On my REC electric bill the main items are my kwhrs IN (used from the REC), my kwhrs OUT (my excess kwhrs fed back into the grid, mostly in the summer), and the REC's Facilities charge ($38/meter/month regardless if any energy is used).  The facilities charge pays for the wires, transformers, linemen, office staff, etc which I use and am glad to pay for. Our local REC does an excellent job of maintenance and improvements.

Note many for-profit utilities bury a large portion of these facility charges in their kwhr charge and have an unrealistically low facilities charge on their monthly bills. This is not PV Solar's fault and will have to change in the future.

In the summer I run a net credit on my electric bill. In the winter I use up that credit with the shorter days, and increased electricity use by my cattle waterers, etc. My goal is to have my net ANNUAL electric bill, including the facility charges, = zero.  My REC credits kwhrs out at the same 11 cent rate as those kwhrs coming in, UP TO my annual usage.  Any annual excess kwhrs generated, above and beyond what I use, are credited at a lower rate which is understandable.

Since the solar panel kwhrs I use internally never go through a meter, such as for air conditioning in the summer it's tough to say exactly how much is saved. I could go to the Enphase website and see the total my panels produced for that month and subtract the kwhrs fed back into the grid from my electric bill but I have a lot of other things to do with my time.

So basically I figure my ROI by taking the difference between my annual electric bill before panels (2014) minus my annual electric bill after panels (2017 about zero) and divide by my total system cost.  In a simple form, that is my annual ROI from solar panels. Not exact but close enough to show the obvious way to go.

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If your current rate is 5 cents/kwhr that is an extremely low rate and will extend the payback period for any solar installation. However what is the rate beyond 3 years? What is your facility charge? Is that likely to change? Given the fact the federal 30% tax credit on the installation costs expires about then the question is do you wait or install solar anyway.  What will happen to electricity rates in the future?

PV Solar requires you take a longer term view. Are you going to be living in the same spot 10 or 20 years from now when the system has repaid itself and now turning a net profit?  What will electric rates be then?

I should add that the first place to invest in electricity savings is in conservation such as switching to LED lighting and more insulation, better windows, etc.

An LED light bulb uses less than 20% of the electricity producing the same light as a standard incandescent bulb. That's an 80% savings right there!