well as governments all over the world in recent years. An important part of these plants,
albeit a relatively lesser developed at the same time, is the storage system. The storage
system helps in resolving two important operational issues: 1) intermittent nature of the
energy source; and 2) reliability of plant operation. A good storage system is capable of
improving the plant performance, and thus the economics of operation, by a significant
margin.
The current study aims to analyse one type of storage structure that is gaining popularity due
to the promise of cost benefits involved: the single-tank thermocline storage system. The
system is assumed to be a combination of porous filler bed and a fluid moving through the
bed during charge and discharge cycles. A one-dimensional transient mathematical model is
presented along with analysis of some important system parameters like the type of heat
transfer fluid, the operating temperature difference, energy loss from the tank wall, bed
porosity and tank diameter.
During the analysis, it was observed that two important aspects for assessing the system
performance are the cyclic behaviour of the system and the time required to attain this
behaviour. This is directly influenced by the discharge capacity and discharge power, and
therefore plays an essential role during system sizing. The temperature profiles and cycle
cut-off criteria are other relevant parameters in assessing the system behaviour for different
cases. It was also observed that Solar Salt performs the best among compared alternatives
for heat transfer fluids with the mentioned assumptions; and that the system performance,
with respect to storage capacity and discharge efficiency, depends highly on the combination
of fluid and filler bed and their respective thermophysical properties.
With appropriate system design, taking into consideration the abovementioned aspects,
substantial performance improvements and economic benefits can be achieved through
minimization of the losses that occur due to internal mixing and the losses to surroundings.
The presented model can be further developed by including an analysis of idle state of the
tank and more accurate data for mass flow rate, cut-off criteria and ambient conditions.
