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Research
    
The concept of a closed loop thermochemical energy storage system using
ammonia
If solar energy is to become a major contributor to our energy supply,
means to store it have to be found. One promising method applicable is
"closed loop thermochemical energy storage using ammonia".
In this system, ammonia (NH3) is dissociated
in an energy storing (endothermic) chemical reactor as it absorbs solar
thermal energy. At a later time and place, the reaction products hydrogen
(H2) and nitrogen (N2)
react in an energy releasing (exothermic) reactor to resynthesise ammonia.
| 2 NH3
+ Heat |
 |
N2
+ 3 H2 |
Feeding the reactors with pure reactants is possible through the natural
separation of reactants and products in the storage system: at the pressures
applied, ammonia condenses.
By ensuring that the stuff leaving each reactor transfers its own thermal
energy (sensible heat) to the stuff going in - using heat exchangers -
most of the solar energy is stored in the change in composition of the
chemicals which are kept at ambient temperature.
Main advantages of the closed loop thermochemical storage system using
ammonia
Apart from the ability of the ammonia system to allow for continuous energy
supply on a 24-hour basis, other advantages, that are not necessarily shared
by other solar thermochemical or photochemical systems, make this process
unique:
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A high energy storage density, by volume and mass.
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The reactions are easy to control and to reverse and there are no unwanted
side reactions.
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All constituents involved are environmentally benign.
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There exists a history of industrial application with the associated available
expertise and hardware.
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A readily achievable turning temperature of 400oC
to 500oC (depending on the pressure). This
helps to reduce thermal losses from dish receivers, avoids some high temperature
materials limitations, and allows lower quality (and hence cheaper) dish
optics to be used.
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All reactants for transport and handling are in the fluid phase, which
provides a convenient means of energy transport without thermal loss. This
is an important point, particularly if large arrays of paraboloidal dishes
are being considered as the method for solar energy collection.
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At ambient temperature the ammonia component of reactant mixtures condenses
to form a liquid, whilst the nitrogen and hydrogen remains as a gas. This
means that only one storage vessel is required for reactants and products.
The success with the prototype solar closed loop using ammonia confirms
that the process works. It is not only simple but also very much predictable
and controllable. Solar energy can thus be effectively captured and converted
without fears of transients.
For details on experimental and theoretical projects worked on in our
group, you can jump to the corresponding pages listed below.
On the "Facilities" page you will also find a collection of pictures
of our group, our laboratory and our concentrators.
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Exergy Analysis
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Reactor Modelling
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Dish Characterisation
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System Modelling
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Control Strategies
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Heat Exchangers
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Economic Analysis
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The world's first closed loop solar thermal system using ammonia (1kW System)
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Scaleing Up:
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15kW Closed Loop
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350kW Pilot Plant
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Catalysts
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Heat Recovery (Synthesis) Reactor
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Chiller
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