Grid-connected photovoltaic power system Solar energy gathered by photovoltaic solar panels, intended for delivery to a power grid, must be conditioned, or processed for use, by a grid-connected inverter. Fundamentally, an inverter changes the DC input voltage from the PV to AC voltage for the grid. This inverter sits between the solar array and the grid, draws energy from each, and may be a large stand-alone unit or may be a collection of small inverters, each physically attached to individual solar panels. See AC Module. The inverter must monitor grid voltage, waveform, and frequency. One reason for monitoring is if the grid is dead
Galois module Z), as can be deduced from the theory of Gaussian periods (the Hilbert–Speiser theorem). On the other hand the Gaussian field does not. This is an example of a "necessary" condition found by Emmy Noether ("perhaps known earlier?"). What matters here is "tame" ramification. In terms of the discriminant "D" of "L", and taking still "K" = Q, no prime "p" must divide "D" to the power "p". Then Noether's theorem states that tame ramification is necessary and sufficient for "O" to be a projective module over Z["G"]. It is certainly therefore necessary for it to be a "free" module.