Solar System Real Savings Example
An Installation on the Pedernales Electric Grid in Austin, TX
The system savings calculations provided by the installer of our solar power system were wildly inaccurate. The calculation is much more complex than reducing your billable kilowatt hours by the system production.
We had an 8 Kw solar system with REC 400W Alpha Black panels and Enphase IQ8+ micro-inverters installed and turned the system on June 22, 2022. As of the end of October, the maximum output has been 6 Kw/hour. It will probably degrade over time from there. PEC bills power as follows:
| Service Availability Charge | $22.50/month |
| Delivery Charge | $0.028405/kWh |
| Base Power Cost | $0.0445/kWh |
| TCOS Pass-Through Charge | $0.01686/kWh |
| Temporary Storm Surcharge | $0.007/kWh |
| Sustainable Power Credit | -$0.05377/kWh |
So, we are charged $22.50 plus $0.089765/kWh for power we pull from PEC less $0.05377/kWh for power we push to PEC.
Power Usage
We have found that peak usage for air-conditioning (the largest power usage) starts around 4pm. Peak power generation is between noon and 3:30 pm. (In August we're still running max A/C till 9 pm.) So, you're going to be pulling power from the utility for cooling while your solar production is low or nill. Also interestingly, the PEC metering will frequently show some power consumption as well as power generation (power you push to PEC) in the same 15 minute interval during peak solar production. So here is some real data:
| Month | Produced kWh | PEC Pulled kWh | PEC Pushed kWh | $ Saved | $ Billed | % Prod Used |
|---|---|---|---|---|---|---|
| June/July | 1,095 | 788 | 618 | 71.45 | 95.86 | |
| July/Aug | 1,176 | 1,088 | 621 | 76.65 | 90.11 | 47 |
| Aug/Sep | 1,036 | 980 | 534 | 67.47 | 90.48 | 48 |
| Sep/Oct | 1,112 | 796 | 697 | 71.52 | 62.44 | 37 |
| Oct/Nov | 755 | 614 | 503 | 47.17 | 55.13 | 33 |
| Nov/Dec | 413 | 841 | 282 | 24.73 | 88.72 | 35 |
| Dec/Jan | 796 | 971 | 473 | 47.56 | 78.17 | 42 |
| Jan/Feb | 692 | 1,215 | 343 | 42.06 | 121.63 | 49 |
| Feb/Mar | 878 | 688 | 555 | 56.28 | 55.78 | 39 |
| Month | Produced kWh | Proposal Est. kWh | Actual Savings | Proposal Est. Savings |
|---|---|---|---|---|
| July | 1,307 | 788 | $85.49 | $106.24 |
| August | 1,044 | 1,195 | $67.32 | $107.56 |
| September | 1,126 | 1,067 | $73.46 | $96.02 |
| October | 1,016 | 997 | $64.98 | $89.72 |
| November | 540 | 876 | $33.50 | $78.82 |
| December | 576 | 772 | $32.72 | $69.45 |
| January | 773 | 835 | $47.94 | $75.19 |
| February | 775 | 871 | $48.99 | $78.41 |
Note: We were out of town for July 11 - 24th. During that time production exceeded usage enough to apply credits to the bills for June/July and July/August.
The next biggest power use (after air-conditioning) is the hot water heater. So, you'll want to wash clothes/dishes/yourself during peak solar generation hours if possible. You really start to understand your power usage when you have the detailed reporting from your solar system and the PEC metering.
Another interesting tid bit, 33-49% of our solar power generated is offsetting our usage and 51-67% is pushed back into the grid and credited at 5.4¢. We would obviously rather be offsetting our usage (ie. not pulling power from PEC) at 9¢ per kWh. This is the greatest reason the actual savings are so much lower than the calculations provided in the proposal from the solar system installer for estimated savings.
I hope this helps you evaluate your investment in a solar system so there are fewer surprises. I'm actually still happy with our decision to install the system even though financially it won't pay back as quickly as the solar installer's basic calculations.