A short review of thermodynamical electricity storage technology – part 2 – Liquid air technologies

Following my last post about technologies for storing electricity using thermodynamics, i’d like to introduce you to the Liquid Air Electrical Storage (LAES) concept.

Liquefied air is known since the 1900s, independently  with the Claude process (giving birth to the company Air Liquide) and the Linde process (and its rival company Linde).

Liquefied air (at approx -190°C and rather low pressure) can store a big amount of energy that can be restored into electricity through revaporization and expansion to atmospheric pressure.

As of today, technology is considered mature and a 300 kWe pilot plant has been started by Highview power in the UK.


This technology is said to have a drawback with is to have a rather low electrical efficiency. I personally found it very interesting.

Lire la suite


A short review of thermodynamical electricity storage technology – part 1 – Compressed air technologies

Hi there !

Cleantech industry is looking for new technologies to store electricity, storing meaning both consuming electricity during a moment of the day and delivering it back at another time. While a great deal of articles are about how battery would change the world (or not), my personal bet is that thermodynamical technologies are the best suited for mid to large scale distributed energy storage (from 1 to 100 MW). So this is a review of some interesting technologies :

  • Compressed Air Electrical Storage (CAES) and Advanced-Adiabatic CAES (AA- CAES)

Storage of electricity through compressing, storing and expanding air is a process well known since the 70s. Here below is main concept (from http://www.arup.com) :



Two existing units of big capacity have been built (and are still in operation), using ground cavern to store the compressed air :

  • in 1978, the 290 MW Huntorf plant, in Germany, with discharge capacity of 3 hrs.
  • in 1991, the 110 MW McIntosh plant , Alabama, USA with discharge capacity up to 26 hrs. This units works in conjunction with heat recovery fro gas turbine outlet to provide additional energy for the air discharge.

Others prototypes units are said to be in operation, or under development, including for surface CAES, meaning that the air is not stored anymore in cavern, there allowing more places to allow such installation.

– One key drawback of CAES plant is their low efficiency (30 to 40%). Storing separately heat and compressed air in an adiabatic system allows to improve drastically the efficiency of the process up to 65%. You can understand it quiclky with the ADELE concept described :

– Another challenge to overcome is to maintain a relatively stable pressure at turbine outlet during discharge. While emptying the storage, pressure goes down, and therefore, both turbine power (because there is less air flow) & efficiency (because the turbine works out of its nominal point) are reduced.

Among the new developments, you may find the lightsail concept interesting combining a piston power block (reverse generator or motor engine), a close to isothermal compression and featuring a heat capture & storage system. Some additional technical description can be found on one of the founder blog here 


Another concept that may be promising is the Hydrostor concept of storing air underwater. Therefore, maintaining a constant pressure while discharging the air storage is possible. With the following video, you may share the concept with your 4years old kids.



Lire la suite

Some Historical background about the ORC technology

Hello all,

I found an interesting page about the ORC technology from the KCORG, and particularly about history of the ORC technology : ORC machine existed before even W. M. Rankine himself

While William M. Rankine (Scotland) developed a theory of the steam engine in 1859, engines using alcohol or ether as working fluid were designed as early as 1825/1826 (Thomas Howard). However leak rate and market price of the working fluid did not allow a full development of the technology for economical reasons.

It is worth also to mention the Du Trembley initiative in 1850, with a cascading steam/ether engine for ships. Du Trembley, an engineer from Lyon in France, developed its solution for ships on the Rhône river, reducing by more than 2 the specific consumption of the engine ! Invention was called « procédé à « vapeur combinées » », allowing to reach a better expansion in 2 stages with 2 fluids :

  • first stage with steam at 6 bar
  • second stage with ether vapor at 2 bar (vaporized at 60°C and condensed at 20°C)

Du trembley 2

It is worth to note that multiple stages expansion with saturated steam was not technically possible, and available steam boiler were not designed with superheaters.

Du trembley

While it is said that production of such motors was interrupted in 1856 due to an explosion in Bahia of such ship (1),  but others authors (2)  mention that explosion happened for other reasons, and that the production and use of the technology kept being used for navigation the following decades.



(1) Closed Power Cycles: Thermodynamic Fundamentals and Applications, by Costante Mario Invernizzi, page 119

(2) Vapeurs sur le Rhône, Jean-Marc Combe, Bernard Escudié, Jacques Payen, Presses Universitaires Lyon, 1991

note : Picturesare  from (2) Vapeurs sur le Rhône, Jean-Marc Combe, Bernard Escudié, Jacques Payen, Presses Universitaires Lyon, 1991.

Combining Geothermal Energy with CO2 sequestration

Today, i’d like to entertain you with recent studies with improvements of geothermal technologies.

As you know geothermal energy use the heat from Earth crust/core to provide energy (heat, electricity or even chill). Most common applications for generating electricity are steam power plant (flash or dry steam) and binary power plant. In both cases, water is use as a thermal media, heated by the rocks and then pumped to the surface to be used directly in steam turbine or go through a heat exchanger and heat/vaporize a second fluid (working fluid), in the case of binary power plants.

If finding temperature on the deep ground is not a big problem (generally between 600m for volcanic regions and up to 6000 m for new generation of European deep geothermal projects), the key problem is to find water in the reservoir, and a good permeability so that the reservoir is not quickly depleted. Some technologies in development, known as EGS (for Enhanced Geothermal System) consider injecting water in some wells and pump it in others (see the project of Soultz, in East of France, a pioneer but costly pilot plant using this technology).

Recently, some researchers have been looking into using transcritical CO2 as a thermal media, instead of water. Transcritical means that the CO2 works about its critical point : at high pressure and high temperature it is not a gas, nor a liquid, but something in between and physical properties of the fluid are different from the two previous states. Some of the properties of transcritical fluids can be interesting, like low viscosity leading to low pressure drops.


CO2 is interesting for several reasons : it is a non dangerous, natural and cheap fluid ; its is abundant, not patented and free of use ; it is transcritical at relatively low temperature (but still high pressure); we would like to reduce its concentration in the atmosphere, and it is very likely that we would have to store some into the ground, to reduce global warming.

Some researchers at Berkeley National Lab in California (USA), have proposed an interesting technological solutions, where transcritical CO2 is used as thermal fluid to recover the heat from the deep (3200 m), then pump it and expand it directly in a CO2 expansion turbine

Cycle4View of the system by Berkeley lab

While costs of drilling cannot be neglected (you may consider roughly 5 Meuros per well), the system offer the possibility to store some CO2 in the process in the dead volume of the reservoir.

In area where the earth crust is hot, but very no/low water (typically where EGS would be useful) use of CO2 could be interesting.

Lire la suite

New video for Enertime ORCHID solution for Waste Heat Recovery

Hey there !

I’d like to share a video where you could see what a 1MW ORC module for waste heat recovery looks like.

This plant has been started in november 2012. It is the first machine we built at Enertime, all design including the turbine has been done by Enertime and its technological partners.

Enjoy !

Comments are in french, i guess that subtitles in english are or would be available.



Caribbean Energy Forum (CREF 2013)


Next week, I will be attending the CREF in Aruba to discuss energy efficiency and clean&distributed power.

In the Caribbean, electricity can rocket above 300 USD / MWh (typically x3 to 4 compared to Europe).

Subject for discussions related with Organic Rankine Cycle Technology :

– Adding +5% to diesel power plant, by transforming the extra heat at the chimney and cooling into electricity;

– Low temperature geothermal power in the Caraïbes;

– Small distributed power unit using green waste and biomass;

– Ocean Thermal Energy Conversion, with Ammonia turbine and heat source at 28°C (surface water) and cold source from 10 to 5°C (1000m depth).