Der Stromanbieter rechnet den Energieverbrauch ab.

Because the verb here is abrechnen, which is a separable verb.

• Infinitive: abrechnen
• In a normal main clause: rechnet ... ab

So:

• Der Stromanbieter rechnet den Energieverbrauch ab.

This is very common in German. The main part of the verb goes to the usual verb position, and the prefix moves to the end.

Compare:

• Ich rufe dich an. from anrufen
• Er kauft ein. from einkaufen

So rechnet ... ab is the split form of abrechnen.

Here abrechnen means something like to bill, to charge for, or to settle the account for.

In this context, the idea is that the electricity provider is officially calculating and billing the amount of energy used.

So it is not just doing math in a general sense. It is more specifically about billing/accounting.

Because Energieverbrauch is the direct object of the verb, so it is in the accusative case.

The noun Verbrauch is masculine:

• nominative: der Energieverbrauch
• accusative: den Energieverbrauch

So:

• Der Stromanbieter = the subject, nominative
• den Energieverbrauch = the direct object, accusative

That is why the articles are different.

In this sentence, der Stromanbieter is doing the action, so it is the subject.

German marks this with the nominative case:

• der Stromanbieter = nominative masculine
• den Energieverbrauch = accusative masculine

A native English speaker may first rely on word order, but in German the article endings are also a big clue. Here the articles clearly show who is doing what.

It is a compound noun:

• Strom = electricity
• Anbieter = provider / supplier

So Stromanbieter means electricity provider or electricity supplier.

German often combines nouns into one long word. This is very normal.

Not exactly.

The basic verb rechnen often means to calculate or to do arithmetic. But with the separable prefix ab-, the meaning changes.

• rechnen = calculate
• abrechnen = bill, settle accounts, charge for, invoice

So you should learn abrechnen as its own verb, not just as rechnen plus a literal ab.

Not with the same meaning.

berechnen usually means to calculate something.
abrechnen here means to bill/account for the consumption.

So:

• berechnen = calculate the amount
• abrechnen = charge or bill for it

In real life, a company may first berechnen the consumption and then abrechnen it. The verbs are related in idea, but they are not identical.

Because German very often forms compound nouns.

Here:

• Energie = energy
• Verbrauch = consumption / usage

Together:

• Energieverbrauch = energy consumption

This is one of the most typical features of German vocabulary. English often uses separate words where German prefers a compound noun.

German usually needs an article more often than English does.

In this sentence, den Energieverbrauch is a specific grammatical object, so German uses the definite article den.

English may say:

• the energy consumption
• or sometimes just energy consumption, depending on context

German is generally less flexible here and more likely to require the article.

Both are possible, but they are not always exactly the same.

• Stromverbrauch = electricity consumption
• Energieverbrauch = energy consumption

If the context is specifically electricity, Stromverbrauch may sound more precise.
If the wording is broader, more formal, or part of technical/accounting language, Energieverbrauch can also work.

So the sentence is grammatically fine; the choice depends on what exactly is being billed.

In a subordinate clause, the separable verb is usually written as one word again and goes to the end.

Main clause:

• Der Stromanbieter rechnet den Energieverbrauch ab.

Subordinate clause:

• ..., weil der Stromanbieter den Energieverbrauch abrechnet.

This is a very important pattern:

• main clause: split verb
• subordinate clause: unsplit verb at the end

With separable verbs, the prefix stays attached in the past participle:

• infinitive: abrechnen
• past participle: abgerechnet

So the sentence becomes:

• Der Stromanbieter hat den Energieverbrauch abgerechnet.

This means The electricity provider has billed/accounted for the energy consumption.

Yes, German word order is flexible, but the finite verb still stays in second position in a main clause.

For example:

• Der Stromanbieter rechnet den Energieverbrauch ab.
• Den Energieverbrauch rechnet der Stromanbieter ab.
• Heute rechnet der Stromanbieter den Energieverbrauch ab.

The emphasis changes, but the sentence remains grammatical.

What does not change here is that rechnet stays in second position and ab stays at the end in a main clause.