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Solar Inverter Undersize

Painting with such broad strokes is fun.

You are making a broad stroke statement about Tesla design being crappy and got one in return. Data here has shown that a 1.7 overstacking has losses on the order of 2% depending on all the factors.

For that approx 2% less kWh production, your Tesla system probably costs 10-30% less per installed DC watt than many competitors. It seems like the biggest issue is the old school thinking that flat topping your production curve is some big issue.

It would be easier to understand this if systems were sold according to the specific yearly output in kWh, and nobody really knew the DC size. Selling based on DC sizing of a PV system is like buying a car based on the displacement of the motor only, without understanding the horsepower which would be affected by turbo/supercharging, fuel injection etc.

For instance head over to PV watts and test a few cases. If you have a 10 kW system with a 1.2 vs 1.7 DC/Ac ratio, the production loss in a year is at most (with perfect azimuth/tilt) 300 kWh, or a value of $120-140 at my electricity prices. So assuming the system lasted 25 years (Inverter will probably last 15 years if taken care of) the total value of the energy not harvested due to flat topping is something like $3500 or less.
As others here have written, and it bears repeating, don't focus on the panel/inverter size, focus on how much power your system is generating relative to what you signed up for. As the old saying goes, "there are many ways to skin a cat", and your specific site details of roof slopes, orientations, and exposure make all the difference to how much power will be generated over the course of a year.

All the best,

With regard to focusing on Power:
I don't have a Tesla system, so I don't know whether it offers much historic data, but I highly recommend solar owners to log their systems on pvoutput.org, as it really allows you to review power daily, monthly, seasonally, annually. I have 8+ years of 5-minute interval data archived for only $10 donation a year. And consumption data too.

It provides a lot of data and graphs for comparison with yourself, or others nearby, which *COULD* be helpful in getting Tesla support to understand something has changed or gone wrong. I could even see the long-term impact from a few southeast trees that were growing taller each year, increasing shade losses, and recovering about 2% annual production when they were trimmed back.
As others have mentioned, you really need to do a comparison of DC/AC ratios using PVWatts with as close to your setup as possible (location, azimuth and tilt are critical). I’m not suggesting Tesla didn’t mess up their design, but it’s easy to get overly concerned based on seeing clipping in your graphs or large DC/AC ratios. I wouldn’t blindly trust any design you receive, especially from Tesla Solar.

Here’s a screenshot of how much I was clipping basically daily last month (roughly five to six hours a day) on an 11.2 kW system with a single 7.6 kW inverter, all east facing panels. I’m estimated to clip yearly about 400 hours. Compared to a smaller DC/AC ratio with another inverter, I’m only losing less than 0.01% in total annual production. It would take me about half a century or longer to break even on the increased cost of an additional inverter, and that’s not even considering panel degradation over time.


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