[staktrace]

Maybe I'm misunderstanding your problem statement. But it seems to me that you are using (and paying for) N units from your regular provider. And then your community solar operation is selling S units to the grid and giving you a monetary credit (the result of the sale) instead. Some customer (due to fungibility, it could be you or anyone else) is getting those S units, and paying the community solar project (indirectly via the grid). And those S units are displacing some other set of S units that were previously generated by fossil fuels, which is (presumably) one of the main goals of this entire exercise. So maybe the answer to your final question is actually "only N units were actually generated, because the fossil fuel plants ran less and produced S fewer units".

[fghorow]

Your take is more sensible than the one I had. The community solar sells S units to somebody else, credits me with the monetary proceeds of the sale (and possibly a share of the associated Renewable Energy Credit proceeds), and charges me 90% of that "accounting fiction". They make money off the difference between the rates they invoice me for and the wholesale rates they actually sell the energy for (via a PPA or something).

I still argue that (N+S) units of energy are actually generated. The original generator of N units has no knowledge of the community solar arrangement, and is producing the N units of energy. Unless the community solar is lying about producing S units of energy -- remember, they are never disclosing S, only the associated monetary amount -- they too are selling S units to somebody else at a wholesale rate but getting their cash flow augmented by invoicing me. What a tangled web of cashflows!

I think that a PV array on the roof is preferable in situations where a purchaser is able to do that. Less financial engineering, and more physics! YMMV.