Energy storage solutions in smart buildings

Renewable energy sources like sunlight and wind are intermittent, producing power only when the sun shines or the wind blows. Such intermittency necessitates efficient energy storage systems to ensure a continuous and stable energy supply.

Acquiring energy storage capabilities allows building operators to increase demand flexibility, a crucial pillar of grid-integrated efficient buildings. This is important because buildings consume 40 per cent of global energy and produce 40 per cent of CO2 emissions. When one can store energy, one can control the timing and the amount of energy used or return it to the grid.

Need for energy storage solutions

Buildings with energy storage systems can dynamically manage their energy consumption, preventing blackouts and supporting grid stability. Furthermore, energy storage increases building resilience by offering a backup power source during outages, ensuring the continuity of critical operations. The following are key reasons why energy storage is essential:

1. Ensuring grid stability and resilience
• Stores energy for backup power during grid failures, blackouts, or power fluctuations.
• Prevents sudden power disruptions, ensuring a continuous energy supply in buildings and industrial operations.
• Supports grid-integrated, efficient buildings, improving demand flexibility.
2. Integrating renewable energy efficiently
• Captures excess solar and wind energy when production is high and stores it for later use.
• Reduces dependency on fossil fuels by ensuring a steady renewable energy supply.
• Enables self-sufficiency for buildings, reducing reliance on unstable grid power.
3. Managing peak demand and reducing costs
• Stores energy during off-peak hours when electricity is cheaper and discharges it during peak demand to lower energy bills.
• Reduces strain on the power grid, preventing overloads and enhancing overall efficiency.
• Supports demand response programs, helping utilities manage supply-demand balance.
4. Enhancing power quality and system efficiency
• Regulates voltage fluctuations and stabilizes frequency for improved power reliability.
• Minimizes power losses and optimises overall building performance.
• Supports smart building technologies and enables dynamic energy management.
5. Strengthening energy independence and sustainability
• It helps businesses and homes achieve energy independence, reducing reliance on external power sources.
• Enables a low-carbon future by maximizing the use of renewable energy.
• Contributes to sustainability goals by reducing greenhouse gas emissions.

Types of energy storage solutions

Various storage technologies are available for smart buildings based on how much energy they hold, how quickly they can supply power, how efficient they are, and how long they last.

A) Battery Energy Storage Systems (BESS):

BESS is a widely used electrochemical energy storage solution in smart buildings, storing electrical energy in chemical form for later use. These systems enhance energy efficiency and reliability by utilizing batteries composed of electrochemical cells, each containing an anode, cathode, electrolyte, and separator. BESS delivers economic benefits through reduced utility costs, promotes energy independence by decreasing grid reliance, and provides critical backup power during outages. The common battery types in Smart Buildings include:

1. Lead-acid batteries: These are widely used due to their low cost and reliability. They offer fast response times and a service life of 6-15 years. However, they have a lower energy density and limited cycle life.
2. Nickel-Based Batteries: Including Nickel-Cadmium (NiCd) and Nickel-Metal Hydride (NiMH) batteries, these are known for durability and moderate energy density, suitable for various applications.
3. Lithium-Ion Batteries: Popular for their high energy density (150-250 Wh/kg), efficiency, and long lifespan (~5,000 cycles), making them ideal for modern smart building applications.
4. Solid-state Batteries: They offer enhanced stability, improved safety with no thermal runaway risk, and a higher energy density of 300-500 Wh/kg compared to traditional Li-ion batteries.
5. Redox Flow Batteries: These provide scalable energy storage with independent power and energy capacity and a long lifespan of approximately 15,000 cycles. Despite their lower energy density, they are ideal for bulk storage.
6. Sodium-Ion Batteries: Sodium-ion batteries work much like the lithium-ion batteries in your phone, but they use sodium instead of rarer lithium. When these batteries are charged, sodium atoms give up electrons and move through a liquid or gel inside the battery. Later, these sodium ions flow back, releasing energy to power the device.

Figure 1: Block diagram of BESS

Fig 1 outlines the main building blocks of a Battery Energy Storage System (BESS), including the rechargeable battery module, battery management system (BMS), power conversion system (PCS), and energy management system (EMS) for efficient operation and control.

Application of BESS includes:

• Backup power: BESS provides uninterrupted power during outages, ensuring critical systems remain operational and protecting sensitive equipment from damage.
• Load shifting: BESS stores energy during off-peak periods when electricity is cheaper and releases it during peak times, reducing energy costs.
• Renewable energy integration: BESS stores excess energy from renewable sources like solar panels, allowing buildings to use clean energy despite low production.
• Emergency lighting: Ensure emergency lighting systems remain operational during power failures, enhancing safety.
• Electric vehicle (EV) charging: Provide efficient energy management for EV charging stations, reducing strain on the grid during peak times.
• Microgrid backup: In microgrids, BESS offers backup power, enhancing resilience against outages.

B) Mechanical Energy Storage Solutions (MES):

1. Pumped Hydro Storage (PHS): Pumped hydro storage is the most widely used mechanical energy storage method, accounting for the maximum amount of global electrical storage capacity. It relies on gravity to store energy by pumping water from a lower reservoir to a higher one during off-peak hours. When energy is needed, the water flows back down, driving turbines to generate electricity. In general, PHS systems offer high efficiency (70%-85%), large-scale storage capacity (1 MW to 3 GW), and a lifespan of over 40 years. Key applications include:

   • Store excess renewable energy by lifting heavy blocks and releasing energy by lowering them to generate electricity.
   • Integrate into skyscrapers to function as emergency generators, enhancing building resilience.

2. Compressed Air Energy Storage (CAES): CAES stores energy by compressing air at high pressure in underground reservoirs such as caverns or abandoned mines. When energy demand rises, the compressed air is released to power a gas-fired turbine, generating electricity. CAES provides large-scale energy storage (over 100 MW per unit) with a lifespan of around 40 years and an efficiency of about 70%. While CAES can store vast amounts of energy, its implementation depends on suitable geological formations. Key applications include:

   • Storing surplus energy by compressing air and releasing energy by expanding the air to drive generators.
   • Providing peak load management by supplying stored energy during high-demand periods.

3. Flywheel Energy Storage (FES): Flywheel energy storage converts electricity into rotational kinetic energy using a spinning mass (flywheel). During charging, a motor accelerates the flywheel; during discharge, the stored kinetic energy powers a generator. FES systems are highly efficient and have rapid response times. It is ideal for applications requiring short bursts of high power and frequent charge-discharge cycles. They feature low maintenance, long lifespan, high power density, and wide operating temperature ranges. Key applications include:

   • Maintain power quality by absorbing short-term fluctuations and providing an uninterrupted power supply.
   • Supporting renewable energy systems by balancing intermittent generation and demand.

C) Electromagnetic energy storage solutions:

Electromagnetic energy storage systems use electric or magnetic fields to store and release energy efficiently. These systems offer rapid response times, long cycle life, and high power density, making them useful for short-term energy storage and power stabilization in smart buildings.

1. Capacitors (CS)

   Capacitors store energy in an electrostatic field between two conductive plates separated by an insulating dielectric material. They charge and discharge quickly, allowing for high-power bursts, and have high efficiency and long cycle life without material degradation. However, their low energy density and high self-discharge limit their use in applications that require short-term power compensation. Capacitors are crucial for voltage regulation and power factor correction in smart buildings. Applications include:

   • Voltage stabilization in elevators and escalators to handle sudden power fluctuations.
   • Power factor correction in HVAC systems to improve energy efficiency.
   • Surge protection for sensitive electronic equipment, such as security systems and automated lighting.
2. Supercapacitors (SCES)

   Supercapacitors, also known as double-layer capacitors (DLCs) or ultracapacitors, store energy as static charge at the interface between an electrolyte and conductive electrodes. Their energy density is significantly higher than that of conventional capacitors (around 20 Wh/kg), and they can charge and discharge almost instantly. They are highly reliable, operate efficiently across a wide temperature range, and can last over 100,000 cycles without degradation. However, they suffer from high self-discharge rates (5%-40% per day) and high capital costs ($6000/kWh), limiting their use to short-duration applications rather than long-term energy storage. Applications include:

   • Emergency power backup for elevators and automatic doors in case of power outages.
   • Energy recovery in regenerative braking systems for automated parking structures.
   • Peak shaving in HVAC systems to efficiently manage short bursts of high-power demand.
3. Superconducting Magnetic Energy Storage (SMES)

   SMES systems store energy in a magnetic field generated by a superconducting coil carrying direct current (DC). Since the coil operates at cryogenic temperatures, it eliminates electrical resistance, ensuring high power density, ultra-fast response times (within milliseconds), and rapid charge/discharge cycles. With cycle efficiency between 85%-95% and a lifespan of over 30 years, SMES is one of the most efficient energy storage solutions. However, maintaining superconducting conditions requires a cryogenic cooling system, which results in high operational costs (up to $10,000/kWh) and self-discharge losses (10%-15% per day). Despite these drawbacks, SMES is highly effective in power quality control and grid stability applications. Applications include:

   • Uninterruptible Power Supply (UPS) for critical infrastructure, such as data centres and hospital emergency systems.
   • Instantaneous backup for high-frequency industrial machinery, ensuring no downtime in automated manufacturing.
   • Voltage regulation in renewable energy microgrids, stabilizing solar and wind power fluctuations in smart buildings.

D) Thermal Energy Storage Systems (TES):

TES systems store electrical energy as heat in insulated containers using ice, wax, salt, or sand. These systems transform buildings into thermal batteries through storage media, refrigeration components, piping, pumps, and controls. TES captures energy from renewable sources for later use, addressing approximately 50% of building energy demand through space conditioning, water heating, and refrigeration. The technology comes in cryogenic and high-temperature varieties, reducing energy consumption while increasing load flexibility. The primary types of TES systems include:

1. Sensible heat storage: These systems store thermal energy by changing the temperature of a storage medium, such as water, rocks, or ceramics. As energy is added, the medium's temperature rises proportionally. Typical applications include hot water storage tanks and concrete thermal mass systems.

   • Space heating, district heating, and cooling systems.

2. Latent heat storage: These systems use phase change materials (PCMs) to absorb or release large amounts of heat during phase transitions (e.g., from solid to liquid). This allows for efficient energy storage and release at nearly constant temperatures. For example, ice storage systems, where water freezes during low energy demand periods and melts to cool during peak times. Applications include:

   • Air conditioning & thermal buffering in buildings.

3. Thermochemical storage: These systems use reversible chemical reactions to store and release thermal energy. It involves converting electricity into high-temperature heat, typically around 500°C. An electrical heater initiates the charging process, storing heat in materials like magnesium oxide bricks or molten salt. During discharge, the stored heat generates steam to drive turbines, producing electricity. This method is efficient for large-scale energy storage and often integrates with renewable energy sources. Applications in Smart Buildings include:

   • Geothermal heating and cooling systems regulate indoor temperatures by utilizing the Earth's consistent underground temperatures, reducing reliance on conventional HVAC systems.
   • Solar water heating systems store excess heat from solar panels during the day and release it for heating at night or during cloudy periods.

Figure 2: Methods of thermal energy storage: (a) sensible heat; (b) latent heat; (c) thermo-chemical storage

Conclusion

Energy storage in smart buildings does more than just save power—it transforms how we live. These systems actively manage energy use, boost efficiency, and promote the adoption of renewable energy sources, creating resilient and eco-friendly spaces. Technologies like predictive analytics, building automation, and real-time monitoring, help smart buildings to cut carbon footprints. As a result, it improves operations and enhance the quality of life for occupants.