Answer: Passive solar technology
Step-by-step explanation:
Passive solar technology is the method of using materials to attract sunlight for warmth. Solar energy is the energy that comes from the sun. To store this energy gotten from the sun you'll need some elements to transfer this energy then store them. According to the passage the individual used a black material (black material is used for conveying and storing heat, it's one of the best form for doing so), the black material and the water helps warm the water needed for the individual after his hiking which actually worked.