Energiankulutus kasvaa talvella.

It is a compound noun: two nouns joined into one word.

• energia = energy
• kulutus = consumption, use

So energiankulutus means energy consumption.

Finnish forms compounds very often, much more freely than English. Where English might write two words, Finnish often uses one longer word.

That -n- is very common in Finnish compounds. It often comes from a form that looks like the genitive.

You can compare:

• energian kulutus = the consumption of energy
• energiankulutus = energy consumption

So the compound is closely related to the two-word structure energian kulutus. For learners, it is usually enough to recognize that Finnish often inserts this -n- in compounds of this type.

It is in the nominative singular, which is the basic dictionary form.

In this sentence, energiankulutus is the subject:

• Energiankulutus = the thing that increases
• kasvaa = increases

So there is no extra case ending here because the subject is in its normal basic form.

It has changed grammatically, but for this verb the 3rd person singular present tense happens to look exactly like the infinitive.

For kasvaa:

• kasvaa = to grow / to increase (infinitive)
• minä kasvan = I grow / increase
• sinä kasvat = you grow / increase
• hän/se kasvaa = he/she/it grows / increases

So in this sentence, kasvaa means grows / increases, not to grow.

Both are possible translations of kasvaa, depending on context.

With something like energiankulutus, English usually prefers increase rather than grow, so:

• Energiankulutus kasvaa = Energy consumption increases

But the Finnish verb is still the same one that can also mean:

• a child grows
• a number increases
• demand rises

Because Finnish usually uses the adessive case (-lla / -llä) with seasons, times of day, and many other time expressions.

So:

• talvella = in winter / during the winter

This is just the normal way to say it.

By contrast, talvessa would usually mean something more like:

• in a winter
• within a winter
• or it could sound like you are focusing on the winter as a kind of period/container in a different way

For the basic time expression in winter, talvella is the natural choice.

Here -lla marks a time expression.

In many other contexts, -lla / -llä can mean:

• on
• at
• by
• with

But with words like seasons and parts of the day, it often corresponds to English in or during.

Examples:

• talvella = in winter
• kesällä = in summer
• aamulla = in the morning
• illalla = in the evening

So you should not translate -lla too literally as only on. Its meaning depends on context.

Because Finnish has no articles.

There is no direct equivalent of English a/an or the. Finnish usually leaves that distinction unspoken unless the context makes it important.

So Energiankulutus kasvaa talvella can be understood naturally as:

• Energy consumption increases in winter
• or The energy consumption increases in winter

English needs an article choice more often; Finnish usually does not.

Yes. Finnish word order is fairly flexible, although the neutral order here is very natural:

• Energiankulutus kasvaa talvella.

You could also say:

• Talvella energiankulutus kasvaa.

That version puts more focus on talvella (in winter), as the starting point of the sentence.

Because Finnish uses case endings, word order is often used more for emphasis and information structure than for basic grammar alone.

Normally it means winter in general: a general fact or tendency.

So the sentence is understood as something like:

• energy consumption increases in wintertime
• energy consumption increases during the winter season

If you wanted to make it clearly about one specific winter, the context would usually show that. On its own, talvella here sounds general.

Yes, the double letters matter a lot in Finnish.

• kasvaa has a long aa
• talvella has a long ll

In Finnish, double vowels and double consonants are pronounced longer than single ones, and this can change meaning.

A rough guide:

• kasvaa ≈ kahs-vaa
• talvella ≈ tahl-veh-lah, with a noticeably longer l

Also remember:

• stress is usually on the first syllable in Finnish:
  • EN-er-gi-an-ku-lu-tus
  • KAS-vaa
  • TAL-vel-la

You do not need to exaggerate the stress, but the first syllable is the main one.