The possibility of the concurrence of a prolonged heat wave and an equally prolonged power failure at the same time is rare, but one should plan against that occurrence. In nearly all such cases, one can obtain a supply of large blocks of ice and place these in the wine cellar until the power goes back on and the room again attains its ideal temperature. Those who keep very large collections or have a stock of very expensive wines, will find that having a generator on hand to supply power in times of extended power failure is a good investment. Humidity is also an important factor. In cellars that are too dry, corks tend to shrink and this lets air into the bottles.
Air is as much an enemy of wine as high temperatures.
A simple humidifier will solve this problem in almost all cases. In those rooms where humidity is too high, cardboard boxes will tend to rot and labels will quickly become unreadable. If high humidity is unavoidable, be sure not to store your wines in cardboard and coat each label gently with scentless hair lacquer before storing it away. As to the requirement of relative darkness, simply use dim lights in your cellar. If the area selected is overly bright and this cannot be controlled, simply cover the bottles with blankets.