Thermal Energy Storage

Objectives

• Optimized design of a TES unit for the AA-CAES operating conditions to give high efficiency and low material cost.
• Development of simplified storage models for AA-CAES unit design.
• Evaluation of diverse materials for high-temperature sensible TES.

Preliminary Storage configuration

TES dimensions

• Length 10m, diameter 6m, solids content 460 tons

Cavern dimensions

• Length 260m, diameter 10m

Air flow

• 1 kg/s

TES storage efficiency

• Greater than 90%

Applicability of rocks, concrete, and ceramics as sensible thermal energy storage material

Temperature-dependent thermophysical properties were used to compare the different materials in a test scenario.

First results:

• Ceramics show the best thermodynamic performance.
• Concrete shows the worst thermodynamic performance.
• Rocks show thermodynamic performance similar to ceramics with much lower costs.

Design & optimization of storage unit for proposed thermodynamic cycle and cavern

Design variables:

• TES length
• Cover insulation thickness
• Particle diameter

Objective functions:

• Material costs
• Exergy efficiency

Constraints:

• dimensions
• and min. air outflow temperature

TES Design

• Existing conventional methods are not applicable to provide required air-tightness of the TES because of the high temperature conditions.
• Lining for the TES has to ensure sufficient thermal insulation to reduce the heat losses.
• This can be achieved by use of multilayer lining: