CELPIP Reading Part 3 Practice Test: Thermal Batteries And Stored Heat

Paragraph A

A thermal battery stores energy as heat or cold for later use. Unlike an electrochemical battery, it need not preserve energy as electricity. A simple hot-water tank stores sensible heat by raising the temperature of a material; the amount retained depends on mass, heat capacity, and the temperature change. Other systems use a phase transition, such as melting a salt, to absorb substantial energy while temperature changes little. Insulation slows losses but cannot stop them entirely, which makes storage duration important. A device that performs well over six hours may be unsuitable for seasonal storage even if both are described with the same energy capacity.

Paragraph B

Storage materials are chosen for operating temperature, cost, stability, safety, and compatibility with containers. Water is inexpensive but boils or freezes within ranges that limit some applications. Rocks, bricks, and concrete tolerate repeated heating, though their bulk can be considerable. Molten salts serve at higher temperatures but may corrode equipment or solidify in pipes if kept too cool. Phase-change materials offer compact storage around a selected melting point, yet many cycles can cause separation or reduced performance. The best material is therefore application-specific: a building cooling system and an industrial furnace do not reward the same temperature range or physical properties.

Paragraph C

Heat can be stored when electricity is abundant and then delivered directly to processes that need steam, hot air, or warm water. Direct use avoids converting the heat back into electricity, a step that introduces thermodynamic losses. Some systems do generate electricity through a turbine or another heat engine, but their round-trip electrical efficiency must be assessed separately from their ability to deliver useful heat. This distinction matters in industrial decarbonization. Replacing a gas burner may require dependable high-temperature output, whereas balancing an electricity grid may reward rapid charging. One device can contribute to both goals, but a single efficiency number rarely describes both services fairly.

Paragraph D

Thermal storage can shift demand away from expensive or constrained hours. A district cooling plant, for example, may make ice overnight and melt it the next afternoon, reducing the electrical load during peak demand without reducing the building's total need for cooling. Economics depend on rate structures, equipment utilization, and heat losses as well as energy price. Materials also have upstream impacts, and tanks, insulation, pumps, and controls require space and maintenance. Demonstration projects therefore monitor actual charge cycles and delivered temperatures. A large stated capacity has little value if the system cannot discharge at the rate or temperature the user requires.

Paragraph E

Not given in any of the above paragraphs.