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Tesla Solar Design Feedback

dareed1

Member
Jan 15, 2021
65
62
Belmont, CA
If you do decide to go with that smaller inverter, ask Tesla to give you a 1.5 ratio of Dc to AC ratio. You will generate max power over a mush longer timespan.
I don't understand the concept of max power over a longer timespan. If the area of solar panels is constrained, it may make sense to use a smaller inverter and use the cost saving to buy more efficient panels, but otherwise it is a loss to use >1 DC/AC ratio.
 
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charlesj

Active Member
Oct 22, 2019
1,106
229
Monterey, CA
I don't understand the concept of max power over a longer timespan. If the area of solar panels is constrained, it may make sense to use a smaller inverter and use the cost saving to buy more efficient panels, but otherwise it is a loss to use >1 DC/AC ratio.
Actually it is not a loss of power overall. You have a limited number of panels that will be installed. Ask for the largest power producing panels that Tesla can install. If they have 400W panels get them. And whatever inverter they will install with them
As to Dc to AC ratio, that may be too hard for some to understand how it work; understood.
People in the know, commercial installations do use that 1.5 ratio to produce max power of inverter over a much longer time frame. Larger panels, power wise, will ramp up faster and stays up longer than a 1:1 system. May want to scour the internet about solar panel clipping inverters.
Technically that is a great way to increase daily production.
 

Ampster

Active Member
Oct 5, 2012
1,753
472
Sonoma, California
I don't understand the concept of max power over a longer timespan. If the area of solar panels is constrained, it may make sense to use a smaller inverter and use the cost saving to buy more efficient panels, but otherwise it is a loss to use >1 DC/AC ratio.
I am not space constrained but I was inverter contrained because of service panel limit. I have a 1.5 to one DC to AC ratio and my inverter ramps earlier and produces longer than if I had less panels. That is what I see as max power over a longer timeframe. The result is more kWHrs. What is not to like about more kWhrs. When you look at the cost per Watt of panels versus inverters it makes sense to me to overpanel. It all depends on where you are standing.
 
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dareed1

Member
Jan 15, 2021
65
62
Belmont, CA
I am not space constrained but I was inverter contrained because of service panel limit. I have a 1.5 to one DC to AC ratio and my inverter ramps earlier and produces longer than if I had less panels. That is what I see as max power over a longer timeframe. The result is more kWHrs. What is not to like about more kWhrs. When you look at the cost per Watt of panels versus inverters it makes sense to me to overpanel. It all depends on where you are standing.
Yes, sure. When one can install more panels it frequently makes financial sense to save money buy buying a smaller inverter and spend it on panels. The clipping of power around solar noon is more than compensated by the additional power generated in the morning and afternoon.

But the OP is constrained in space, Tesla only sells one class of panels (340W) at present, and have either 3.8kW or 7.6kW inverters. charlessj recommended (originally, and that's what I responded to) that the OP ask for the smaller inverter. That advice was wrong: the OP can't add panels, so the only result would be unnecessary power clipping in the middle of the day. The fact that the smaller inverter would be maxed out for a lengthy period is a worse outcome than not maxed out at all.
 

albertm3

Member
Sep 13, 2019
40
13
NorCal
IMO, powerwall never make a financial sense if you're purely looking for ROI.

Here's the major reason
1. powerwall has a shorter lifetime than your PV, 10 years of warranty. Yes, it will work after 10 years, but it doesn't have warranty coverage. YMWV.
2. powerwall will save you money to store the off-peak power and use in peak. But the maximum rate different is around 20-25% only in summer. So your saving is not 100%, powerwall only saving you 20-25% only.
3. If powerwall require you to upgrade panel or moving main panel, that's on top of the PW cost.

The number one reason of getting PW in Nor-cal is power outage. That's depends on how much are you willing to pay. You should take out PW when you calculate ROI. PW is consider as a backup power. Backup generator cost 3-5k + installation. Using that mindset is better. You have to ask yourself, how much you are willing to pay for backup power.

Another alternative is to compensate TOU peak and non-peak rate for PV system is to oversize your system 20-30% different.
PV produce power at off-peak (selling to pge at cheaper rate), and use that at peak rate. As long as you produce 20-25% more power than you use, then it will off-set the rate differences.

If you're purely looking at ROI, oversized PV system is the best option. You can easily get ROI in anything in between 5-8 years.
The moment you put in PW, the equation will extend to 20 years.

Also remember, everything is base on you can keep the system on your roof for the ROI timeframe. If your calculation is 20 years, and you have to change your roof in less than 20 years. You will never make you ROI. What about you move after 10 years.

If Tesla battery technology improve to million mile battery to PW. Then it will change the equation. But the existing one is difficult to make a financial sense.

I hope that helps.
 

charlesj

Active Member
Oct 22, 2019
1,106
229
Monterey, CA
Yes, sure. When one can install more panels it frequently makes financial sense to save money buy buying a smaller inverter and spend it on panels. The clipping of power around solar noon is more than compensated by the additional power generated in the morning and afternoon.

But the OP is constrained in space, Tesla only sells one class of panels (340W) at present, and have either 3.8kW or 7.6kW inverters. charlessj recommended (originally, and that's what I responded to) that the OP ask for the smaller inverter. That advice was wrong: the OP can't add panels, so the only result would be unnecessary power clipping in the middle of the day. The fact that the smaller inverter would be maxed out for a lengthy period is a worse outcome than not maxed out at all.
I guess I misunderstood the OP then thinking that the 6.12 kW system was the smaller inverter already but if he can get the 7.6kW inverter for that 6. KW panels then that is what he needs as the smaller would be more than 1.6 ratio, undersized. On the other hand those panel ratings are not real world rating and would have a 1.5 ratio. With that 7.6 inverter he will have a 0.8 ratio. Decisions, decisions.
 
Mar 1, 2021
119
36
San Diego, CA
I guess I misunderstood the OP then thinking that the 6.12 kW system was the smaller inverter already but if he can get the 7.6kW inverter for that 6. KW panels then that is what he needs as the smaller would be more than 1.6 ratio, undersized. On the other hand those panel ratings are not real world rating and would have a 1.5 ratio. With that 7.6 inverter he will have a 0.8 ratio. Decisions, decisions.
There is nothing inherently wrong with a 0.8 ratio. If Tesla charges the same for either inverter, get the bigger one. If they charge more for the bigger one, probably still get it. You can still set up strings at a 0.8 ratio to have extremely high efficiency. Clipping for hours a day loses more than the efficiency gain the rest of the day.
 
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Ampster

Active Member
Oct 5, 2012
1,753
472
Sonoma, California
You can still set up strings at a 0.8 ratio to have extremely high efficiency. Clipping for hours a day loses more than the efficiency gain the rest of the day.
Apparently inverters used to vary in efficiency depending on how they were loaded. That meant that there was efficiency to be gained by running them closer to 100% of capacity. My understanding is that with todays extremely efficient electronics there is no longer the same argument. The broader question of DC to AC ratios is a little like trying to decide if the glass is half full or half empty? It all depends on where you are standing. There will be some that will also remark that the glass is the wrong size. My earlier remarks were more philosophical supporting higher DC to AC ratios if the circumstances warrant. I was ignorant of the OP's particular circumstances.
 

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