Jo høyere nettleien er, desto dyrere blir strømregningen.

It means the higher ..., the more expensive ....

This is a very common Norwegian pattern used to show that one thing changes together with another:

• Jo høyere X er, desto dyrere blir Y.
• The higher X is, the more expensive Y becomes.

So in your sentence:

• Jo høyere nettleien er = the higher the grid fee is
• desto dyrere blir strømregningen = the more expensive the electricity bill becomes

It is a correlative comparative structure, like English the more ..., the more ....

No. Here, jo does not mean yes.

Norwegian jo can have different meanings depending on context. In this sentence, it is part of the fixed comparison pattern jo ..., desto ....

So:

• Jo here = the in the sense of the more / the higher
• not yes

That is why you should learn this whole structure as one unit:

• jo ..., desto ...

In this structure, desto means something like the more / all the more.

It is usually not translated word-for-word by itself. Instead, the whole pattern is translated together:

• Jo høyere ..., desto dyrere ...
• The higher ..., the more expensive ...

So it is better to think of desto as the second half of a pair, not as an isolated word with one neat English equivalent.

They are the comparative forms of the adjectives:

• høy = high

• høyere = higher

• dyr = expensive
• dyrere = more expensive

In a sentence like this, Norwegian uses comparatives because you are comparing degrees:

• jo høyere = the higher
• desto dyrere = the more expensive

This is exactly parallel to English higher and more expensive.

Because those are the definite forms of the nouns.

In Norwegian, the definite article is usually attached to the end of the noun:

• nettleie = a grid fee / grid charge

• nettleien = the grid fee / the grid charge

• strømregning = an electricity bill
• strømregningen = the electricity bill

So the sentence is talking about a specific type of charge and bill in a general, understood sense:

• the grid fee
• the electricity bill

This is very natural in Norwegian, especially when referring to familiar categories or standard charges.

Nettleie is a specifically Norwegian term for the fee you pay to use the electricity grid.

It is not the same as paying for the electricity itself. In simple terms:

• strøm = the electricity you use
• nettleie = the fee for having that electricity transported through the power grid to your home

So if nettleien goes up, your total electricity-related costs often go up too.

Because they express slightly different ideas:

• er = is
• blir = becomes

In the first clause:

• Jo høyere nettleien er
• The higher the grid fee is

This describes the level of the grid fee.

In the second clause:

• desto dyrere blir strømregningen
• the more expensive the electricity bill becomes

This focuses on the result or change: the bill becomes more expensive.

You could sometimes see er in both parts in other examples, but here blir sounds natural because the bill is understood as ending up at a higher cost.

Because Norwegian has verb-second (V2) word order in main clauses.

The second clause starts with the element desto dyrere. When something other than the subject comes first, the finite verb usually comes next:

• Desto dyrere blir strømregningen
• not Desto dyrere strømregningen blir in ordinary main-clause order

Here is the structure:

• desto dyrere = first element
• blir = verb
• strømregningen = subject

This is very normal Norwegian word order.

Compare:

• Strømregningen blir dyrere.
  The electricity bill becomes more expensive.

If you move dyrere to the front in this kind of structure, the verb comes before the subject.

Yes. That is also possible and very common.

Both of these work:

• Jo høyere nettleien er, desto dyrere blir strømregningen.
• Jo høyere nettleien er, jo dyrere blir strømregningen.

In modern Norwegian, many speakers use jo ... jo ... very naturally in everyday speech. Jo ... desto ... can sound a bit more formal or traditional, but it is absolutely correct.

Yes, the comma is standard here.

The sentence has two linked parts:

• Jo høyere nettleien er
• desto dyrere blir strømregningen

The comma helps separate the two halves of the comparison. In writing, you should include it.

Not very naturally.

A word-for-word translation would sound awkward. The best approach is to translate the whole pattern, not each word separately.

Natural English:

• The higher the grid fee is, the more expensive the electricity bill becomes.

Or more naturally still:

• The higher the grid fee, the more expensive the electricity bill becomes.

So for this kind of sentence, think in patterns:

• Norwegian: jo ..., desto/jo ...
• English: the ..., the ...

It is a general pattern that you can use with many adjectives and situations.

For example:

• Jo mer du øver, desto bedre blir du.
  The more you practise, the better you become.

• Jo eldre hun blir, desto mindre sover hun.
  The older she gets, the less she sleeps.

• Jo lenger vi venter, desto vanskeligere blir det.
  The longer we wait, the more difficult it becomes.

So your sentence is one example of a very useful Norwegian structure.