Without enough Energy Units you will not be able to build any structures. Every structure requires a certain amount of Energy Units to function properly. When expanding your Island, you will soon use up the Energy Units you have build so far.
There are six different types of Energy Unit production facilities: Windmills, Generators, Solar power plants, Nano Generators, Tesla generators and Quantum generators. They all vary in size and costs, so depending on your Energy Unit needs and the available space on your Island you might want to make a well-advised decision which Energy Unit production facility to build.
The Windmill (Upgrade 1) is the most cost-efficient facility available in the game. It will provide you with 40 Energy Units for only $ 850, a bargain! Windmills and Generators with their smaller sizes can fit in irregular spaces such as along the shore, but currently there is a limit of 6 Windmills and 5 Generators. So, at a certain point when expanding your Island, you will need to start building Solar power plants. But try to get your hands on as many Nano, Tesla, or Quantum Generators. They will save you lots of precious space in comparison to all the Solar power plants you would need to power your island.
The table below gives an overview of the Energy Units that are produced at the corresponding upgrade levels.
|Facility||Size||Initially||Level 1||Level 2||Level 3||Level 4||Level 5||Level 6||Level 7||Level 7|
|Solar power plant||5x5||210||260||310||360||410||460||510||560||22.4|
|Tidal power plant||5x5||430||495||560||625||690||755||820||885||35.4|