Integración de energías renovables en la gestión de edificios existentes

Integrating renewable energy into existing buildings requires a rigorous energy diagnosis that identifies actual thermal and electrical loads, the availability of collection surfaces, and structural limitations of the property. The standard EN 16247-2:2014 establishes the energy audit methodology for buildings, which includes consumption monitoring over a minimum of 12 months, a thermographic survey of the building envelope, and analysis of hourly demand profiles. According to IDAE (2022), the Spanish building stock comprises 25.7 million dwellings, of which 81% were built before the 2006 CTE took effect and display average heating consumption of 145 kWh/m² per year, compared with the 40-60 kWh/m² per year required by current regulations.

The average cost of a comprehensive energy audit for a multi-family residential building ranges from 2,500 to 6,000 euros, according to data from the Asociación de Empresas de Eficiencia Energética (A3e, 2023). The return on this investment is immediate: audits identify an average savings potential of 35% on existing consumption, of which 40% to 55% is attributable to replacing fossil fuel sources with renewables. The Joint Research Centre (JRC) of the European Commission published in 2021 the report Energy Renovation of Existing Buildings, analyzing 3,400 cases across 18 countries and concluding that buildings retrofitted with renewable integration achieve average reductions of 62% in non-renewable primary energy consumption, ranging from 40% for minimal interventions to 90% for deep nZEB-level renovations.

Solar photovoltaic energy is the renewable technology with the greatest integration potential in existing buildings, owing to its modularity and the 89% cost reduction experienced between 2010 and 2023 according to the International Renewable Energy Agency (IRENA, 2023). The average installed cost of a rooftop photovoltaic system on a residential building in Spain stands at 1,100-1,400 euros/kWp, with annual outputs of 1,400-1,800 kWh/kWp depending on the climate zone. A typical apartment building in Madrid with an available flat roof of 300 m² can accommodate a 40-50 kWp installation generating between 56,000 and 72,000 kWh/year, covering 30-40% of the communal electricity consumption. Royal Decree 244/2019 on self-consumption facilitates surplus compensation and collective self-consumption in residential communities.

BIPV (Building Integrated Photovoltaics) systems allow the integration of solar generation into existing building ventilated facades during envelope renovations. The PVSITES project, funded by Horizon 2020 with 4.8 million euros, developed thin-film photovoltaic modules integrated into facade louvres with efficiencies of 12-16% and costs of 180-280 euros/m². The Energiesprong building renovation in Nottingham (United Kingdom) demonstrated that combining 35 kWp on the roof with 12 kWp of facade BIPV achieved a net-zero energy balance in a block of 8 social housing units built in the 1960s, with an additional cost of 18,000 euros per dwelling and annual energy bill savings of 2,100 euros, resulting in a payback period of 8.5 years.

Air-source heat pumps have established themselves as the primary alternative to gas and oil boilers in existing buildings, with EU sales reaching 3 million units in 2022, a 38% increase over 2021, according to the European Heat Pump Association (EHPA). Current air-to-water units achieve COPs of 3.5 to 4.2 under nominal conditions (outdoor air at 7 °C, water at 35 °C), meaning that for every kWh of electricity consumed they produce 3.5 to 4.2 kWh of thermal energy. By comparison, a condensing gas boiler achieves efficiencies of 0.95-0.98. Direct substitution in a residential building in Madrid with a heating demand of 80 kWh/m² per year reduces primary energy consumption by 55-65% and CO₂ emissions by 50-60%, considering the 2023 Spanish electricity mix with 50.3% renewable generation.

Low-enthalpy geothermal energy delivers higher efficiencies — COPs of 4.5 to 5.5 — by exploiting the stable subsurface temperature, which on the Iberian Peninsula ranges from 14 to 18 °C at depths of 100-150 meters. The drilling cost for vertical borehole heat exchangers ranges from 40 to 60 euros per linear meter, making installation more expensive than air-source heat pumps: a geothermal installation for a building of 20 dwellings requires between 6 and 10 boreholes of 120 meters, with a total drilling cost of 28,800 to 72,000 euros. The GEO4CIVHIC program, funded by Horizon 2020 with 7.7 million euros, demonstrated across 4 pilot buildings in Italy, Ireland, Belgium, and Spain that geothermal combined with underfloor heating achieves savings of 70-80% compared with oil boilers and payback periods of 10 to 14 years, reduced to 7-9 years with 40% subsidies.

Effective integration of renewables into existing buildings requires energy management systems (EMS) that optimize self-consumption and minimize grid export. Lithium battery storage systems allow daytime photovoltaic surpluses to be stored for nighttime use, with costs that have fallen to 350-500 euros/kWh of installed capacity in 2023, according to BloombergNEF. A residential building with 40 kWp of photovoltaics and a 50 kWh community battery increases the self-consumption rate from 30-35% (without battery) to 60-70%, according to modeling by the Fraunhofer ISE (2023). The Storegio project in Bordeaux (France) installed 250 kWh community batteries in 5 renovated social housing blocks, achieving self-consumption of 72% and a 45% reduction in electricity bills.

Energy Management Systems (EMS) based on artificial intelligence predict solar generation and electricity demand 24-48 hours ahead and automatically adjust flexible loads — electric vehicle charging, domestic hot water heating, appliance scheduling — to maximize self-consumption. The SEMIAH platform, developed under the Horizon 2020 program, demonstrated in 140 pilot dwellings in Germany and Switzerland that intelligent flexible load management increases photovoltaic self-consumption by an additional 15-22% without the need for batteries. In Spain, the company Stemy Energy manages over 500 energy communities with predictive algorithms that have generated average savings of 38% on participants' electricity bills, optimizing surplus distribution between deferred self-consumption, grid export, and storage based on hourly electricity market prices.