Technology

SLPI’s unique design is based upon proven, technologically sound principles and adapts technologies well established in other fields. Our design has unique advantages not offered in today’s CSP plants:

• The SLPI system is designed to operate on 24/7-basis at rated capacity utilizing cost-effective latent heat storage.
• The system is scalable and fully modular at nominal 5MW, enabling flexibility in siting, construction, and maintenance.
• Ability to follow Load.
• The high storage temperatures enable electricity generation using a single-pass, air-driven Brayton-Cycle turbine with improved efficiency over combustion/steam turbines.
• As a result, the SLPI CSP system does not require water for steam generation or steam condensing (cooling), which are essential in all existing CSP Tower designs.

Thermal Storage

In SLIP’s unique, high temperature thermal storage system, storage occurs in a simple, insulated tank containing common, low-cost sodium chloride salt at its melting point of 801 °C. The tank insulation limits loss to a few-%/day. With 60% freeze/melt fraction of the salt, the resulting thermal storage is about 120 MW-h/m 3 . Heat is extracted from the liquid-solid salt mixture using a proprietary technique that avoids both pumping of hot liquids and solid formation (icing) on material surfaces.

Electricity Generation

The high storage temperature enables electricity generation using a single-pass, air-driven, Brayton-cycle gas turbine with both improved efficiency over steam turbines and little/no cooling-water requirement.

To store/regenerate electric power, energy from a primary source is used to melt the tank’s salt to a 60% frozen-fraction. Then, by re-freezing the salt as needed, the released stored energy is used to heat the compressed-air stream of a Brayton-cycle turbine/generator to regenerate electricity. The estimated turn-around cost including regeneration is in the range $30-40/MWe-h, to be sharpened with more detailed engineering.

The primary energy to be stored must be capable of transferring heat at 800 °C, the temperature of the tank’s liquid-solid salt mixture. For non-solar applications, i.e., for primary sources with temperature less than 800 °C, tank heating uses embedded heater elements driven by electricity generated by the primary source.

The heat extracted by freezing the liquid fraction of the salt is used in a specially designed heat exchanger to heat the Brayton-turbine air stream, replacing the combustion chamber common in Brayton turbines. The operating time after cessation of the primary power input can be varied by design but is typically ~10 hrs.