An energy inventor like myself must always look for 'energy hills'. There isn't actually a 'hill', just conditions where there is more energy in one place than another, or there is a 'flow' of energy or there is a source of renewable potential energy.
Most energy tends to be homoginous because of 'positive entropy'.
In other words, energy tends to spread out evenly, become disorganized. Once we find organized energy conditions that we think we can turn into electricity, then we need to design devices that will actually do it. Another example is a river, in which we can insert a water wheel or turbine. Another example is hot and cold, in which we insert a heat engine of some type. Notice that every type of energy flow requires a different kind of device.