PROBLEM $1$

Consider three thermal energy storage systems featuring sodium sulfate decahydrate, water and rocks, respectively. Identify the required thermophysical properties of the storage materials from literature sources of your choice.

Questions:

$($a$)$ Compare the thermal energy storage capacity of sodium sulfate decahydrade $($Glauber$\text{'}$s salt$)$ in the temperature range $30-60C$ with that of water and rock in the same temperature range.

$($b$)$ Compare the volumes of storage for the three media.

$($c$)$ Cite the literature sources used.

PROBLEM $2$

Design a spherical sensible heat storage tank for the concentrator that can store $4MWh$ of energy at $565C$ using draw salt per weight$).$

$($a$)$ Assuming a $95\%$ heat recovery efficiency from the storage tank, determine the required mass and volume of salt, including the radius of the sphere that contains the required volume of salt.

$($b$)$ Assuming no wind and an ambient temperature of $20C,$ determine the thickness of mineral wool insulation with thermal conductivity $k=0\mathrm{.}018W{m}^{-1}{K}^{-1}$ that will enable this tank to limit heat loss to $1C$ per day.

$($c$)$ Scale the storage up to $40MWh,$ recalculating its size and insulation. Comment on the scalability of the system, i$.$e$.$ is it better to build a small or a large storage tank?