In November 2015, a world first for energy storage was unveiled in downtown Toronto
Jurisdictions around the world are turning towards renewable forms of energy – such as solar and wind – to lower emissions and protect the environment. The expected benefits offered by renewable energy are numerous but only available when the sun shines or the wind blows. So, how can these intermittent resources provide firm power needs? Solving this and other dilemmas is where energy storage plays a key role in unlocking the modern grid.

Presently, electricity is the most widely used and least stored commodity in the world. We store grain, oil and water, yet electricity is generated upon demand, which means it misses the efficiency opportunities that storage brings. Without storage, renewable energy can only provide a fraction of peak demand (typically only around 30%). On a hot summer’s day, peak load is satisfied by dispatching expensive peaking generation resources. In contrast, periods of low demand often result in selling off surplus power below cost simply because some base load generation resources don’t maneuver easily. Operating this way has worked in the past, but this inefficiency represents real costs in the power markets and higher environmental emissions.

Imagine being able to store low-cost excess power during off-peak periods and drawing upon this during subsequent high cost on-peak periods in place of expensive peaking resources. Imagine better utilizing transmission lines during off-peak periods to reduce transmission loading following on-peak periods and deferring the need for expensive transmission upgrades. Imagine converting intermittent renewable energy to a firm dispatchable resource. Imagine storing electricity underwater in the form of compressed air. Now stop imagining as a company called Hydrostor has now developed this technology.

Hydrostor
Based in Toronto, Hydrostor is a Canadian start-up that has brought Underwater Compressed Air Energy Storage (UCAES) from a dream to a reality. This past November, the company started up the world’s first UCAES located on Toronto Island and connected to the city’s distribution system with support from the utility host Toronto Hydro. Hydrostor currently has contracts to build additional facilities within the province and in the Caribbean.

How it works
At first glance, Hydrostor seems like a wild idea; however, the actual physics behind it are quite simple. Hydrostor takes electricity from the grid and uses it to run a compressor, thus transforming the energy in the electricity to pressurized air. This air is pressurized to the same hydrostatic pressure found at the depth where the system’s accumulators are located. The air travels from the compressor to the accumulators where it can be held indefinitely. When power is required by the grid, the flow is reversed and the weight of the water pushes the air back to surface at the same pressure where it’s used to drive a generator, converting the stored energy back into electricity for the grid and completing the storage cycle.

The system is mechanical in nature using no toxic chemicals, which makes it an environmentally friendly method of storage. The system’s charge rate, discharge rate and duration are all decoupled so unlike batteries, this system can be tailored to meet specific needs. In other words, you can easily design the system to soak up large amounts of electricity in a short amount of time and return it over a long period of time, say in the case of storing excess solar or wind production.

Prototypes and challenges
Designing Hydrostor was only half the battle; building a working demonstration plant was another. With financial support from both the private and public sectors, Hydrostor embarked on a journey involving complex marine engineering and construction, drilling below a lake, welding 80 tons of steel into a single connection pipeline and integrating components from Canada and around the globe to finally pump in and expel air into the working UCAES. Working in a marine environment has unique challenges. During construction, Hydrostor encountered an unexpected rogue wave causing damage to the accumulators and piping. Many other lessons were learned on all aspects of the plant, including heat recovery systems, air-water separation and underwater methods. This is what makes a demonstration so valuable: learn the lessons and incorporate improvements to strengthen future projects.

Finding a partner to test this idea
As a Toronto start-up, Hydrostor wanted to test this idea locally. Fortunately, Toronto is located on a large lake (Lake Ontario) and Toronto Hydro saw potential in the technology.

Toronto Hydro is in the midst of a massive capital program to renew and upgrade its electricity system. It’s actively exploring energy storage as a way to manage peak demand, relieve system congestion and extend the life of some of its equipment and is looking towards innovation as a way to do that. This is where Hydrostor fits into the strategy by offering Toronto Hydro a real-world application of energy storage to assess system benefits. Toronto Hydro provided Hydrostor direct access to its electricity grid and in kind project support with engineering, interconnection, host project site and operational support to test the system. Together, Toronto Hydro and Hydrostor are moving UCAES forward.

Why it’s needed
Utilities all over the world are facing challenges to provide reliable, cost-effective and environmentally friendly power. Ever-growing demand is placing higher loads on aging assets and infrastructure. Modern distributed renewable generation resources, such as solar, are introducing two-way energy flows, and electrical grids must be managed differently. Storage is an enabler for all these changes. It allows for assets to be better utilized while extending their life, addresses the inherent power fluctuations of renewable energy and gives grid operators the flexibility to accommodate new technology and demands.

Island nations are a prime example of rapidly changing grids. Currently, these nations are utilizing expensive diesel generation resources, which produce relatively high emissions and many island nations are seeking cheaper, cleaner wind and solar generation resources for their electrical needs. Without storage, most are limited to the amount of generation infrastructure they can install, leaving entire economies vulnerable to the price of oil. With a Hydrostor system, these island nations are able to break the fossil fuel habit, reducing their electricity costs and environmental footprint. Cities – such as Toronto – that face rapid population growth are another good application. As a city grows and sprawls outward, energy demand grows and transmission lines fill during the day, but have capacity at night. With a storage system able to directly support congested load centres, such as the financial core, the need for costly transmission line expansions can be deferred.

Why there’s so much buzz
Hydrostor is clearly unique in the storage marketplace. Batteries are often utilized for electricity storage but are best suited for applications under four-hour duration because of high cost and capacity degradation over the long-term. UCAES offers a scalable system for bulk energy storage beyond four-hour duration with many benefits: low capital cost, low operational costs, 30-plus years of life, minimal standby-efficiency losses and operational flexibility.

The electricity system must adapt and evolve. Hydrostor’s energy storage is part of that evolution.
 

About the Author

With nearly 15 years of manufacturing experience of oil-field production equipment in Alberta, Mr. Lewis has worked directly with all types of process equipment meeting all types of needs both domestic and abroad. He has prior experience with a number of start-ups including Delaney Energy Manufacturing, Chadco Canada, Armadillo Card Company, and most recently Environmental Electric Company, developing wind farms in Ontario.