Energy storage allows electricity to be saved for later use, reducing demand on the grid and providing backup power. ARPA-E supports research into long-duration storage technologies like lithium-ion and redox flow cell batteries.
Pumped storage technology has long been available, yet now there are megawatt-scale technologies entering the market that provide instantaneous power delivery during grid changes. Unlike traditional generation methods, such technologies can deliver power instantly within seconds of an event occurring on the grid.
Hydroelectric Storage
Pumped storage hydropower is one of the oldest, largest, and best-established forms of grid-level energy storage, offering energy balancing, grid stability and storage capacity as well as providing other ancillary services such as network frequency control and reserves.
It works by connecting two water reservoirs at different elevations and pumping their contents through a turbine to produce electricity, with energy released during periods of high demand for it to be released at lower cost on nights and weekends when electricity prices drop significantly compared to peak periods. At nightfall and weekends when electricity rates decrease further still, however, energy from the grid is used instead to pump water back uphill towards its upper reservoir and recharges itself using lower cost energy from grid to pump the excess back up to its source reservoir.
Pumped storage can help facilitate the integration of renewable energy sources by mitigating their intermittent nature and improving overall energy generation efficiency. Pumped storage also has other uses, including relieving strain from base load power plants during peak demand times and providing energy security benefits. Pumped storage stands out as one of the most energy-efficient forms of storage technology with higher efficiency than lithium-ion battery technology or compressed air systems.
Lithium-Ion Battery Storage
Lithium batteries have become the backbone of modern energy storage, powering everything from smartphones and EVs to grid energy storage, helping balance out renewable sources and increase overall efficiency.
Lithium-ion batteries do present certain challenges. For instance, they contain flammable electrolytes which may become toxic when damaged or mishandled; furthermore, many key materials for lithium batteries come from mines located in remote arid regions that mine conflict minerals such as cobalt.
With renewable energy adoption on the rise, comes an increased need for energy storage systems to accommodate its intermittent nature. Battery energy storage systems (BESS) store excess solar or wind energy for use later, enabling greater adoption of renewables on the grid.
Lithium-ion batteries are among the most popular BESS options due to their high energy density and efficiency, matching that of older lead acid batteries found in cars. Their operating voltage typically averages at 3.2V per cell.
Combined Heat and Power (CHP) Storage
CHP technology is an extremely cost-effective means of producing both heat and electricity simultaneously using just one process, reaching up to 80% efficiency with various fuel options available to it. When combined with thermal energy storage solutions it becomes even more effective.
By adopting a CHP system, industrial facilities and homeowners alike can become independent from large electricity suppliers while saving money on power and heating bills. Furthermore, its simultaneous generation of heat and power reduces emissions.
CHP systems have proven more resilient during natural disasters than traditional back-up generators, as evidenced by Hurricane Sandy when hospitals, apartment complexes and wastewater treatment plants powered by CHP continued providing power and heat to their communities despite having thermal energy storage that charges during low price periods and releases it when there’s high demand.
Solar Thermal Storage
Solar thermal power (CSP) systems use concentrated sunlight to generate electricity that can either be consumed directly, or stored until needed in tanks – making CSP an efficient way of producing renewable energy that’s flexible or dispatchable as needed.
Molten salt is currently used as both the heat transfer fluid and thermal storage medium in state-of-the-art CSP plants, however higher temperature systems could utilize various alternative materials as both heat transfer fluid and storage medium.
Passive solar design involves the integration of building orientation, window glazing, shading, thermal chimneys and large containers containing water or phase-change chemical material for mechanical heating needs. As the energy demands drop dramatically during less sunlit periods, thermal storage can offset energy production for periods when sun cannot shine as brightly.