Solar roof production before PTO vs after PTO

[Redhill_qik]

I think I'm getting the gist of all this so I hope these are my last noob questions.

When trying to compare the actual performance of my system to the expected performance of my system, neither the rated 11.3 kW nor expected 9.97 kW are useful numbers because those only represent instantaneous peak production numbers. And I now understand that's not very useful information plus it can be inaccurate due to lensing. Correct?

So the only way to really evaluate system performance is to compare actual production on any given day with whatever a solar production estimation tool predicts for that day. I can't just look at the app to know. Correct?

And until I have PTO, the only way to know how much I power my system can generate would be on a cloudless day, that doesn't get too hot and my production isn't idled by my batteries hitting 100%. I don't see that happening because the only time I don't hit 100% is on the hottest days when my AC is running like mad. So then after PTO I will know how exactly how much I am generating because there will be no idle time and then I can compare that with a solar power estimator. Correct?

All of these are on target.

The only thing to keep in mind is that the solar estimates include historical weather data, so a day might be historical sunny with a high production estimate while this year it might be cloudy with low production and the reverse will be true as well. Look at the macro trends and not the micro events and expect that everything will average out.

What did Tesla estimate for your annual production? This should have been on the original panel location plan they gave you.

 

[BGbreeder]

Not sure if I'll have any success, but before I pay I'm going to try to get them to commit to some amount of time by which they will file the PTO paperwork. Any insight as to how long is reasonable? And then how I can confirm when it was actually filed?...

In short, no. Even if you ask the Tier 1 customer service person nicely. Just keep in touch with your utility and Tesla on a regular basis. Many folks have had it go through without any issues, and others have had the paperwork mislaid, so it runs the spectrum. All part of having Tesla as your partner.

On the bright side, it looks like your install went according to plan.

All the best,

BG

 

[uscpsycho]

What did Tesla estimate for your annual production? This should have been on the original panel location plan they gave you.

"
"Estimated energy produced: 16,577 kWh /yr"

Sound right?

 

[jboy210]

I think I'm getting the gist of all this so I hope these are my last noob questions.

When trying to compare the actual performance of my system to the expected performance of my system, neither the rated 11.3 kW nor expected 9.97 kW are useful numbers because those only represent instantaneous peak production numbers. And I now understand that's not very useful information plus it can be inaccurate due to lensing. Correct?

Correct. The size of the system determines what that instantaneous peak value can be.

So the only way to really evaluate system performance is to compare actual production on any given day with whatever a solar production estimation tool predicts for that day. I can't just look at the app to know. Correct?

The tools are a reasonable approximation. But that have assumption that may be correct for your particular installation. If you are getting close to their numbers that is IMHO enough.

And until I have PTO, the only way to know how much I power my system can generate would be on a cloudless day, that doesn't get too hot and my production isn't idled by my batteries hitting 100%. I don't see that happening because the only time I don't hit 100% is on the hottest days when my AC is running like mad. So then after PTO I will know how exactly how much I am generating because there will be no idle time and then I can compare that with a solar power estimator. Correct?

All correct.

However, don't get hung up on using PvWatts or another estimator on a day-by-day basis to see if your system is performing as specified. Your contract guarantee is based on annual production. And an estimator tool can give you a reasonable monthly estimate but can be off by quite a bit, and you still meet or exceed your annual production number, because you exceeded the estimate in other months.

 

[Redhill_qik]

"
"Estimated energy produced: 16,577 kWh /yr"

Sound right?

When I used the PVwatts calculator I got 19,440 kWh/year and @dareed1 used a different calculator that with the Tesla SR72T2 panels that resulted in less peak and less total production, but they didn't mention what the estimated annual production was. I thought it might have been the CSI-EPBB calculator and when I use the parameters below, I got an annual production of 17,074 kWh. I think that you will safely get the 16,577 kWh/year that your thought you were buying when you installed your solar roof.

 

[offandonagain]

And until I have PTO, the only way to know how much I power my system can generate would be on a cloudless day, that doesn't get too hot and my production isn't idled by my batteries hitting 100%. I don't see that happening because the only time I don't hit 100% is on the hottest days when my AC is running like mad.

If you have an EV, charging its battery during the day is a good way of avoiding all that solar going to waste pre-PTO (and seeing what your total solar output will look like).

 

[jboy210]

If you have an EV, charging its battery during the day is a good way of avoiding all that solar going to waste pre-PTO (and seeing what your total solar output will look like).

Yep. This was we did for the 5-month wait between paying the final invoice and getting PTO. Thanks, Covid. We cycled through our EVs charging and then driving them. One day we would drive the 3 and charge the X. The next day we drove the X and charge the 3. We would also take a bucket of kWhs over to the neighbors.

 

[charlesj]

... We would also take a bucket of kWhs over to the neighbors.

Was it heavy or just lots of vibration?

 

[BGbreeder]

Was it heavy or just lots of vibration?

I bet it was shockingly light.

 

[jboy210]

Was it heavy or just lots of vibration?

Almost weightless, just like quantum mechanics and Heisenberg predicts.

 

[dareed1]

When I used the PVwatts calculator I got 19,440 kWh/year and @dareed1 used a different calculator that with the Tesla SR72T2 panels that resulted in less peak and less total production, but they didn't mention what the estimated annual production was. I thought it might have been the CSI-EPBB calculator and when I use the parameters below, I got an annual production of 17,074 kWh. I think that you will safely get the 16,577 kWh/year that your thought you were buying when you installed your solar roof.

I used a different kind of calculator put out by New Mexico State University. It has quite a bit of detail not provided by PVWatts, but it isn't useful for projecting annual production--it calculates the output assuming no shading and clear weather. I augmented the spreadsheet by adding a tab that gives expected solar power for a given day at 5 minute intervals, using their equations. I find that this kind of calculation is good for evaluating whether a solar installation is working correctly, and it is also useful to see the interplay between direct, reflected, and diffuse insolation, as well as the effect of air mass ratio, and typical atmospheric opacity. PVWatts takes into account an estimate of expected daily weather, and this is very good for estimating annual production, but it can be difficult to extract clear day estimates in the "green" ( as opposed to "brown") part of the year in California.

However, I think it yielded almost identical results as you obtained with PVWatts for June 21. Minor differences in power are likely due to assumed temperatures and efficiencies.

 

[haali77]

I think this because it’s actually just the legend at the top of the y axis. The bottom is labeled 0 kW and the top corresponds to the highest graphed value because the axis adjusts to fit the chart.

 

[worried_guy]

Bringing this thread back to the original question -- I'm in pretty much the same situation as uscpsycho except that my pre-PTO system seems to be doing worse relative to the expectations than uscpsycho's system is ...

41 400W panels to make a 16.4 kW system. Tesla's estimated annual production is 13,723 kWh.
4 powerwalls (including two powerwall +), set to keep 50% in reserve. They never make it to 100% full.
On most days, daily peak production is 3.6 kW. There was one outlier day over the past 2 weeks where it was 5 kW.
Daily total production has varied from 12 kWh to 18 kWh over the past two weeks, most often around 13 kWh.
I'm located in the SFO bay area. There are lots of trees around, but my understanding was that the Tesla estimate is supposed to take them into account.

So, my system is never getting close to the levels at which it would export power. It's never even filling the powerwalls completely and does not appear to be max'ing out inverter capacity. Tesla's annual estimate divided by 365 would be 38 kWh vs the 13 kWh or so I get on most days. Even accounting for the fact that we should be below average now (and above that average in summer), I'm having trouble believing I'll get anything close to the Tesla estimate unless the pre-PTO throttle is throttling my system, i.e. even though the system is never close to the point where it would try to export power.

A technician recently came back to put in a ground rod, and he checked everything and confirmed that the wiring appears to all be correct, and all strings are online. He was surprised to hear about my numbers, but doesn't know details of what the throttle does.

Does anyone know if the pre-PTO throttle could be limiting my system currently? Have others tended to get the annual production that Tesla esimated, or at least been within say 80% of it?

Some mentioned a "contract guarantee" -- I guess I have not read all my paperwork carefully enough. Does Tesla actually guarantee some amount vs the estimate?

Sorry for all the newb questions. I have tried reading through a few similar threads. This one seemed to be asking the exact question that's on my mind too. Thanks!

 

[jboy210]

Bringing this thread back to the original question -- I'm in pretty much the same situation as uscpsycho except that my pre-PTO system seems to be doing worse relative to the expectations than uscpsycho's system is ...

41 400W panels to make a 16.4 kW system. Tesla's estimated annual production is 13,723 kWh.
4 powerwalls (including two powerwall +), set to keep 50% in reserve. They never make it to 100% full.
On most days, daily peak production is 3.6 kW. There was one outlier day over the past 2 weeks where it was 5 kW.
Daily total production has varied from 12 kWh to 18 kWh over the past two weeks, most often around 13 kWh.
I'm located in the SFO bay area. There are lots of trees around, but my understanding was that the Tesla estimate is supposed to take them into account.

So, my system is never getting close to the levels at which it would export power. It's never even filling the powerwalls completely and does not appear to be max'ing out inverter capacity. Tesla's annual estimate divided by 365 would be 38 kWh vs the 13 kWh or so I get on most days. Even accounting for the fact that we should be below average now (and above that average in summer), I'm having trouble believing I'll get anything close to the Tesla estimate unless the pre-PTO throttle is throttling my system, i.e. even though the system is never close to the point where it would try to export power.

A technician recently came back to put in a ground rod, and he checked everything and confirmed that the wiring appears to all be correct, and all strings are online. He was surprised to hear about my numbers, but doesn't know details of what the throttle does.

Does anyone know if the pre-PTO throttle could be limiting my system currently? Have others tended to get the annual production that Tesla esimated, or at least been within say 80% of it?

Some mentioned a "contract guarantee" -- I guess I have not read all my paperwork carefully enough. Does Tesla actually guarantee some amount vs the estimate?

Sorry for all the newb questions. I have tried reading through a few similar threads. This one seemed to be asking the exact question that's on my mind too. Thanks!

Others can respond for sure, but I thought pre-PTO they now do throttle the system.

Regarding the guarantee, if there is one it should be in your contract. Note it is an annual number, and we are way past peak solar generation days. Assuming no shading from homes, trees, clouds, etc., and south facing panels, the peaks usually around the summer Solstice, June 21. Now, we are much closer to the worse days, around Dec 21, the winter Solstice. Our solarroof is generating less than 15% of the peak daily production this time of year because the date (low weak sun) and considerable shading.

 

[tbx1203]

Yes. Tesla will try to prevent your system from exporting before PTO.

If I have more time I will try to answer your other questions but I'm hoping others will be beat me to them.

I'm trying to figure this out also. I just got a 9.6kw system with 2 x Powerwall+ installed. Battery never makes it to 100% charge. Most I got was 80%, usually around 60-70%

 

[tbx1203]

Yes. Tesla will try to prevent your system from exporting before PTO.

If I have more time I will try to answer your other questions but I'm hoping others will be beat me to them.

I'm trying to figure this out. Also. I just got a 9.6 kW system installed with two powerwall+. I notice I never get to 100% charge. Max, I got up to was 80% but usually hovers around 60 to 70%. I live in New Jersey and my solar production is roughly 4 to 5.6 kw.

 

[arnolddeleon]

I'm trying to figure this out. Also. I just got a 9.6 kW system installed with two powerwall+. I notice I never get to 100% charge. Max, I got up to was 80% but usually hovers around 60 to 70%. I live in New Jersey and my solar production is roughly 4 to 5.6 kw.

First, we need help you sort out kW vs kWh. They are related but not the same. Think of kW as a rate or kWh (kilo Watt hour) as total. Do some searching with your favorite search engine for "kW vs kWh" and find an explanation that works for you. Once you understand the difference the rest of this hopefully will make more sense. BTW pretty much everyone gets this wrong initially. I've been explaining solar to a lot of people recently and this always one of the things that needs to be explained.

Since you are in thread then I'm going to assume you are pre PTO.

You have two Powerwalls. They can hold roughly 13 kWh each (for the pedant's I'm going to round and use numbers from memory to speed writing this). So you have an energy bucket that is roughly 26kWh in size.

You say you have 9.6 kW system. This means that under ideal (but practically unobtainium conditions) the system could produce around 10 kW (rounding up) so it can fill your Powerwalls in about 2.6 hours if all the energy went to the Powerwalls (That's 10 kW x 2.6 hours to produce 26 kWh). Note that this will never happen. Your roof doesn't move and face the sun perfectly all day. Furthermore, as the season changes the angle of the sun changes.

You say your system production is 4 to 5.6 kW. When talking about production I would usually talk about kWh not kW. Based on the numbers you are giving, I'm guessing you are giving us your peak power output. That's not nearly as helpful as your power production. My finger in the wind guess for the production of system such as you have under sunny conditions would be around 20 kWh per day at this time of year.

So if the batteries were "empty" your solar will fill the batteries around 77% (20/26), amazingly within the range that you are seeing.

Most likely you are batteries are not going to empty but also most likely all the solar is not going to batteries either. You are likely consuming some it during the day and only the surplus is going to the batteries. Most likely your batteries are draining down to the reserve at night and then being filled up by the little bit of surplus solar. If you are landing roughly at the same percentage each day, then your PV system is producing roughly the same amount you are consuming. You will not reach 100% either you raise your reserve (you may not have control if you are pre-PTO, I don't know what settings Tesla gives pre-PTO) or the days get longer (more solar) or you consume less.

We will need more information if we are figure out if something is wrong but none of the information you have shared so far suggests a fault.

 

[twowheels]

I am learning that peak production is not such an important variable. But before I knew this, when I complained to Tesla that my peak production was not as high as I expected, they told me that it was because I didn't have PTO and that after PTO my peak production would go up. As irrelevant as peak production might be in the big scheme of things, what they said is false. If I trusted them, I'd be expecting that peak number to go up after PTO and it would not.

As I've always understood it, nothing will change after PTO other than the fact that I will start to export my extra capacity to the grid. There is no other artificial cap. So theoretically, if I used so much power that my batteries never hit 100%, I would generate the same amount of solar power before and after PTO. The difference between before/after PTO is what happens when the batteries are at 100%. Correct?

LOL! That was a hard one to get answered! Everyone wanted to answer their owned question or a question they felt was correct. But I was told almost the exact same thing. I would produce more energy, after PTO. Difficult to understand why, but I think the software may update after PTO. Maybe max production is withheld for payment? I don't know, but I was told they exact same thing. I was also told I would "test" PTO on the app without ramifications. I'm not 100% clear on that one. Of course they don't want to say it's okay or be connected with saying it's okay incase something happens. I haven't done that yet. I just passed inspection and would like to test it, but probably won't. You have probably received PTO. Did your production go up? Thanks!

 

[jboy210]

LOL! That was a hard one to get answered! Everyone wanted to answer their owned question or a question they felt was correct. But I was told almost the exact same thing. I would produce more energy, after PTO. Difficult to understand why, but I think the software may update after PTO. Maybe max production is withheld for payment? I don't know, but I was told they exact same thing. I was also told I would "test" PTO on the app without ramifications. I'm not 100% clear on that one. Of course they don't want to say it's okay or be connected with saying it's okay incase something happens. I haven't done that yet. I just passed inspection and would like to test it, but probably won't. You have probably received PTO. Did your production go up? Thanks!

I wonder if they now do not let or limit the solar generate power that was sent back to the grid prior to PTO.

I was told that I could not make the solar active prior to PTO. And then in a hushed tone, told to monitor it if I was "testing", and turn it off if it started sending power back to the grid. (Cue Keystone cops' music of me swapping car chargers between X and 3 to eat up the "test" solar generated kW and avoid sending excess to the grid.) This was in 2020 with the older Gateway.

 

[Matt-FL]

As of last year they were not limiting. My pre-PTO numbers were no different than post-PTO. Installed Aug 29, 2022, PTO Jan 27, 2023.

My lead Tesla installer turned the system on and said I could leave it on since I had batteries, but (cue Keystone cops' music, once again ) if I was pushing a lot of power back, to switch to off-grid mode.

When my utility came out to inspect, he didn't say anything about it being powered. He did his inspections, checked grounds and neutrals, then swapped the meter for a 2-way and was on his way.