(This post is now the latest in this on-going series. Here is Part 1).
The sales information on solar panels state that year two may see a loss of power produced of about 2%. Unfortunately, there is no way to tell if that occurred for our panels. In order to measure this, the weather would have to be identical each year, including the timing and density of clouds and rain. These two items play a much larger factor in how much this site produces.
This year snow was a small factor. Usually we have a warmer, sunny day after a snowfall. This year it snowed just ahead of the polar vortex that caused so much trouble in Texas and other places, so instead of melting off almost immediately, the snow stayed on the panels for several days, reducing output for those days.
Did I mention that my dog ate my homework? OK, enough excuses, here are the numbers:
Again we had 8 months of 0 billing and partial billing for 4 months. The sun does not provide much energy in the winter months.
Following are the meter readings at the beginning and at the annual anniversaries:
| Date | Meter Reading | Accumulated Production | Annual Production |
| 03/26/2019 | 00012 | 0 | 0 |
| 03/26/2020 | 00455 | 9.67 MWh | 9.67 MWh |
| 03/26/2021 | 01098 | 18.77 MWh | 9.10 MWh |
The meter reading indicates that we are falling further behind (continuing to use more power than we produce.
Year 1: 9.67 + 0.433 means we used about 10100 KWh
Year 2 the meter went up 643 KWh over Year 1 (01098 – 00455). So year 2 usage is 9.10 + .643 = 9743 KWh. So we cut our usage by about 357 KWh for the year, but due to some combination of weather and normal 2nd year reduction, production dropped 570 KWh. Clouds got in the way.
Here is the full spreadsheet:
Our cumulative spend for this period is $469.07. Subtract out about $200 for the meter costs (typically $8.32 a month) for an adjusted cost of $270.
BGE zeroes out any accumulated surplus based on the end of April reading. They pay us for the supply price of the surplus we generate in March and April. We will not have this number until late May. The cumulative total of the previous 2 checks was $83.50.
Assuming for the sake of discussion we get about $40 this coming May, these checks total about $123.00.
The price of electricity all in (supply, delivery, taxes) has actually gone DOWN since we installed our system. It was a little over 0.12 per KWh in year one and a little less than 0.11 per KWh in year 2. For a quick calculation, let’s use .1125 to see how much we have saved:
18770 KWh * .1125/KWh = $2112 – estimated value of energy produced.
Our last data point is the dollar value of the SRECs produced. To date we have received $895. In May we will receive $55 for the SREC produced in March, bringing this total to $950.
Approximate dollar value realized to date – $3185:
$2112 + $950 + $123 = $3185 – This is how much we did not pay ($2112) + real checks we got from BGE. Our installation cost after incentives was $16500. To date we have recovered about 19.3% of these costs (3185/16500). Because electricity costs have gone down (and perhaps because of those persnickity clouds) we are on track to recover our costs in a little over 10 years now.
The following chart shows that weather may play the most important role in power production:
| Monthly Generation – Predicted vs Actual | |||||
| Predicted | 2019 Actual | 2020 Actual | 2021 Actual | ||
| January | 487.8 | 326.78 | 302.78 | ||
| February | 607.3 | 516.92 | 376.02 | ||
| March | 944.8 | 848.07 | 1020 | ||
| April | 1095.4 | 949 | 1010 | ||
| May | 1231.5 | 1110 | 1150 | ||
| June | 1295.4 | 1260 | 1260 | ||
| July | 1284 | 1310 | 1320 | ||
| August | 1121.7 | 1130 | 1040 | ||
| September | 950.2 | 831 | 733 | ||
| October | 765.4 | 463 | 428.86 | ||
| November | 473.3 | 349 | 305.71 | ||
| December | 392.9 | 254 | 231.54 | ||
| adjustment* | 354 | ||||
| 10649.7 | 8010 | 9170.88 | |||
| *Note: April, May 2019 had some reading errors so totals are really higher | |||||
| About 355 KWh readings not recorded properly |
As noted above, April and May of 2019 had some monitoring errors (corrected by the company that collects the data) so these numbers are not necessarily comparable against 2020. It is clear that this past fall we had much poorer conditions than the previous fall. But then look at March 2021 – Much better readings than March of 2020 and much higher than the predicted number.
Last year I concluded that if we had installed two more panels that produced at least as well as our poorest producing panels we would break even. That still seems to be about true:
The worst panel shows a two year cumulative production of 513.62 KWh. The best panel produced 621.13 KWh during this period. So, 2 panels producing somewhere in-between would have broken even more or less.
As the surplus generated in March and April is paid off in May instead of crediting against the following fall/winter shortage, it would take another panel or 2 to avoid having a bill at all, except for the meter cost.