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Inverter Size and number of strings

Pearl1!

Member
Oct 2, 2021
21
14
Florida
What size inverter(s) should you expect with each system size? How many strings?

Tesla is not direct or clear as to what inverter you get you system or the number of strings.

Tesla solar comes in 4 sizes small (4.25kWh), medium (8.5kWh), larger (12.75kWh), and extra large (17.0kWh). Tesla offers 2 size inverters, 3.8kW and 7.6kW. Rule of thumb is solar(DC)/inverter(AC) ratio of 1.2.

Since everyone has to buy at least one powerwall, small should have the 3.8 kW inverter with a PW2 (ratio 1.12). Medium 7.6 kW (inverter or PW+) (ratio 1.18). Large 7.6 (PW+) + 3.8 inverter, total 11.4 (ratio 1.18), extra large 2x7.6=15.2 (ratio 1.11).

Thanks
 

jjrandorin

Moderator, Model 3, Tesla Energy Forums
Moderator
Nov 28, 2018
12,514
14,937
Riverside Co. CA
"rule of thumb" isnt code, so this will likely depend on each persons specific roof / setup. There is very little that is completely standard between homes on construction projects, of which this is one.

You will need to ask for the design for your home from tesla to see what they propose for your home.
 

Pearl1!

Member
Oct 2, 2021
21
14
Florida
I bought a large system older panels, 12.24 kWh, 2xPW. Tesla required I get $1m in liability insurance b/c AC rated > 10 kWh, so tier 2 per FPL. Install is 12.24 solar with 1xPW+, 1xPW2. So only 1x inverter, 7.6 kWh.

PW+ only is not going to get it done. It taps out at 7.6 kWh. Tesla app support article concerning performance says to expect 50% rated power in winter and 80% in summer. Its October and weather has been great. The inverter is max'd out from about 11a to 4p. I'm only seeing 62%, and that all I'll ever see. A single inverter won't survive the summer.

Hindsight, I trusted Tesla, but the purchase agreement is not specific as to inverter or powerwall configuration or number of strings. Original plan set called for 2xPW+ with 6x strings (yeah, I have 6 arrays, complicated roof). Now I have just 1xPW+ with 3 strings. If I'd known they'd short the inverter I would have gone with the smaller system. As currently configured, it's a waste of solar panels.

Of course, when they come out to install, the plans are all different. I brought to the installers' attention, but they said designers know what they are doing. So I trusted Tesla. Mistake.

As part of the process, I thought the Tesla inspector would come to the house, but in my area that is not the case. Following the building inspector yesterday, I brought this issue up with Tesla, I spoke with the Tesla inspector who said he would bring the issue to the design team and install manager and that I would hear something in a week.

The Tesla mission is to accelerate the transition to sustainable energy. That's not happening when cut corners and don't optimize the solar they're installing.

BUYER BEWARE
For those with installs in process or are considering solar, for any install, get specifics - be in the weeds. If, like me, you're thing it's Tesla, I trust them, thats a BIG MISTAKE. Understand, you're dealing really with the remnants of Solar City, a company that almost went bankrupt. Get your plan set. Go over the plan set BEFORE they show up to install. Know what your getting, duh.

It's not just the panels! It's really the inverter. You can have all of the solar you want, but if your limiting factor will be the inverter. The systems are intentionally designed to have inverter capacity less than total solar panel output. You have adequate inverter capacity, but an MPTs on the inverter that are max'd out because they didn't run enough strings from the panels.

Know what your are getting.
 

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