Kipas digunakan ketika cuaca panas.

Breakdown of digunakan:

• Root: guna (use)
• Suffix: -kan (makes it causative, so gunakan = “to use [something]”)
• Prefix: di- (passive marker)
  Put together: di- + guna + ‑kan → digunakan (“is used”).

Yes. Pakai also means “use,” so dipakai is its passive form.
Example: Kipas dipakai ketika cuaca panas.
Nuance:

• digunakan (from gunakan) is slightly more formal or technical.
• dipakai (from pakai) is common in everyday speech and also means “worn” (for clothes).

Ketika means “when” in a temporal sense. It’s somewhat formal or literary. Other options include:

• apabila (more formal, used in writing)
• bila (colloquial/spoken)
• masa or waktu (generic words for “time,” often followed by yang or directly by a clause)

Absolutely. In everyday conversation, bila cuaca panas is perfectly natural:

• Kipas digunakan bila cuaca panas.
  It’s less formal than ketika, but means the same thing.

Malay nouns don’t change form for number. Kipas alone can mean one or multiple fans, depending on context. To mark plural, you add quantifiers or reduplication:

• beberapa kipas (several fans)
• semua kipas (all the fans)
• kipas-kipas (some fans, colloquial)

Yes, you can say pada cuaca panas:

• Kipas digunakan pada cuaca panas.
  Nuance:
• ketika/ bila focus on the exact moment something happens.
• pada is a general preposition (“at,” “on,” “during”) and is also common in formal writing. Both are acceptable.

No specific person is mentioned; it’s an agent-less passive construction. It implies a general or habitual use—essentially “people” or “you/one” whenever the weather is hot. If you wanted to specify an agent, you could add oleh:

• Kipas digunakan oleh penghuni rumah ketika cuaca panas.