With the proliferation of renewable energy production facilities around the world, especially wind and solar, the intermittent and non-constant production of these renewable sources is a problem that calls for a solution. A Canadian company, Hydrostor, thinks it has the solution: balloons filled with compressed air.
The Toronto-based company carried out its first test by sinking several large balloons in Lake Ontario, then using renewable energy to power a compressor, which fills the bags with compressed air. Later, when electricity is needed, the air will be drained from the balloons and a turbine will turn on. The result was the world’s first aquatic compressed air storage. This Hydrostor animation explains how your system works:
Using compressed air to store energy is not a new idea. The first of these systems appeared in 1870, by this time compressed air was stored in underground caverns, in pipes and even in small tanks to power cars and locomotives. Variants of the idea of underwater storage have been studied since the 1980s.
Hydrostor’s CEO Curtis Vanwalleghem tells us his company started researching this technology four years ago as part of a side project to a wind farm it wanted to develop.
The concept is quite simple: when the balloon is anchored underwater, at least 25 meters deep and ideally 100 meters or more, the weight of the water naturally puts the air under pressure, allowing more air. to enter, and therefore energy, to be stored in a certain volume. (The pressure increases by about 1 atmosphere every 10 meters.) At depths greater than 500 meters, Garvey says, “the cost of this storage becomes negligible compared to the costs of the energy conversion machines.”
One of problems found a way capture the heat released by the compression of the air then use it to heat the air which cools during expansion.
The air can reach temperatures of up to 650 ° C during compression. If you don’t recover this waste heat, you lose efficiency.
The solution was a heat exchanger, off the platform, linked to water tanks with insulating walls. The Efficiency reached would be between 60 and 80%.
In Toronto, flexible accumulators, as Hydrostor calls them, will be deployed to a depth of 80 meters and are expected to be able to supply about one megawatt of electricity for about 3 hours.
Although the technology is still in the experimental phase, the need for this type of energy storage is obvious. Much of the world’s population lives near the coast. One of the causes of energy losses occurs in transport, with this system we want to keep energy production and storage as close as possible to its load.
Today, the company presents its latest project, Hydrostor Terra, a system that uses excess electricity to compress air and store it underground in specially constructed reservoirs.
Later, when additional electricity is needed, the pressure is released and used to drive turbines that generate electricity. What sets the Hydrostor process apart from other compressed air storage systems is that the air released from storage is usually heated with natural gas to gain efficiency in the turbines. Naturally, burning a fossil fuel harms the zero-emission premise of using renewable energy.
But by compressing a gas, you generate heat and the Hydrostor system captures that heat and stores it in a thermal management system. When pressurized air is released, the recovered heat is used to raise the air temperature instead of burning natural gas. Hydrostor claims their system is 70% effective. Traditional systems that use natural gas to heat the air have an efficiency of about 42 to 54%. Battery-powered storage systems can be up to 95% efficient.
AECOM works with Hydrostor to build underground tanks specially designed for compressed air.
Although the exact details and prices depend on the project, it is estimated to be between $ 1,000 and $ 2,000 per kilowatt.