In the environment-conscious world of today, the search for a feasible and efficient supply of renewable energy is something akin to the quest for the Holy Grail. A group of engineering students at The University of Queensland, however, may have the answer.
Unveiled at a media conference last week, UQ engineering team M-CAES have developed a few simple yet inspired modifications to existing energy storage systems that could be the solution to one of the renewable energy industry’s biggest problems.
Renewable energy, because it is produced by natural elements such as the wind or the sun, does not provide a consistent flow of energy. When the wind isn’t blowing, for example, energy supply ceases. To counter this, the industry uses compressed air to essentially store energy underground, which can then be drawn upon as necessary.
The energy initially captured by solar panels or wind turbines is used to run a nearby air-compressor, which in turn compresses air into a large underground storage space, often a natural cavern. Hours later, when the energy is needed, the air can be expanded and released to run power generation turbines, which create electricity once more.Before the re-expanded air can be fed into the turbines however, it must be heated. This, according to M-CAES lead engineer Jack Porter, is the key problem.
“It’s just like using deodorant on your skin and it feels cold. When you re-expand the air after it’s been compressed, you usually need to use natural gas to re-heat it. Unfortunately using natural gas reduces the efficiency of the process, because you have to put energy in to get energy back out; it also generates carbon emissions.”
Whilst compressed air energy storage is not a new idea, the heating of the re-expanded air is where M-CAES comes in. Advanced adiabatic compressed air energy storage (AA-CAES) will capture heat exhaust from the compressing process and utilise it when heating the re-expanded air.
“It eliminates the need to use natural gas. Just like expanding a gas cools it down, the opposite is also true, and when you compress a gas it generates a lot of heat. What we want to do is use a thermal storage system to capture that heat and re-use it to warm the air.
“Just like a clay pot can stay hot hours after it’s been taken out of the oven, we use special bricks which have excellent heat retention, and are well insulated, so that when the heat is generated off the compressor, it is stored in the bricks for 12 hours while the air is stored. Then while the air is expanded, you pass it over the bricks.
“Employing this stored energy to reheat the air upon re-expansion negates the need for external heat sources and creates an economical and emission-free process.”
With the world’s dwindling fossil fuel stocks expected to run out within two generations, renewable energy is more important than ever. The Australian government predicts a 20% dependence on renewable energy by 2020. Accordingly, the M-CAES team, made up of Jack Porter, Rachael Jukes, Renee Nicholson, Gregor Tischljar, and Daniel Rowley, aim to have an AA-CAES plant up and running by 2018.
“The need to address climate change and reduce global CO2 emissions means that renewable energy sources are going to play a critical role in the development of a sustainable energy industry.“While CAES has been implemented commercially in several locations around the world, the new AA-CAES technology is the first technology to offer a process with a competitive efficiency and no greenhouse emissions.”
