In order to write a good topic sentence about this issue, you first need to know what you are going to say about the issue. You need to know what your arguments are and then sum them up in your topic sentence.
For example, let's say that you want to argue that solar power is an important way to reduce America's dependence on foreign oil. If that were your argument, you might say something like this:
Today, America gets much of its oil and natural gas from places with oppressive and possibly unstable governments. If we do not use solar power, we will have to rely more and more on such governments to provide us with the energy we need.
These sentences show what you are going to talk about in your paragraph without actually getting into details. The rest of your paragraph can fill in those details, talking about where our oil and gas come from and what kinds of governments they have.