I had 11.6 kW of solar panels and 3 Powerwalls installed about a month ago here in Miami, FL. It's summer so the days are pretty long, and even on the clearest day, I seem to only generate about 7.0 or 7.5 kW of power from the solar panels. Anyone else having this experience? I feel like I should at least hit a "peak" of 11 kW on a clear day when the sun is just right. PS I just ordered another 4.25 kW of panels (another $8k) so I can generate more power.
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Solar Panels only generating about 60% [of peak production number]
- Thread starter MiamiBrian
- Start date
Welcome to TMC.
This is a very common question (someone asks some variation of this question at least a couple times a month). The very short version of the answer is, just because you purchased a "11.6kW" system, that doesnt mean you will ever see a peak input of 11.6kW of solar production.
Unless you have:
1. Inverter capacity rating of 11.6 or higher
2. all panels pointing in the optimum southern direction
3. Perfect pitch on your roof for maximum solar production.
You will likely never see that number (and that number isnt important, actually). Solar production is tracked over weeks and months, Not hitting 11.6 for an 11.6 system doesnt really matter for overall production.
To check your production, go to a site like pvwatts and input all your variables.
In the vast majority of these questions, it is "completely, 100% normal and expected" to not ever hit the peak number for the solar you purchased. Most dont, actually.
This is a very common question (someone asks some variation of this question at least a couple times a month). The very short version of the answer is, just because you purchased a "11.6kW" system, that doesnt mean you will ever see a peak input of 11.6kW of solar production.
Unless you have:
1. Inverter capacity rating of 11.6 or higher
2. all panels pointing in the optimum southern direction
3. Perfect pitch on your roof for maximum solar production.
You will likely never see that number (and that number isnt important, actually). Solar production is tracked over weeks and months, Not hitting 11.6 for an 11.6 system doesnt really matter for overall production.
To check your production, go to a site like pvwatts and input all your variables.
In the vast majority of these questions, it is "completely, 100% normal and expected" to not ever hit the peak number for the solar you purchased. Most dont, actually.
What is your inverter size? You will never get more than that. Its not summer. My production is down over 50% from like June, and it will get worse!! And you will never hit your panel ratings!! I have 15K of panels and best I got was like 11K out of them with a 11.4k inverter
Also, OP, for that additional "4.25kW" of solar you are buying, the inverter probably isnt "4.25kW" or larger. Its probably 3.X (3.6 or something). that means your new 4.25kW of solar wont add a peak of 4.25kW to your peak production number. It wont add more than the inverter to that peak number, however, the yearly production will likely be more than 4,250kWh of additional PV production over a years time.
I wonder why so many think that can produce their panel ratings? Why many seems to have no idea their inverter size how it limits output? Why so many do not seem to understand how the time of year, direction of panels have such a huge impact on production. For what this stuff costs, and how easily one can google any question, do folks just write the checks and not understand the limitations? Now with that said, I talk to plenty of folks asking about, or getting solar, and yep, they have no idea the answers to these questions. But, this site is sure a great place for folks to learn, even if after the fact. Too bad many do not do the research and, IMO, put on as many panels that their roofs can support. Adding afterwards can really mess up the installation, IMO! Just having multi inverters would be a pain!! And with NEM3 coming, could totally change the dynamics of solar installs.
the other post is but I was told my batteries could run my house for 2.5 days. Yea, another great sales line. Of course, there is no details on what that meant
I believe thats a bit harsh, actually. The fact that so many people ask, means its not easily understood. I dont think its out of bounds for someone to think "I bought a 15kW system, it should go to 15kW... right?". We know these answers because we either already knew the technology, researched it because we are "into that" or someone explained it to us.
Thats one reason people end up here, trying to understand it, or confused. So, while its asked a lot, to me at least, its understandable why its asked.
On the "X number of days backup" , on the order form through tesla it says "based on your address and utility bill of $XXX, we estimate you need Y number of powerwalls for Z days of backup. To me, its fairly obvious that there are way too many variables there to assume any sort of backup without knowing how much power you use, but they put an estimate in there (which looks pretty inaccurate to me btw).
Its certainly not strange for people to see that estimate and think "oh cool I have 2 days of backup, thats what they said" even though they wont get nearly that with their pool pump, mini splits, etc etc. Sort of like people looking at a "350 mile range" EV and thinking it will actually travel 350 miles at 80MPH.
Anyway, I think its a bit harsh to come down on people looking into this, even if its after the fact. Sometimes people dont even bother looking until they think there is an issue (very common), so lets cut them some slack.
Thats one reason people end up here, trying to understand it, or confused. So, while its asked a lot, to me at least, its understandable why its asked.
On the "X number of days backup" , on the order form through tesla it says "based on your address and utility bill of $XXX, we estimate you need Y number of powerwalls for Z days of backup. To me, its fairly obvious that there are way too many variables there to assume any sort of backup without knowing how much power you use, but they put an estimate in there (which looks pretty inaccurate to me btw).
Its certainly not strange for people to see that estimate and think "oh cool I have 2 days of backup, thats what they said" even though they wont get nearly that with their pool pump, mini splits, etc etc. Sort of like people looking at a "350 mile range" EV and thinking it will actually travel 350 miles at 80MPH.
Anyway, I think its a bit harsh to come down on people looking into this, even if its after the fact. Sometimes people dont even bother looking until they think there is an issue (very common), so lets cut them some slack.
IMO, I like to think I do my research before buying stuff, and searching the Internet was the least helpful thing I did when looking into Solar and Batteries. All the search results are shills or sites trying to profit off of lead generation.
The only useful places I found to give good insights were TMC and one of those Solar DIY forums. Even then the solar forum was mostly filled with nerds spouting specs and stuff... they weren't really helpful to explain things in a way for a novice to understand. The only reason I even found TMC was because I was searching about metering non-backup loads on a partial home backup. Had @Vines not given me so much insight about how this stuff works, my "expertly designed and well researched system with a local solar company" would have been absolutely trash.
Look at the way Solar is sold. They advertise kWp (DC) systems that expect to hit an estimated annual kWh production figure. This allows a salesperson to just boast about the overall coverage of solar on the roof (watts per panel x number of panels). And people fixate on the total annual generation against expected annual consumption thing. They never get into the specifics of daily production curves, the area under said curve, and how the inverter plays any role at all. Since solar and ESS tech is fairly new, there is no huge body of generational experience people have learned over time (like with automobiles or home purchases).
And batteries are just sold as resiliency devices. Zero salespeople I spoke with knew about TOU shifting or running self-powered even on non-backup-loads. I literally had to try to explain to them what I was going for and they were coming back to me telling me I was full of crap.
Thanks for this reply and the others in this forum. I'm brand new to this forum, tons of good info on here.
Inverters: I honestly had no idea there was so much to know about inverters and that these can somehow limit production? I have 3 Powerwalls with capacity of 40.5 kWh, with "an integrated storage inverter/charger capable of producing a combined 15.00 kW of continuous power and 21.00 kW of surge power." I would appreciate it if you could educate me on what this means. And some people have 2 inverters?? PS My home generally requires around 100-120 per day. Thanks again everyone.
Welcome to the form. There is a lot to learn here, so good on you for seeking the knowledge.
The inverter inside the Powerwall has a 5 kW Power Rating, and a 13.5 kW energy rating. It can surge to 7kW at times.
The PV inverter size is the maximum size in watts that the inverter can output in AC. Often the DC size is 120-130% of the AC size, but the real calculation to pay attention to is how much you pay, compared to your kWh per year generated.
Looking at the peak output power is almost useless, as it really doesn't inform you much. A system who's output graph with a high peak often has narrow shoulders, which means you probably have too much inverter for a given area under the curve.
Almost all systems these days clip a little bit, but in the vast majority of cases this is not an issue as long as you optimize cost of system compared with kWh generated per year. You can always throw more money at a larger inverter and make a longer payback, but unless you like lighting money on fire, then just don't.
Also, as your system ages, the PV output goes down. So if you buy a system with no clipping year 1, you will waste even more of your inverter as the panels age.
charlesj
Active Member
A couple of things to add to what others have posted.
You may think it is summer there but checking day length for Miami today your daylight is only 11:33 hours, sunrise to sunset.
On Dec 21 you have 10:31 hours of daylight and on June 21 you have 13:44 hours.
So, today you have 2 hours less daylight. Interestingly, your day length only changes 3 hours during a year.
Mine changes 5 hours with 14:40 hours on June 21 and 9:40 on Dec 21.
Because of the sun's overhead angle changes throughout the year, your real solar generation per panel will change as well, not uniform throughout the year.
The other consideration is your inverter size. Yes, your added solar panels will generate more power(kW) and more energy(kWh) in a day than your present production but, always a but,
, your peak power(kW) will not be higher than your inverter size. However, you will produce closer to max inverter capability for more hours (kWh) in a day than what you have now.ps. one more to add: panel rating you read is not a realistic real world number as it can be 5% less or more perhaps.
pps. from your responses is seems you just didn't know the questions to ask whoever you bought the system from and they didn't explain the ins and outs of solar and batteries.
We would need more info about your system and what you used annually in previous years.
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J or any other mods
Any thought of putting together a sticky thread on "Why do I never see my system generate the quoted output in the app"? As you point out this is a common question. And one that I think most solar purchasers at some point have when they look at their data. Finally, the answer depends on a number of interconnected factors.
I have thought about it, actually. While we get the question fairly often, its phrased differently each time so that makes previous threads on that topic harder to track down.
I looked for a few minutes this morning (to move this thread into a recent on one this topic, actually) and could not easily find one, so figured that If I couldnt find one quickly, a new user likely wouldnt have either, so I stopped looking and just replied in this one.
The fact that the answer depends on a number of interconnected factors, as you so aptly put it, also makes putting a "general" FAQ type post together a bit problematic. I might turn this one into a sticky, but wanted to see what it looked like ( was it representative of the other discussions on this topic) before I did that.
I looked for a few minutes this morning (to move this thread into a recent on one this topic, actually) and could not easily find one, so figured that If I couldnt find one quickly, a new user likely wouldnt have either, so I stopped looking and just replied in this one.
The fact that the answer depends on a number of interconnected factors, as you so aptly put it, also makes putting a "general" FAQ type post together a bit problematic. I might turn this one into a sticky, but wanted to see what it looked like ( was it representative of the other discussions on this topic) before I did that.
Yeah the internet at large is a poor source of info just because everyone wants to make $. TMC users don’t seem to have the motive to spin things and make a sale.
interestingly enough someone wrote this comprehensive side-by-side of Tesla Vs Sunpower. For disclosure, I didn’t write this and I think it’s not a good article. It’s an obvious shill piece where he’s trying to clip $500 coupons and get referral money.
SunPower & Tesla Solar â Rooftop Solar Comparison - CleanTechnica
Sign up for daily news updates from CleanTechnica on email. Or follow us on Google News! As part of my familyâs journey to learn more about residential renewable energy, I decided to look into solar panels for our house. We are in the middle of Texas, and who can forget ... [continued]
cleantechnica.com
But these are the types of things that pop up on internet searches. Look at what the author says about the 8.5 kWp DC Tesla system vs the 7.2 kWp DC SunPower system. The author believes the Sunpower is better producing because the panels should degrade less. He never says anything about inverters or the orientation of the panels.
It’s easy to imagine how confused someone might be if they buy a system after doing all this research and don’t see anything near 7.2 kWp AC.
I don't know that you mentioned how many inverters you have, but you could have one or two. What the other posters are referring to is that inverter size is always some fraction of system size. In my case its 16.32 kw system with two 7.6 inverters.
Those in the know would say that 15.2 inverter capacity on a 16.32 system is "more" inverter capacity than you need, but its fine by me (since I wouldn't have saved much by asking for a smaller inverter) and I plan on adding panels at some point now that I see the size of the system.
Next up, if you require 100 to 120 per day you should have gotten the largest size system in the first place. My 16.32 in so cal does not get over 100 per day all year. Sure, over 100 on the best days, but not all.
Next, next up. Your original question. Even on the days my system produces 120, it never reaches 16.32. The best hour is around 12. something. But you get to 120 by having 14 hours of daylight and maybe six hours of production over 10? Today I will get around 75 and only three hours of production were 10 or above.
Next, next, next up. Now that you don't worry about reaching the system size in terms of production, what do you, or should you, get? Its all about location of your house, roof angle, and shading, and how the panels are arranged.
Finally, your last question is sort of the least relevant. Those numbers are what the PWs can put out. Its certainly "relevant" but other than when A/C is starting up, your PWs are hopefully not outputting 15 continuously. I mean, at 15 they would only last like two hours and a bit allowing for a 20% reserve.
What actually happens is, that you will figure out what your house draws at night, average. For us its about 1.5 to 2.5 kwh. Then, do the math, ten hours of that is 15 to 25 kwh. If you have a 20 percent reserve, subtract 8 from your 40.5 and its 34. Remember, I used ten hours to make the math easy, during winter you are going to have 14 hours a day of full darkness and another hour in the morning and evening of not enough sun to power the house.
So, 14 hours at 2 kwh per hour uses up 28 of your 34 available PW.
I mean, 21kwh of surge power? I certainly hope not!
So its:
A. The size of the system has to be converted to your location and roof, then you can get estimated power production.
B. If you use 100 a day you need a big ass system. Probably need a 4th PW. Otherwise, (i) the system won't produce enough to cover house usage, and (ii) part of that means you need to fully charge the over and above house usage, so that (iii) the PWs can make it through the night, or at least the average night, or at least most of the average night.
This is why, when you look at the boards, all the people who already have solar always tell every one to just get the biggest system you can fit on the roof.
Yes, this is the way. But the PG&E could dump all over you and cap you with their stupid rules on over-producing. Unless your name is h2ofun. That guy must have friends at PG&E...
Unfortunately solar salespeople have a tough time rationalizing this ideology for normal customers since they'd be all upset about over-producing and not getting their money's worth. I think TMC users also tend to get EV's, heat pumps, electric water heaters, etc so they'll naturally evolve into using all that energy.
I think the OP might not be clear on the concept that each Powerwall includes an inverter so it can output AC power, but the replies here are not talking about the inverters in the Powerwalls. They are talking about the solar inverter. If you have a Powerwall+, the solar inverter is the box on top. Otherwise, it's a separate box.
I wondered about the ease of the add, often. It would make some sense if, at least in part, PG&E's views change depending on local variables, such as how much power does the customer use in a day/month/year (@h2ofun clearly has a track record of high usage, as his powerwalls don't last very long), current infrastructure (transformers, HV supply lines), local demand, and how many folks already have solar. I am not saying that they are always logical, far from, as their track record demonstrates, but I am open to the possibility that there are some parts that might be.
(I think you (@holeydonut) just drew the short straw, and got someone really cranky. Sorry. But it makes for great stories around the campfire, "...then the inspector of all things electrical past appeared to me, dragging his chains and disconnect boxes, and drew me onward to see the melting batteries with no disconnects... Gasp!")
All the best,
BG
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