Wij hebben stroom opgewekt in plaats van die te kopen.

Both are correct. Wij and we both mean we.

• we is more common in everyday speech
• wij is a bit more emphatic, clearer, or slightly more formal

So:

• Wij hebben stroom opgewekt
• We hebben stroom opgewekt

both mean the same thing here.

This is the present perfect tense.

The verb is opwekken = to generate / produce.
Its past participle is opgewekt.

So:

• hebben = auxiliary verb
• opgewekt = past participle

Together, hebben opgewekt means have generated or, in natural English, often simply generated.

Dutch uses this tense very often for completed past actions, especially in speech.

Because opwekken is a separable verb.

It consists of:

• op
  • wekken

In some forms, the prefix separates:

• Wij wekken stroom op = We generate electricity

But in the infinitive and past participle, it joins back together:

• opwekken
• opgewekt

That is very common with separable verbs in Dutch.

Literally, stroom can mean current, flow, or electricity, depending on context.

In this sentence, it means electricity / electric power.

So stroom opwekken means to generate electricity.

In a normal Dutch main clause, the finite verb usually comes in second position.

So here:

• Wij = subject
• hebben = finite verb
• stroom = object
• opgewekt = past participle at the end

This is the standard pattern for a perfect tense in a main clause:

subject + auxiliary + object(s) + past participle

So Wij hebben stroom opgewekt is the natural order.

In plaats van means instead of.

It is a fixed expression.

Examples:

• in plaats van koffie = instead of coffee
• in plaats van te gaan = instead of going

In your sentence, it introduces the alternative action:

• in plaats van die te kopen = instead of buying it

After in plaats van followed by a verb, Dutch normally uses te + infinitive.

So:

• in plaats van te kopen = instead of buying
• in plaats van die te kopen = instead of buying that/it

This is similar to English instead of buying, but Dutch uses te + infinitive rather than an -ing form.

Here, die refers back to stroom.

The noun stroom is a de-word:

• de stroom

When you refer back to a de-word, Dutch often uses die.

So:

• stroom → die

If the noun were a het-word, you would usually use dat.

In this sentence, die means it and refers to electricity.

Because die is the object of kopen, and in Dutch, object pronouns often come before the infinitive.

So:

• die te kopen = to buy it

This order is normal in Dutch subordinate infinitive constructions.

Compare:

• Ik probeer het te doen = I try to do it
• Wij besloten die te kopen = We decided to buy it

So die te kopen is the expected order.

Yes, that is grammatically possible, but it sounds less natural in many contexts.

The original sentence is smoother because it presents:

1. what we did
2. what we did not do instead

So:

• Wij hebben stroom opgewekt in plaats van die te kopen

is a very natural way to say it.

Dutch often puts the main action first and the in plaats van phrase after it.

In grammar terms, it is die, but in natural English translation here it is usually it.

So:

• die te kopen = to buy it

Dutch uses die/dat where English often just uses it.

Not here.

Om ... te is often used to express purpose:

• Ik ga naar de winkel om brood te kopen = I’m going to the shop to buy bread

But after in plaats van, you normally just use:

• in plaats van te ...

So here:

• in plaats van die te kopen = correct
• in plaats van om die te kopen = not correct in normal Dutch

Because it is part of the phrase in plaats van ... te + infinitive.

The main completed action is:

• hebben ... opgewekt

The alternative action is not expressed as a second completed past event. It is just the action that was not chosen:

• die te kopen = to buy it

So Dutch uses the infinitive kopen, not a participle like gekocht.

The dictionary forms are:

• opwekken = to generate
• kopen = to buy

In the sentence, they appear as:

• opgewekt ← past participle of opwekken
• kopen ← infinitive after te

So this sentence is a good example of two different verb forms being used together.