Learn Spanish (Latin America): Ese es el generador solar que habré arreglado para mañana. - That is the solar generator that I will have fixed by tomorrow.

This is the future perfect tense. It is made by using the future tense of the helping verb haber (here, habré means 'I will have') followed by the past participle of the main verb. For arreglar (to fix), the past participle is arreglado. Together, habré arreglado gives us 'I will have fixed'.

Why is para used here instead of por to mean 'by'?

When talking about a deadline or a specific time in the future by which an action will be completed, you always use para. If you used por with a time frame, it would mean 'during' or 'around' that time, rather than the strict deadline of 'by tomorrow'.

Why does the sentence start with Ese and not Eso?

Even though it is the first word in the sentence, 'That' specifically points to el generador, which is a masculine noun. Therefore, you must use the masculine demonstrative pronoun Ese. You would only use the neuter Eso if you were referring to an abstract idea, an entire situation, or an unidentified object.

Can I leave out the word que, similar to how we often drop 'that' in English?