SSonnentag
埃隆•馬斯克
Peak production in the northern hemisphere is around May 20. In my case, our 12.5 kW system peaked out at 10.5 kW on that day last year. That is 84% of the system's theoretical maximum output. Your system is working normally.
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My Tesla Solar Roof is underperforming by at least 20%
- Thread starter jimm01
- Start date
Peak production depends on a lot of factors besides the hemisphere: roof angle, atmosphere optical density, panel temperatures, location, etc .
Is there a time of day when there is no shading anywhere on the active tiles? What time is that?
It seems to be just as conservative (based on my solar roof, and that of others previously reported - can't say if it has changed more recently.) As mentioned above, I am trending towards 3% above estimate (and am actually expecting to be above that based on relative performance in summer vs winter, but we will see.)
Beyond that, the calculation is no different from or more difficult to understand than for panels. It is still an XX kW system which should produce YYYY kWh annually. The issues regarding peak power versus nameplate rating are all the same for both system types.
I do agree that Tesla could do more to educate consumers on what to expect, but this issue is not in any way unique to the solar roof offering.
I'm a little confused, as earlier you said you have a 10.6 kW DC system, but various sites say Solar Roof v3 is 58.25W per tile, which would be a 13.3 kW DC system.
Also, what size is your inverter?
PVWatts, based on the above, and using 10% system losses (PV Watts defaults to 14%, not sure what's appropriate but have the impression that's very pessimistic), thinks the maximum hourly AC production on a 10.6 kW DC should be 9400W for the first month of May. That would be perfect conditions and assumes no clipping.
It also thinks that with a 1.2 DC/AC ratio (8.8 kW inverter), you wouldn't actually lose any annual production--even though AC production would be curtailed this time of year, apparently its inverter model says that the greater inverter efficiency at other times of the year would make up for it. Not sure if that is true for Tesla's inverter.
Cheers, Wayne
I don't have anything to add since I do not know much about this, but I can share my limited 20 days experience with my 6.5 kW solar roof + 2 PWs system. When I placed the order the project advisor basically asked me how many kWh annually I would need from the roof, I told him my last 3 years consumption was around 7000 kWh so anything above that would be fine. At that time I forgot that we were usually out of the country for at least 30 to 40 days a year but not anymore after the pandemic, I should have asked for a 8000 kWh system. Anyway the system was installed in February 2021 and got PTO in March while I was away from home, turned it on after April 9 2021. I've seen good days and very bad days and actually got some range anxiety. I've seen the roof peaked at 6.9 kW for seconds several times but mostly consistent 5.2 to 5.3 kW at best for a period of up to 2 hours in the last 20 days of April. PVWatts gave me the highest output day in April as 37.8 kWh but my best day in April was 40.3 kWh though my total output in April is still less than PVWatts, I also got quite a few foggy or cloudy days. I was concerned at one point and asked Tesla about it and I was told that 6.5 kW is only burst output on the best perfect day and would not last even if I manage to see it, the bottom line is the energy produced at the end of the day. With 2 PWs I did not have to pull anything from PG&E since I turned on the system and along the way I've sent back 250 kWh to PG&E, hopefully I will send back enough to get me through the lean months to keep me off grid.
I was just offering, since I changed my heating from propane to heat pumps, I can use 30 to 60kwh per day. And in the dead of winter, when my solar
might produce only 5kwh for the day, batteries will be gone fast.
One of the things to be aware of with PVWatts, is it seems the daily numbers are based on the average conditions for that day in history (don't recall how many years are involved.) But the result is that you generally can't compare their daily numbers to yours - only the monthly or annual are going to be fairly close. And, you would expect to see days that beat the PVWatts best as well as ones that are worse than the PVWatts worst because of the way PVWatts calculates the data.
As I mentioned above, we are trending towards about 3% above Tesla's number, but this is also about 7% below PVWatts. Some of that may be PVWatts underestimating some shading issues, and it also likely is partly user error on my part not entering in all the correct parameters for the solar roof.
Sorry, there are two delta model M4-TL-US; the specs from Tesla states 1.3 max DC/AC ratio; nominal power output at 240v is 3840W. BTW, I'm concerned how they split the load and just wanted them to check--they wouldn't. I not expecting perfection but as I said earlier nary one reading at +8.4kW? Since PTO (early March) I'm generating 102% of my usage, but I'm about to turn on 5 tons of 12 SEER A/C.
I feel like you answered your the question right there. You have a 10.6 kW peak DC system. But the two inverters are Delta M4-TL-US. These have a peak AC of only 4 kW each. So the measured output of your solar system is constrained by the two Delta Inverters. You should *not* see more than 8 kW AC whenever your solar array is performing at maximum. Your DC/AC ratio is 1.325... which is slightly higher than the target 1.20 DC/AC ratio that some installers shoot for.
I think solar installers can do better to educate people on this... but the topic is usually too complicated for most customers and I can see why salespeople avoid it.
Edit: I had one installer that I got solar quotes from speak in terms of inverter size rather than in terms of DC watt size. He basically said he would put whatever panels he had available that would achieve 7kWp of AC output at peak out of the inverters. I think it's because he said he was expecting a shipment of 335 watt panels but said sometimes 355 watt panels showed up. But I remember when he said this that all I thought was "wtf why isn't this guy able to say he's getting the 355 watt panels?."
Anyway, the solar companies usually sell on DC because it's the bigger number and more enticing. Like, look at all the DC you're buying! Look at how low your cost is per DC watt! But your real benefit is the AC inverter output which is why both DC and AC aspects are important considerations before signing a contract.
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Yep, no matter what "size" panels, roof, one installs, the inverter(s) output limit!!!!
Deceptive in the sense that when you see an advertisement for a McDonald's hamburger, you know that's not what it looks like when you actually buy one.
But it's not Deceptive in legal sense... at least with current regulation and laws.
I can see from a consumer protection standpoint, solar and ESS have many avenues for improvement. Even though we may think of Solar as a fairly developed industry, it's still pretty new for most customers. As such, the government hasn't been too strict on imposing oversight (thank goodness); and has broadly left the industry to "self regulate" how they do sales.
So at this time, all Tesla (or any solar company) has to do is to publish your DC array size (your 10.6 kWp); and they have to estimate your expected annual kWh generation. This is because the array size in DC wattage is industry standard. People by panels that are 345 watt. Or solar roofs that are 10.6 kW). And Tesla has informed you what total kWh of generation you should expect from the system over a 12 month period. This estimate is based on the physical characteristics of all the hardware that you purchased, your geographic location, and any known obstructions (like your own house).
Tesla could technically let you know that the Delta M4 inverter was a bit tight for you; and they should have informed you about what extra kW (AC) you'd get with a pair of M5 inverters (or even 1 M4 and 1 M5). And of course they could have given you the choice to pay a bit extra to get the bigger inverter. That's where I think Tesla kind of messed up. They simply sold you a system and picked the cheapest equipment they could that would still mostly work for you.
IMO, this is why I gave the example in another thread about how AC SEER is a crock of BS. 99.9% of buyers are being misled by SEER claims with their HVAC. I'm fairly confident when someone sold you that 5 ton outdoor condensing unit model as a "12 SEER" what they actually said was "up to 12 SEER". Every HVAC professional knows the "up to SEER" is only obtained by the 2 ton units *edit and with oversized evaporator coil*. Once you go to 5 ton, you're looking at much worse SEER simply because of physics. But, the homeowner doesn't know this. They just hear that the particular condensing unit model "could be XX SEER" and sign on the dotted line. This allows HVAC companies to also skimp on evaporator coils, interior air handlers, and all sorts of BS to sell inefficient gear at higher margins.
So your "up to 12 SEER" air conditioning system could really just be 6 SEER. Just about zero normal homeowners (@wwhitney is likely the only exception because his is like superhuman) across the USA know how to search the AHRI certificate for the real SEER of the particular equipment they bought. You are welcome to try here:
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I don't see it as deceptive, as long as the contract has an estimate of your annual production and it was arrived at by Tesla in good faith, incorporating all factors (system size, inverter size, roof planes, shading, etc.) To me, that is the essence of the solar contract. A buyer pays $X, expecting to get Y kWh of solar annually for a number of years. With a solar roof, you are, of course, also paying for the roofing aspect in addition to the solar generation aspect. Yes, it would be nice if Tesla spent more time explaining how you will get to those Y kWh (monthly numbers, typical daily production curves, etc.) but failing to is not deceptive - just creates different headaches for them when customers call in with questions.
It is also not entirely clear how undersized the inverters really are without getting more information on the roof and where the solar is located on the roof. While various industry standards exist, the best ratio for a given install can vary greatly.
Not sure what the goal of your post is. If it's to get help, you should post your system details, panel layout, shading conditions. Have you compared it with pvwatts? Can you see your panel level production or are you on a Tesla inverter with no panel level optimization?
And if he's in Denver or Boulder, then the solar radiation is a bit more through a mile less atmosphere ....which is the densest mile.
On cooler days in the Central Valley, my 8.16kw system is peaking at 7.5 kw.
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