This is the 14237th most frequent Spanish word.
térmicas
"Térmicas" means "thermal" or "related to heat."
In this context, 'térmicas' describes the nature of the plates, indicating they are related to or utilize heat or temperature for protection or function.
Las placas térmicas protegen el circuito eléctrico.
The thermal plates protect the electrical circuit.
Here, 'térmica' qualifies the clothing, specifying its purpose of heat conservation to provide warmth.
En invierno, uso ropa térmica para mantenerme caliente.
In winter, I wear thermal clothing to stay warm.
In this example, 'térmica' modifies 'energía' to specify the type of energy generated, namely heat energy.