Let's assume for a moment that your house uses an average of 16kWh of electrical energy per day. If you could covert  the mass o

Holy cow !

Before we do the mass-energy conversion, and then relate that to the
household energy usage, we have to get some numbers in order, and
massage some units etc.:

46 grams = 0.046 kg
c = 3 x 10^8 m/s
c² = 9 x 10^16 m²/s²
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Household daily energy consumption:

(16 kilowatt-hour) = (16 x 1,000watt x hour) = (16 x 1,000 joule/sec x hour)

16,000 (joule-hour/sec) x (3,600 sec/hour) = (16,000 x 3,600) = 5.76 x 10^7 joule

I just noticed that the question GAVE us the joule equivalent of 1 kWh, so it
wasn't necessary to derive it.  I checked my figure here against that one, and
got the same number ... 5.76 x 10^7 joule per day.   So I'm OK so far.    yay!
===========================

Now we have everything we need:

E = m c² = (0.046) x (9 x 10^16)  =  4.14 x 10^15 joules in a golf ball of mass.

(4.14 x 10^15 joules) / (5.76 x 10^7 joules per day) = <u>71,875,000 days</u>

That's roughly  <em><u>196,783 years</u></em>  of typical household electrical energy use.
(assuming that every year was, is, and shall always be  365-1/4 days.)