Energy is used to____________ a lot of electrical things. (product)            

1. There will be a____________ of energy in the near future. (short)         

2. I don’t think so. The solar panels are becoming__________ and easy to install. (cheap)

3. Scientists are looking for clean and ____________ sources of energy. (effect)

4. I know it is also clean and safe to the environment. But does it cost a lot of money to install the____________ panels on the roofs? (sun)