Energy storage analysis

Online Editor

Ed Ansett explores sustainable infrastructure and the future of energy storage

Sustainability agenda-driven changes at an industrial scale are probably most visible in the transition of the energy sector. In view of this, the power system of the future is unlikely to be solely reliant on infrastructure that spins up in faraway power stations in response to demand for electricity.

Solar and wind energy, captured and turned into electricity when the sun shines and when the wind blows will be stored until is it needed. And energy storage is going to be pushed to the edge of the network.

Interest and investment in energy storage is rising. Some systems being proposed are new and some based on existing (and in the case of kinetic energy, ancient) technologies. Many may be small in scale, but some of those currently being explored are gigantic.

Here we offer a high level ‘what is...’ list of just some of the technologies in use today and those that could quickly find their way into data centre power systems.

Gravity storage

Gravity storage has the potential to deliver gigawatts of power. A gravity storage scheme involves a piston with millions of metric tons raised by water pressure to store energy. As the piston descends this pushes water through a generator turbine to deliver electricity.

Prototype gravity storage projects are being developed by firms such as Scotland-based, Gravitricity, which is building a prototype 250kW gravity power unit using towers. It says its units could deliver peak power outputs of between 1MW and 20 MW, functioning for up to 50 years with no loss of performance to deliver full power in under one second.

At the other end of the scale, gravity storage concepts are based on the hydraulic lifting of a large rock mass using water pumps. The rock mass acquires potential energy and can release this energy when the water that is under pressure is discharged back through a turbine.

According to Heindl Energy Gravity Storage, a rock mass with a diameter of 250m would result in a storage capacity of 8GWh. It says gravity storage of this type is a concept with which unprecedentedly large quantities of power can be stored over long periods.

Compressed gas storage

Liquid air energy storage (LAES) stores liquid air inside a tank where it is then heated to its gaseous form, and the gas is used to rotate a turbine. Compressed gas storage systems have high reliability and a long-life span that can extend to over 30 years.

Also referred to as cryogenic energy storage (CES), LAES is a long duration, large scale energy storage technology that can be located at the point of demand. The working fluid is liquefied air or liquid nitrogen (~78% of air).

Kinetic energy systems

Flywheels have been used to store energy for thousands of years. Today across the world, tens of thousands of flywheels are used for short-term energy back-up or ride-through power. As the name suggests, kinetic energy is energy generated via motion of an object. In classical mechanics, kinetic energy (KE) is equal to half of an object's mass multiplied by the velocity squared. Kinetic energy = ½ (mass)*(velocity)2.

A flywheel system stores energy mechanically in the form of kinetic energy by spinning a mass at high speed. Electrical or mechanical inputs keep the flywheel rotor spinning until it is called upon to release the stored energy. The amount of energy available and its duration are governed by the mass and speed of the flywheel. In the US, Beacon Power is building a 20MW flywheel system, said to be the world’s largest. Development projects are also underway in Scotland for large flywheels to support the UK power grid.

Lithium-ion batteries and BESS

Higher energy density, rechargeability and management has seen the range of uses for lithium-ion batteries increase from consumer electronics to cars and now at industrial scale. Li-ion energy storage is becoming a key component in renewable energy distribution for meeting carbon emission cuts.

Compared with lead acid batteries, li-ion benefits include lower weight and more compact footprint, superior energy capacity, lower battery discharge through efficiency, extended lifespan; software optimisation enhancement and remote management capability.

There are questions about how sustainable li-ion is when measured across its entire lifecycle, from sourcing raw materials to operation, disposal and recycling. However, there is a huge amount of investment and activity in the li-ion recycling space and the use of li-ion battery systems in data centres, industrial and commercial sites of all sizes will continue to grow in the near term.

One such example from SSE is its battery energy storage system (BESS) investment through the acquisition of a 50-MW battery storage site in UK in South West England.

Nothing is entirely carbon free

All material uses, whether mining for raw materials for batteries, forging steel for flywheels or pouring cement and building large gravity or compressed gas infrastructure, will come with an embodied carbon cost. But if it can deliver low or no carbon emitting energy for decades, it is likely to be considered a price worth paying.

Ed Ansett is chariman of i3 Solutions Group


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