# tableau synthèse tom Article | Maths accesibility | Trust | Benefits | Distance from the PoW solution --- | --- | --- | --- | --- | --- Permacoin | 2 | 2 | 3 Use energy for distributed storage | Use the PoW puzzle uPow | 3 | 1 | 2 Use energy to solve useful problems | Really close except the computed problem Empty blocks | 1 | 3 | 1 Reduce the energy cost | Does not use the PoW puzzle