I just got my first utility bill with a community solar monetary credit. I wrote the following piece attempting to figure out the energy flows -- as opposed to the dollar flows.
-- cut here --
OK. I have a(n energetic) head scratcher with my latest unbundled electricity bill. It's the first one that includes a community solar subscription. For geeks, this is almost a thermodynamics question about systems and surroundings -- but it's camouflaged as a monetary problem in disguise...
1) My utility company (NYSEG) charges me a per kW-hr fee for "transmitting" electricity and servicing their infrastructure. Fine and dandy. I understand that perfectly.
2) There is a separate per kW-hr fee from a different supplier of electricity with whom I have contracted for power. Again, I understand that perfectly.
3) Now the head scratcher. My "community solar" account just started contributing PV energy to the grid from a recently completed solar farm. My fraction of energy generated from their deployment just showed up as a monetary credit to my total bill. They will invoice me of 90% of that credit, and claim that I "saved 10%" on my electricity cost. There is no statement whatsoever of the amount of electrical energy corresponding to that monetary credit.
That's the monetary accounting. Now let's examine the energy accounting.
Let's call the amount of energy from 2) above "N" for my "normal" source of electrical power. Similarly, let us call the (unknown) amount of energy from 3) above "S" for my solar PV power. (In principle, once I knew the fee per kW-hr I was being charged for the PV energy, I could convert the monetary charge to the numerical value for S. Let's leave that as an exercise to be dealt with later after I receive an invoice from the community solar provider -- which hopefully will tell me their cost-per-unit of energy.)
Clearly, I paid my normal provider for producing N units of energy. However, I actually consumed (N-S) units of their energy, because I (notionally) also received S units of solar energy. I understand perfectly that electricity on a transmission line is fungible, hence I don't actually receive "electrons" (so to speak) from either of them. The community solar project will also get paid (at their claimed "discounted" rate) for producing S units of energy and delivering it to me via NYSEG.
My conundrum: It seems to me that (N+S) units of electrical energy have been produced and paid for, but only N units have been consumed. Hence there are (N+S) - N = S units of electrical energy "somewhere" that are generated but not consumed via this accounting system.
Where are those S units? Who owns them? Are they simply going towards heating up the transmission lines, or is somebody benefiting from them?
Is it simply the case that NYSEG no longer has to pay for the energy consumed in heating up their transmission lines, but are still charging me the same transmission fees???
I don't know the answer to this problem.
Discuss.