Our electrical drawings arrived today. Sixty-eight panels, 17.00 kW, that should yield 90% of our annual electricity use. I’m often asked how we chose this size, which has is a complicated answer. In our case, we did extensive ROI calculations and found two key inflection points:
1. Tri-County Electric Cooperative does offer net metering, but they will only provide a credit for net electricity import/export within the same month. Because of the extreme summer heat, electricity bills will still be quite high when the A/C runs. Arrays built to reduce summer expense will produce more than will be reimbursed during the other seasons, and that excess production is a “gift” to TCEC.
2. The most straightforward way to connect the array to the grid is by attaching it to the load side of the service panel. It’s a bit of an oversimplification, but you can likely add 20% of the bus bar’s amperage rating in solar power. We have 2x200 ampere service panels, so we can have 2x40 ampere arrays. Arrays beyond this size require potentially significant electrical work, either by reducing the size of the main breaker, or replacing the service panel with a higher amperage bus bar. In fact, TCEC is very familiar and comfortable with the load-side configuration and had no difficulty approving this installation.
Given these two limitations, and the difficulty getting approval from the utility and potentially the city for anything larger, we decided to just install the largest array possible without a rewire — 80 amperes, 68 panels. Like I mentioned above, we expect it to produce 90% of our electricity usage and 75% of our electrical bill. If we find that we’re producing significantly more electricity than we use in the cold months, we will consider replacing one of our gas heatings systems with electric.