One Year post-PTO Solar Roof in MD

[wjgjr]

Our solar roof was installed in March, 2020, but we did not get PTO until 7/20/2020, so we have now been fully operating for just over a year (and numbers below are mostly for 8/1/2020-7/31/2021 for convenience.) The system is about 8.19 kW (split 50/50 north/south) with a 7.6 kW Delta Solivia inverter, and we did install 2 PWs. Overall, everything has performed great. We produced almost 6% more electricity than the Tesla estimate, and the system operated without issue the entire time. We had about 25 backup events, though all appeared to be brief blips - no actual outages. We did, however, operate offline for about 3 days total to test the system.

Below are our actual numbers, and a comparison to various estimates.

Source	Annual Production (kWh)	Actual Compared to Estimate (%)
Actual	8342​	0​
Tesla	7876​	5.9​
PVWatts	8698​	-4.1​
SRECTrade	8501​	-1.9​

The Tesla number comes from the contract, while the PVWatts number comes from using their website, and may be a slight overestimate based on not providing correct parameters. A closer estimate should be the numbers from SRECTrade. Because we have a system under 10 kW, Maryland allows us to receive SREC credits based on estimated production instead of actual results, and SRECTrade produces those estimates (and is also based on PVWatts.)

What is notable is that our system has matched or outperformed the PVWatts/SRECTrade numbers in the spring and early summer, and significantly underperformed for much of the fall and winter. While weather could be part of it, I also suspect that being in a fairly densely-built neighborhood, the effects of some trees and houses blocking the sun nearer the horizon are likely more pronounced at that time of year. Below are two charts illustrating the monthly performance (Tesla does not provide monthly numbers, so these were estimated based on the PVWatts numbers.)

Finally, with an east-coast system, it is interesting to look at the daily data to illustrate how variable it is compared to some other climates. While the annual cycle is clear, the variation from day to day can be significant. Overall, our best three days were all in June, with it being relatively cool in the second half of the month just as we hit the solstice:

1. 6/17/21: 47.7 kWh
2. 6/23/21: 47.6 kWh
3. 6/16/21: 46.4 kWh

The worst-performing days were all fall/winter days with big storms:

1. 12/16/20: 0.7 kWh
2. 2/18/21: 0.8 kWh
3. 11/11/20: 1.1 kWh

The red/yellow boundary is the Tesla estimate, and the yellow/green is PVWatts. The blue line indicates how production to date was trending. As with the monthly graphs above, the trend was down towards the Tesla average, which we more or less hit at the end of February, before rebounding again in the spring.

 

[jboy210]

Thanks for the information and great presentation format. We have a slightly larger system, 12.75 kW, and see similar performance to yours in the winter (we have large trees to the South and West) and about 50 kW peaks in summer (now that they replaced a lot of tiles).

When I last looked PvWatts did not have solarroof tiles as a choice. Do they have them now?

 

[wjgjr]

Thanks for the information and great presentation format. We have a slightly larger system, 12.75 kW, and see similar performance to yours in the winter (we have large trees to the South and West) and about 50 kW peaks in summer (now that they replaced a lot of tiles).

When I last looked PvWatts did not have solarroof tiles as a choice. Do they have them now?

Last I looked, which was a while ago, they did not, so I had to do my best estimate as far as the parameters.

 

[Vines]

Thanks for sharing your detailed analysis!

Not surprised your winter production is poor, if it's something like a 30-degree roof and you have panels facing true north.

Those panels are worth almost half of those facing South as far as yearly production is concerned, as the sun won't even shine on them due to low sun angle much of the year.

Still, I am surprised your production is as good as it is honestly.

 

[wjgjr]

Thanks for sharing your detailed analysis!

Not surprised your winter production is poor, if it's something like a 30-degree roof and you have panels facing true north.

Those panels are worth almost half of those facing South as far as yearly production is concerned, as the sun won't even shine on them due to low sun angle much of the year.

Still, I am surprised your production is as good as it is honestly.

Even slightly higher (8/12 - ~34°). So, I was certainly expecting lower production in winter, and PVWatts estimated, for example, only 56 kWh for the north-facing panels (technically 7°) in all of December. But, even those low estimates from PVWatts and SRECTrade turned out too high for winter (whereas they were close or even low for spring/early summer) which was interesting to me and suggests something else at play not captured in those estimates - whether it is some shading or related to inverter performance or just the way the weather was this year.

 

[sorka]

I just passed 9000 kwh in the first 7 months since going PTO with my 8.16kw system, but I'm in California with all panels facing 205 degrees southwest (perfect for peak TOU NEM) and 25 degrees of latitude.

Way higher than Tesla's estimate and 800 kwh higher than pvwatts.

 

[Vines]

I just passed 9000 kwh in the first 7 months since going PTO with my 8.16kw system, but I'm in California with all panels facing 205 degrees southwest (perfect for peak TOU NEM) and 25 degrees of latitude.

Way higher than Tesla's estimate and 800 kwh higher than pvwatts.

This year hasn't had much weather so many systems are outperforming the estimates. Especially with traditional panels, this is well known, and production estimates are very accurate when accurate inputs are used.

Solar roofs OTOH are much less well known, so it's interesting to see how they perform or not compared to the estimates.

 

[jboy210]

This year hasn't had much weather so many systems are outperforming the estimates. Especially with traditional panels, this is well known, and production estimates are very accurate when accurate inputs are used.

Solar roofs OTOH are much less well known, so it's interesting to see how they perform or not compared to the estimates.

FWIW, Ours is right at the estimates from Tesla. I am actually a little surprised at how good Tesla's production estimates are considering we have quite a bit of shading (large 60-foot Oak tree due south and row of 50-foot trees due West). I guess they have a good design/estimate software package.

 

[sorka]

This year hasn't had much weather so many systems are outperforming the estimates. Especially with traditional panels, this is well known, and production estimates are very accurate when accurate inputs are used.

Solar roofs OTOH are much less well known, so it's interesting to see how they perform or not compared to the estimates.

Where I live in the Central Valley, there's never any weather except sometimes in winter. I'm exceeding in every summer month where there's almost never overcast.

 

[bourgain]

I'm in Maryland and have been waiting for about 2 months for PTO. wjgjr was your extremely long PTO due in part to the COVID lockdown starting right after your installation?

Not happy with my wait so far and I hope I don't have to wait 4 months or so like you did!

 

[wjgjr]

I'm in Maryland and have been waiting for about 2 months for PTO. wjgjr was your extremely long PTO due in part to the COVID lockdown starting right after your installation?

Not happy with my wait so far and I hope I don't have to wait 4 months or so like you did!

There were a few factors. I think COVID was actually a small piece, as the county really did a pretty good job of handling things, including having their inspector sit in a car and video chat with a Tesla tech who showed them our system for the inspection. The bigger issues were Tesla being slow in submitting revised paperwork (as the plans had some changes from what was originally filed) and PEPCO being slow. For the former, about all you can do is keep bugging Tesla (but reports elsewhere on this forum seem to indicate they are really overworked, so there may not be much to do.) For the latter, PEPCO does have specific timelines for things. In retrospect, I probably should have contacted them earlier and might have saved a couple weeks off the timeline - they had met all their timeline targets (essentially to the day) until the last step, and I have a feeling something might have gotten lost on their end as I got PTO very soon after contacting them about the delay.

 

[bourgain]

There were a few factors. I think COVID was actually a small piece, as the county really did a pretty good job of handling things, including having their inspector sit in a car and video chat with a Tesla tech who showed them our system for the inspection. The bigger issues were Tesla being slow in submitting revised paperwork (as the plans had some changes from what was originally filed) and PEPCO being slow. For the former, about all you can do is keep bugging Tesla (but reports elsewhere on this forum seem to indicate they are really overworked, so there may not be much to do.) For the latter, PEPCO does have specific timelines for things. In retrospect, I probably should have contacted them earlier and might have saved a couple weeks off the timeline - they had met all their timeline targets (essentially to the day) until the last step, and I have a feeling something might have gotten lost on their end as I got PTO very soon after contacting them about the delay.

Thanks for your reply. Tesla hasn't submitted anything to BGE and it's been almost 2 months. Not happy about that. Have called them a couple of times. They say that in the contract I signed it says PTO can take up to 90 days. I tell them that I didn't "read the fine print" and might not have gone with them if I knew about this. Unacceptable.

 

[trautmane2]

Thanks for sharing this data @wjgjr . I've been dealing with a solar roof production issue that I hope Tesla was able to fix during a service visit in early August. I plan to post about that soon. Would you mind sharing your monthly total values for July and August 2021? Since we are geographically close, I was hoping to use your actuals for those months (and their ratio) to compare to my before and after fix actuals.

 

[wjgjr]

Thanks for sharing this data @wjgjr . I've been dealing with a solar roof production issue that I hope Tesla was able to fix during a service visit in early August. I plan to post about that soon. Would you mind sharing your monthly total values for July and August 2021? Since we are geographically close, I was hoping to use your actuals for those months (and their ratio) to compare to my before and after fix actuals.

Sure - 1051 kWh for July and 861 for August. (And August, 2020, was 864, so virtually identical production compared to last year.)

 

[chucklesn]

Tesla hasn't submitted anything to BGE and it's been almost 2 months. Not happy about that. Have called them a couple of times. They say that in the contract I signed it says PTO can take up to 90 days.

I made the mistake of giving Tesla the 90 days after installation to get PTO from PEPCO. Our solar roof install was in May 2021 and the site supervisor told me to expect it to take 90 days to get install. After the three months I started emailing my project advisor and texting to the number from Tesla that set up county inspection. Basically got a couple of non answers and then ghosted. Finally ended up working directly with PEPCO to get PTO in Oct 2021. PEPCO had been asking for resubmissions of the paperwork that Tesla had filled out in February with the wrong name and technical numbers. After I had explained that Tesla had ghosted me and even the contact info on the submitted paperwork by Tesla were wrong (disconnected number in Las Vegas) , PEPCO was kind enough to spoon feed me the correct numbers to put into the forms. So 5 months to PTO and three project advisors that left the company according to auto-replies. Of course the day after I received PTO and turned on the inverters I get an automated congratulations text message from Tesla saying I can turn on the system.
See if you can work directly with BGE on the PTO.