Can someone explain in simple words how the Home Energy Credit works, what "carried forward is", and why I am only getting 15% of the full credit this return?

I had solar panels installed on my house in the year 2022. My full Home Energy Credit is 30% of the amount for them. Of that 30% amount, I am only getting 15%, while the other 85% being carried forward. What exactly does that mean, and why not the full 30%?