In my estimation for my family, at the lowest cost, each year we have to pay 12,000,000 VND. If you use the house for about 60 years, you'll not be in loss of money anymore. But after one year of the 60th year, each year you'll save 12,000,000VND. And in 80 years, you have saved 240,000,000VND!!!
And because you don't have to pay more to use more, you can turn on aiconditioner 24/7 and all lights on too(unless it got on fire)...