New potential buyer questions

New potential buyer questions

1) can a power wall be charged from the grid at off peak rates ( TOU) ( can the utility tell Tesla to cripple the power wall I believe in Australia 11kwh power walls are crippled to 3kwh)

2) If as an example the house has a 10kw power demand and solar produces 5kw can the solar be blended with the utility electron flow or are the electrons from the panel and electrons from the grid forced to go into separate loads on the electrical panel.

3) In peak house demand can electrons from the panel and electrons from the power wall and electrons from utility be blended together or again are they restricted to individual circuits.

4) If the panels fill the power walls and electrons are left over and you don't want to sell them to the utility can you dump them...feed them into the resistance ( impedance) in the panels. This avoids the net metering tier fee from some utilities which seems based on max possible electron flow into the grid.

5)If the utility is out, can you direct the power wall and any solar into specific circuits or are the circuits fixed and determined or are they selectable by the homeowner on the fly.

Jones | June 16, 2020

1- Depends on your locale. In the US, the answer is simply no with the exception of the emergency feature called storm watch. There are different rules in other countries.
2 - The solar and battery both terminate on the same power bus, so the electrons are shared by definition. The controller gives you the ability to modify conditions where power is directed via rules.
3 - This will be subject to your actual installation and whether you have total house support or just partial. See #2 for blended power.
4 - Sounds like you actually want to be off grid. If you are connected, you pay the fee irrespective of actual use. In an overproduction state (off grid), if you are producing more power than can be used or stored, the solar output will be shut down. Putting excess power into a bus in the form of resistance will end up in a call to the local fire brigade or melted appliances or melted wiring or all of the above in rapid succession.
5 - if your grid is out and you want to save or direct electrons...the switch at the point of use is best...turn stuff on or off that you want or need. If you want to exercise macro control under those conditions, opening a breaker is certainly an option. | June 16, 2020

On #1, you may be a bit confused and mixing various power levels. The Powerwall has a 27 kW battery. You can pull a total of 5 kWh continuous, and 7 kWh peak. No idea what they 11 kWh number you are referencing. I'm in the USA with 2 phase, so it is possible your Powerwalls are spec'ed differently, but I sort of doubt it.

The 3 kW limit is when you have a single Powerwall, and you draw power very poorly across the three phases. When a house is built, they are supposed to balance the phases so that they are not highly unbalanced. What I mean is if you have a 3-phase HVAC, you can pull the maximum 5 kW and 7 kW peak. If you have a single-phase heater that is 3 kW, and no other devices pulling power on the other phases, you will be blocked from pulling any more power from the same phase that the heater is on. I suspect this is a limitation few will ever encounter.

If you have two Powerwalls, the 3 kW issue goes away. | June 16, 2020

2) Yes.

3) Yes.

4) No, although you could turn off the Solar power at the inverters. Seems like a pain though as it's nice to be fully automatic.

5) With the grid off, you can't direct the power, but you can turn on and off various loads in your house. In this case, you might turn off large loads to extend the power available. In the summer, I'm really off the grid as the solar provides all the power I need during the day while also charging the Powerwall. When the sun goes down, the Powerwall gives me enough power for the rest of the night until the sun comes up. This includes charging my car. This depends on how large a system you buy. I do have 2 Powerwalls.

dougk71 | June 16, 2020

TeslaTap and Jones thank you for the answers. The Tesla power wall has me confused. Does it have a 13.5 Kwh energy capacity? TeslaTap is your 27Kwh coming from 13.5+13.5 two units? I guess the 11kwh comes from the idea of not ever fully discharging or charging ( leave approx 10% at either end)
I'm in Florida and Tesla is adding Florida sales Tax to their quote this correct I thought FL was exempt for solar)?
If I have this right then the only way to charge a power wall is via the panels or from the utility at regular rates since you say TOU is forbidden.
I'm not going off grid it is just the utility has a tiered fee structure for net metering so I'm concerned that their fee to put an electron into their grid would very much exceed the value the electron would have to reduce the monthly utility bill.
This is a learning experience as it was for our Model X and Model S.
Again thank you both for your expertise.

dougk71 | June 16, 2020

Do I have this right conceptually?
When the solar panels supply power or the power wall supplies power or both but the hose needs more power the effect is the utility power meter spins slower than it would do without panels or power walls. If the panels had excess over the house then conceptually the meter would run backwards.

Jones | June 16, 2020

Yep - you now understand the workings of the Tesla Power system. You are ready to proceed. | June 16, 2020

@dougk71 - Sorry, I should have said 13.5 kWh for one Powerwall. I do have two.Powerwalls.

I don't know about FL tax laws, although it would seem if it is for solar only, it might not cover Powerwalls. The federal credit does cover the Powerwalls when installed with solar at the same time.

dougk71 | June 17, 2020

TeslaTap you were very informative when we were newbies to our Model S. What seemed concerning like super charging or internal discharge when parked , in home driveway service calls etc. now seems obvious. As kids we learn about ICE cars from our parents but for EV's we would be on our own if it were not for the advice we get from others.
Odds are we'll proceed with the solar installation in fact this week we will have a site survey from Tesla.
So far it is I guess from satellite photos of our roof that they came up with suggestions but the site survey will be more definitive and result in a more assured by Tesla quote.
Is there an opinion on string conversion... versus charge optimization ...versus micro-inverters
Thanks for the support

Jones | June 17, 2020

I have couple of different generations of solar (SunPower) on my roof as well as another home with a single generation of SunPower. My oldest system is from 2007 and is a typical string on single central inverter and the newest is a micro inverter system. Combination of the two homes is 20kW. Back in the day...microinverters were considered cutting edge but reliability was a question. Nowadays, there seems to be a reliability equivalence (though my microinverter system installed in 2016 had one fail inside of 24 months necessitating replacement of the entire string (under warranty). The central inverters (total of three) are all going strong. The house with multi system install has two significant orientations - which is a primary reason for microinverters. The other systems are all single uniform orientations with no shading. My personal preference is central inverters but I see very little difference in actual output versus rated capability across the various systems. If there are shading or diverse orientation issues - I would go with microinverters.

dougk71 | June 18, 2020

Jones the above was very well written..thank you.
It was informative to hear that systems can be extended with time and don't require a complete refit. So you can replace the headlight bulbs and don't need to buy a new car to get the issue resolved.
Do panels in a string have to be identical?
If one panel in a string fails does it take the string down and would the whole string need to be replaced if an identical panel was no longer available?

Jones | June 18, 2020

There are nuances to the answer about performance of central inverters, so I will oversimplify (and expect corrections and clarifications from other members). In general, solar systems are all set up as strings - even the panels themselves. Let's start at the panel level. It is essentially composed of a string of individual cells. Depending on the manufacturer, it may be a single string or several strings bound together for a single output. The performance of any string of cells is limited by the minimum performance of the worst performing cell in the string. One bad solar cell and it brings down the performance of the entire string. Panel manufacturers mitigate this by grouping individual cells into mini-strings such that a single cell failure will only impact a portion of the output.
Central inverters work in much the same concept - a string of panels will only perform as well as the worst panel in the string. (This answers your question about mixing panels - don't go there). Yes I have had a single panel fail after about 10 years - replaced under warranty with an old shelf stock panel of the same size. SunPower initially intended to replace with a used panel removed from a refit - the installer and I had a fairly intense conversation resulting in a return a week later with a freshly boxed panel.
Back to the strings of panels - conceptually, all panels in a string should be on the same plane and orientation to minimize "worst panel" impacts. The central inverters generally have two input strings that are balanced so if you have two orientations, one will be on one inout and the second orientation on the second input. Your designer will take this into account. There are also aggregators that group portions of strings together so that you in effect have multiple mini-strings - again to minimize shading and failure issues.
Lastly - you have microinverters that essentially put each panel (or pair of panels) on a single inverter to fully eliminate individual panel failures for impacting other panels. The downside (IMHO) is that you have a huge number of electronics boxes on your roof getting baked and exposed to environmental influences. Take your favorite stereo amplifier, seal it in a box and put it on your roof. Not my version of ideal.
All of the electronic components of all of my installs are in my garage - protected (except for my one string of microinverters). Personal preference. | June 18, 2020

@dougk71 - I agree with just about everything Jones says although I'm more agnostic on the microinverter vs. inverters. I think both systems are as reliable. If you have a lot of random shaded areas, perhaps due to trees, I'd favor microinverters, but otherwise, favor inverters. Not a big deal either way to me. The best on any system is to avoid a lot of shade. I removed one tree that was causing some shade and was way out of control anyway.

Ok, my first solar system used microinverters. It worked well and I never had a problem. I had that removed and replaced it and the roof with a solar roof which has two inverters each with two sections (4 total). The solar roof for my case has four separate sections, one for each facing north, east, south, and west. So far it has also worked perfectly. My surprise was how much power the north-facing section generates. It may be the rough glass surface better redirects angled light into the cells. My prior system didn't have any north side panels, so I don't know if they would have worked as well or not.

dougk71 | June 18, 2020 Thank you and Jones for sharing your expertise
You had a functioning system but switched to a solar roof. Was that because you needed a roof replacement or something else? | June 18, 2020

@doug - Yep, I needed a new roof. I had a number of roofing quotes and the solar roof was cheaper than other non-solar roofs I considered, ignoring existing solar system that could have been transferred to a new roof. I was looking for a high-quality roof, and they were more expensive than a plain asphalt style roof. In addition, I wanted a larger solar system and power walls, so it was really a fairly easy choice. In case you missed it, I wrote it all up and made a short video of the roof installation:

dougk71 | June 21, 2020

My utility is Florida Power and Light (FPL). The proposed system is 13.86Kw.
FPL requires an $1 million Home Owners Insurance Agreement ( an umbrella type policy) in order for them to allow activation of the system.
Is this a poison pill and are other utilities in other states requiring $1 million insurance provisions? | June 22, 2020

@dougk71 - That's crazy. Not required in CA or other states. Quite a scam by the utility. Ok, you should at least check what the cost is. Perhaps the insurance companies charge a couple of dollars a year for it, but perhaps it's expensive. I have no idea. I'd be curious how much the extra insurance costs if you find out.

gregbrew | June 22, 2020

A $1M umbrella policy can sometimes be as simple as an added extension of the liability portion of your homeowners insurance. It will probably pencil out to about $250 a year. It's a relatively cheap and easy hoop to jump through.

Call your homeowners insurance agency.

I'm in CA, too, so I don't need it for solar either, but I do have it for other reasons (income property). It's not a bad thing to have anyway, but most people don't carry it.

dougk71 | June 22, 2020

Well yes, a Florida $1 million policy starts at say $300 but with inflation and over 25 years that is say avg $500 or $12,500 added to the life time cost of panels. Further depending on how many cars you own or boats ( each add to the umbrella premium so it can go as high as 600 or $25,000 over 25 years)
Next if you are ever to be the subject of a lawsuit the guy with the umbrella policy is the first to be blamed, if there is more than one to blame the one without an umbrella policy is often persuaded to testify against the one that does)...deep pocket approach by lawyers.
FPL doesn't allow Time of Use with batteries so Power walls become backup batteries mostly.
Sure if the panels over produce what the house needs the power wall could absorb some power but it is mostly negated since FPL ( my utility) forces net metering giving it a similar function of absorbing the excess power.

I believe as far as FPL goes having any system except just panels rated to (after inverter losses) of less than 10kw AC is non economical.

Its a bit of an exaggeration ....Florida is the sunshine State but above 10kw FPL owns the photons from the sun.

dougk71 | June 22, 2020

My Tesla order is for panels only and the power will be 11kw DC or less to avoid the (and I got a quote for $590 for the umbrella policy ) if I were to go for a higher wattage.
Adding $25,000 ( $590 plus inflation over 25 years) to the lifetime cost of panels destroys the concept of pay pack.

Next if you sell your house the new owner must get the umbrella policy ( or rip out the >10kwAC panels) to have the utility that means you must disclose it as part of the sale.
It is a poison pill all round.

gregbrew | June 24, 2020

The additional cost of your umbrella policy to cover things besides the solar should be excluded from your calculations. Throwing them into the mix is unfairly burdening your solar ROI.

If your insurance carrier has such ridiculously high rates, and is increasing premiums by that exorbitant amount, it's time to find a new carrier.

dougk71 | June 25, 2020

Even if it was $300 that is 1 month's energy cost or 8% additional...I have assets like a Model X and Model S etc that take the premium higher.
Then there is the need to have any future buyer of the house take out there own umbrella policy just to have the grid connection. Real Estate broker strongly advise against any must do for potential buyers.
Anyway I have ordered 11 kw for the panels and a 10Kw inverter and no power walls.
I'll consider power walls if and when FPL allows TOU with them.