There are basically two types of Photovoltaic (PV) systems. Utility-Scale, and Small, Distributed-Scale. The latter frequently have the same name as this post’s title, abbreviated BTM. This is because each PV array provides power to specific residential, commercial or industrial customer (the latter two are usually grouped and called C&I), and the facility of that customer is metered by its supplying electric utility. Occasionally a PV system produces more power than the load consumes, pushing power back into the grid. This requires a four-quadrant meter, that can separately measure consumption and supply. The other two quadrants are Watts (real power) and VARs (volt-amps reactive or reactive power). The utility tariff (or rate-schedule) for a given customer defines how much the customer pays for consumption and is paid for supply, and for C&I, whether they are charged for supplying too many VARs (via a power factor adjustment).
Behind the meter PV Systems have been rapidly increasing in popularity and volume since 2010, and their costs have been rapidly declining to where their levelized cost are now less expensive than most utility generation. The down-side is that they are variable – they only supply power when the sun is shining, and supply less on cloudy days.
