2nd PowerWall Battery - Life is GOOD!

It seems I got my single battery PowerWall in January 2019.

 https://wmckemie.blogspot.com/2019/01/powerwall-install.html

After two very painful years of having uninstalled spare PW batteries in stock but unused, I FINALLY succeeded!  

Since shortly after the original install, I realized I need at least two batteries to semi-gracefully get through longer term power failures.  I asked several installers to do the upgrade, including the one that did the install.  All declined or offered exorbitant pricing.  I used an installer (instead of Tesla) because Tesla seemed snowed under with demand.  Later, I had a pretty significant failure:

https://wmckemie.blogspot.com/2021/02/powerwall-failure.html 

https://wmckemie.blogspot.com/2021/05/powerwall-lives.html

Several installers as well as Tesla refused to make a service call.  As detailed in the above, I ended up fixing it myself.   That's as I finally had to do to get a second battery installed.    My PW ended up out of service for several months.

I first ordered a PowerWall when they were first offered,  Was that about 2015?  When the PWs finally became available years later, Tesla refused to install as well as refused to service.  I still have that PW on order from Tesla.  I ended up buying a package of three batteries plus the gateway from a Tesla driver that earned the PW as an incentive for selling a bunch of cars.  The guy I bought from was unable to get Tesla to do an install or get installers to install stuff not purchased from the installers.  

Recognizing that the batteries likely had a limited shelf life, I was semi-frantic to get them working and charging before they became depleted.  I found installation instructions and became familiar with what was necessary.  I eventually got one installed but it failed to work.  A chance encounter with a Tesla Energy service person offered a clue:

https://wmckemie.blogspot.com/2022/01/supercharger-service-in-columbus.html

I first did not realize that each battery on a multiple battery system should be wired so that the two split phase wires needed to go to the same AC power connections on the battery.   For most 240vac wiring, that is not a concern.  Each battery must be on it's own breaker so there is opportunity to make that mistake.

11/20/22

I just got my 3rd PW battery installed and working a couple of weeks ago.  Quite a comfort!  With the three, a low use night leaves me with about 85% of the charge about the time the sun comes up.  Heating (and likely cooling) will bring the morning state of charge down to about 70%.  I might conclude that I can last about three days of grid-down AND minimal sunlight.  Twice that long if I can forego heating and cooling.  When we have decent sun, the batteries get fully charged well before the end of the day.   That is, I can get through LONG periods of grid-down as long as we have a decent sun day every couple of days.

I have a 4th battery that I apparently have killed.  I hope to dig into it and decide if it has a future.

SuperCharger Service in Columbus

 

Approaching the Columbus SuperCharger, I thought it had been ICEed by a monster Ford pickup truck.  But, no, it was a Tesla Energy guy doing some service.  A very nice and loquacious guy.  Works out of Houston but sometimes covers SuperChargers across the USA.   Some of his tales:

1) Power cables get swapped out regularly.  See new cables hanging on the right side of the truck.  The connectors do get worn out in normal use.

2) The guy allows that Tesla drivers, in general, are pretty nice.  He has been "cussed out" only twice.  One was a S Plaid driver that took exception to having his charge necessarily temporarily interrupted.  The repair guy was informed that he was fired by the disgruntled Plaid driver.  Though the Plaid guy was not a Tesla employee.

3) A Tesla employee was fired after visiting Boca Chica and taking (and distributing on FaceBook) some photos taken from the wrong side of the property line.  The Tesla employee was "off the clock" and visiting Boca Chica for his own edification.  Much as I have done.

4) The rentacops that SpaceX has been using at Boca Chica have been causing SpaceX some trouble.  They have been denying public access to public roads.  I think I was turned back there by a rentacop while on a public road.

5) A common act of vandalism is stuffing something in the SuperCharger connector wells.  So that the "nozzle" can not be properly mated to the car.  The guy reported that, in most cases, he can just dig out the foreign material.  I've encountered such vandalized nozzles but did not try to do the digging myself.  Next time, I'll give it a try.  Understanding that the connectors are not hot until properly connected to the car.  Dental or lock picks seem like ideal tools.

6) He reports that, in California, repair folks such as himself, may be given Model Xs for their work.  For a while he had a Model Y but expressed a preference for a ICE pickup.  I imagine the Xs and Ys driven by Tesla Energy people are not allowed to accumulate many miles and are sold at a modest discount as "demos".  Just like "loaners" offered to customers having repair work done.

7) The guy reported a problem he had witnessed near Houston where a big utility scale battery was being installed.  The problem: when multiple chargers/inverters are being used, it is important to see that the two split-phase legs go to the same places on individual devices.  For instance, I now see I probably crossed them between the old PW battery and the new battery I am attempting to install.

 https://photos.app.goo.gl/EzNayp4juoTna1u48

I believe I've seen a Tesla service person at only one other SuperCharger.  In Cheyenne 6-8 years ago.  That guy had flown into Denver, rented a small ICE car, and driven the ~100 miles to Cheyenne.

 

PowerWall Lives!

 Right after our big long freeze event in February, my PowerWall quit working.  It was refusing to use grid power.  Pleas to Tesla Energy for a service call went nearly ignored.  After the better part of a day trying to get back on grid power, I decided to wire around the PowerWall Gateway.  The only way to do that safely was to pull my meter.  So, I notified Bluebonnet, cut the seal and pulled the meter.  After I figured out what needed to be done, it was a less than half hour job to do it.  The primary obstacle was bending and moving very heavy copper wire.  I was extremely relieved when I plugged the meter back in and found I had grid power again.  

 With essentially zero help or advice from Tesla, I determined that a big switch in the gateway box was just a 200 amp breaker rather than a transfer switch as I first thought.  A search on the part number told me it was a very common unit.  So, I ordered one.  Installing the new one was a long, tedious, and painful job because of obscured mounting bolts and general congestion.  I ordered several sets of deep sockets of approximately the right size.  The right size turned out to be 10mm.  Weeks later, the new breaker was in place.  But, I had lost enthusiasm for the project and kept postponing putting the PW back in the circuit.   I was uncertain that the bad breaker was the only problem.  I would rather have hired Tesla or others to do the job.  Meanwhile, I had bought a new three battery PW from an individual, not Tesla.  I've become sensitive to the possibility of allowing the batteries to run down and become ruined.  The "new" batteries have likely been in storage more than a year.  The new gateway is "gen2" and my installed gateway is "gen1".  I hope that tells me that the batteries are not very old.  The "gen2" gateway seems not to have the 200 amp breaker that failed me.

So, today was the day.  May 20.  About three months after I disconnected the PW.  Things went rather smoothly other than not being able to get the heavy wires stuffed down into the gateway box so it can be properly closed.  Pull meter.  Change four big wires from one set of lug connections to the others.  Reinstall meter.  Flip breakers, switches, disconnects back on.  Everything works.  The single positive result of all my pleadings with Tesla back in February was that my PW got properly associated with my Tesla account so that the PW, like cars, shows up on my Tesla smartphone app.  I had had no communication with my PW for three months and I was extremely pleased to see it show up on the app with 70% charge.  The sun was out so it immediately started charging at 5kw with excess power going to the grid.

 The next step:  I have three PW batteries, NIB, that have never been used or installed.  So, I want to get them hooked up, either all together or one at a time, and make sure that they are not in danger of totally self discharging.   The new batteries weigh maybe 300 pounds each and I am not very mobile.  Moving them from my Sprinter to the house will be daunting.  So, I'll likely wait to gain better mobility before I attack that project.

While writing this, the PW battery became fully charged.   I believe I have it configured so it uses battery power after sundown until the battery gets down to 50%.  Then, grid power, saving the last 50% for a power failure.

A little later.... I emailed Bluebonnet this morning to tell them the meter was ready for a seal.  This afternoon, a guy showed up and installed a seal.  With zero grief to me.  No complaints about "only Bluebonnet people are supposed to remove seals".    It is no wonder that I like being a Bluebonnet customer.  More accurately, having Bluebonnet as a customer.

New 12000 btu "hyper heat" mini split heat pump

 Just installed.  "Hyper Heat" meaning that it extracts heat from air temperatures below zero F rather than the older types would require resistive heat below about 40 deg F.  SEER of 22.5.  Another choice was a 9000 btu unit of SEER 25.

https://photos.app.goo.gl/outQ6QGDURUsNm2M7

The unit may not be big enough to supply all needed cooling and heating.  The window unit, I believe, is about 18000 btu which is sufficient for cooling the area.  The major impetus is to not have to build fires in the stove when heating needs are moderate.  Current infirmities have made fire tending tedious and painful. 

https://www.ebay.com/itm/DiamondAir-Mini-Split-12k-BTU-Hyper-Heat-22-5-SEER-Heat-Pump-D2012SHO-DF2012HMSI/254362573571?hash=item3b3930db03:g:uMUAAOSwbsddgQt2

Picked up at Houston warehouse of

 https://www.budgetheating.com/

Installation by Paige Aire:

http://paigeaire.com

 Cost: about $1400 plus $800 for installation.

Product specifications:

 https://www.diamondaircorp.com/ProductDetails.asp?ProductCode=906

 Full heat capacity down to 5 deg F!  I'm now thinking the 18000 btu unit might have been a better choice, though less efficient.  I was first drawn to the 9000 btu unit because it is more efficient than the purchased 12000 btu..

7/15/2021

I've been running the 12k btu unit now for over two months and I'm well pleased with it.  I have in hand a similar 9k btu unit that I intend to put in my bedroom.  Together, I think the two units will both heat and cool the entire house.  For back up cooling, I will leave in place the two window units: a 18k btu in the dining room and a 6k btu in the bedroom.  I'm thinking ahead for the winter in case my limited mobility problem does not get better and I don't feel up to tending a fire in the winter.  Even with improved mobility, I will likely do a lot of winter heating with the heat pumps.

Electric energy is generally not a problem.  During the day, I produce and send to the grid at least 10 times as much as I can hope to squander on heating and cooling.  My only (slight) worry is that, if grid is down, I may have not be able to heat and cool as much at night as I would like.

Here are some stories of interest:

https://cleantechnica.com/2021/07/30/ductless-heat-pumps-demystified/

 https://cleantechnica.com/2021/08/12/why-heat-pumps-are-the-answer-to-heat-waves/

PowerWall Failure

Since it was installed more than two years ago, I have been unsuccessful in getting Tesla to associate my PowerWall with my Tesla app so that the PW could be monitored remotely just like my cars.  I finally gave up and relied only on the local monitoring that the PW provides on my LAN. 

Since proving it's worth during our recent record cold spell, my PowerWall has been malfunctioning.  First, nearly a week ago, it stopped reporting data on my LAN.  No power flows, no state of charge.  I suspected a software update from Tesla might be the source of the trouble; they have done that to me before.  This Sunday morning, I found it was behaving as if the grid was down; supplying power to the house with the transfer switch set to grid off and PW on.  But, I found the grid was not down and I had the expected voltage into the PW gateway.  I did much thrashing around.  Resetting, powering every thing off and on.  I ended up with the PW NOT supplying house power AND the transfer switch refusing to supply grid power to the house.

I've attempted to use Tesla PW service in the past and found it abysmal.  But, I reported via a web form in the middle of last week.  No response.  I could not wait for weeks with no house power for Tesla to give me some attention.  I final resolved to cut the PW out of the path of power to my house.  For that, I needed to kill power to the house to change wiring.  I asked two electricians to handle it for me.  No response.  So, I decided to do it myself, cutting the seal on my meter and removing the meter while I did the work.  Once I decided the easiest way to do the job and lined up the needed tools, it took only about 15 minutes.  So, here I am with power back to the house but with no PW.

The two wires from the meter formerly entered the top of the transfer switch at the top of the gateway box.  The two wires to the PW are disconnected and hanging in space.  The two wires from the meter are now connected where the PW wires were.  That connection then feeds power to my main breaker box, off the photo to the left.

2/21/2021

After the deed was done, I finally got a response from Tesla to my web form request.  The woman was most helpful and in only a few minutes got my PW connected to my Tesla app.  It only took two years and a failed PW.  The next step, I am informed by Tesla "service" is to rewire my PW back between the meter and my main breaker box.  I am convinced that the PW is broken and if I hook it back up I will again be without power  in my house.  Tesla "service" continues to insist that I follow their script.  We are at an impasse.   I likely pissed off Bluebonnet by cutting their seal and removing their meter without their oversight.  I will resist doing again.  Even though Tesla "service" insists.

Higher resolution versions of photos:

https://photos.app.goo.gl/DUSqXj4yzH1yjjgG9

 2/22/2021

The roof top PV was feeding into the breaker box below the gateway box.  With that configuration, I was getting no power from the roof top PV.  Since this situation gives every indication of continuing for a long time, until Tesla finally decides to make a service call, I decided to connect the roof top directly to my main breaker box.  I left the two wires to roof top PV in the PW breaker box but wirenutted them to a cable going to a breaker in the main breaker box.   The whole thing looks even more kludgy than is my norm.  But, it works; I have house power and am selling normal amounts of power to the grid.  I just do not have any grid backup.

2/25/2021

Some communication with Tesla PW "service" indicates I may be able to get a service call appointment by making a phone call.  Which I am resisting.  Reflection and observation leads me to believe that my transfer switch has failed.  It can no longer be manually moved from the "on" (PW) position to the "off" (always grid connected, PW not connected).  I may look into availability of replacement parts with an eye to replacing it myself.  High resolution of below photo indicates "Siemens EO  8695".  Maybe "EQ".

Testing PowerWall off grid

The test is now complete.  I ran from about 5pm Tuesday 2/19/2021 continuously through about 10:30am Monday 2/25/2021 with the grid disconnected.  It was a highly successful test.  I'll put a synopsis here and leave the "stream of consciousness" stuff below for you to decipher if you wish.

The questions that needed answers are:

1) What happens if PV power can not be accommodated by local demand including PW charging? 

My PV production can reach about 25kw while the PW charging can accept only 5kw.  The short answer is that the PW shifts the frequency off of the standard 60hz and all inverters are expected to respond by suspending production.  That happens and the PV quickly shuts down and the PW can continue to supply less than 5kw of local demand from the PW battery.   The PW and PV can get into a cycle of PV being shut down and restarting 5 minutes later only to be immediately shut again.  Things go more smoothly if PV capacity is reduced to approximate the PW capacity to charge.

2) What happens if local demand exceeds the 5kw power capacity of the PW?

The PW shuts down and stops supplying local demand.  This should be avoided for several reasons.  One is that, due to inverters shutting down, the power will be down for about five minutes.  Another is that many devices such as clocks will have to be reset.  Another is that monitoring stops working and it is difficult to figure out what is going wrong or has gone wrong.  One fix for this is to adjust demands.  For instance, I have to watch the operation of my 5kw water heater closely to be sure that there are no other significant loads a the same time.

3) What happens when you try to charge a car?

Obviously car charging should be avoided unless there is good PV production.  It is risky to attempt to charge above the 5kw limit of a single battery PW.  However, up to 5kw charging is entirely feasible if one closely monitors other significant local loads.  I have a nattering nabob friend who has declared that car charging could not be done from a PW while off grid.  He is incorrect.  But, loads  such as a water heater must be managed to avoid conflicting with car charging.  PV production may be highly variable so it is best to insure that the PW battery can supply the loads if PV power disappears unexpectedly.  While experimenting charging my Tesla, I was surprised to find that Tesla has fairly recently integrated PW and Tesla car software to force the car to slow charging when it appears the PW may fail to supply demand.  I have more testing and study to do on that feature. 

The problems cited all become much easier if a PW has a generous number of battery units.  Each battery unit adds 5kw of supply capacity and 5kw of variable PW charging demand.

I did not address the possible problem of the PW battery becoming depleted.  If it does become depleted, one may well be left with no electric power whatsoever. for an indefinite time.  Once down and without grid power the PW will take 5 minutes to get the PV started again.  During that time, the PW will have to be supplying local demands even with good sun.  I imagine the PW has some reserve capacity which might be used for restarting especially if grid power can handle local loads immediately.

 Older parts of posting:

 I've had the PowerWall for about two years now and not done much testing in preparation of a long term grid down situation.  The reason is that I've been reluctant to lose the revenue from PV energy sales to my utility.  In fairly good production weather, that is around $10/day.  Sometimes near $20.

Due to a friend's questioning of off grid PW use during cloudy weather, I've decided to do a multi day test while we have a long period of overcast weather in the forecast.  The low production overcast weather will minimize the lost revenue as well as reduce the problem of the PW being unable to handle high PV production.  I switched off grid about dusk on Tuesday 2/19/2021.  The PW had a state of charge of about 95%.  This very cloudy morning, Wednesday 2/20/2021, the SOC bottomed out 25% about 9am.  At about 9:30, even though it is very cloudy, the PW is charging at about 2.5kw.  Since the charge power limit of my single battery PW is 5kw, something interesting will happen when my PV production goes above the ability of the PW ability to accept.  That is either 5kw or zero depending on whether the PW battery is charged or not.

In good weather while grid connected, I can sell large amounts of PV power to my utility.  Off grid, the PW is unable to deal with PV power above about 5kw; zero if the PW battery is fully charged.  Now, about 10am, the PW charge power is around 3.5kw and I can see trouble coming.   I'll first observe if the PW is able to shut down PV inverters when power is too high.  The PW attempts the shutdown by shifting the "islanding" frequency off of 60hz.

Yesterday, a very cloudy and grid connected day, I produced about 32kwh and sold the utility 26kwh.  There must be some measurement error there because the difference should be about 20kwh.  About  10-12kwh to charge the PW and about 10kwh for daytime house consumption.

 11am 2/20/2021.  Still very cloudy but production has been very near 5kw.  I first turned off the 5kw roof top which faces south and produces well for only about 4 mid day hours.  Then turned off another major production block  leaving my most recent projects which are mostly E+W facing and produces 8-9 hours.  PW is at 68% and charging at less than 3kw.  My hope is to get to about 4-5pm with a PW battery that is near 100%.  If that comes to pass, I'll likely leave only that production block on for tomorrow.  Then, tomorrow about noon, evaluate to see if I want to turn more PV back on to get charged by the end of the day tomorrow.

 4pm 2/20/2021.  About 22 hours into the test, things are going VERY well.  I babied it past the water heating but, since then, no worries whatsoever.  The PW became fully charged about 1pm so the PW has been turning PV off regularly.  The PV goes down quickly and gracefully.  After going down, it takes about 5 minutes for inverters to come back up.  The PW is maintaining about 98% charge.  The PV comes on briefly and goes up to above 2kw every 5-6 minutes.

7am 2/22/2021.  Since there is sun in today's forecast, this test is near it's end.  I've been off grid for two days and three nights.  The test is a near total success.  Here are some takeaways:

1) With a single battery PW, I will likely run out of energy if we have two days in succession that are FAR more overcast than the very cloudy weather we've recently had.  My estimate is that that is perhaps a once a year occurrence.

2) By frequency shifting, the PW very quickly and gracefully shuts down PV when needed.  That is, when PV power overwhelms the local demand including the possible 5kw  battery charging.  Even in this cloudy weather, battery charging is generally complete by about noon so the PW cycles PV on and off all afternoon.  During typical sunny weather, my full PV system supplies far more than the 5kw that can be used for PW charging.  Under those conditions, the PW would cycle PV on and off all during the day.

3) A problem is that it takes the PV inverters about 5 minutes to recover or come back on after a shut down.  That means that local demand can not exceed the 5kw PW supply limit during those 5 minute periods. 

4) The consequence of the PW being asked for more power than it can supply is PW shutdown.  Which leaves the house without power for a few minutes until the PW attempts to restart.  When the PW shuts down, the observer becomes blind.  He can not tell what the PW is doing; he can not tell what the PV is doing.

5) During the test, I avoided PW shutdowns.  But just barely.  My 5kw water heater operated during battery charged period so PV was being turned on and off every ~5 minutes.  Early in the day, when the PW was charging, the battery provided a buffer of available power.  That is, during the battery charge period more than 5kw loads can be accommodated.  That might be water heating or car charging.

6) For the test, I did not attempt to make use of the additional power available during the battery charging period.

7) Should we experience a long term grid outage in the near term, I would first lower my water heater demand well below 5kw which would remove the threat of PW shutdown due to high demand.  For the longer term, I plan to add either one or two PW batteries; that would increase my available PW power from 5kw to 10kw or 15kw.

8) I don't know whether the frequent cycling of PV inverters is damaging to the inverters.  In case it is, I would likely turn off large sections of my PV during a long term grid down.  That would both reduce the number of inverters being cycled and reduce the period of the cycling.  Better matching PV capacity to the demand.

9) I should mention that I have changed two demands for the test.  Normally, when grid connected, I allow 36v golf cart charging and 48v lawn mower charging during day light hours.  Neither was used during the test.  I do not normally charge cars at the house since the cost is much lower at another of my meters.  Each of the chargers is 1-1.5kw which does not threaten the off grid 5kw limit.  But, power demand would be too high with either charger plus the water heater.  So, I would likely set my charger timers to morning hours or other to not allow water heating at the same time.

4pm, Saturday 01/23/2021.  I thought I could stop.  But, I just can't.  Test still running.  Yesterday was pretty sunny and I decided to see how the PW behaved with full PV cranking.  Starting about noon, after the PW was fully charged, and about once an hour during high production, the PW shut down leaving me without power.   I watched carefully to see if I should turn off some PV.  But, it behaved fairly gracefully, taking 5-10 minutes each time to get back to normal.  So, I am adding 10) and will continue test at least until Sunday morning.  That will be 5 days and 6 nights by my reckoning.  On second thought, I think I'll do a little car charging tomorrow before going back on grid.  I have a nattering nabob full of shit friend who has opined that a PW could not be used for car charging while off grid.

10) With 20+kw of PV power, the PW can fail to get PV shut down promptly enough.  Leaving the house without power for a few minutes.  So, during real long term grid outages with my 5kw PW, I will have to disconnect some PV.

 

 

If you find any of the above confusing, post a comment and I will either edit or respond to the comment.

PowerWall agumentation, new layout

 https://photos.app.goo.gl/1wHoSgrKHEsAT3n66

Last photo of wall mounted components:

1) Upper left: two 250w grid tie micro inverters as intended for  60 cell PV panels.
2) Upper right: two "500w" 12vdc grid tie inverters.
3) Lower center:  12vdc  to 36 vdc converter.
4) Lower right:  240vac recepticles used to accept power.

Several possible configurations, some could be concurrent:
1) 36vdc from batteries into either one or two 250w micro inverters.  Batteries from hoverboards repurposed to power golf carts are shown in first two photos.  Up to about 80 4ah hoverboard batteries are on hand to be paralleled.  About 12 kwh of available energy.
2) 36vdc from the 12v to 36v converter powered from a car into either one or two 250w micro inverters.
3) 12vdc inverter powered from a car.

In my case, "car" could be one of two Mitsubshi imievs or a Tesla Model 3.
With either type of car, the 12vdc can be up to about 1kw and depletes the car's main battery through the car's DC-DC which converters main battery voltage to about 14vdc.

For my purposes, 500 watts of augmentation is more than sufficient so no more than two micro inverters need be used.  Though several more could be easily configured.  The MC4 splitters photographed have space for one more inverter;
power outputs can easily be daisy chained together.
The 12vdc inverters are undesirable because of low efficiency; they produce only about 200 watts each and that not efficiently.  Producing ~400 watts overnight nearly depletes an imiev 16kwh battery.  Energy supplied at 240vac would be only about 6kwh.   The micro inverters are 95%+ efficient.

I have a single PowerWall which can supply 10-12 kwh at up to 5kw.  The battery size is marginal for using night time air conditioning during the summer.  Cloudy days can result in not full PW charges at dusk.  Either condition can make augmentation desirable.

I have about 112 kwh of energy available from four sources: 12 kwh from hoverboard batteries, 70kwh from the Tesla, 15kwh from each of two imievs.  Efficiency from the hoverboard batteries is very good, 95%+.  Efficiency of cars into the 12vdc inverter is poor, perhaps as low as 50%.  Efficiency going through the 12vdc -> 36vdc converter (car -> converter -> microinverters) is yet to be undetermined.  With some additions and reconfiguring, peak powers could reach 3-4kw.  Starting with fully charged batteries, I have hope of getting through about a week with no grid and no sunlight.  The single battery PowerWall will do 5kw with ~12kwh stored.  The PowerWall supplies power as demanded; the augmentation supplies fixed power.  The fixed power augmentation typically goes into demand.  If demand is insufficient, the augmentation power is either sold to grid or charges the PW battery.  In order to avoid sales to grid, with my current PW set up, I must go off grid.

See previous augmentation discussion:
https://wmckemie.blogspot.com/2019/09/micro-grid-and-augmentation.html

1/15/2020

A series of very cloudy days, leaving me starting some nights with ~50% PW charges, have encouraged me to do some more testing.
1) The 36v golf cart battery -> one or two microinverters -> house 240vac continues to work very well.  One inverter gives a solid continious ~230 watts; two inverters gives twice that.
2) 12vdc from an EV -> 12vdc/36vdc "upverter" -> microinverters works less well.  Output power varies quite a bit from the expected to near zero.  Average is about half that expected.  This is almost certainly a microinverter power tracking problem that I do not yet have a solution to.  Perhaps I'll find a high efficiency gridtie microinverter without power tracking to test.  Suggestions solicited.
3) 12vdc from an EV -> 12v cheap chinese inverter -> house 240vac has not recently been tested due to previous inefficiency.

Overnight air conditioning on PowerWall

Since I got the PowerWall installed, I've used essentially no energy from the grid; I've only sold energy to my utility.  I've been dreading the time when I don't feel comfortable at night without air conditioning.   Thursday night, 5/23/19, was a bit uncomfortable with a low of about 78 deg.  So, I left the air conditioner on last night, 5/24/19.  It wasn't a good test because the low was about 76 deg.

The result: about 7:30 am I'm producing over 1kw.  The air conditioner pulls a peak of about 1300 watts but relatively briefly.  Average is 300-800 watts.  So, the PowerWall has hit it's minimum.  That is 12%.  The PW will revert to grid power at 10% in order to leave a little energy for a real power failure.  So, a near thing.  Especially for a not very demanding night.

It is silly for me to worry about pulling a little grid energy.  My cost would be around $.10 per kwh used.  For an hour or two in the early morning hours, that cost would likely be $.05 to $.15.  Insuring remaining off the grid would require a second PW battery.  Cost, around $8k.

I can continue to make the claim of having used no grid energy since the PowerWall install.  Let me look that date up.....1/26/19.
 https://wmckemie.blogspot.com/2019/01/powerwall-install.html
Four months tomorrow!  I may continue to forgo night time air conditioning for a while.  Though I'm sure now that a hot night will exhaust the PW battery.

I finish writing this about 7:50 and the PW is charging at a few hundred watts whenever the air conditioner is cycled off.  Charge level remains at 12%.  This is a cloudy morning, so far.  12 hour overnight air conditioner consumption was 3.91kwh.  The first hour consumed .62kwh due to the warmer conditions.

Sunday, 5/26/19
It looks like we are in for a string of mid 70s nights so I have suspended overnight air conditioning experiments.

Sunday, 6/9/19
I just went through the first night with air conditioning running all night.  My minimum charge level was about 13%.  I'll probably start running the air conditioner around the clock.

Saturday, 6/22/19
I've been through several nights running the air conditioner.  I've come close to hitting the reserve threshold of 3%; the lowest has been 6%, I believe.  Once the threshold is hit, grid power is used.  So, I have so far avoided using grid power even using overnight air conditioning.

I decided to buy a 6k btu window unit for the bedroom so I could avoid running the big unit overnight.  Last night was the first using only the small new unit.  The PW got down to 30% just before morning production  began.  So, a success!  This gives me confidence that I can sleep comfortably during a long term grid down situation.  A major step!

April electric bill with PowerWall

My usage matches what I've been monitoring.  I was billed for 2 kwh.  That represents noise on the PW's attempt to use no grid energy; every once in a while, it will pull ~100 watts from the grid.

Under the "new" rate structure I expected to receive a credit at the end of each billing period rather than the previous annual credit.  Hasn't happened.  They added my over production, 1275 kwh, to my "banked" total.  Banked total on that meter is now 2169 kwh.  The month's over production should be worth about $63 which should have more than covered the "overhead" amount of $22.50 for which I was billed.

With my current configuration, I should be earning a bit more than $1/day from my electric supplier; that is above the $22.50 connection fee.  I have hope of getting that up to around $5/day.

3/18/19
The reason for the failure of BlueBonnet to transfer to the new rate structure:  The PW installer failed to notify BB that the final bit of work was ready to inspect.

As I understand, the changes to the rate structure:
1) Producers are debited immediately for any power pulled from the grid.  Hour by hour.  Old rate structure: power pulled is offset at full retail rates by power produced within the billing period.
2) Over production is credited monthly rather than annually.
3) Rates paid are a bit more.

With the PowerWall, I can contrive to almost never be impacted by 1).  Without a PW, the average producer's bill will go significantly higher.  So, I hope to preserve the old rate structure for my two meters that do not have PowerWalls and sell BB a lot of power from the meter with PW.

Off Grid

With my new found realization on how easy it is, with a PowerWall, to go off grid, I'm thinking of what might be done in remote places on my property.  I had my first epiphany on utility independence about 10 years ago when I put in my rainwater system:
 Austinfarm.us photos

For off site constructed housing, this seems like a good starting point.  Though alarmingly expensive.
 Mustang Ridge modular place

I'm thinking maybe a moveable PV carport kind of thing as the starting point for PV.

Back of my mind ideas: rental for horse riders, rental for COTA visitors,  a retreat for myself, another guest house.

Suggestions solicited.

PowerWall Install

"Pretty good" PowerWall article:
 https://cleantechnica.com/2018/10/12/tesla-powerwall-price-features-new-coming/


Single PowerWall is sitting on a pad.  The pad was selected instead of wall mount because up to three PowerWalls can be "stacked" on the pad.
Currently, non-functional awaiting BlueBonnet to turn off power, then connect to new power drop.

Last photo:
New BlueBonnet connection will be to the 4th box from left.  The PowerWall transfer switch and controls is the 3rd box from left.  Breaker panel is 2nd from left.  Leftmost is the existing meter housing; meter to be moved the 4th box.  String inverter for roof top PV is just the right of the window.  Just to the right of that, the single PowerWall.

https://photos.app.goo.gl/dKJdfDSTVg5NC5zj7

I just realized that there should be a 30% income tax credit associated with this deal.

1/26/19
Install is complete, online, working.  I do not have access for monitoring or control.
 https://www.youtube.com/watch?v=B1wOK9yGUYM

1/27/19 11am
Yesterday, I turned off the grid for a while to observe PV production after the battery was fully charged.  So after production went to zero, I felt I had a fully charged battery going into the late afternoon.
I turned off the grid about 5:45pm yesterday and went through the night ok. As evidenced by monitored PV production, I judged I was charging the battery before 9am.  Again, evidenced by zero monitored PV production, the battery was fully charged about 10:30am.  I just turned the grid back on to allow me to sell production to the grid.  The charging took less time than expected; it started cloudy and became partly cloudy.  Not very good PV production conditions.  This tells me that I could charge quite a few battery units in a not especially good production day.  Other than cost, that is very encouraging for going off grid with 3-5 battery units.  Of course running air conditioning will change things significantly.
I've been getting disappointing support on getting monitoring from both Tesla and the installer.  I hope things will move faster after we get past the weekend; my install was completed late on Friday.

1/27/19 8pm
I finally hit on a way to access the gateway this afternoon.  It was more difficult than it should have been because the installer told me it was using my wifi access point for internet access.  It turned out to be using cell network for that access.  Anyway, I now have limited and local only access to my gateway.  Presented are power to and from the grid and the battery, and power from one of the PV systems.  The percent state of charge of battery is also presented.  Though I don't know whether that is based on 14kwh or less.  I see no control.  And no power to energy integration.
 Now, I can see my house demand is around 5% of battery capacity per hour and is 300-500 watts.  My non PV production period is about 15 hours.  So my best guess right now is that I will be at about 25% of battery capacity when I start charging about 9am tomorrow.   I'll not be here at that time but hope to return about the time the battery is charged and I need to connect to the grid.

12/27/19 7am
Actual remaining capacity was just over 50%.  I ran the bathroom heater about half an hour on the battery and used CPAP all night.  Will try testing all night use of a fan though the fan is not needed in this season.

1/27/19 11am
Typical of my hour by hour BlueBonnet data when running PowerWall overnight and turning grid back on only when I have power to sell.  PW battery was charged back in the first couple of hours of PV production.  The battery seems to charge at a maximum of 2.5kw.
The below day time over production chart represents about $2 worth of electricity if sold at $.055 / kwh.  PV energy used during the day to charge the battery would be about  $1 if purchased from Bluebonnet for $.12/kwh.   PV energy used during the day to power the house would cost about $2 if purchased from BlueBonnet.  If it lasts me 10 years, the PowerWall will cost about $3.50 / day.  If it lasts me 20 years, the PV will cost about $3.40 / day.   Factoring in the 30% income tax credit, the two numbers would be about $2.50 and $2.60.  I did not claim the tax credit on all of the PV.


2/1/19 10am
The PW has been on just a few hours short of a week.  In that week, I have not bought any power from BlueBonnet and have been selling between 1.2 and 40 kwh each day.  Battery charging can be completed as early as about 10 am and as late as about 5pm.  Yesterday was very cloudy and resulted in the late charging completion.  Minimum states of charge in the mornings have been about 30%, meaning I need to produce around 8 kwh to recharge.  Since I have that 30% cushion in the battery, I can likely get through two nights that are separated by a very low production day.  I look forward to seeing what happens with a string of very low production days.  If I see a string of low production days coming, I will forego morning bathroom heat and will start the days with near a 50% charge.  Other parts of the year, using fans and/or air conditioning will be challenging.
I STILL do not have access to settings that need to be changed.  The installer has declared he wants nothing more to do with me and I'm seeking another for future PW projects.  I am absolutely thrilled with the operation and potential of the PW.  But, I've found both Tesla and installer support lacking.

2/5/19
Reflecting on using air conditioning with PowerWall.
Looking at my Curb, which monitors my room air conditioner circuit, I see average daily use during the four peak air conditioning months is about 10 kwh.  I'm guessing the ~15 no sunlight hours might account for 5 kwh of that.  So, the ~13.5 kwh PW might barely make it on an average day.  Now, with ~17 hours non-producing hours in a day, the PW gets me through the period on 50-60% of capacity, a maximum of about 8 kwh.  The shorter nights should reduce PW demand by about 1kwh.  Deviations from averages certainly indicate a 2nd PW to get through the summer without altering use patterns.
"Altering use patterns" might include turning air conditioner off at night and trying to "make do" with fans.
On this date, I am about 10 days into using the PW with no power taken from the grid.

3/17/19
Time for an update, I suppose.

The PowerWall has performed beyond expectations.
Aside from poor support from both the installer and Tesla.  I am limited to local monitoring; I've been unable to convince the Tesla miscreants in Las Vegas to associate the PowerWall with my Tesla account.  That should allow me to monitor, via the Android app, from anywhere there is internet access.

I did get "installer" access to the Power Wall.  That allowed me to correct a poorly set parameter.  That parameter is the fraction of  battery capacity reserved for a real power failure.  When battery charge level falls below that threshold, the Power Wall attempts to pull power from the grid instead of the battery.  Whenever battery level is above that threshold, power is supplied from the battery.  The PW was initially set to 75%; it is now set to 10%.

To date, for close to two months, I could have been "off grid".  I've used no power from the grid, I have only pushed power into the grid.  Had I actually been off grid, all the power I've sold to the grid would have been lost.

On the typical 50% overcast winter cloudy day, I have the PowerWall battery full recharged from night time use by noon.  My house PV, where the first PowerWall is located, now produces near 80kwh on a good sunny day and my energy use is around 15kwh plus whatever EV charging I do.  That is, if I do no EV charging, I can sell about 65kwh to the grid.  Successive very cloudy days have come close to exhausting the ~14kwh available from the PW battery.  That is, very cloudy days may not produce enough energy to completely recharge.  Typical overnight use, about 14 hours from low afternoon sun to a bit after sunrise, is 50%-60% of PW capacity.  So, if the recharge during a cloudy day is insufficient to bring the charge up to near 70%, it may not make it through the following night.  That has not yet happened though we have had long spells of very cloudy weather.

I doubt that the single Power Wall battery I have will carry me through a hot summer night requiring air conditioning.   My options are to add a second Power Wall battery (at a cost of about $8k) or just use a bit of grid energy during hot nights.  I don't believe I can justify the cost of a second battery.

3/20/19
BlueBonnet bill for period 2/12/19 to 3/13/19

The bill shows, for the house meter which has the PowerWall, 3kwh consumed and 466kwh delivered ("pushed" to the grid).  The 3kwh consumed, no doubt, due to the brief periods when the PW fails to exactly match battery use with demand.  At times, the grid is shown supplying about 100 watts.  I apparently am not yet on the rate schedule that specifies that I am paid monthly for over production.  463kwh was added to my annual "banked" production for which, under the old rate schedule,  BlueBonnet pays annually about February.