Equipment installed on this project
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Complete oil-to-solar transformation: 10kW DEYE solar, 10kWh battery, 8kW Daikin heat pump and 180m² underfloor heating. 80% energy cost savings.
Mijas Villa: Complete Oil-to-Solar Retrofit with Heat Pump & Underfloor Heating
Case Study: 10kW Solar + 10kWh Battery + 8kW Heat Pump + 180m² Underfloor Heating - From Oil Boiler to 80% Energy Self-Sufficiency
Written by Ben Hayden, Independent Energy Advisor
80%
Cost Savings
10kW
Solar
COP 4.2
Efficiency
5
Zones
Location
Mijas, Costa del Sol
Property Type
Traditional Villa (220m²)
Previous System
Oil boiler with radiators + portable AC units
New System
10kW DEYE Solar + 10kWh Battery + 8kW Heat Pump + Underfloor Heating
Total Capacity
Complete integrated energy system
Installation Date
Completed 2026
The Challenge
The villa owners faced the common Costa del Sol challenge of modernizing an older property's heating and cooling:
Our Integrated Retrofit Solution
We designed a complete energy transformation using an 'energy cascade' approach - where solar powers the battery, battery powers the heat pump, and heat pump feeds the underfloor heating:
10kW DEYE Hybrid Solar
Premium solar panels with hybrid inverter capable of grid-tied operation and battery backup
10kWh Battery Storage
Stores excess solar energy for evening and overnight heat pump operation - maximizing self-consumption
8kW Daikin Heat Pump
Sized perfectly for the 220m² property with COP 4.2 - efficient heating, cooling, and hot water
180m² Underfloor Heating
Low-temperature radiant heating throughout living areas - ideal pairing with heat pump technology
Running Costs Comparison
Actual costs before and after the retrofit (12-month comparison):
Based on actual utility bills and oil purchases. 220m² villa with 5 occupants, full year occupancy.
| System | kWh/month | Cost/month | Annual Cost |
|---|---|---|---|
| Previous (Oil boiler + portable AC) | N/A | €165 | €1,980 |
| New Integrated System | ~300 kWh grid import | €35 | €420 |
€130
Monthly Savings
€1,560
Annual Savings
80%
Cost Reduction
8-10 years
Payback Period
Oil costs based on average 1,100 litres/year at €1.10/litre. New system includes grid feed-in compensation averaging €15/month for surplus solar. View source
Professional Installation
The complete retrofit was completed over 4 weeks:
Expert Insight
"This project showcases the power of integrated system design. The oil boiler was replaced with an 8kW Daikin heat pump that feeds 180m² of new underfloor heating - a far more efficient combination than the old radiator system. Underfloor heating operates at 35-45°C water temperature versus 60-70°C for radiators, which puts the heat pump in its efficiency sweet spot. The COP stays above 4.0 all year round. Combined with the 10kW solar array and 10kWh battery, the system achieves 80% energy self-sufficiency. The owners went from €1,200/year in oil costs to under €300/year in electricity imports - and that's with cooling included, which they never had before."
Rob Greeves
HVAC Director, Agua Therm
Energy Cascade Design
"The key to this installation is what we call 'energy cascading'. During the day, solar generates electricity which first powers the home, then charges the battery, then exports surplus to the grid. In the evening and overnight, the battery powers the heat pump during its scheduled heating cycles. This means the underfloor heating is essentially running on free solar energy stored from earlier. The DEYE hybrid inverter manages all of this automatically, prioritizing self-consumption over grid export. We've added smart scheduling so the heat pump pre-heats the floors during peak solar hours, and the thermal mass of the concrete screed keeps the villa comfortable through the night with minimal additional input."
Craig Whitham
Electrical Director, Agua Therm
Client Feedback
"We were spending a fortune on heating oil and the house was still never properly warm. The old radiators took ages to heat up and some rooms were always cold. Now with the underfloor heating, every room is perfectly comfortable at 21°C and our feet are never cold on the tiles anymore. The solar panels and battery mean we're generating most of our own electricity, and on sunny winter days the system runs entirely on solar. Our annual heating bill went from over €1,200 to less than €300 - and that includes air conditioning in summer which we never had before! Agua Therm managed the whole project brilliantly."
Villa Owners
Mijas
Premium alternative · What we could also have installed
How Airzone could take this underfloor heating to room-by-room control
This Mijas villa already runs on a top-tier integrated system: 10 kW of DEYE solar, a 10 kWh battery, an 8 kW Daikin Altherma 3 M heat pump and 180 m² of underfloor heating split across 5 manifold zones. It is exactly the kind of multi-zone hydronic installation that Airzone — a manufacturer headquartered in Málaga, under 20 km from Mijas — designed its Acuazone/Hydrozone range for. An added control layer turns those 5 basic zones into proportional, room-by-room comfort, synchronised with the solar production.
As accredited Airzone installers on the Costa del Sol — the system is deployed and documented in our Mijas Airzone Flexa 4.0 UFH case study · more on our Airzone work — we know the three product paths that apply directly to an installation like this one. Each solves a different problem.
24 V electrothermal actuator heads fitted to the existing manifold return loops, plus a Blueface or Think thermostat per room. Turns today's 5 basic zones into up to 6–10 independent zones, each with its own setpoint and schedule — bedrooms at 22 °C overnight, living room at 24 °C by day, bathrooms only during the morning shower.
The 5-port manifold already in place accepts standard 24 V NC actuator heads — no pipework is touched.
Aidoo Pro Heat Pump gateway wired into the Altherma 3 M's P1/P2 bus. Exposes heating/cooling/DHW mode, weather-compensation curve and the 200 L cylinder setpoint to the Airzone Cloud app and to the zoning board — one single brain decides production and emission together.
Supports KNX, Modbus RTU/TCP and BACnet IP for future home-automation integration.
The Webserver Cloud HUB syncs heating schedules to peak solar production hours. The heat pump boosts the UFH at midday — the screed's thermal mass holds the heat — so the 10 kWh battery is preserved for genuine evening demand.
Local REST API + Home Assistant integration to bridge with the DEYE inverter.
Quantifiable benefits of adding Airzone
Why Airzone is a technical fit for this project
The 180 m² of underfloor heating we laid in this villa uses a standard Eurocone multi-port manifold — the exact format that Acuazone's 24 V electrothermal heads screw onto. The Daikin Altherma 3 M exposes its P1/P2 bus, onto which the Aidoo Pro Heat Pump gateway wires directly (no dry contacts, keeping inverter modulation and weather curve intact). The electrical board we left for this home has DIN-rail headroom to add the 24 V transformer that feeds the Acuazone central board, and the 65 mm screed thermal mass over the PERT-AL-PERT pipework is the natural ally of Airzone Cloud's solar scheduling.
Want to add Airzone to your underfloor heating?
We provide no-obligation technical surveys for Acuazone, Aidoo Pro and Airzone Cloud on heat-pump-fed underfloor heating installations in Mijas, Marbella, Fuengirola and across the Costa del Sol.
Request an Airzone quoteSources: Airzone (airzonecontrol.com) · European Building Automation and Control Association — eu.bac · Universidad de Córdoba · KNX Association. Savings figures published by the manufacturer; actual performance depends on the home, occupancy patterns and setpoints.
Verified Efficiency Data
Performance data for integrated solar + heat pump + underfloor heating systems:
10kW solar produces 15,000+ kWh/year
Based on 1,500+ annual sun hours in Mijas, Costa del Sol
Heat pump COP 4.2 with underfloor heating
Low-temperature underfloor systems optimize heat pump efficiency
Underfloor heating 15-20% more efficient than radiators
Lower water temperatures and radiant heat distribution reduce energy waste
10kWh battery covers overnight heat pump operation
Average winter night heating cycle requires 6-8kWh
80% reduction in energy costs vs oil
Oil at €1.10/litre vs solar-powered heat pump electricity at €0.04/kWh effective rate
Heat pump systems paired with underfloor heating are recognized by IDAE as the most efficient retrofit solution for Spanish homes. Solar self-consumption is regulated under RD 244/2019.
Frequently Asked Questions
Also see
About the Author
Ben Hayden
English-Speaking Electrician & Independent Energy Advisor
Ben Hayden is an English speaking electrician and independent energy advisor based in Marbella, Spain, with over 15 years of electrical experience across Europe. He provides independent energy and electrical checks for overseas property owners and managers across the Costa del Sol — helping clients cut electricity bills, navigate Spanish regulations, and make confident decisions on solar PV, heat pump, EV charger and battery storage projects.
Ben advises in plain English on projects where the paperwork is in Spanish and the stakes are high. His writing has appeared in ExpatArrivals, The Olive Press, Euro Weekly News, BuildingTalk and pv magazine.