Prognoza zużycia jest inna niż zużycie energii.

Because the noun zużycie is doing two different jobs here.

• In prognoza zużycia, it means forecast of consumption, so zużycie is dependent on prognoza and appears in the genitive singular: zużycia.
• In zużycie energii, zużycie is the main noun of the phrase, so it stays in the nominative singular: zużycie.

So Polish is not changing the meaning of the word here; it is just changing the case.

Energii is the genitive singular of energia.

Polish very often uses a pattern like:

• noun + genitive noun

to express English of:

• zużycie energii = consumption of energy / energy consumption

So energia changes to energii because it depends on zużycie.

Because inna has to agree with prognoza.

• prognoza is feminine singular
• so the adjective must also be feminine singular
• therefore: inna

Compare:

• Ten plan jest inny. — masculine
• Ta prognoza jest inna. — feminine
• To zużycie jest inne. — neuter

So in your sentence, inna matches prognoza, not zużycie energii.

Niż means than in comparisons.

So:

• inna niż = different from / different than

In this sentence:

• Prognoza zużycia jest inna niż zużycie energii.
• The consumption forecast is different from the energy consumption.

A very close alternative in Polish is to use od:

• inna od

Both patterns exist, though inny/inna/inne niż is very common.

Not because of niż. Niż itself does not force a special case the way some prepositions do.

The phrase after niż is simply the thing being compared:

• zużycie energii

So it appears in the form that fits its own structure:

• zużycie = nominative singular
• energii = genitive singular

A good way to think about it is: niż introduces the comparison, but it does not automatically turn the next noun into genitive or anything like that.

Yes, in normal standard Polish, jest is needed here.

With a predicate adjective like inna, Polish normally uses być:

• Prognoza zużycia jest inna.

Leaving it out would sound incomplete in an ordinary sentence.

Polish sometimes omits forms of to be in very informal notes, headlines, or certain special structures, but not in a standard sentence like this one.

Zużycie is a noun meaning consumption, usage, or sometimes wear depending on context.

It comes from the verb zużyć / zużywać, related to using something up.

Common examples:

• zużycie energii — energy consumption
• zużycie paliwa — fuel consumption
• zużycie materiału — material usage
• zużycie opon — tire wear

So here the meaning is clearly consumption/usage, not wear.

Because Polish has no articles.

English needs words like a, an, and the, but Polish does not. Whether something is definite or indefinite is usually understood from context.

So:

• Prognoza can mean a forecast or the forecast
• zużycie energii can mean energy consumption or the energy consumption

The exact English translation depends on context, not on separate article words in Polish.

Yes. Polish word order is more flexible than English.

Your sentence has a neutral, straightforward structure:

• Prognoza zużycia jest inna niż zużycie energii.

But you could also rearrange it for emphasis, for example by changing what comes first in the discussion. For instance:

• Zużycie energii jest inne niż prognoza zużycia.

That shifts the focus slightly.

Still, the original version is perfectly normal and easy to understand.

It is grammatically correct, but depending on context, it can sound a bit incomplete or unusual semantically.

Why? Because it compares:

• a forecast of consumption with
• energy consumption

In real technical or everyday usage, people often make the contrast more explicit, for example:

• Prognoza zużycia energii jest inna niż rzeczywiste zużycie energii.
  • The forecast of energy consumption is different from the actual energy consumption.

So the original sentence is fine for grammar practice, but in real-life usage you might expect a more specific comparison.

Roughly:

• zużycia ≈ zoo-ZHI-cha
• zużycie ≈ zoo-ZHI-che

A few useful notes:

• ż sounds like the s in measure
• ci before a vowel, as in cia, sounds roughly like ch in a soft cheese-like sound
• Polish stress is usually on the second-to-last syllable, so:
  • zu-ŻY-cia
  • zu-ŻY-cie

The exact Polish sounds are not identical to English ones, but those approximations are a helpful start.