Maximum temperatures in glass-melt solar storage

Temperature field in a glass-making furnace in °K. (1820 °K = 1550 °C.)  Image quoted from L. Pilon et al.

As calculated in a previous post, the minimum (i.e., empty) temperature of a glass-melt storage is about 1340 °C (1610 °K) because of the need to supply high radiant flux (about 250 suns) to the steam tubes in order to achieve rated output. The maximum temperature depends on the high temperature materials available for the tank, the furnace roof, and the shading elements that modulate the radiant flux on the stem tubes.

Properties of ultra-high-temperature ceramic insulation. Image quoted from Rath USA.

Being optimistic, I'll say 1800 °C is an acceptable maximum glass-melt temperature—that's 250 °C hotter than a glass making furnace.

The storage temperature range is 1800 °C - 1340 °C = 460 °K, and the mean temperature is 1470 °C.  From Pilon et al., the specific heat, c, of molten glass between 1000 °C and 2000 °C is about 1231 J/kgK, so a 460 °K storage range stores 460 * 1231 = 566,000 J/kg. The density of molten glass in this temperature range is about 2300 kg/m3, so the volumetric energy storage is 1.3 E9 Jthermal/m3.

From the previous post, we need 5.3 E6 Jthermal/m2-land to store 15 hours of heat for rated output, so, spread over the land area of the heliostat field, the storage glass would form a layer 5.3 E6 / 1.3 E9 = 4 mm thick. That is less glass than would be needed for the mirrors!

Again from the previous post, the total land area for 3.2 GWe Gemasolar plant is 71 E6 m2, so the total storage volume is 71 E 6 * .004 = 284,000 m3, equivalent to a hemisphere with radius, r:

pi * 2/3 * r^3 = 284,000

r = 51 m, a pool with a perimeter of 2*pi*r = 320 m

At a thermal efficiency of 0.46, the rated thermal power is 3.2 E9 / 0.46 = 7.0 E9 Wthermal.

At 250 suns, the furnace wall area is 7.0 E9 / 250,000 = 28,000 m2.

With furnace wall area arrayed around the 320 m perimeter of the pool, the furnace wall is 28,000 / 320 = 87 m high, that is close to the height of the actual furnace walls at Plant Bowen, which appear to be about 75 m tall in photos. But I think 87 m is too tall in relation to the pool diameter (102 m) to comport with the earlier assumption of a 0.7 view factor, so this calculation is going to need more iterations.