Air-source heat pumps with solar panels and batteries: how to size your system in Spain (2026)

Combining an air-source heat pump with solar PV and batteries is accelerating the shift towards full self-consumption: heating, cooling and domestic hot water (DHW) powered by renewable energy, less dependence on the grid and lower bills. At Ecoforest, we integrate the entire ecosystem (ecoAIR+, ecoGEO+, surplus energy management and storage) to make the system truly efficient and cost-effective. If you would like a more general introduction to combining a heat pump and solar power, I recommend starting with the article “Heat and cool your home with a heat pump and solar panels”, then returning here when you are ready to fine-tune the sizing of your panels and batteries.

When is it worth adding solar panels and batteries to an air-source heat pump?

It is particularly worthwhile when these conditions apply: moderate to high annual heating and cooling demand (detached houses, SMEs, buildings with centralised systems), good solar potential (a south- or southwest-facing roof with little shading), high or volatile electricity energy charges, access to subsidies and, importantly, modulating equipment with surplus energy management to “shift” PV output into useful heat (DHW, thermal storage). In 2026, the use of natural refrigerants such as R290 in equipment like ecoAIR+ improves seasonal performance, while falling PV and storage prices shorten the payback period.

Sizing steps (the Ecoforest methodology)

Professional sizing is essential: it must be carried out by a certified installer after assessing the property’s floor area and building envelope, its heating, cooling and DHW needs, and its actual solar potential (orientation and shading). Based on that assessment, the practical methodology consists of six steps.

1. Heating and cooling load profile of the home or building
   Estimate annual demand for heating, cooling and DHW. If no thermal load calculation is available, use historical consumption and building type as a starting point. For an initial estimate, calculate the target annual thermal energy E_th (kWh/year).
2. Demand curve and modulating operation
   The total alone is not enough: how demand is distributed throughout the year and day also matters. Modulating heat pumps (ecoAIR+, ecoGEO+) adjust their output to follow that curve, improving operation during solar production hours and compatibility with batteries and buffer/DHW tanks.
3. Seasonal performance by climate zone (SCOP/SEER)
   Convert thermal demand into the air-source heat pump’s expected electricity consumption. If SCOP is the seasonal heating performance, annual electricity consumption for heating is:

For DHW and cooling, use equivalent seasonal COP/SEER figures. In Spain’s temperate climates, with R290 and a good installation, a SCOP of 3.5–4.5 is a common indicative range.

4. Expected annual photovoltaic output
   Size the PV system to cover as much of that consumption as possible, plus some other electricity uses. As a simplified guide, in much of Spain annual output can be estimated as:

where Y is usually between 1{,}200 and 1{,}700 text{ kWh/kWp·year}, depending on the actual location and orientation. A study of shading and orientation (south-facing, with a 10–35° tilt) is critical to determining Y.

5. Usable battery capacity and charging strategies
   The aim of storage is to shift surplus solar energy to peak demand periods (evenings and nights, cloudy days) and reduce exports to the grid. An initial estimate of usable, rather than nominal, battery capacity for a home can be expressed as:

where αalphaα is usually between 0.6 and 1.2, depending on whether you also use thermal storage (DHW/buffer tanks). If your heat pump can raise the DHW temperature when the sun is shining, you can reduce the electrical battery capacity somewhat because some of the “storage” takes the form of thermal energy.

6. Integration and control: smart inverters/controllers
   To get the most out of the system, integrate surplus energy management: prioritise powering the heat pump directly during solar production hours, divert energy to DHW or thermal storage when there is spare capacity, and only then charge the battery. When there is no sun, discharge the battery down to a set threshold and draw on the grid if necessary. Compatible inverters/controllers automate this coordination with our solutions.

Sizing examples: flat vs detached house

Example A: well-insulated flat, 90 m², temperate climate zone
Assumptions: total annual thermal demand of 6,000 kWh (4,000 heating, 1,000 cooling, 1,000 DHW). Heating SCOP 4.0; cooling SEER 4.0; DHW COP 3.0.
Annual electricity consumption of the air-source heat pump:

• Heating: 4,000 / 4.0 = 1,000 kWh
• Cooling: 1,000 / 4.0 = 250 kWh
• DHW: 1,000 / 3.0 ≈ 333 kWh
  Total heat pump consumption ≈ 1,583 kWh/year. Other household consumption: 2,000 kWh/year.
  Proposed PV system: 2.5 kWp with a specific yield of 1,400 kWh/kWp·year → 3,500 kWh/year.
  Usable battery capacity: 3–5 kWh if there is no substantial thermal storage; 2–3 kWh if “solar DHW” is prioritised at midday. With this setup, renewable energy could cover 70–85% of annual consumption.

Example B: 160 m² detached house, high demand and DHW for 4 people
Assumptions: demand of 12,000 kWh/year (9,000 heating, 1,500 cooling, 1,500 DHW). Heating SCOP 4.2; SEER 4.0; DHW COP 3.0.
Annual electricity consumption of the air-source heat pump:

• Heating: 9,000 / 4.2 ≈ 2,143 kWh
• Cooling: 1,500 / 4.0 = 375 kWh
• DHW: 1,500 / 3.0 = 500 kWh
  Total heat pump consumption ≈ 3,018 kWh/year. Other household consumption: 3,000 kWh/year.
  Proposed PV system: 5 kWp → 5 kWp × 1,400 ≈ 7,000 kWh/year.
  Usable battery capacity: 7–10 kWh if the house is empty during working hours; 5–7 kWh if there is daytime consumption and thermal storage is used (DHW/buffer tank). Potential annual coverage of >80% and very close to self-sufficiency in spring and autumn.

Note: these figures are illustrative and intended to show the process. An actual project requires a thermal calculation, shading study and specific control settings.

Costs in 2026 and estimated payback

With available subsidies and correct sizing, the typical investment and payback ranges we work with are:

• Detached house: €13,000–€17,000; savings of €800–€1,300/year; payback in 6–8 years.
• Apartment building: ~€9,500/home; savings of €850–€1,200/year; payback in ~7 years.
• SME or business: €28,000–€40,000; savings of €3,500–€4,500/year; payback in 5–7 years.

Adding batteries increases the investment, but it can raise the self-consumption rate above 80% and stabilise energy costs, shortening the payback period for households or businesses with night-time consumption and tariffs with large time-of-use price differences.

Common mistakes that make the project more expensive

• Sizing for peak power rather than annual energy and the demand curve, resulting in an oversized PV system or heat pump.
• Ignoring shading, orientation and actual flow temperature: these affect PV output and SCOP.
• Failing to use modulation and surplus energy management to preheat DHW or charge thermal storage.
• Undersizing (or oversizing) batteries relative to the actual surplus and night-time use.
• Overlooking regulatory registration and subsidy coordination, delaying commissioning.
• Combining unsuitable heat emitters (high-temperature radiators without adaptation) and forcing high flow temperatures that reduce SCOP.

Technical requirements and procedures in Spain

You will need outdoor space for the air-source heat pump unit, a sunny roof for the panels, and power and control electronics. The required administrative procedures include a building permit, self-consumption registration and, ideally, applications for national or regional subsidies, which can cover up to 80% of the system cost depending on the programme and eligibility requirements. We support you throughout the process alongside certified installers.

Quick project checklist

• Energy audit and thermal load calculation by a certified installer.
• Selection of a modulating heat pump compatible with solar integration (ecoAIR+, ecoGEO+).
• Solar assessment covering shading, orientation and tilt to determine kWp and output.
• Storage strategy: electrical batteries, thermal storage or both? Define usable capacity.
• Inverter/controller with smart management of surplus energy for DHW/thermal storage/batteries.
• Arrange permits, regulatory registration and subsidies before purchasing.
• Monitoring and preventive maintenance plan.

Practical summary for designers, installers and users

Always consult a certified installer; prioritise modulating equipment with surplus energy management; size the PV system according to annual energy needs and actual usage patterns, not peaks; choose battery capacity based on daytime surplus, night-time use and how much energy you can “shift” into thermal storage through DHW/buffer tanks; and apply for available subsidies to significantly reduce the initial investment. Ecoforest’s ecoAIR+ and ecoGEO+ ranges are ready to integrate with solar PV and batteries, optimising self-consumption and overall system efficiency.

Frequently asked questions

• What COP/SCOP should I use to estimate consumption?
  As a guide, a heating SCOP of between 3.5 and 4.5 is common in well-designed installations in Spain. The precise value depends on the heat emitters, flow temperature, climate and installation quality.
• How do I choose battery capacity?
  Start with the average PV surplus in the months of highest demand and adjust for your night-time consumption and the possibility of “storing” energy in DHW/buffer tanks. For homes, 3–10 kWh of usable capacity covers most cases; larger capacities are assessed for apartment buildings and SMEs.
• Are batteries essential?
  No, but they increase self-consumption, reduce exports to the grid and provide greater resilience against tariff changes. Even without batteries, diverting surplus energy to DHW/thermal storage already offers significant savings.
• What maintenance does it require?
  Periodic heat pump inspections, filter cleaning, and checks of the PV installation and storage system. Maintenance requirements are lower than for traditional boilers.