TRUE costs are different for CELL manufacturers than they are for PANEL and inverter manufacturers, regardless of tax incentives or after-the-fact rebates. ANY manufacturer worth their salt knows to the penny the per unit cost and every component of cost going into their product on a daily basis. Production and supply chain is where you make or break your bottom line.

Cells are mostly poly or mono silicon molded under pressure and heat and infused with mixtures of gallium, copper & other conductive materials, mostly under automated control. R&D, capex equipment and utilities are the biggest cost components. A buck per potential watt on mass-produced Si and maybe halt that on thin film would be my assumption.

The law of conservation of energy states energy cannot be created or destroyed only changed in form. So what you are considering is changing kinetic energy to potential energy. With regards to electricity that would be electrons.

In a DC circuit electrons flow in one direction and in an AC circuit they flow in two directions (within the confines of a wire). Power P = VI voltage (or potential) times current (flow).
Consider the flow. If we connect a capacitor to a DC source, electrons will flow off of one plate and onto the other plate of the capacitor until the voltage rises to the DC buss voltage (kinetic energy).