Thomas White Global Investing
Green Reports

May 26, 2010

The Green Report

Gravel Battery Might Increase Wind Energy Reliability
Gravel Battery might Increase Wind Energy Reliability

In 2009, Isentropic had raised around $1 million in funding and recently received another $2.3 million in 2010.

Nature can be fickle. And the wind and the sun often are the most unpredictable. In recent times, due to climate change, they have become all the more erratic. The flow of energy stops the moment the sun hides behind the clouds or the wind ceases to blow. So harnessing clean power from these elements is not an easy task.

But a UK-based startup named Isentropic may have found a solution to combat the capriciousness of nature’s elements. The company has invented giant gravel batteries that can store electricity for the times when the forces of nature decide to play spoilsport.

Today, one of the challenges of renewable energy usage is the dilemma of storing energy. One of the few solutions that exist, and one of the most popular, is a water pump technique named as “pumped hydro”. Water is pumped from a lower to a higher point and stored in a reservoir. When electricity is needed the water is let out and its flow creates the energy required. But this type of pumped water storage requires vast amounts of space and is expensive.

Isentropic, the creation of former UK Civil Aviation Authority engineer Jonathan Howes, is offering a more practical alternative, which harnesses the energy from pumped heat instead of water. Using gravel as its mainstay for electricity generation, Isentropic’s Pumped Heat Electrical Energy Storage (PHES) technology consists of a heat pump that can both store and release energy when desired. This heat pump applies thermodynamic principles to leverage the gravel’s ability to retain heat. To understand the concept, just imagine walking barefoot on sun-baked gravel, only later to return in the cool evening, to find the gravel still warm.

“If you bolt this (heat pump) to a wind farm, you could store the
intermittent and relatively erratic energy and give it back in a
reliable and controlled manner,” explains Howes to The Guardian.

So how can heated gravel produce electricity? Simply put, Isentropic’s heat pump creates electricity from the stored heat energy in the gravel, which acts as a thermal battery. Basically, two large containers of gravel are kept side by side. A machine pumps hot argon gas into one and heats the gravel up to temperatures of 500 degrees Celsius. Once the gravel is heated up, the same gas is fed into the second container where its temperature is dropped to -150 degrees Celsius. This process is reversed to generate electricity.

While pumped water energy storage is costly and impractical, Isentropic claims that its PHES plant would occupy 1/300th of the area at a cost of $55 kWh. Mark Wagner, the company’s chairman, points out that their system is made up of low-cost ingredients like heat, gravel and argon gas and is easy to rig up. The PHES plant is flexible too. It can be deployed underground or underwater, which is extremely useful for offshore wind stations. Moreover, the company pegs its heat pump system’s energy efficiency levels at 80%. According to Howes, his gravel batteries are very durable, and even if left unused, in three years, only half the energy would seep out.

Isentropic does have a few believers. It was selected by the U.K.’s Technology Strategy Board as one of Britain’s most promising clean technology startups, among 20 others. The firm met potential investors in the Silicon Valley in the U.S. early this year, as part of the 2010 “Clean and Cool” trade mission.

John Loughhead, executive director of the UK Energy Research Centre, appreciates the fact that Isentropic has managed to work out a simple way, which in theory, would implement an otherwise expensive and technically complex process. Yet, he remains skeptical. “The question is does it work?” he asks in The Guardian. According to Loughhead, the temperature differences are too drastic and gravel particles could block the system and potentially cause damage.

To answer his detractors, Howes is busy building a pilot plant that has the capacity to store 16 mWh of energy, which is sufficient to power thousands of homes. He is also seeking sponsorship from an unnamed utility company to help him construct a large-scale demonstrator system.

If proved to work, the PHES system would be invaluable to the U.K.’s planned green revolution. In the 2009 budget, the government pledged a 34% emissions cut by 2020 and plans are on the anvil to dot the English landscape with thousands of wind turbines.

And the PHES system could potentially supply the energy to set those turbine blades whirling. David Bott, director of innovation programs at the Technology Strategy Board sums up, “Isentropic has done something very exciting by revisiting scientific theory and coming up with a new technology that answers the need to match the generation of electricity with its use.” Hopefully, PHES will prove to be a steady and practical solution in the face of a fickle mother nature.




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