על אף צריכת החשמל הנמוכה, חשבון החשמל גבוה.

על אף means despite or in spite of. It introduces a contrast:

• על אף צריכת החשמל הנמוכה = despite the low electricity consumption

It is a bit more formal than some everyday alternatives. A very common synonym is למרות.

So this sentence could also begin with:

• למרות צריכת החשמל הנמוכה...

Because צריכת is the construct form of צריכה.

Hebrew often links two nouns together in a structure called סמיכות (the construct chain). In English, this often corresponds to X of Y:

• צריכה = consumption
• צריכת החשמל = electricity consumption / consumption of electricity

For many feminine nouns ending in -ה, the construct form changes to -ת:

• צריכה → צריכת
• מכונה → מכונת
• שיטה → שיטת

So צריכת החשמל is a normal Hebrew noun chain.

Because in a construct chain, the definiteness of the whole phrase is usually determined by the second noun.

So:

• צריכת חשמל = electricity consumption / consumption of electricity
• צריכת החשמל = the electricity consumption

Even though the first word צריכת has no ה־, the whole phrase is definite because the second noun is definite:

• החשמל = the electricity

This is a very common Hebrew pattern.

Because the adjective is describing the whole construct phrase צריכת החשמל, not just the word צריכת by itself.

In Hebrew, when an adjective modifies a construct chain, it usually comes after the entire chain:

• צריכת החשמל הנמוכה = the low electricity consumption

Not:

• צריכת הנמוכה החשמל ✗

So the order is:

1. construct chain: צריכת החשמל
2. adjective describing that chain: הנמוכה

There are two things happening here:

1. Gender and number agreement

The head noun is צריכת, from צריכה, which is feminine singular.
So the adjective must also be feminine singular:

• masculine singular: נמוך
• feminine singular: נמוכה

2. Definiteness agreement

The phrase צריכת החשמל is definite, so an adjective attached to it must also be definite:

• צריכת החשמל הנמוכה = the low electricity consumption

In Hebrew, attributive adjectives agree with the noun in:

• gender
• number
• definiteness

Because in Hebrew, the verb to be is usually omitted in the present tense.

So:

• חשבון החשמל גבוה literally looks like the electricity bill high
• but it means the electricity bill is high

This is completely normal Hebrew.

Compare:

• הילד עייף = the boy is tired
• המחיר גבוה = the price is high

In the past or future, Hebrew usually does use a form of היה:

• חשבון החשמל היה גבוה = the electricity bill was high
• חשבון החשמל יהיה גבוה = the electricity bill will be high

Because גבוה here is a predicate adjective, not an adjective directly attached before/after a noun inside the noun phrase.

Compare:

Attributive adjective

• חשבון החשמל הגבוה = the high electricity bill

Here the adjective is part of the noun phrase, so it takes ה־.

Predicate adjective

• חשבון החשמל גבוה = the electricity bill is high

Here גבוה is saying something about the subject, so it usually does not take ה־.

This is the same reason you say:

• הבית גדול = the house is big

not

• הבית הגדול unless you mean the big house

Because they describe different nouns.

הנמוכה

This describes צריכת החשמל.
The head noun is צריכה, which is feminine singular.
So the adjective is feminine singular:

• נמוכה

גבוה

This describes חשבון החשמל.
The head noun is חשבון, which is masculine singular.
So the adjective is masculine singular:

• גבוה

Hebrew adjectives must agree with the noun they describe.

Yes. חשבון החשמל is another construct chain:

• חשבון = bill/account
• חשבון החשמל = the electricity bill / the electric bill

Just like צריכת החשמל, the second noun makes the whole phrase definite:

• חשבון חשמל = an electricity bill / electricity bill
• חשבון החשמל = the electricity bill

So this sentence contains two construct chains:

• צריכת החשמל
• חשבון החשמל

Yes, על אף is somewhat formal or written in tone. It is perfectly correct, but in everyday speech many people would more naturally say למרות.

So these are both good:

• על אף צריכת החשמל הנמוכה, חשבון החשמל גבוה.
• למרות צריכת החשמל הנמוכה, חשבון החשמל גבוה.

The second one may sound more conversational.

A simple pronunciation guide is:

al af tsrikhat ha-khashmal ha-nemukha, kheshbon ha-khashmal gavoha

A few notes:

• ח / כ here sound like the ch in German Bach or Scottish loch
• צריכת is roughly tsri-KHAT
• נמוכה is roughly ne-mu-KHA
• גבוה is roughly ga-VO-a

The main stress is usually near the end of these words:

• tsriKHAT
• nemuKHA
• kheSHBON
• gaVOha