Molten-Salt Storage

What is modelled

Mirrors focus sunlight on a receiver on the tower. The heat goes into molten nitrate salt that is pumped from a cold tank at 290 degrees to a hot tank at 565 degrees. The turbine takes heat from the receiver and from the hot tank, and any surplus is stored or, if the tank is full, defocused.

Equations

• Solar geometry sin(h) = sin(φ) sin(δ) + cos(φ) cos(δ) cos(ω) and clear-sky beam irradiance 1353 (1 + 0.033 cos(2πn/365)) τAM0.678.
• Receiver heat = irradiance × mirror area × optical efficiency × receiver efficiency.
• Salt: cp = 1443 + 0.172 T J/kg/K, store capacity = hours × turbine heat demand, mass = heat / (c_p ΔT).
• Stored heat changes by receiver heat minus turbine heat minus defocused heat minus a 1 % per day tank loss.

Checks run in the page

• The 48 h energy balance.
• The numerical integral of c_p and the salt mass.
• Day length from the hour angle against a numerical sunrise search.
• Time-step independence of the electricity produced.

Honest simplifications

The optical efficiency is a simple function of the sun height, the turbine runs at a fixed efficiency of 41 percent above a minimum load, clouds are a smooth random dimming, and the tanks stay at fixed temperatures without start-up, freeze protection or parasitic pumping.

• Press No storage to speak of and watch the turbine stop at sunset.
• Press Winter and compare the day length and the output.
• Press Large field, 14 h storage and read the capacity factor graph.