Whole house UPS

[gadfly56]

For the cost of two power walls you could probably have a standby generator to power the entire house; Something to think about. And it would carry you through a prolonged outage if necessary.


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For the cost of two Powerwalls ($13,400), I could get a generator to run the whole house, pay for the electrician, the plumber, and probably have enough left over to run the generator for a week.

Let's see, an 18KW Generac from Home Depot is about $4,500. Add another $5,500 for the sparky and the plumber, and I have $3,400 left over. Hmmmm, found a web site, 7kW unit uses 118 CFH, so 18kW will be 300 CFH, times 24 hours and $3.25/1000 CF or about $23/day. At full load, and that ain't gonna happen. So, I can go almost 150 days and break even on the Powerwall cost alone, less installation.

 

[caribconsult]

Yes. The only restriction is that in the US, because there is currently a tax credit for solar installations, and because that tax credit applies to Powerwalls if they are charged only from solar, then if you have solar at the time of Powerwall installation, Tesla insists on configuring the Powerwall to charge from solar only.

Cheers, Wayne

We live in Puerto Rico, a known part of the US, but the tax credit, even though it's federal, doesn't apply to us. We found that out long after we bought the system and it was tax time. I'd imagine the same rule might apply to other US territories, like the Virgin Islands, Guam, etc.

 

[jaggedben]

A generator isn't going to switch on fast enough to keeps one's digital clocks from having to be reset. A Powerwall might. SolarEdge Storedge will not. Enphase IQ8 probably will, but is not available quite yet. Not sure about the switchover time on Pika Energy equipment. Anyway, all of these are a lot of money to spend to avoid resetting clocks if there's no other benefit.

 

[caribconsult]

When I look at Tesla's site and run the calculation for handling my house size, it recommends two powerwall modules. They don't say how long two modules can run the house, but I assume it's a lot longer than five minutes, therefore I can probably use just one or a half of one if I can find a similar product in a smaller size.

It's a lot longer than 5 minutes, unless you are running an electric stove, dryer, a few A/C units and a welding machine all at the same time.

But you've got the cart before the horse. You need to first know what your house's average consumption is. Look at a recent electric bill, and divide the billed Kwh by the number of days covered. Our average consumption is just under 12kwh/day, because we don't have any air conditioners, we have a gas stove and water heater, all energy efficient lights and we're careful about leaving stuff on that doesn't need to be. Our only major consumer of electric is the clothes dryer, and when we use that, we switch the house to the grid, otherwise we're on the PW full time. Our average grid bill is about $12/month. When the dryer burns out, we'll replace it with a gas unit.

The single PW is good for about 13Kwh, and it's not a good idea to drain it completely...if you do it might not restart without some external help. So ours might last a full day with no sun to recharge it. Your mileage may vary. And the choice between a generator and a PW is somewhat illusory...the gen uses gasoline and oil continuously, makes lots of noise and requires regular maintenance or you'll burn it out. The Tesla is silent and you'll always have free power if there's sun. And if you run yours 'off grid' as we do, you're not subject to surges, lightning spikes and brownouts from the grid. When we were on the grid full time, we had a mountain of microwaves, TV's, computers, wireless phones and similar devices get fried by spikes and surges from the grid. That needs to be factored in to overall costs.

Feel free to ask more questions...we've learned a lot about this system over the last 1.5 years.

 

[winnie]

We get frequent short outages of a few seconds to a minute. I have UPS's on my computer and the DVR which help, but I still have to reset a bunch of clocks like the range and microwave. Is there a small whole house UPS available I could wire in before the panel? If it had five minutes of battery power that would be plenty.

So I know that I already answered that you are looking for a beast with big transistors (power handing capacity) but small batteries (energy storage), and that you shouldn't expect to find it because the big transistors generally come with matching big batteries.

But I just noticed a category of product that turns this on its head: 'lithium jump starters'. Their output is 12V (not 120/240V AC) so this is not a complete answer. However I am seeing things with energy storage of 50-100 watt hours, but with (very short duration) output ratings of 1000 or even 2000A. This is an excess of 10kW of power with less than 0.1kWh of energy storage.

Turning this technology into a 'whole house UPS' that would run a normal house with all of its loads for say 30 seconds would not be for the faint of heart, but I guess it would be possible.

-Jon

 

[Jraef]

100A 240V is roughly going to require a 25kVA UPS. Even with minimal battery time, you still need the power rating so figure $10,000 to $12,000 for the UPS, plus materials to mount and wire it. Is it worth that much to keep from resetting your clocks?

Hint:
You could buy all new clocks that have little supercaps inside that allow them to ride through about 12 hours of being powered off; you can get that feature on a microwave too. that might set you back a thousand total if you are some sort of clock fanatic. My wife was always complaining about the stove clock being reset. Black electricians tape and a little clock as mentioned above mounted over the stove fixes that.

 

[LarryFine]

Black electricians tape and a little clock as mentioned above mounted over the stove fixes that.

Works on "check engine" lights, too. :thumbsup:

 

[caribconsult]

A generator isn't going to switch on fast enough to keeps one's digital clocks from having to be reset. A Powerwall might. SolarEdge Storedge will not. Enphase IQ8 probably will, but is not available quite yet. Not sure about the switchover time on Pika Energy equipment. Anyway, all of these are a lot of money to spend to avoid resetting clocks if there's no other benefit.

There's another little factor involved: the PW/Gateway combo lowers the panel's output via a frequency shift upwards to about 61-64 cps once the battery is charged during daylight. It doesn't return to 60Hz until dark. If you run 'off grid' as we do, this increase in Hz will cause your clocks to run faster! We had no idea what was causing this until a Tesla engineer explained it. It's a little annoying but we've learned to live with it for the benefits of living on the sun. Doesn't seem to bother the fridges, clothes washer, ceiling fans, power tools or my computer's UPS. And we have a few battery operated clocks to tell us the real time.

 

[Petethefeet]

Maybe overstating the obvious... How about getting a small UPS for each room? Amazon has 425VA 260W UPSs for about $43 each. One behind the microwave can power the microwave, coffee maker, stove, and all your other small appliances on the counter. One in each bedroom should take care of the clocks, lamps, and even smart speakers. You should be able to cover the entire house for less than $300!

 

[hillbilly1]

I quoted one in the Caymans about 20 years ago, don’t remember what the quote ended up being, but large house (bedroom was as big as my house) the owner was complaining about how flakey the utility feed was, regularly dropping out a couple of minutes ever couple of hours. He also was wanting three phase in order to run a desalination unit to water his yard. The installer convinced him it would be cheaper to run. (As a friend of mine once said, if you have to ask how much it costs, you can’t afford it!)

 

[nerys]

Maybe overstating the obvious... How about getting a small UPS for each room? Amazon has 425VA 260W UPSs for about $43 each. One behind the microwave can power the microwave, coffee maker, stove, and all your other small appliances on the counter. One in each bedroom should take care of the clocks, lamps, and even smart speakers. You should be able to cover the entire house for less than $300!

This won't work. you need a 900 to 1200w ups to run the microwave. remember that UPS has to be able to handle the max load that device might command. even a small nuke is 900w (each $150 a pop) but 1200w is a lot harder and more expensive.

I got a server ups 1600w to run my minisplit. power here is very bad and I feared the browns and momentary outs killing the minisplit

I have since upgraded to a 240v 3 head unit so I can't UPS it anymore sadly

I also would LOVE a whole house UPS. I have 100amp service so that UPS would NEED to be able to handle and DELIVER 100amp of service.

I imagine it would be quite expensive. if I could do it for under $5k I probably WOULD do it eventually. the peace of mind knowing that all my expensive stuff won't be trashed by dirty power. right now I have something like 14 UPS all over the house on the more important things but I can't do that do the high power stuff. The car The water Heater the Minisplit etc..

 

[Jon456]

then if you have solar at the time of Powerwall installation, Tesla insists on configuring the Powerwall to charge from solar only.

Can a Powerwall be easily re-configured after installation to allow charging from the grid? What about charging from both?

 

[Jon456]

As someone else already said, if you have any electronics capability a diode and 8 AAA cells added to a microwave will run the clock thru a 2 year long outage. (If you don't already know how to do that, don't ask, not DIY even for many electricians

Seems to me an appropriate electrolytic capacitor on the DC power input to the clock circuit would work without the need for batteries.

 

[Jon456]

Our only major consumer of electric is the clothes dryer, and when we use that, we switch the house to the grid, otherwise we're on the PW full time.

I wonder if anyone has wired their home to have two independent electrical circuits: off-grid and on-grid. High electricity demand appliances like a clothes dryer or air conditioner could be on the on-grid service. Everything else could be on the off-grid system (with some form of transfer switch or other way of powering the off-grid side from the grid when required/desired).

 

[Joe.B]

Can a Powerwall be easily re-configured after installation to allow charging from the grid? What about charging from both?

I have seen a Tesla Powerwall installed to provide whole house back-up without any solar. I don't remember what was special about it but it operated off of the utility to stay charged, and automatically transferred over in an outage without any noticeable drop of power on the user side. One thing I do remember is they were not eligible for any rebates or discounts.

I wonder if anyone has wired their home to have two independent electrical circuits: off-grid and on-grid. High electricity demand appliances like a clothes dryer or air conditioner could be on the on-grid service. Everything else could be on the off-grid system (with some form of transfer switch or other way of powering the off-grid side from the grid when required/desired).

I've seen a owner-built house that was wired for both standard grid power, and an independent 12v DC system that he installed using lots of marine and RV components. Pretty cool setup. Most of his lighting was on the 12v system, charging ports for phones, computers, etc... Some of his small appliances even, like the coffee maker. I think he even had a fish tank that ran mostly off of the 12v, although I think the tank heater was 120v.

 

[Little Bill]

2 year old thread.............closed

 

[GoldDigger]

There's another little factor involved: the PW/Gateway combo lowers the panel's output via a frequency shift upwards to about 61-64 cps once the battery is charged during daylight. It doesn't return to 60Hz until dark. If you run 'off grid' as we do, this increase in Hz will cause your clocks to run faster! We had no idea what was causing this until a Tesla engineer explained it. It's a little annoying but we've learned to live with it for the benefits of living on the sun. Doesn't seem to bother the fridges, clothes washer, ceiling fans, power tools or my computer's UPS. And we have a few battery operated clocks to tell us the real time.

One side effect will be that internal timers (defrost cycle, fill time on ice maker in a refrigerator; cycle time on washer and dryer; timers on light circuits; etc.) will definitely run fast. 4 Hz out of 60 is a little over 6%. Whether this causes any noticeable problems is a valid question. I could live with smaller ice cubes, for example. Errors in the other direction could be more of a problem.