Well now, depending on the acceptable range of DC into your inverter system, you may be able to use a 3 phase motor like an auto alternator to feed that existing net metering system. I don't know your background, but this is what I am looking into. An auto alternator is a 3 phase AC generator. Those 3 phases are rectified into DC and combined.Â
When you rectify single phase AC
into DC you get this. There is a huge ripple which requires a large bank of filter caps to clean up. The ammount of capacitance is related to the ammount of current being drawn so a high current filter bank would be massive.
When you rectify 3 phase AC and combine the outputs, all the tips overlap at a much higher voltage and you only get a fraction of the ripple.
The output DC would actually look more like this,only showing the waveforms above that point at which they meet.
This requires much less filtration to improve the DC quality. Auto alternators typically have very little or no filtration and batteries deal with this ripple well and finish the cleanup process. Something that I just learned fairly recently though is that because of their claw rotor design, auto alternators are not terribly efficient at turning mechanical into electrical energy. Perhaps 50%-60% depending on load and RPM. For years I thought they were better than that. They were designed to provide power in a small lightweight package and they do that well.Â
If you were to take an induction motor and add running caps to each leg, it would self excite when spun beyond it's syncronus RPM. The ammount of capacitance controls the ammount of excitation and therfore the output voltage in this standalone generation mode. If you then rectified and combined the output DC, you should be able to get the same low ripple waveform as above, but at nearer 90% efficiency? Now of course none of these numbers are even carved in mud, but I know some pretty smart people who think this is possible, and I have a 5HP 3 phase motor to experiment with so I plan on exploring the possibilities.
Add to this a switching DC to DC supply to provide some regulation, or perhaps some switched capacitance to provide some regulation at the source, you might be able to get within the input specs for that grid tied DC inverter. The good thing about the net metering inverter is that it's load should be pretty constant. Up to it's capacity, either you are using the power or it is going back onto the grid.
But again, you are on an island, if it isn't found naturally there for fuel, it has to be delivered and the utility producing in mass will probably win the price war. With the ammount of coin in a grid tied solar setup, you might be better served with more panels, but then that dosn't get you a roid to play with. One bad thing about a net metering system is that when you have a grid power outtage, your lights go out as well, even if you have good power comming from the panels(prevents backfeeding power down the line). Now if you added batteries and just didn't use any power from the grid at all, the roid would serve the usefull purpose of topping up the cells during low sun and to provide for proper battery maintenance and equalization. Self generation would allow you to maintain your power when the neighborhood goes dark(never happens in Hawaii:))
Ron