Kulutuspiikki näkyy aamulla.

Because it is a Finnish compound noun. Finnish usually writes compounds as a single word, where the first part modifies the second:

• kulutus = consumption
• piikki = spike, peak

So kulutuspiikki literally means something like consumption spike or peak in consumption.

This is much more normal in Finnish than writing the parts separately.

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

In this sentence, it is the subject:

• Kulutuspiikki = the thing that is visible
• näkyy = is visible / can be seen

So the structure is basically:

[subject] + [verb] + [time expression]

Because here the noun is a normal singular subject, so nominative is the expected form.

Kulutuspiikkiä is the partitive form, and that would usually appear in different kinds of sentences, especially negatives or certain existential-type meanings. For example:

• Kulutuspiikki näkyy aamulla.
  = A consumption spike is visible in the morning.

• Kulutuspiikkiä ei näy aamulla.
  = No consumption spike is visible in the morning. / You can’t see a consumption spike in the morning.

So in the positive sentence you gave, kulutuspiikki is the normal choice.

Näkyy is the 3rd person singular present form of näkyä.

Depending on context, näkyä can mean:

• to be visible
• to be seen
• to show
• to appear

In this sentence, a natural English idea is is visible or shows up.

No.

• nähdä = to see
  This is what the observer does.
• näkyä = to be visible / to be seen
  This is what the thing itself does.

So:

• Näen kulutuspiikin. = I see the consumption spike.
• Kulutuspiikki näkyy. = The consumption spike is visible.

English often switches between active and passive-like wording here, but in Finnish näkyä is just a normal verb.

Because the subject kulutuspiikki is singular, so the verb is in 3rd person singular present.

The dictionary form is näkyä, and the present singular form here is näkyy.

If the subject were plural, the verb would change too:

• Kulutuspiikit näkyvät aamulla.
  = Consumption spikes are visible in the morning.

Aamulla means in the morning.

It is based on aamu = morning, with the ending -lla/-llä, which is the adessive case.

The adessive often means on / at, but Finnish also uses it in many time expressions. So:

• aamulla = in the morning
• illalla = in the evening
• yöllä = at night

So this is a very normal Finnish way to express time.

It can mean either, depending on context.

• In a specific context, aamulla can mean this morning / in the morning / one morning.
• In a general statement, it can mean in the morning as a regular time when something happens.

If you want to clearly say in the mornings as a repeated habit, Finnish often uses aamuisin:

• Kulutuspiikki näkyy aamuisin.
  = The consumption spike is visible in the mornings.

So aamulla is somewhat context-dependent, while aamuisin is more clearly habitual.

Because Finnish has no articles.

There is no direct equivalent of English a/an or the. Finnish leaves that distinction to context.

So kulutuspiikki could be understood in English as:

• a consumption spike
• the consumption spike

Which one sounds best depends on the situation and the translation choice.

Yes. Finnish word order is more flexible than English word order, because the endings carry a lot of grammatical information.

Your sentence:

• Kulutuspiikki näkyy aamulla.

You could also say:

• Aamulla kulutuspiikki näkyy.
• Aamulla näkyy kulutuspiikki.

These versions are not identical in emphasis:

• starting with aamulla puts more focus on when
• starting with kulutuspiikki is more neutral if the topic is the spike itself

But all are understandable Finnish.

Yes. Finnish does not need a dummy subject like English it in sentences such as It is visible.

The noun kulutuspiikki is already the subject, so the sentence is complete:

• Kulutuspiikki näkyy aamulla.

Finnish also often leaves out subject pronouns when they are not needed, but here there is no missing pronoun at all.

A few useful points:

• Finnish stress is usually on the first syllable of each word:

  • KUlutuspiikki
  • NÄkyy
  • AAmulla

• Double letters are important:

  • piikki has a long ii and a long kk
  • aamulla has a long aa

• y is a front rounded vowel, not the English y sound

Very roughly for an English speaker:

• kulutuspiikki ≈ KOO-loo-toos-PEEK-kee
• näkyy ≈ something like NAE-kyy, with Finnish y
• aamulla ≈ AA-mool-la

The exact vowel quality matters in Finnish, especially long vs short sounds.