Answer: The same amount of energy that there was yesterday.
The same amount that there will be tomorrow, and the next day, and
on until the end of the universe.
How can the above statement be true? After all, we all say that power plants generate energy in the form of electricity. We can watch as a ball steadily loses energy with each bounce. The idea that energy cannot be created or destroyed goes against all of our experience and intuition. And yet it is true. If one could measure all of the energy entering and leaving any particular reaction or activity, the totals would balance. All energy comes from somewhere else and goes somewhere else. The bouncing ball, for example, gives energy to the floor in the form of heat. And those power plants don't really generate energy, they merely convert it from one form - say the chemical energy in coal - to another, such as the energy of an electrical current.
Scientists know that the universe is gradually cooling. But that doesn't mean that it is losing energy. It just means that the energy is getting more and more spread out. Eventually, the universe will be at a uniform, very cold temperature. But even then, the universe will contain the same amount of energy as when it was born in the Big Bang.