Opportunity
The global transition towards carbon neutrality has accelerated the adoption of renewable energy sources like solar and wind. However, their intermittent and variable nature poses significant challenges to grid stability, creating an urgent need for efficient, large-scale energy storage solutions. Existing technologies face substantial limitations. Pumped hydro and compressed air energy storage are geographically constrained. Electrochemical batteries suffer from high costs and short lifespans. Recent Carnot batteries, which store electricity as thermal energy, offer advantages like lower costs and longer life but are plagued by critical inefficiencies. Specifically, Brayton and Rankine Pumped Thermal Energy Storage (PTES) systems suffer from low round-trip efficiency (RTE) and energy storage density (ESD), along with high self-discharge rates due to heat loss from sensible thermal storage. Liquid Air Energy Storage (LAES) also exhibits low RTE and requires complex, costly heat recovery systems. The overarching problem is the lack of a compact, geographically flexible, long-duration storage technology that can achieve high efficiency, high energy density, and minimal standby losses to effectively integrate volatile renewables into the power grid.
Technology
The present invention addresses these shortcomings with a novel Absorption-desorption-based Carnot Battery (ACB) system. Its core innovation lies in storing electrical energy in a stable thermochemical form—specifically as a concentration difference between a solution (e.g., LiBr/H₂O) and a pure refrigerant—rather than as a temperature difference. The system operates through a meticulously controlled four-process cycle (charging, pre-discharging, discharging, pre-charging) that manages heat and mass flows between a solution tank and a refrigerant tank. During charging, surplus renewable electricity drives a vapor-compression heat pump. This heats the concentrated solution, causing refrigerant vapor to desorb, flow to the refrigerant tank, condense, and store energy by increasing the solution's concentration. Crucially, the condensation heat is recaptured by the heat pump to improve efficiency. The pre-discharging process uses an internal heat loop to equalize temperatures between the tanks, amplifying the vapor pressure difference and creating a strong driving force for the subsequent discharge. During discharging, the high-concentration solution spontaneously absorbs refrigerant vapor evaporated from the refrigerant tank. This vapor flow drives an expander to generate electricity. The internal heat loop again plays a vital role by recovering absorption heat from the solution tank to reheat the refrigerant tank, sustaining the evaporation process and deepening the discharge. Finally, a pre-charging process cools both tanks to reset the system. This design fundamentally shifts the energy storage mechanism to a more stable, low-loss thermochemical state.
Advantages
- Achieves a high round-trip efficiency (RTE) of up to 48.4%, significantly outperforming many existing Carnot battery technologies.
- Delivers a very high energy storage density (ESD) of 7.6–21.8 kWh/m³ due to compact thermochemical storage, offering superior system compactness.
- Exhibits an extremely low self-discharge rate (SDR) of less than 1% after 80 days of standby, as energy is stored in a stable concentration gradient rather than as perishable sensible heat.
- Offers operational flexibility for combined power and thermal energy storage, capable of providing cooling or heating effects during discharge.
- Presents a lower levelized cost of storage (LCOS) compared to PTES systems, demonstrating strong economic viability for large-scale deployment.
- Has no geographical constraints, unlike pumped hydro or compressed air storage, enabling wider application.
Applications
- Large-scale grid energy storage for balancing supply and demand, integrating intermittent renewable energy sources like solar and wind farms.
- Backup power systems for critical infrastructure such as hospitals, data centers, and telecommunications facilities.
- Combined cooling, heating, and power (CCHP) systems for industrial plants, commercial buildings, and district energy networks.
- Off-grid and microgrid energy solutions for remote communities or islands.
- Load-shifting applications for industrial consumers and utilities to capitalize on time-of-use electricity pricing.
