The first level loads must ensure the stability and sustainability of the electricity supply. Therefore, a lot of storage batteries and grid-connected electricity network should be selected, which makes the hardware cost highest.
The second level loads need keep the electricity supply stable and sustainable as well as possible, and they need less storage batteries. Therefore, the investment cost is lower than the first level loads. The third level loads need not usually keep the electricity supply stable and sustainable. When the renewable energy is available, they work. It is obvious that their investment cost is lowest.