We have colder weather where I live, but I see I used 550 kwh per month (at most). Even if my house is half your size, 70 kwh seems like a lot for a daily baseline. I have a similar situation (kids at home studying, me working at home).

Does the the car that drives up your electricity usage that much?

Car adds about 500kwh/mo. During offpeak rates charging this amount cost between $1 and $12 for the month.

Does your AC has not heating function (I assume everyone in Texas has AC)?

I'm guessing most Texas AC systems don't have a reversing valve, and a defrost system and all the other goodies you need to run it for heat. It adds to the equipment cost when many years heat isn't needed, and if the temperatures are 10F, you'd still likely need other heat sources.

> a defrost system

What does a defrost system includes? My dad manages a place where defrost system on one of the devices broke. Technician replaced something and hence it was fixed. IIRC it was temperature sensor. All defrost system does is periodically warms up the outside grill basically. It used to get stuck at -15C or so.

That's the gist. It's not much, but if the outside unit is iced over, there's not going to be a lot of heat exchange into the working fluid, so you're not going to get heat into your conditioned environment.

So, a defrost system will include a temperature sensor, and a resistance heater, and often something to signal the inside unit to run the emergency/auxiliary heat until (unless) the outside unit can get up to a temperature where it will work.

Heat pump systems can sometimes be an upgrade to standard air conditioning systems