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Can solar only be used to charge powerwalls during a power outage?
- Thread starter voip-ninja
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charlesj
Active Member
It's a complex calculation that cannot be well planned for as weather is unpredictable, length of power outage is also unknown.
I am only looking at two power walls. My usage is around 650-800kwh per month depending on season. 20kwh would be enough to run the home for close to 24 hours during a power failure with no solar generation such as winter if panels are covered in snow.
If I disconnected non essential loads and just used the power walls to run essentials such as furnace, refrigerator, internet and some lights, I could easily stretch that to a couple days.
Matt-FL
Member
For using heat tape, I'd be more concerned on voiding warranty than anything else. From what I researched, if you can clear snow off part of a panel, once the sun hits it, they tend to heat up quickly on their own and melt most of the surrounding snow. It's getting that first bit to appear that can be tricky depending on your roof. Where I live, I don't tend to have snow problems. Last time it snowed here was probably either the late 80's or the ice age.
Heat tape might be the way to get that first bit to show, if it stays stuck during the summer months when the panels are really hot.
Heat tape might be the way to get that first bit to show, if it stays stuck during the summer months when the panels are really hot.
I just stumbled upon this thread. I may be too late to be useful, and you may have already figured this out, but here goes:
I have a similar setup - 9kW of solar (well shaded by pine trees in the winter, so minimal winter production) and 2 powerwalls. Gateway is v2. I have an electric range, electric dryer, no central A/C, a well pump, chest freezer, and a server rack with ~250W continuous load.
The gateway functions as an automatic transfer switch to take over anti-islanding functions from the inverter. When the grid goes down, the contactor in the gateway disconnects the house from the grid and the Powerwall inverters take over. The powerwall inverters kick in and provide power to the house. There is a quick flash of lights when this happens, but nothing seems to be disturbed. All my critical systems are on UPS's from the pre-powerwall days; I have one non-UPS'ed desktop that rides through the switchover fine.
I don't know if the powerwalls are already synced to the grid waveform before the switchover. If not, that probably explains why it may take a few minutes for the solar to come back on-line (if it drops off).
During an outage, the powerwalls, house, and solar inverter(s) are all interconnected on the house side of the gateway, isolated from the grid. The powerwall inverters are synced to each other in phase. The solar inverter(s) see the powerwall output as a grid signal and sync to that.
The gateway has current transformers to measure house load, solar production, etc. With excess solar, the powerwalls will dynamically ramp the chargers up and down to soak up the excess solar production. When the batteries approach full, it shifts the 60Hz frequency a bit to force the inverters to shut down (thinking the grid is out of spec). You'll then run off the batteries, until they are low enough for the chargers to kick back in, at which point the powerwall inverters return to 60.0Hz and the solar inverters re-sync and start producing again.
There is nothing magic about this system (well, v2, anyway) that requires Tesla solar inverters. I have a Solaredge HDWave 10kW.
You must have enough powerwalls so that the combined charger capacity is at least the output of your solar inverter, to prevent the system voltage from going out of spec if the solar is overproducing (solar output > house load+charger capcity). So a 5-10kW system must have 2 powerwalls, 10-15kW must have 3, etc. I don't think Tesla does single battery systems anymore - I was told they found that one powerwall can't handle big motor starting loads (like my well pump)
I ran through a 36 hour outage last December with minimal solar production. I did shut down the server rack a few hours in. I did not run the range or dryer (microwave dinner and do laundry later). We were close to full when the outage hit and finished around 20%.
Is this a daily cycle or only a couple of times a month? If occasionally, go for it. I am on a similar plan with Liberty Utilities in NH. Instead of buying the batteries and getting a rebate, they lease them to me at a discount. They are not daily cycling; they only discharge a couple of times a month to hit the monthly system peaks to reduce wholesale transmission costs. Their discharge events go down to 20%; the batteries recharge nightly during off peak. I did have a brief outage one night after a discharge, but it was quick (<1hr).
ArizonaJon
Member
I have 2 powerwalls with just under 10kW DC solar with the Tesla controller system. When the grid goes down, I don't see much impact on my home. Even the electric clocks hold their time. The only thing that seems to notice is my Dish Hopper DVR which does an automatic reboot. The system keeps in sync with the grid power so it can react immediately.
Matt-FL
Member
I still use UPS devices on my more sensitive electronics, but I've not seen more than a quick lights flicker when I switch over. My UPS's used to continue beeping, due to the hz frequency change, but Tesla support adjusted it so they no longer do that.
RKCRLR
Active Member
I had to put my home router and DVR on a UPS when I got Powerwalls. Before the Powerwalls they would just boot up after a power was restored after an outage. When I got the Powerwalls the brief power interruption during switchover wasn't enough to trigger a reboot but would put them in limbo. The DVR would lockup and the router would stop routing. I had to manually reboot them to get them to start working again. Was frustrating to come back from vacation to find my shows weren't recording.
charlesj
Active Member
Same here, had to do this except I needed 3 UPS, modem(different outlet), router, DVR. Small price for less headaches.
4 UPS units for us. My systems, wife's systems, AV rack with security recorders and NAS, Comm rack with 32 ports, cable modem, PIs and other SBCs, etc.Same here, had to do this except I needed 3 UPS, modem(different outlet), router, DVR. Small price for less headaches.
Folks may want to start looking into portable power stations going forward for many use cases - technically most are EPS, as their switchover time can be greater than 20-50ms so not technically UPS. Won't handle the switchover quickly for a desktop computer, but works great for router/modem, switches, and other things. I ran a UPS for router/modem for years, but tired of them dying every 2-5 years (and of course the replacement batteries are usually as expensive as a new UPS), now have it on a power station.
Mostly being LFP these days, the power station batteries will last way longer than lead-acid UPS technology. Slightly downside that they might have slightly more power consumption from keeping an AC inverter powered (still only like10 watts or so), even in passthrough mode, compared to a UPS - but for my modem/router setup, I avoided that by removing their wall warts (saving even more conversion inefficiencies) and using common adapter cables to power directly from 12V DC. Now in the process of seeing if I can switch over my aquarium pumps too - they have 24V AC adapters. But just purchased a USB-C PD dongle that outputs 18-20V DC from USB-C, will see if the pump can run off it. Hopefully it works, esp as efficient, variable-flow aquarium pump like mine are actually DC-based pumps.
But that's just nitty-gritty - the portable power stations work just fine as EPS powering equipment from the standard AC outlets as well.
Mostly being LFP these days, the power station batteries will last way longer than lead-acid UPS technology. Slightly downside that they might have slightly more power consumption from keeping an AC inverter powered (still only like10 watts or so), even in passthrough mode, compared to a UPS - but for my modem/router setup, I avoided that by removing their wall warts (saving even more conversion inefficiencies) and using common adapter cables to power directly from 12V DC. Now in the process of seeing if I can switch over my aquarium pumps too - they have 24V AC adapters. But just purchased a USB-C PD dongle that outputs 18-20V DC from USB-C, will see if the pump can run off it. Hopefully it works, esp as efficient, variable-flow aquarium pump like mine are actually DC-based pumps.
But that's just nitty-gritty - the portable power stations work just fine as EPS powering equipment from the standard AC outlets as well.
charlesj
Active Member
Yep, wife's happiness is very important.
Are they all the same VA rated? That rack may need a good bit for instant transfer and maybe for a bit longer usage while transferring.
The UPSes are all the same, 1500VA/1000W. They react very quickly, and the Powerwalls takeover almost instantly. Usually, the only way we know that we loss power is the click from the UPS or message on the app. As far as the AV rack goes, it is getting more and more sparse as we shutoff dead/unused electronics like Tivo, DVD player, gaming systems, etc. With everything online no need for a lot of that.Yep, wife's happiness is very important.
Are they all the same VA rated? That rack may need a good bit for instant transfer and maybe for a bit longer usage while transferring.
Wife's system is important since her tech courses earn more money than mine do. :->
12-24V DC buck/boost systems are pretty common. They are used commonly to run military or large truck electronics on normal 12V vehicles, and vice versa.
Prices for the 12V to 24V step up versions start at about $10 and go up.
Ah, good to know, thanks!
I did have a chance to try the $7 USB-C dongle though, and interestingly it works! It looks like a short USB-C adapter cable to 5521 plug common on many 12 and 24V AC power supplies, so it plugs right into the controllers for the aquarium pumps. But since USB-C power supplies need some signaling on what voltage and amps to supply, apparently there's a bit of circuitry in the dongle that specifically signals USB-C PD 18-20V (meant really for laptops and some high-end phones).
I used a compact USB-C PD 65W wall wart for testing, and was able to power not just one, but simultaneously two separate pumps together drawing 35-40 watts. I guess their bulky AC adapters were fairly efficient though, using a watt meter only saw 0.5W less consumption from the wall compared to the USB-C wall wart. Of course the long-term plan is to use the portable battery station in DC mode to provide the USB-C PD power/backup.
Speaking of AV backup, I do have one of those big expensive APC AV Power Conditioners / UPS units that protected my home theater equipment. It has also been sitting in a closet for 10 years, after the internal batteries died within 2 years, and just wasn't willing to shell out big $$ for the two APC brand battery replacements every couple of years.
There are other sources for the UPS batteries, and if you don't sweat the exact battery model, often a few Ah up or down may be much cheaper, but also may, or may not, fit in the box, and might need a few inches of adapter cables.
Prior to my current pure sine UPS, my prior UPS went through more than a decade on a pair of replacement SLA batteries that more than doubled its outage runtime. When it comes time to replace my current (Eaton) UPS, I will buy a 12V lithium battery, a lithium specific charger, a surge protector strip, and a pure sine wave inverter, and make my own modular UPS. In this day and age, I think all the pure sine wave UPS units ought to have moved to lithium phosphate or sodium batteries.
All the best,
BG
Regarding the UPS batteries, I have Cyberpower UPSes, and as you experienced their replacements are expensive. But I checked on Amazon and found generic batteries for a fraction of the costs. Cyberpower wanted something like $150 for the one on a $250 UPS. I found a 3rd party one for around 1/4 the cost. It has been working for over a year.
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