Cost & Value: Sol-Ark vs. Powerwall

[Mayer]

I am investigating back up power for my home in Pennsylvania after installing a 15.33 kW SunPower array last year.

I come to this post without a reasonable understanding of the technology but learned a great deal over the weekend after posting about compatibility of SunPower with Powerwall.

I am communicating with a Tesla approved installer with solid Google reviews who just quoted $46k for 3 Powerwalls (Tesla quoted $33k with install per screen shot below).

Installer appears to be nudging me toward Sol-Ark, which appears to be good option since I would like to preserve ability to add a generator.

I’m wondering what someone more knowledgeable thinks about the installers pricing pitch. My concern is that if the quote for Powerwalls is unreasonably high, is the quote for Sol-Ark also unreasonably high.

The pricing quotes are as follows:

“We can install 2 Tesla PowerWalls for $31,495.
This would provide you with 27 kWh of storage.
If you wanted a 3rd Powerwall, for a total of 40 kWh of storage, then you would be looking at a cost of $45,995

One big thing here is to make sure that you have enough wall space available inside, near your main panel for the powerwall.

If you are interested in other options, we can set you up with a Solark/Homegrid system. This system comes with a SolArk 15 kW Inverter and Homegrid Batteries ranging from 10 kWh of storage up to 40+ kWh of storage. With this system you have a bit more flexibility in terms of battery size, as well as adding batteries in the future.

15 kW SolArk with 10 kWh of storage would be your minimal entry point for a cost of $22,500. We can add 5 kWh increments of storage for $4,000 a piece.
The other nice feature with this system is that it has an input for an external generator as well.“

 

[cali8484]

Sounds like there are plenty of options to consider. In the end, options could be limited to what the reputable service provider in my neck of the woods is working with. Maybe I can convince that outfit to consider something like the FranklinWH

Yes, many options. You many also want to ask your installer about Schneider as well. In general, they can all provide backup power during grid outages. However, as an earlier post indicated, it's still early stage tech so there various trade-offs when you dig deeper. I would suggest you make a clear list of specific requirements and make the installer guarantee to meet them in writing upfront. It's a major project and you will want to be explicit about things you want to avoid being disappointed after it's all installed. Some examples:
* Do you want to fully utilize all available solar energy while running on backup power (i.e. no grid)? If yes, FranklinWH may not be the best choice because it doesn't support proportional power control from your solar inverters since it doesn't support frequency shifting. So, when the batter is nearly full it will just use a relay to turn off all solar power and power loads from the battery. This results in wasted solar energy and potentially require more batteries. Also, there have been reports of Sol-Ark and Schneider not able to maintain stable full AC coupled solar power especially with newer microinverters. Powerwall is probably the best in this area.
* Do you mind potential lights flickering when running on backup power under some conditions? There have been reports of Sol-Ark with the problem.
* Do you want a built-in display to show you (or your significant others) the system status (e.g. power, battery state,etc) without having a working Wifi and configured phone app in a blackout? If yes, Sol-Ark would be better than the others (e.g. Powerwall).
* Do you need to run large motor loads (high start surge power) when on backup power? If yes, Sol-Ark, Enphase and Powerwall have lower surge power capability due to their high-frequency inverter design. Schneider and FranklinWH have low-frequency inverter design with higher surge power capability.
* Do you want to be able to charge battery from the grid at will? If yes, Powerwall may not be the best choice as it doesn't always allow that.
* Do you want to play the incentives game (e.g. sell-back, VPP) to justify the system cost (to you or your significant other)? If yes, Sol-Ark could be better as it provides more flexible controls. Schneider has some known problems in this area.

Good luck with your project.

 

[Mayer]

Yes, many options. You many also want to ask your installer about Schneider as well. In general, they can all provide backup power during grid outages. However, as an earlier post indicated, it's still early stage tech so there various trade-offs when you dig deeper. I would suggest you make a clear list of specific requirements and make the installer guarantee to meet them in writing upfront. It's a major project and you will want to be explicit about things you want to avoid being disappointed after it's all installed. Some examples:
* Do you want to fully utilize all available solar energy while running on backup power (i.e. no grid)? If yes, FranklinWH may not be the best choice because it doesn't support proportional power control from your solar inverters since it doesn't support frequency shifting. So, when the batter is nearly full it will just use a relay to turn off all solar power and power loads from the battery. This results in wasted solar energy and potentially require more batteries. Also, there have been reports of Sol-Ark and Schneider not able to maintain stable full AC coupled solar power especially with newer microinverters. Powerwall is probably the best in this area.
* Do you mind potential lights flickering when running on backup power under some conditions? There have been reports of Sol-Ark with the problem.
* Do you want a built-in display to show you (or your significant others) the system status (e.g. power, battery state,etc) without having a working Wifi and configured phone app in a blackout? If yes, Sol-Ark would be better than the others (e.g. Powerwall).
* Do you need to run large motor loads (high start surge power) when on backup power? If yes, Sol-Ark, Enphase and Powerwall have lower surge power capability due to their high-frequency inverter design. Schneider and FranklinWH have low-frequency inverter design with higher surge power capability.
* Do you want to be able to charge battery from the grid at will? If yes, Powerwall may not be the best choice as it doesn't always allow that.
* Do you want to play the incentives game (e.g. sell-back, VPP) to justify the system cost (to you or your significant other)? If yes, Sol-Ark could be better as it provides more flexible controls. Schneider has some known problems in this area.

Good luck with your project.

This is a helpful list of issues/solutions.

I had not considered being unable to monitor the data (App) during power outage when internet goes down. We have terrible cell service when Wi-Fi goes down, which is one reason we need backup power.

But most important, you said:

Do you need to run large motor loads (high start surge power) when on backup power? If yes, Sol-Ark, Enphase and Powerwall have lower surge power capability due to their high-frequency inverter design.

Answer:

Yes, we would like to run our central air whenever solar is providing power (sunlight hours), and at nighttime too, in a pinch, to at least keep temperatures reasonably cool.

Hopefully SunVault can manage that solution as it seems SunVault is our likely choice given estimate received today from the same outfit that installed our panels.
One battery is $17k installed and two likely about $27k.

Tesla’s webpage quoted $24,417 for two Powerwalls installed but seems like SunVault might be a better solution as I’d also like to add a small generator, eventually. And who knows if Tesla installer will increase price after site inspection, scheduled for 8/15.

So far I have not heard anything too concerning with SunVault;
it edges out Powerwall with slightly higher surge power capacity and integrates with a generator easier.

And, the company that installed my SunPower panels gave me this quote and, as far as I can tell, they did an outstanding job on that installation. And their pricing seems better than the outfit that was pressing Sol-Ark (a Tesla certified installer who quoted $7k more for Powerwall than Tesla webpage).

Aesthetically, Powerwall beats all the competition and the pricing for the Powerwalls, as quoted on Tesla’s webpage ($24,417), is at least $2,500 less than the SunVault.

But Sunvault’s product and installer makes more sense right now with a better solution to higher power surges, generator compatibility, and (unlike other units) should enable us to fully utilize all available solar energy while running on backup power, reserving full battery at sundown (sun permitting of course).

Any thoughts or concerns?

 

[jjrandorin]

I had not considered being unable to monitor the data (App) during power outage when internet goes down. We have terrible cell service when Wi-Fi goes down, which is one reason we need backup power.

You can monitor powerwall status directly from the gateway, in the case of a power outage and not having internet.

Note that, you likely mean "wi fi goes down" to say "internet goes down" but a lot of our members in this subforum are technical ones (with quite a few IT people I think too). If you have a backup battery, its entirely possible for you to not have internet because your entire neighborhood is out (for example) but your internal to your home wifi still work fine if you have power.

Would be relevant if you have devices internal to your network that you want to use (like I have a NAS storage device with a lot of movies / media on it). I can use it just fine with no connection to the internet, as its on my internal network.

Anyway, during a power outage, if you have batteries of some sort, its likely your router / wifi at your home is still up. Whether you have internet or not will depend on if the power outage is impacting the ISPs equipment in your neighborhood, whether they have some sort of backup power themselves etc.

In practical terms, the times I have had power outages since getting powerwalls, my internet has functioned fine as my ISPs equipment in my neighborhood was not down, and since my equipment still had power, neither was I.

 

[Mayer]

You can monitor powerwall status directly from the gateway, in the case of a power outage and not having internet.

Note that, you likely mean "wi fi goes down" to say "internet goes down" but a lot of our members in this subforum are technical ones (with quite a few IT people I think too). If you have a backup battery, its entirely possible for you to not have internet because your entire neighborhood is out (for example) but your internal to your home wifi still work fine if you have power.

Would be relevant if you have devices internal to your network that you want to use (like I have a NAS storage device with a lot of movies / media on it). I can use it just fine with no connection to the internet, as its on my internal network.

Anyway, during a power outage, if you have batteries of some sort, its likely your router / wifi at your home is still up. Whether you have internet or not will depend on if the power outage is impacting the ISPs equipment in your neighborhood, whether they have some sort of backup power themselves etc.

In practical terms, the times I have had power outages since getting powerwalls, my internet has functioned fine as my ISPs equipment in my neighborhood was not down, and since my equipment still had power, neither was I.

Yes, as you can see, I am not tech savvy.

I see you have Powerwalls.
I understand it is not too difficult to integrate a generator with the Powerwalls.
So that’s a minor issue.
Do you have an opinion on two Powerwalls’ ability to manage central air?

I prefer to support Tesla, actually, but if the Powerwall price changed after site inspection I’d definitely stick with SunVault.

On the other hand, if SunVault is truly a better fit, and not backordered, I might cancel Tesla site inspection so as to not waste anyone’s time.

 

[jjrandorin]

Yes, as you can see, I am not tech savvy.

I see you have Powerwalls.
I understand it is not too difficult to integrate a generator with the Powerwalls.
So that’s a minor issue.
Do you have an opinion on two Powerwalls’ ability to manage central air?

I prefer to support Tesla, actually, but if the Powerwall price changed after site inspection I’d definitely stick with SunVault.

On the other hand, if SunVault is truly a better fit, and not backordered, I might cancel Tesla site inspection so as to not waste anyone’s time.

Yes, I have an 8.65kW Solar install, and 2 powerwalls. If I had the amount of PV you mention having, I would get a minimum of 3 powerwalls (but I think I mentionedd that previously).

As for the "powerwalls ability to manage central air" question, I happen to be a big believer in backing up everything you can putting everything you might possibly want to use) oin the backup loads side, because it gives you options.

Even with that, however, whether or not you can use your central air for any real length of time depends on how many powerwalls you have, and what kind of draw your central air has (getting past the "Can I even start it up" question, assuming with 2-3 powerwalls you can start most central air systems)

Ill give you an example of what I am saying, using my own home. I live in a place where its common to need to use AC during the summer (temps regularly reach high 90s low 100s and sometimes I have seen temps over 110 here). I have (2) 3 ton AC units at my home, one for downstairs and one for upstairs. The home itself is 3300 ish square feet. Each of my AC units came with the home, which was built in 2005. Each unit is a standard, builder grade unit, which means they are not variable speed, etc.

Each one of my AC units, when running, Draws 4.1kW, so an hour usage from one of my units is 4.1kWh. That obviously means if both are running, that would be 8.2kWh of power used, in 1 hours time, running the AC. I have 2 powerwalls, so that means I have 13.5kWh X 2 of storage, or 27kWh of storage. If my AC units run for 3 hours, they will get very close to completely draining my powerwalls, and that does not count ANY other home loads.

My home runs about 1.1 to 1.5kWh for its regular "run rate" without talking about AC (just regular run rate, TVs, lights, fridges, etc). Every single home has its own electricity run rate, and mine is already been optimized (LED lighting,etc etc). So, running my AC units for 3 hours, if both were running, would completely drain my powerwalls from 100% to 0, when combined with my normal run rate.

Now, even with the above, I wanted my AC backed up, because IF I was in a power outage, I obviously would not run both my AC units for an hour at a time. I would increase my thermostat from the temp I normally keep it at (which is actually 80-81, as I have gotten my wife and I used to that temp vs like 72-75 degrees) to something even higher. I would probably only let it run for 15-20 minutes at a time, and only run one at a time (either upstairs or downstairs).

In other words, I would "manage" it, but its also just my wife and I, we are empty nesters. MUCH harder to do this with a house full of people, especially when because (like I believe you are already finding out) most of them tend to say "Thats why we got solar, right? Why do I have to turn off the lights, what did we spend all the extra money for?" Even in a power outage, it would be "But I thought we had batteries, and I need to XXXX / YYYY", why did we get the batteries then?


Back to your question. Can my powerwalls manage my central air? Yes, I can turn it on. Can I run it with impunity? No, I cant, I dont have either enough solar, nor enough powerwalls for that. Can I take the edge off if needed? Yes, I can. For me, its "managed" but your idea of what "manage" is (or more importantly "She/He who must be obeyed" (S/HHMBO), Idea of "managed" might differ.

I cant run my AC all night, off grid, and most people wont be able to... well @h2ofun probably can, and @CrazyRabbit probably can, but they have more powerwalls than you can count on one hand, lol.

 

[Mayer]

Yes, I have an 8.65kW Solar install, and 2 powerwalls. If I had the amount of PV you mention having, I would get a minimum of 3 powerwalls (but I think I mentionedd that previously).

As for the "powerwalls ability to manage central air" question, I happen to be a big believer in backing up everything you can putting everything you might possibly want to use) oin the backup loads side, because it gives you options.

Even with that, however, whether or not you can use your central air for any real length of time depends on how many powerwalls you have, and what kind of draw your central air has (getting past the "Can I even start it up" question, assuming with 2-3 powerwalls you can start most central air systems)

Ill give you an example of what I am saying, using my own home. I live in a place where its common to need to use AC during the summer (temps regularly reach high 90s low 100s and sometimes I have seen temps over 110 here). I have (2) 3 ton AC units at my home, one for downstairs and one for upstairs. The home itself is 3300 ish square feet. Each of my AC units came with the home, which was built in 2005. Each unit is a standard, builder grade unit, which means they are not variable speed, etc.

Each one of my AC units, when running, Draws 4.1kW, so an hour usage from one of my units is 4.1kWh. That obviously means if both are running, that would be 8.2kWh of power used, in 1 hours time, running the AC. I have 2 powerwalls, so that means I have 13.5kWh X 2 of storage, or 27kWh of storage. If my AC units run for 3 hours, they will get very close to completely draining my powerwalls, and that does not count ANY other home loads.

My home runs about 1.1 to 1.5kWh for its regular "run rate" without talking about AC (just regular run rate, TVs, lights, fridges, etc). Every single home has its own electricity run rate, and mine is already been optimized (LED lighting,etc etc). So, running my AC units for 3 hours, if both were running, would completely drain my powerwalls from 100% to 0, when combined with my normal run rate.

Now, even with the above, I wanted my AC backed up, because IF I was in a power outage, I obviously would not run both my AC units for an hour at a time. I would increase my thermostat from the temp I normally keep it at (which is actually 80-81, as I have gotten my wife and I used to that temp vs like 72-75 degrees) to something even higher. I would probably only let it run for 15-20 minutes at a time, and only run one at a time (either upstairs or downstairs).

In other words, I would "manage" it, but its also just my wife and I, we are empty nesters. MUCH harder to do this with a house full of people, especially when because (like I believe you are already finding out) most of them tend to say "Thats why we got solar, right? Why do I have to turn off the lights, what did we spend all the extra money for?" Even in a power outage, it would be "But I thought we had batteries, and I need to XXXX / YYYY", why did we get the batteries then?


Back to your question. Can my powerwalls manage my central air? Yes, I can turn it on. Can I run it with impunity? No, I cant, I dont have either enough solar, nor enough powerwalls for that. Can I take the edge off if needed? Yes, I can. For me, its "managed" but your idea of what "manage" is (or more importantly "She/He who must be obeyed" (S/HHMBO), Idea of "managed" might differ.

I cant run my AC all night, off grid, and most people wont be able to... well @h2ofun probably can, and @CrazyRabbit probably can, but they have more powerwalls than you can count on one hand, lol.

So my aspirations for central air are likely unrealistic. I guess I was hoping on a sunny day the solar would provide all the power we needed to run the AC, at least while the sun is high.

Anyway, that is a ton of helpful information to digest and examine as to my home. I’m sure my home’s run rate is off the charts, which is why we moved to solar. I know it was just over 30 kW for June and certainly higher in July.

And your right, I’m sure. My family won’t understand the limitations. As they say, champagne problems.

Kids were fine when we used candles but they are teens now so ….

I wish we had two condensers.
Mini split might be next.
Thank you.

 

[jjrandorin]

So my aspirations for central air are likely unrealistic. I guess I was hoping on a sunny day the solar would provide all the power we needed to run the AC, at least while the sun is high.

Anyway, that is a ton of helpful information to digest and examine as to my home. I’m sure my home’s run rate is off the charts, which is why we moved to solar. I know it was just over 30 kW for June and certainly higher in July.

And your right, I’m sure. My family won’t understand the limitations. As they say, champagne problems.

Kids were fine when we used candles but they are teens now so ….

I wish we had two condensers.
Mini split might be next.
Thank you.

Just for clarity sake, My run rate I was talking about was hourly (I dont think I said). My home uses 1 to 1.5kWh an hour, so 24-36 kWh a day, if I dont charge my car. My car will take just about as much as my house (so 24kWh), which was fascinating to me when I first discovered that it cost as much power for me to drive to work and back as it takes to run my house.

 

[BGbreeder]

Just for clarity sake, My run rate I was talking about was hourly (I dont think I said). My home uses 1 to 1.5kWh an hour, so 24-36 kWh a day, if I dont charge my car. My car will take just about as much as my house (so 24kWh), which was fascinating to me when I first discovered that it cost as much power for me to drive to work and back as it takes to run my house.

Yes, cars take an amazing amount of energy. I had a friend who was hacking EV race cars, who at point handed me this little brick that was the power control block for his car 600,000W! I thought it was insane, but you do the math and it is only a 600HP roadster, which is nothing in race cars. He held a couple of early world records.

But back to @Mayer's issues. While it is important to be able to start your AC, the big picture is, I think, @jjrandorin's point that you need sufficient stored energy to be able to power the desired "essentials". This gets to why I think that the generator or battery storage question is a false dichotomy for people trying to have sustained backup, e.g. off grid, or long outages. It is easy and relatively cheap to stockpile a week or two of propane or diesel, but insanely expensive and complicated to stockpile that much energy in batteries. The cheapest watt to power is the one that you save via energy efficiency (insulation, LED bulbs, heat pump hot water...)

All the best,

BG

 

[cali8484]

Any thoughts or concerns?

SunVault should work well for you as it's a pre-integrated package of a Schneider inverter with SunPower batteries in select capacities. Schneider has a long track record for very well (over?) engineered inverters that can run for 20 years. The inverter works great for large motor loads as it can actually provide much higher actual surge power than its specs. Most other inverters generally struggle to meet specs under real world conditions. The main problem reports with Schneider are about limited sell back control options and AC coupling issues with Enphase iQ8 (but not earlier models) microinverters during grid outages.

 

[Redhill_qik]

So my aspirations for central air are likely unrealistic. I guess I was hoping on a sunny day the solar would provide all the power we needed to run the AC, at least while the sun is high.

This isn't a one-size-fits-all situation, I have two Powerwalls with a partial home backup with one 4.0 ton AC unit on the backup and the other 5.0 ton AC condenser not on the backup. Both could operate in steady state below the 10kW that the two Powerwalls can deliver, but the LRA startup for the 5.0 ton AC exceeds what two Powerwalls can support. There is a CT on this circuit, so when the 5.0 ton AC kicks on during peak any solar production plus the Powerwalls are providing that power with help from the grid to get it started.

 

[Mayer]

Yes, cars take an amazing amount of energy. I had a friend who was hacking EV race cars, who at point handed me this little brick that was the power control block for his car 600,000W! I thought it was insane, but you do the math and it is only a 600HP roadster, which is nothing in race cars. He held a couple of early world records.

But back to @Mayer's issues. While it is important to be able to start your AC, the big picture is, I think, @jjrandorin's point that you need sufficient stored energy to be able to power the desired "essentials". This gets to why I think that the generator or battery storage question is a false dichotomy for people trying to have sustained backup, e.g. off grid, or long outages. It is easy and relatively cheap to stockpile a week or two of propane or diesel, but insanely expensive and complicated to stockpile that much energy in batteries. The cheapest watt to power is the one that you save via energy efficiency (insulation, LED bulbs, heat pump hot water...)

All the best,

BG

Great point: the cheapest watt to power is the watt saved through efficiency
Now if I could only get my family on board with that program.

For those in this subgroup with back up generators, is there a consensus as to whether it’s best to go large or could a smaller generator work well in tandem with 2 Powerwalls or similar sized battery?

Would a 125 gallon fuel tank ever be enough (so it can sit next to house) or do most homes really need at least 500 gallons?

 

[Mayer]

SunVault should work well for you as it's a pre-integrated package of a Schneider inverter with SunPower batteries in select capacities. Schneider has a long track record for very well (over?) engineered inverters that can run for 20 years. The inverter works great for large motor loads as it can actually provide much higher actual surge power than its specs. Most other inverters generally struggle to meet specs under real world conditions. The main problem reports with Schneider are about limited sell back control options and AC coupling issues with Enphase iQ8 (but not earlier models) microinverters during grid outages.

Perfect.
Regarding the concern with AC coupling issues with Enphase iQ8, I would not need to worry about that issue with Enphase IQ7HS inverters?

 

[Mayer]

This isn't a one-size-fits-all situation, I have two Powerwalls with a partial home backup with one 4.0 ton AC unit on the backup and the other 5.0 ton AC condenser not on the backup. Both could operate in steady state below the 10kW that the two Powerwalls can deliver, but the LRA startup for the 5.0 ton AC exceeds what two Powerwalls can support. There is a CT on this circuit, so when the 5.0 ton AC kicks on during peak any solar production plus the Powerwalls are providing that power with help from the grid to get it started.

This reminds me of how much I don’t yet understand. But I guess your saying if my AC unit is 5.0 ton or more, a 2 battery system may be unable to complete a startup without help from the grid?

Would that change if there was plenty of kW being generated from the solar panels at the time the AC unit is kicking on?

 

[Redhill_qik]

This reminds me of how much I don’t yet understand. But I guess your saying if my AC unit is 5.0 ton or more, a 2 battery system may be unable to complete a startup without help from the grid?

Would that change if there was plenty of kW being generated from the solar panels at the time the AC unit is kicking on?

Not all AC condensers are the same, so my single motor 5.0 ton unit likely won't have the same startup LRA requirements as another 5.0 ton unit. You can get soft start add-ons that lower the LRA levels, but the better choice is a variable speed motor unit that is more efficient and requires less startup surge.

There multiple be threads here on this topic and more knowledgeable people than me in this topic. If you are still getting the Tesla site inspection they will cover this and let you know what is possible.

 

[Mayer]

Not all AC condensers are the same, so my single motor 5.0 ton unit likely won't have the same startup LRA requirements as another 5.0 ton unit. You can get soft start add-ons that lower the LRA levels, but the better choice is a variable speed motor unit that is more efficient and requires less startup surge.

There multiple be threads here on this topic and more knowledgeable people than me in this topic. If you are still getting the Tesla site inspection they will cover this and let you know what is possible.

I’ll keep the inspection.
Thank you all

 

[BGbreeder]

Great point: the cheapest watt to power is the watt saved through efficiency
Now if I could only get my family on board with that program.

For those in this subgroup with back up generators, is there a consensus as to whether it’s best to go large or could a smaller generator work well in tandem with 2 Powerwalls or similar sized battery?

Would a 125 gallon fuel tank ever be enough (so it can sit next to house) or do most homes really need at least 500 gallons?

This goes back to my earliest post on your other thread;

Post in thread 'SunPower Compatibility with Powerwall'​

SunPower Compatibility with Powerwall​

How long do you want to plan to have backup power, when do you think your worst case outage is, and how much of your home loads do you want on? I can't think of many families who could eke out an existence from a 125 gallon tank in the winter. To do so takes frugality, wood or propane heat, a well insulated home, and willingness to turn back the clock on life and amenities. The summer is a little easier because you would have 60-70kWh of additional solar to play with, but if it is August, and you want AC...

For perspective, a 20kW Generac generator burns 3.6gal/hr of propane at full load, and about 2.4gal/hr at 50%.

https://www.generac.com/generaccorporate/media/library/content/all-products/generators/home-generators/guardian-series/20kva/generac-home-backup-generators-3phase-spec.pdf

You can save a lot of money, or gain a lot of backup time by understanding where your electrical demands are, and trimming the low hanging fruit of large inefficient loads. That whole "Watt saved" thing.

Just to add grist to the mill: we have an older home, with a 4T energy hog of an AC (5kW/hr, and an LRA of 91A), but the baseline home usage is 0.3kW, and we can easily turn it down to down to about half of that, if needed. I have run the house on a little 4kW gasoline generator for everything but the AC (which we almost never use) and the electric 5.4kW dryer, and routinely run the house with a 5kW generator, again no AC, no electric dryer, with propane heat. The right 10kW generator would run the AC, just (no soft start). We have 6kW of solar and three powerwalls. In principle, the three powerwalls might start the AC (87.5A, from the Powerwalls, vs the AC's LRA of 91), but that's doubtful. If we were serious about long off grid backup times, the AC and dryer would need to be modern heat pump units. Not a pricey upgrade, but I'm waiting for more heat pump dryers to get rolled out in "American" 7cu.ft. sizes. In contrast, one of my neighbors has five ductless heat pump AC units, a 22kW propane generator, and gets 2-6 days out of her 500 gallon propane tank. The two days is high load in 32F conditions because the cold leaves something like 120 gallons in the tank because the propane tank gets too cold to evaporate enough propane to feed the generator. Small propane tanks are a real issue for cold weather generator backup. Again, I would download the Generac manual for the unit(s) that you are considering and look up the recommended tank sizes.

Choosing a propane tank size is a combination of how much load do need to support, how much do want to support, how many hours of backup run time do want, will the backup ever be in the winter, and if so, what is the minimum possible temperature, or will you bury the tank? Once you know those items you can choose the generator size, figure out the expected and maximum propane consumption, figure out the number of gallons of propane you need based on the backup time (remember propane tanks are quoted by volume, but capacity is a maximum of 80% of capacity). Then with the number of gallons you need, and the minimum temperature, you can figure the propane tank size. It is almost always much larger than people think, due to the 80% tank factor and the cold temperature evaporation rates from high capacity generators.

All the best,

BG

 

[Mayer]

This goes back to my earliest post on your other thread;

Post in thread 'SunPower Compatibility with Powerwall'​

SunPower Compatibility with Powerwall​

How long do you want to plan to have backup power, when do you think your worst case outage is, and how much of your home loads do you want on? I can't think of many families who could eke out an existence from a 125 gallon tank in the winter. To do so takes frugality, wood or propane heat, a well insulated home, and willingness to turn back the clock on life and amenities. The summer is a little easier because you would have 60-70kWh of additional solar to play with, but if it is August, and you want AC...

For perspective, a 20kW Generac generator burns 3.6gal/hr of propane at full load, and about 2.4gal/hr at 50%.

https://www.generac.com/generaccorporate/media/library/content/all-products/generators/home-generators/guardian-series/20kva/generac-home-backup-generators-3phase-spec.pdf

You can save a lot of money, or gain a lot of backup time by understanding where your electrical demands are, and trimming the low hanging fruit of large inefficient loads. That whole "Watt saved" thing.

Just to add grist to the mill: we have an older home, with a 4T energy hog of an AC (5kW/hr, and an LRA of 91A), but the baseline home usage is 0.3kW, and we can easily turn it down to down to about half of that, if needed. I have run the house on a little 4kW gasoline generator for everything but the AC (which we almost never use) and the electric 5.4kW dryer, and routinely run the house with a 5kW generator, again no AC, no electric dryer, with propane heat. The right 10kW generator would run the AC, just (no soft start). We have 6kW of solar and three powerwalls. In principle, the three powerwalls might start the AC (87.5A, from the Powerwalls, vs the AC's LRA of 91), but that's doubtful. If we were serious about long off grid backup times, the AC and dryer would need to be modern heat pump units. Not a pricey upgrade, but I'm waiting for more heat pump dryers to get rolled out in "American" 7cu.ft. sizes. In contrast, one of my neighbors has five ductless heat pump AC units, a 22kW propane generator, and gets 2-6 days out of her 500 gallon propane tank. The two days is high load in 32F conditions because the cold leaves something like 120 gallons in the tank because the propane tank gets too cold to evaporate enough propane to feed the generator. Small propane tanks are a real issue for cold weather generator backup. Again, I would download the Generac manual for the unit(s) that you are considering and look up the recommended tank sizes.

Choosing a propane tank size is a combination of how much load do need to support, how much do want to support, how many hours of backup run time do want, will the backup ever be in the winter, and if so, what is the minimum possible temperature, or will you bury the tank? Once you know those items you can choose the generator size, figure out the expected and maximum propane consumption, figure out the number of gallons of propane you need based on the backup time (remember propane tanks are quoted by volume, but capacity is a maximum of 80% of capacity). Then with the number of gallons you need, and the minimum temperature, you can figure the propane tank size. It is almost always much larger than people think, due to the 80% tank factor and the cold temperature evaporation rates from high capacity generators.

All the best,

BG

Hope for the best, prepare for the worst.

If money was no obstacle, the solution(s) would be obvious but this is helpful to better understand the drawbacks on propane generators and smaller tanks. I will start looking closer at the specs on different models. Also, seems like a mini split in our bedroom would be a good long-term solution to save kWh as we do use more AC at night to sleep.
Thank you BG.

 

[BGbreeder]

You are welcome. I know that this isn't a simple decision, and I think that the pros and cons are often (usually?) unique to each individual circumstance. I think that you are doing the right thing taking your time and evaluating options.

Over time, we have moved from relying a small generator, then added solar, added a second more fuel efficient and reliable generator, then batteries, and a larger and quieter generator over the years. It is a process.

All the best,

BG

 

[jjrandorin]

Just to add grist to the mill: we have an older home, with a 4T energy hog of an AC (5kW/hr, and an LRA of 91A), but the baseline home usage is 0.3kW, and we can easily turn it down to down to about half of that, if needed.

I dont have (and have never had) a generator, and as I said my normal home run rate is 1.1 to 1.5kWh (with no AC). Overnight, when we are sleep, my house consumes about .5 to .7kWh an hour. I have tested how low I could get it during a power outage by simulating one and going through and "turning X off, and unplugging Y" and I can get down to about .3kWh an hour with no AC.

I think I mentioned this in another thread, but my wife and I went room by room in the house, and made a spreadsheet (she loves making documents), that has the room name, whats plugged in there, and what to do with it in a a power outage (both a short one with a known end point, and one of undetermined length.)

The list gave both my wife and I some comfort. We both now know "the plan" with an executable document so to speak.

 

[Mayer]

I dont have (and have never had) a generator, and as I said my normal home run rate is 1.1 to 1.5kWh (with no AC). Overnight, when we are sleep, my house consumes about .5 to .7kWh an hour. I have tested how low I could get it during a power outage by simulating one and going through and "turning X off, and unplugging Y" and I can get down to about .3kWh an hour with no AC.

I think I mentioned this in another thread, but my wife and I went room by room in the house, and made a spreadsheet (she loves making documents), that has the room name, whats plugged in there, and what to do with it in a a power outage (both a short one with a known end point, and one of undetermined length.)

The list gave both my wife and I some comfort. We both now know "the plan" with an executable document so to speak

I guess every home has innumerable vampires that need enumeration.