Learn Hardcore Japanese: syouenekaden wo tukattara, denkidai ga yasuku narimasu. - If you use energy-saving appliances, your electricity bill will go down.

省エネ (shōene) is a contraction of 省エネルギー (energy saving). When used as a compound, 省エネ家電 literally means energy-saving home appliances or energy-efficient appliances. It’s common to drop の in fixed technical or marketing terms to make them shorter and catchier. If you wanted to add の, 省エネの家電 is also grammatically correct.

Why is the particle を used after 省エネ家電, and why not は or が?

を marks 省エネ家電 as the direct object of the verb 使う (to use). In this sentence the focus is on the action of using energy-efficient appliances. If you used は, you’d be emphasizing 省エネ家電 as the topic. If you used が, it would mark it as the subject, but here 使ったら is a conditional clause built on the verb 使う, so を is required.

What grammatical form is 使ったら, and what does it mean here?

使ったら is the past tense plus ら conditional form (the たら form). It means if/when you use energy-efficient appliances, focusing on the result after the action. In this context it’s best translated as if you use or when you use.

Why is 電気代 marked with が, not を or は?

In 電気代が安くなります, 電気代 is the subject of the intransitive verb 安くなる (to become cheap(er)). Japanese uses が to mark the subject of intransitive verbs like なる.

Why is 安く used instead of 安い before なります?

To express becoming X in Japanese, take an い-adjective like 安い, change it to its adverbial form 安く, and then add なる. So 安い → 安く → 安くなる means to become cheap(er).

What’s the difference between using たら (使ったら) and ば (使えば) in conditionals?

Both can express if or when, but:

たら often suggests once, since, or when focusing on a specific condition or event.
ば is more hypothetical and general.
In everyday advice both are fine. 使ったら might feel more conversational or emphasize the result after you start using them.

Why is there no explicit subject (like you or I) in this sentence?

Japanese frequently omits subjects when they are obvious from context. Here the subject is understood as you or people in general, so there’s no need to say あなたは or 私たちは.

Why is the verb in the polite ます form (なります) instead of the plain form なる?

Using なります makes the sentence more polite or formal, which is common in public announcements, advice, or written materials. The plain form 安くなる would be used in casual conversation or among friends.