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What Are Water Batteries and How Do They Work?

As the share of electricity generated from renewable yet intermittent sources grows, effective grid-scale energy storage solutions become increasingly vital. Water batteries, also known as pumped hydro storage, are emerging as a sustainable battery option with enormous potential to facilitate clean energy at scale.

The Early Evolution of Water Batteries

While the modern concept of pumping water uphill to store energy dates back to the late 1800s, the first working water battery was unveiled in 1930 in Connecticut. Engineer Dr. Boris Bannister developed a distributed pumped hydropower design using two existing reservoirs located 10 miles apart and 1000 feet different in elevation near New Milford.

Water could be pumped uphill to the higher Graf Reservoir during periods of excess electricity generation. To discharge the battery, valves opened to let water flow downhill through pipes back to the lower Candlewood Lake, spinning turbine generators along the way to produce electricity on demand.

This first operational closed-loop system effectively stored energy in the form of water‘s potential gravitational energy. However, only a handful more pumped hydro storage (PHS) facilities were erected over the next few decades. Favorable high elevation terrain was required, greatly limiting site options. Most installations became immobilized assets once built, restricting relocation if conditions changed.

Beginning in the 1990s, adjustable-speed pump turbines were incorporated to boost efficiency by matching Pump and turbine speeds precisely to grid frequency changes. Variable speed operation widened the effective operating range considerably.

Recent engineering innovations have introduced modular and standardized water battery designs to reduce the geographical restrictions of early systems. Startup GrafTech produces container-sized water battery modules which can be combined to achieve scalable storage capacity almost anywhere sufficient water access exists. New pumped storage tower architectures further shrink the physical footprint.

Surging Global Renewable Generation Driving Adoption

As the world moves aggressively to decarbonize electricity production this century, renewable energy is seeing massive growth. Total global renewable generation is projected to swell over 280% from 2020 to 2050 according to BloombergNEF’s New Energy Outlook 2021.

Most of this influx will come from inherently variable solar and wind resources which depend heavily on daily weather conditions. Compared to fossil fuels, effectively integrating such high volumes of intermittent renewables necessitates a more dynamic and resilient electricity grid.

Energy storage is the critical missing piece which can balance volatility in renewable generation with grid reliability needs. By charging up during sunny, windy periods and discharging through cloudy low-wind lulls, storage smooths net load profiles. The renewable bounty is stored for use whenever required instead of being curtailed.

Long-duration storage with discharge periods exceeding 10 hours will be especially pivotal. It cost-effectively enables renewables to displace fossil fuel "baseload" generation once thought indispensable for reliable grid function.

With benefits like 70-80% round trip efficiency, minimal geographic constraints, and low long-term operational costs, water batteries are positioned to provide the bulk of future large-scale, long-duration energy storage required.

Real World Renewable-Water Battery Systems

Cutting edge projects around the world demonstrate how effectively water batteries integrate solar and wind resources and ensure reliable, sustainable electricity.

The Kidston Pumped Storage Hydro project commissioned in Australia provides a model for collocating water battery storage with large solar plants. The 250MW Kidston facility pairs with the adjacent 150MW Kidston Solar Farm comprised of over 500,000 PV panels.

During sunny middays when solar output exceeds local demand, excess energy is stored by pumping water uphill to the upper reservoir. This stored solar energy can then be dispatched on demand during evening peaks and through the nights. By shifting generation profile to better match demand, the integrated system increases self-consumption of the renewable energy generated.

Initial testing indicates roundtrip efficiencies exceeding 80% with negligible daily water losses even in Australia‘s hot climate. Financial returns are strong as well – electricity sold at peak rates in the evenings is more than double the midday solar price.

In Germany‘s Black Forest region, the 1414 Technology water battery demonstration facility couples directly with local wind turbines. Featuring a 130 foot tall pressure tower design, the small footprint system generators over 2MWh per cycle.

When ample wind energy is being produced locally, excess generation spins subterranean turbines which pump water up into the tower against gravity. As regional wind supply slows later on, outlet valves open to send high-pressure water crashing down and re-spinning turbines to regenerate electricity.

Still in the pilot phase, roundtrip efficiency stands at 70% for this innovative tower architecture. By providing a pathway for far greater wind energy utilization in space constrained regions, the potential is immense. 1414 Technology envisions towers storing GWh levels deployable anywhere sufficient water access exists.

Cutting Edge Advancements to Unlock Wider Adoption

While most current global pumped hydro storage utilizes mountainous terrain, emerging novel architectures reduce geographic constraints that previously limited growth. Companies like 1414 Technology, Hydrostor, and Energy Vault are pioneering systems with flexibility akin to containerized data centers.

Energy Vault has developed a composite tower design combining conventional hydro with cranes and special concrete blocks. The composite tower reaches heights up to 400 feet using far less concrete and steel than traditional structures. Further, block lifting motor energy is partially recovered during lowering.

Smart predictive algorithms control block raising/lowering to match supply and demand needs while optimizing generation assets and electricity prices. Round trip efficiencies currently exceed 80% for the technology.

Hydrostor takes an underground approach – using excess electricity to compress and inject air into underwater balloons. As compressed air displaces water, it is forced uphill into an above-ground holding tank. Discharge reverses the process, pushing water downhill to spin hydro turbines.

With site topology flexibility, Hydrostor systems have proven well suited for coupling with wind farms or solar parks. Container-sized Hydrostor models support modular capacity expansion as needed. Minimal evaporation and chemical-free operation ensure reliable, low-cost operation.

Comparison to Other Rechargeable Battery Technologies

While lithium-ion batteries have seen massive adoption in electric vehicles and behind-the-meter applications, limitations remain in providing long-duration grid storage. High material costs also challenge lithium‘s potential to scale affordably to the multi TWh capacity ranges required.

Water batteries compare very favorably to lithium alternatives on metrics like discharge duration, lifecycle stability, and operational costs. The following table summarizes how top rechargeable battery technologies stack up.

Battery Type Cycle Life Discharge Duration Energy Density Round Trip Efficiency Operational Years Safety
Lithium Ion 1K-10K cycles 2-4 hours 150-250 Wh/L 75-90% 5-15 years Thermal runaway risk
Flow Battery 10K-13K cycles 10+ hours 25-50 Wh/L 65-75% 20+ years Low risk
Pumped Hydro Unlimited cycles 10+ hours 0.5-1.5 Wh/L 70-80% 50+ years Minimal risk

With unlimited cycle life, low operational costs, and long system lifetimes, water batteries stand apart on metrics decisive for grid-scale storage applications. New architectural advancements are set to unchain deployments from geographic limitations as global renewable generation swells.

Outlook for Exponential Growth

BloombergNEF projects global energy storage installed capacity will soar over 200 times from 9GW / 22GWh today to 2,850GW / 7,300GWh by 2050. Of this, an estimated 60% will be medium/long duration storage well aligned with pumped hydro storage capabilities.

UBS forecasts US$228 billion in capital investment flowing into long-duration energy storage like pumped hydro and compressed air through 2050. Supportive policy incentives for storage-renewable pairing expected in progressive regions will further accelerate rollouts. Corporate sustainability goals are also driving behind-the-meter adoption.

Particularly in Europe, major expansion of cross-country transmission infrastructure will unlock greater sharing of renewable resources across entire continental grids. Integrating massive volumes of distant solar and wind depends heavily on geographically flexible pumped storage capacity scaling in tandem.

With proliferating pilot projects proving feasibility across an array of site conditions, water batteries are on the cusp of exponential global growth. Uniquely positioned to meet surging long-duration energy storage demand, they will play an integral role in realizing our zero-carbon future.