Energy can be represented as an orange fluid: how much fluid is a result of a particular calculation. The calculation can be named long before it can be done, and all such calculations appear as
The semi-quantitative (more or less energy filling or emptying a particular store) allows children to get a grip on the core ideas of energy early on. Such descriptions can also serve to guide and discuss calculations once these become accessible.
Note the store gets fuller or emptier in moving from one situation to another: its only the changes in energy that you're describing or calculating.
Strictly speaking energy is an abstract quantity with a calculated number and a unit of measurement. However, even the fastest learners will do few calculations, and even then only for a limited range of situations. So the orange fluid stands in place of the quantity, to engage the imagination. Although such a representation does not have much predictive power, it does have considerable value as a tool to think with. I think you'll need to use one like this, if not this one.
In choosing examples concentrate on changes where comparatively few stores account for all of the energy changes. So no orange fluid can cross the boundaries of what you describe. The fluid may move around, and even become more spread out with time, but there is still the same quantity of fluid. Furthermore, this fluid behaviour is familiar, following the everyday behaviour of water.
Power is also a calculated quantity, and it is useful to have placeholders for these calculations as well, allowing more complex semi-quantitative descriptions.
Differentiating between lived-in-world of tangible objects, the physical descriptions and the stores and pathways helps to keep descriptions separate.