While solar or wind farms are now contributing more energy than ever to the world's power supply, traditional energy sources are often required at peak times or to supplement renewable sources during dips in availability - at night, for example. So Canadian startup Hydrostor has invented a system of pressurised underwater balloons that can store renewable energy until it's needed, which could reduce the need for diesel or gas as a back-up source of power.

The company says its solution can last twice as long as the best batteries we have today, and at a much lower cost. The first facility has been set up in Lake Ontario near Toronto, with a series of balloons set 55 metres under the surface of the water and connected to the power grid via a pipeline.

"Compressed air's been around for 40 years," Hydrostor CEO Curtis VanWalleghem told Canadian Manufacturing. "It's finding places to store the air that's been the problem [and] why it hasn't been massively adopted. We open it up to thousands more sites because we use hydrostatic water pressure."

The material used by the underwater balloons - known technically as accumulators - is the same used to raise sunken ships from the ocean floor. Compressed air is at the heart of the system: excess energy is converted into compressed air via Hydrostor's proprietary technology, while heat generated by the process is stored as well through heat exchangers.

When required, the natural pressure of the lake is used to pump the air back to land, driving a turbine and generating electricity as it goes. The balloons in Lake Ontario are capable of holding enough energy to power 330 homes, and the developers of the system say it can be easily scaled up.

"We're now focused on commercialising this technology globally to bring our green energy storage solution to countries around the world," Vsaid VanWalleghem. "The G20 is talking about getting off fossil fuel by 2050. To do that, our electricity system has to incorporate storage so we don't need as much backup diesel and natural gas capacity - that's what this can do."

Here's how the system will work: