Solar Panels

Limitations

I was researching the topic and the products, and I found there might be (niot 100% confirmed) some technical limitations of the tesla solar/battery system.

1.
Since the Powerwall2 battery is only able to absorb 5kW, having a >>5kw solar installation would result in being unable to charge the battery from solar when the grid is out. So I would be without power when the grid is out and the sun is shining, simply because of the power mismatch, despite the Gateway2 off-grid capability. Still tesla allows purchase of one powerwall with 8kW and 16kW solar config. Can someone confirm this?

2.
The battery 5kW limitation is known to many, as no air-conditioning when the grid is out, unless the customer purchases 2 or 3 powerwalls. But 2-3 powerwalls have so much capacity that is not needed, and takes up space and money. This could be solved on Powerwall-3, if it had same capacity 14kWh as Powerwall-2, but 10-15kW of load/charge rating.

3.
Wind-borne debris caused by hurricanes can damage 1-2 panels, then the whole system would be down, when using the default string inverters. The "power-optimizer" option might resolve the issue, I dont know. No documentation talking about fault tolerance. Tesla seems to not let the customer decide whether they want or can get power optimizers or not.

Comments

  • 1 - Nope - you have this one wrong. If the grid is down, the sun is shining and your have a powerwall - you will have power. Home use is prioritized so you will have whatever power is coming from your solar to run the house and any excess goes to recharge the battery.
    2 - The limitation for your AC startup would only be at night when you are running on battery alone. At the time your AC starts up, the system will provide power from both the battery and solar - so if the sun is shining - you have AC. You can only buy available products, not theoretical ones. If you need the extra power to start up your AC at night get another powerwall. Also keep in mind that storage capacity of your powerwall will limit the length of time you can have power without sunlight.
    3 - if a panel is damaged but still connected, it will in all likelihood still allow power production on the entire string, possibly at a reduced level.
  • The AC startup surge can be corrected with a soft-start device. They're pricey, but relatively easy to install.

    You size the system for your needs. Saying that a single PW system is inherently problematic because it's inadequate for a power hog like a central AC is ridiculous. It's the reason PWs were designed to be stacked. Simply buy two.
  • When the house consumes 0.5kW, the solar panel produces 8kW, the battery is able to absorb 5kW, where does the excess 2.5kW go? In case the grid is down it has nowhere to go. I learned that the solar panels cannot produce less than their rated power (affected by sun intensity), like a current or power source, instead of a voltage source.

    2 Powerwalls would have so much capacity that will remain un-utilized. Seems wasteful with resources.
  • Your "excess" production in an off-grid situation with a fully charged battery will cause the logic built into the powerwall controller to change the frequency of your 60 Hz power - this in turn causes the solar inverters to shut down. After you have consumed enough electrons from the powerwall to bring the charge low enough, the frequency changes again to bring the solar back on line. It works.
    In my case - I did not want to "waste" that production, so I actually started charging my car to soak up the production and keep the solar producing. Oddly enough - I also told my wife to go ahead with washing clothes and running an electric dryer to also absorb some of that production. Insanity prevails ! It actually worked and I micromanaged our little local "grid" to keep the solar on line, keep the batteries charged and do some useful work - in the middle of a grid failure.
    The number of Powerwalls simply dictates your maximum charge rate and your total storage capacity to survive in a grid failure. More storage means longer survival.
    YMMV.
  • > @gregbrew_98470014 said:
    > The AC startup surge can be corrected with a soft-start device. They're pricey, but relatively easy to install.
    >

    I just had one installed on my AC in anticipation of my Tesla solar install. The installed price of the start capacitor was $250. Not bad for smoothing the loads on the powerwalls.
  • With two Powerwalls, I've not had any problems with my whole house HVAC and I never bothered with a soft-start device. The HVAC is less than 5 years old, so perhaps it is better designed than older units. Each PW has a higher peak power rating of 7 kW, or 14 kW for two PWs like I have.

    Even with the grid available, you're better off using solar power when it's available. That means running the dishwasher, washer, dryer, charging the car, etc. during the peak solar generation time. Seems contrary to what you may have done if you use to have Time-of-day utility pricing.

    Here are more details in an article I wrote about it a few months ago: https://teslatap.com/articles/solar-powerwall-system-optimizations/
  • Can the battery and the solar generate 3-phase (2 phase) power? My quote mentions single phase devices are backed up. What about off grid use with solar and battery (in an outage) while the sun is still up? Does it give 3phase or not?
  • If you get only one powerwall (as a neighbor did) - it was installed on only one leg of the panel and only 110v lights and appliances are covered and protected. I had two powerwalls and my full home is protected including electric kitchen and AC.
  • Powerwalls in the USA run the common residential standard split-phase, not three-phase. Three-phase is typically for commercial power applications. What's nominally 240V in a residence is usually 208V, off one phase in a three-phase environment.
  • > @gregbrew_98470014 said:
    > Powerwalls in the USA run the common residential standard split-phase, not three-phase. Three-phase is typically for commercial power applications. What's nominally 240V in a residence is usually 208V, off one phase in a three-phase environment.

    Most appliances are 110V and one phase plus neutral plus safety ground. These type of wall outlets are rated to 16A max, so it means 1800W max. There might be a higher current 110W outlet with 3-prong barrel connector, but most high power appliances (aircon, furnace, oven) use 2 phases plus neutral plus ground, what they call as 3-phase in common slang, often referred to as 220-240V. The real 3-phase with 3 phases plus ground (neutral not needed) is used in industrial. This is generic stuff, can be looked up.

    What cannot be looked up, is how the tesla inverters and gateways operate, their 1 page datasheets dont give away too much info. For example, in order to run 3-phase really 2 phase) appliances, you really need 2 powerwalls? The missing phase is just one limitation, the other better known one is the 5kW load limit of each Powerwall2, meaning an aircon needs 2 powerwalls. But... Does it need 2 powerwalls because of the 5kW limit, or because of the single phase arrangement of one powerwall?
  • Residental three-phase is typical in a lot of European countries. It requires two Powerwalls to support 3 phase. A single Powerwall is limited to a single phase on a three-phase system. There are no similar limits on USA installs.
Sign In or Register to comment.