Molten-Salt Heat Storage

What is modelled

The mirror field heats salt taken from the cold tank to the hot tank whenever the sun is up. The power block takes salt from the hot tank to make steam during its working hours and returns it cooled. A field larger than the block needs (solar multiple above 1) fills the tank by day, and the tank carries the plant through the evening or the night. If the tank is full the surplus mirrors are defocused; if it is empty the block stops.

Equations

• Heat content E = ρ(Th) V ∫ cp dT with cp = 1443 + 0.172 T J/kg K and ρ = 2090 − 0.636 T kg/m³ (T in C).
• Block efficiency η = fc (1 − Tcond/Th); heat demand Pe / η.
• Field output P = SM Pth sin(π(t − 6)/12) between 06:00 and 18:00.
• Storage balance dE/dt = Pfield − Pblock − Ploss − Pdump; idle tank T − Ta = (T0 − Ta) e−t/τ, τ = m cp / U A.

Checks run in the page

• The simulated solar energy against the half-sine integral.
• The stored-heat balance including losses and dumped energy.
• Simpson integration of the salt specific heat against the closed form.
• The tank volume for ten hours of storage, and the idle cooling against the exponential.

Honest simplifications

Every day is a clear day with a fixed sine profile, the whole stored salt is treated as a single energy pool (no tank levels or thermocline), the block runs at a fixed heat rate with a constant efficiency (no part-load behaviour), pumping power and receiver losses are left out, and the tank loss is a simple wall coefficient. Sizing here shows the trade-off between tanks and mirrors, not a plant design.

• Press No storage (solar multiple 1) and see the block stop at dusk, then press Solar tower, 10 h storage for a plant that runs into the night.
• Press Small tanks, big field and watch the mirrors defocus once the tank is full.
• Press Poor insulation and see the idle tank lose temperature faster in the last plot.