG Subsidy−25 %
- Net Investmentca. 3.000–9.000 €
Heat Pump
- Air-to-Water15.000–25.000 €
- Ground Source20.000–35.000 €
- BEG Subsidy−30–70 %
- Net Investmentca. 5.000–17.500 €
💡 Important: Solar thermal is cheaper to purchase but cannot fully replace an existing heating system. The heat pump costs more but is a complete heating system. The overall view over 15–20 years is what matters.
Efficiency and Yield Throughout the Year
This is where the biggest difference lies: solar thermal delivers surpluses in summer but drops off in winter — exactly when heat demand is highest. From November to February, a typical system covers only 10–20% of heating demand.
The heat pump, on the other hand, works consistently all year round — with higher efficiency in transitional seasons and reliable performance even in sub-zero temperatures. Modern air-to-water heat pumps operate down to −20 °C.
Seasonal Coverage Rate
Solar Thermal
- Summer80–100 %
- Transitional30–50 %
- Winter10–20 %
Heat Pump
- Summer100 %
- Transitional100 %
- Winter100 %
* Solar thermal coverage rate refers to hot water + heating support. The heat pump covers the entire heat demand as a standalone system.
When Solar Thermal Is the Better Choice
Solar thermal is not obsolete — in certain situations it remains the smart choice:
Existing Heating System Stays
If your gas, oil, or pellet heating still works well and you just want to supplement hot water production, solar thermal is an ideal and cost-effective addition.
Limited Budget
At €4,000–6,000 (before subsidies) for a hot water system, solar thermal is significantly cheaper than a complete heating replacement. Payback is 8–12 years.
South-Facing Roof Available
A south-facing roof surface with 30–45° pitch offers optimal conditions. Just 4–6 m² of collector area is enough for hot water production in a 4-person household.
No Complete Heating Replacement Planned
If you want to modernize your heating system step by step, solar thermal can be a meaningful first step — which can later be combined with a heat pump.
When the Heat Pump Wins
In most cases, the heat pump is the more future-proof solution — especially in these scenarios:
Complete Heating Replacement
When the old heating system needs replacing anyway, the heat pump as a standalone system is the most economical solution — especially after deducting subsidies of up to 70%.
New Build or Well-Insulated Existing Building
Well-insulated buildings with low flow temperatures (30–45 °C) enable seasonal performance factors of 4.0–5.0 — drastically reducing operating costs.
Combination with Photovoltaics
PV + heat pump is the dream team of the energy transition: your own solar electricity powers the heat pump. This reduces operating costs by 30–50% and makes you largely independent of electricity price fluctuations.
Future-Proofing
From 2045, no fossil heating systems may operate. With a heat pump, you are already independent of gas, oil, and rising CO₂ levies.
💡 Tip: Check if your roof is suitable for a PV system. The combination PV + heat pump is more economical in most cases than PV + solar thermal, because electricity is more flexibly usable.
Combination: Best of Both Worlds?
Technically, it is possible to combine solar thermal and heat pump: the solar thermal system handles hot water production in summer and relieves the heat pump. This can extend the heat pump's lifespan and reduce electricity consumption by 10–20%.
Economically, however, the combination is often not optimal. The additional investment in solar thermal collectors, storage, and piping rarely pays off compared to the alternative of using the same roof area for photovoltaics.
Solar Thermal + HP
- ✓Relieves heat pump in summer
- ✓Saves 10–20% electricity
- ✗High additional cost (€5,000–10,000)
- ✗More complex hydraulics and controls
PV + Heat Pump
- ✓Saves 30–50% operating costs
- ✓Electricity also usable for household
- ✓Feed-in tariff for surplus
- ✓Simpler system integration
⚠️ Our recommendation: In most cases, PV + heat pump is the economically better combination. Roof space is used more efficiently, operating costs decrease more significantly, and the generated electricity is more versatile. Solar thermal + heat pump is mainly worthwhile for very high hot water consumers.
Which Solution Fits Your Building?
We analyze your building, compare the options, and calculate the optimal solution — including a subsidy check. Free and without obligation.