Generación y almacenamiento de energía en edificios autónomos

Solar photovoltaic generation is the primary energy source in 92% of documented autonomous buildings worldwide (IEA, Solar Energy Perspectives 2023). The latest-generation monocrystalline silicon modules achieve commercial efficiencies of 22.5-24.5% (TOPCon and HJT technologies), compared to 15-17% for standard polycrystalline panels from 2010. A 200 m² flat roof in Madrid (global horizontal irradiance: 1,661 kWh/m²·year, PVGIS) fitted with 580 Wp TOPCon modules generates approximately 44,000 kWh/year, covering the average consumption of 8-10 dwellings of 90 m² with energy rating B. Certified annual degradation has been reduced to 0.25-0.40% for n-type modules, guaranteeing 87.4% of nominal power after 30 years of operation in accordance with the IEC 61215:2021 standard.

Facade integration (BIPV) extends the building's generating surface. CIGS thin-film glass-glass modules (copper-indium-gallium-selenide) from manufacturers such as Avancis and Manz achieve efficiencies of 16-18% with adjustable luminous transmittance between 10% and 40%, acting simultaneously as glazing and generator. The Freiburg Rathaus (ingenhoven architects, 2017) integrates 880 m² of BIPV on its south facade and roof, generating 161 MWh/year which exceeds the building's annual consumption (155 MWh/year), making it the world's first net-positive-energy town hall. BIPV costs range from 180 to 350 EUR/m², compared to 120-200 EUR/m² for a conventional ventilated facade in porcelain stoneware, resulting in a net additional cost of only 60-150 EUR/m² when the replacement of the facade finish is taken into account.

Small-scale wind energy (< 100 kW) complements photovoltaics at sites with average wind speeds above 4.5 m/s. Vertical-axis wind turbines (VAWT) of the Darrieus-H and Savonius types offer advantages for architectural integration: they operate with multidirectional wind, produce noise levels below 35 dB(A) at 5 m distance, and do not require yaw systems. The Aeolos-V 5 kW model starts generating at wind speeds of 1.5 m/s and reaches its rated power at 12 m/s, with a typical capacity factor of 15-22% in urban settings. The estimated annual output for a 5 kW VAWT at a location with a mean wind speed of 5.5 m/s is 7,500-9,000 kWh/year, equivalent to the annual electricity consumption of 2-3 energy-efficient dwellings.

Hybrid solar-wind systems maximise renewable generation availability: while photovoltaics peaks in summer and during daytime, wind compensates with higher winter and nighttime output. A study by Fraunhofer ISE (Quaschning, 2019) demonstrated that a hybrid PV-wind system sized to cover 100% of a dwelling's annual demand in mid-European latitudes requires 30-40% less storage capacity than an exclusively photovoltaic system. The BedZED project (Beddington Zero Energy Development, Sutton, London, 2002, Bill Dunster Architects) integrated 777 m² of photovoltaics and 135 kW of biomass CHP (combined heat and power) for 82 dwellings and 2,500 m² of offices, reducing CO₂ emissions by 56% compared to an equivalent conventional development. Building-integrated wind turbine (BIWT) technology is evolving towards solid-state devices such as piezoelectric generators that produce electricity from wind-induced vibrations, with MIT prototypes generating 3 W/m² of facade exposed to winds of 6 m/s.

Lithium iron phosphate (LFP) battery storage has established itself as the benchmark technology for autonomous buildings owing to its intrinsic safety (no thermal runaway below 270°C), cycle life exceeding 6,000 cycles at 80% depth of discharge (DOD), and cost of 139 USD/kWh in 2024 (BloombergNEF). An autonomous residential building with 4 dwellings in Madrid requires an installed capacity of 40-60 kWh to guarantee 2-3 days of autonomy under low winter irradiation conditions. Sodium-ion (Na-ion) batteries, with projected costs of 77 USD/kWh by 2025 (CATL) and energy densities of 140-160 Wh/kg, represent a viable lithium- and cobalt-free alternative. BYD and CATL have commenced mass production of Na-ion modules for stationary storage with capacities of 10-280 Ah per cell.

Thermal storage complements electrochemical storage at significantly lower costs. Stratified hot water tanks store heat at 60-95°C with losses of 0.5-1.5%/day and costs of 3-15 EUR/kWh thermal, compared to 100-300 EUR/kWh for electrical storage. Phase change materials (PCM) based on paraffins or hydrated salts with melting temperatures of 22-28°C store between 150 and 250 kJ/kg of latent heat within a range of 4-6°C, stabilising indoor temperature with 25-40% less HVAC energy. The HYBUILD project (Horizon 2020, 2017-2021, coordinated by COMSA Corporación) developed a compact thermal-electrical storage system for Mediterranean buildings combining sorbitol PCM (97°C melting point), a transcritical CO₂ heat pump, and LFP batteries, demonstrating a 40% reduction in primary energy consumption and 85% solar self-consumption in a pilot block of 12 dwellings in Athens.

Seasonal storage — the ability to transfer surplus summer generation to winter consumption — remains the outstanding technical challenge for autonomous buildings. Electrochemical batteries are economically unviable for seasonal cycles (cumulative self-discharge over 6 months exceeds 15-25% in LFP). Green hydrogen produced by water electrolysis offers a solution: a PEM (Proton Exchange Membrane) electrolyser with an efficiency of 65-75% (LHV) converts photovoltaic surpluses into hydrogen compressed to 350-700 bar or stored in metal hydrides at 20-30 bar. A PEM fuel cell reconverts the hydrogen into electricity at an efficiency of 50-60%, resulting in an overall round-trip efficiency of 33-45%, lower than the 90-95% of batteries but acceptable for long-duration storage.

The Phi Suea House pilot project (Chiang Mai, Thailand, 2017) demonstrated the viability of a fully autonomous 4-dwelling residential community with hydrogen: 76.5 kWp of photovoltaics, 85 kWh of LFP batteries for the daily cycle, a 40 kW electrolyser, and storage of 168 kg of H₂ (equivalent to 5,600 kWh) in composite tanks at 30 bar, with a 10 kW fuel cell. The system operates off-grid at an energy cost of 0.15 USD/kWh. In Europe, the HAEOLUS programme (Horizon 2020, 2018-2021) installed a 2.5 MW PEM electrolyser in Berlevåg (Norway), powered by a 45 MW wind farm, demonstrating green hydrogen production at 4.5 EUR/kg. The European Hydrogen Strategy (2020) sets the target of 40 GW of installed electrolysers by 2030 and a production cost of 1.5-2.0 EUR/kg, which will enable seasonal storage in buildings at costs competitive with connection to the conventional gas grid.