Maltese researchers developing compressed air ‘battery’ to store excess wind energy

A look into the future could see the waters around Malta dotted with floating wind and solar energy farms supplying clean electricity to an energy-hungry country.

But no matter how far into the future we look, wind turbines and solar panels will remain intermittent sources of energy. In short, their output depends entirely on nature’s whims – if there is no wind, turbines will not turn and if it’s a cloudy day, the solar panels will be useless. Additionally, a windy night may produce too much energy when the demand is low.

To overcome this difficulty, these technologies will have to be supported by energy storage infrastructure that collects the excess energy produced on good days for use when nature is unkind or when demand grows.

This is where the University of Malta is stepping in with a project to study the use of subsea pipelines to store energy generated from offshore wind and solar farms.

The project, dubbed SAICOPES, is being funded by the Malta Council for Science and Technology, and aims to address the emerging need to invest in long duration energy storage infrastructure.

The mismatch between the renewable energy supply and consumer demand over lengthy periods implies that storage technologies should be able to hold energy for many hours, typically between eight and 24 hours.

Researchers say that relying solely on Li-Ion batteries, currently used in mobiles, laptops and electric vehicles, is unsustainable due to the short lifetime and use of crucial materials such as cobalt.

They believe that adding mechanical-based technologies, such as compressed air, to the technology mix will be essential for a smooth transition towards meeting the ambitions of the EU Green Deal.

The researchers are looking at subsea pipelines similar to those already in use that transport oil, natural gas and water across large distances.

The SAICOPES project is evaluating how countries such as Malta can leverage established offshore pipeline technology to be able to store energy in the form of compressed air.

The researchers say that excess energy from offshore wind or solar farms can be used to power subsea hydro-pneumatic compressors that would pressurise a network of subsea pipelines using a combination of air and water to store energy.

During periods of high consumer demand, the stored compressed air is released to drive expanders and generate electricity.

Researchers Charise Cutajar and Luke Aquilina from the university’s Department of Mechanical Engineering are developing comprehensive computer models to simulate the operation and efficiency of such systems.

Engineer Tonio Sant, professor at the Department of Mechanical Engineering, is coordinating the project. He believes there are immense benefits in exploiting subsea pipelines for compressed air energy storage.

“Apart from having a long lifetime of at least 30 years, which is at least threefold more than that of batteries, the compressed air pipelines are located offshore thus avoiding the need for additional land requirements to accommodate energy storage infrastructure,” Sant said.

He added that the same pipelines could also be used to interconnect different countries to enhance security of supply of renewable energy.

“The benefits for a densely populated island like Malta, located on the periphery of Europe, cannot be underestimated,” Sant said.

Daniel Buhagiar, CEO of FLASC BV that is supporting the university team on industrialisation aspects of subsea compressed air technologies, said there was keen interest among oil and gas players in such niche opportunities for diversifying present activities and contributing to the green transition.

Malta has embarked on an ambitious process to exploit the sea around it and floating wind and solar farms are a key part of that vision.

The Energy Ministry recently issued a market consultation for projects to install solar farms at sea.

The purpose of the preliminary market consultation is to gauge market readiness for nearshore floating solar technology projects.

These 50MW farms are expected to be implemented within the sea area extending up to 12 nautical miles off the Maltese coast, at a potential offshore site south of Marsaxlokk, with a corresponding cable route to Delimara Power Station.

The government is also gauging interest for floating renewable energy projects in Malta’s Exclusive Economic Zone (EEZ), which covers six potential areas outside the 12-mile limit of the territorial waters.