Så lenge strømmen er fornybar, beholder vi avtalen.

Here så lenge means as long as or provided that.

It introduces a condition:

• Så lenge strømmen er fornybar, ... = As long as the electricity is renewable, ...

A useful warning: så lenge can also mean for such a long time in other contexts, so the exact meaning depends on the sentence.

For example:

• Jeg ventet så lenge. = I waited so long.
• Så lenge du kommer i tide, er det greit. = As long as you arrive on time, it’s fine.

In your sentence, it is clearly the conditional meaning.

Strømmen is the definite singular form of strøm.

• strøm = electricity / power
• strømmen = the electricity / the power

Norwegian often uses the definite form where English might use a more general noun. In a sentence like this, strømmen can refer to the electricity being supplied under the agreement, so the electricity/power sounds natural.

Also remember that Norwegian usually puts definiteness at the end of the noun:

• en strøm = an electricity/current (not very common in this meaning)
• strømmen = the electricity

In this sentence, strømmen most naturally means electricity or power supply.

The word strøm can mean several related things:

• electricity / electric power
• current
• flow / stream in some contexts

But in everyday Norwegian, if people talk about strøm in a household or contract context, they usually mean electricity.

So here, strømmen er fornybar means the electricity being supplied comes from renewable sources.

Because fornybar agrees with strømmen, which is a singular common-gender noun.

The adjective fornybar changes depending on what it describes:

• en-words, singular: fornybar
• et-words, singular: fornybart
• plural: fornybare

So:

• strømmen er fornybar
• huset er fornybart
• ressursene er fornybare

Here the adjective is used predicatively (after er), but it still agrees in number and gender.

This is because of the Norwegian V2 rule (verb-second).

The sentence begins with the subordinate clause:

• Så lenge strømmen er fornybar

When that whole clause comes first, the finite verb of the main clause must come second, before the subject:

• Så lenge strømmen er fornybar, beholder vi avtalen.

So the structure is:

1. Fronted element: Så lenge strømmen er fornybar
2. Finite verb: beholder
3. Subject: vi

If you put the main clause first, the order becomes more like English:

• Vi beholder avtalen så lenge strømmen er fornybar.

Both are correct.

Because subordinate clauses in Norwegian normally keep subject + verb order.

So after så lenge, you get:

• strømmen er fornybar

not

• er strømmen fornybar

The order verb + subject is used in main clauses because of the V2 rule, but subordinate clauses do not follow that pattern in the same way.

So compare:

• Er strømmen fornybar? = main clause question
• ... så lenge strømmen er fornybar = subordinate clause

The comma separates the initial subordinate clause from the main clause.

• Så lenge strømmen er fornybar, beholder vi avtalen.

In standard Norwegian writing, it is normal to place a comma between a subordinate clause and the main clause, especially when the subordinate clause comes first.

So the comma helps show the structure:

• condition first
• main statement second

Avtalen is the definite singular form of avtale.

• en avtale = an agreement / a contract
• avtalen = the agreement / the contract

It is the direct object of beholder:

• beholder vi avtalen = we keep the agreement

Again, Norwegian usually marks definiteness with a suffix:

• -en for many common-gender singular nouns

Beholder is the present tense of beholde, which means to keep or to retain.

Forms:

• å beholde = to keep
• beholder = keep / keeps
• beholdt = kept (past tense and past participle in many uses)

So:

• Vi beholder avtalen. = We keep the agreement.

In your sentence, it means that the agreement remains in place under that condition.

Yes, absolutely.

That version is also correct:

• Vi beholder avtalen så lenge strømmen er fornybar.

The difference is mainly one of focus and style:

• Så lenge strømmen er fornybar, beholder vi avtalen.
  Starts with the condition, so it emphasizes the condition.
• Vi beholder avtalen så lenge strømmen er fornybar.
  Starts with the main statement, so it sounds slightly more neutral.

Both are natural Norwegian.

Not always, because English as long as can mean different things.

In this sentence, så lenge is correct because it expresses a condition.

But English as long as can also refer to length:

• The table is as long as the sofa.

That kind of comparison would not use så lenge in the same way.

So for learners, the key idea is:

• så lenge = as long as / provided that when talking about a condition

Yes, depending on the exact meaning you want.

• fornybar = renewable
• grønn = green / environmentally friendly (less precise)
• bærekraftig = sustainable (not exactly the same thing)

If you are specifically talking about electricity from renewable sources, fornybar is the best and most precise word.

So:

• strømmen er fornybar = the electricity is renewable

is the most natural choice here.