Dirt Cheap Storage

Wednesday 25th June 2014

Renewable energy is really taking off, growing by a factor of 53 over the last nine years, but there is a dam holding back the flood - that dam is energy storage. Hence, every bit of research and development in improving energy storage is another brick out of that dam.

Today’s post reveals a development that has led some to wonder if this is the breakthrough the renewable industry has been waiting for?

The problem with renewable energy generation, and nuclear power, is that the energy supply is intermittent, often producing more than is needed or at other times not enough power - so the importance of good storage to hold the surplus, until it is needed.

What you need is something that is readily available, something that can be used to make large-scale energy storage. So how about using dirt? Which is exactly what UK company Isentropic are looking to promote.

They have developed a heat-pump system that uses the thermal mass of small rocks, practically gravel. The system is a highly reversible, gas cycle machine that works as both an engine and a heat pump. It is the first time that a reversible system has been developed both to store and recover electricity using a thermodynamic approach.

The received wisdom is that thermodynamic devices are not very reversible, but that certain thermodynamic processes in isolation can be highly reversible. This view led them to the direct incorporation of heat exchange to a storage medium within the gas circuit of our heat engine. The key innovation is the reduction to four highly reversible processes within the cycle with integrated heat exchange to the storage medium.

The storage system uses two large containers of mineral particulate, gravel, which is basically dirt. Electricity is used to pump heat from one vessel to the other resulting in the first container cooling to around -160°C and the second container warming to around 500°C. The specially designed heat pump machine can be thermodynamically reversed to operate as an engine and the electricity is recovered by passing the heat from the hot container back through the machine to the cold container, while the machine drives an electrical generator. During the process, the containers return close to their original temperatures.

The innovations that have allowed high efficiency to be realised are primarily concerned with ensuring that each individual process within the system is performed with minimum losses. This results in an electricity-in to electricity-out (round trip efficiency) in the range of 72 to 80%.

Is this the breakthrough that will tip the balance for renewable energy storage? Time will tell, but it seems to be a viable system, but it is not the only one that could be the answer - more than likely there will be several competing and complementary systems available in the future.

To understand the Isentropic system, watch their video below:

Categories: General, Renewable, Reviews, Technology

Wednesday 25th June 2014


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