Backup power - Generator vs Battery

The Powerwall has 13kWH of energy storage capacity but can only provide 5kW of continuous power so it's not an apple-to-apple comparison with a 18kW continuous power generator in terms of power. If you choose a 5kW continuous power generator it would be much cheaper.

Also remember solar is not a reliable source of energy. In case of cloudy skies caused by wildfires in CA, your solar system likely won't produce nearly enough power for your critical loads during the day and charge the Powerwall enough for power through the night during a longer grid outage. If you ever drain a Powerwall during a grid outage it will not come back on or recharge until the grid power is restored even if you have full sun.

I suggest you write your requirements down so you get a better comparison. Like Solardreamer said above, apples need to be compared to apples. It sounds like you want whole home backup for everything in your house for xx amount of time. Take the time to inventory every power consuming item in your household. A serious company is going to ask you to do that anyway.

I have 10kw of solar in Oregon. I didn't have an issue with just solar until we had a wildfire (power out for a week), then an ice storm (power out for 12 days). I opted to get a whole house NG generator. It is very labor intensive to modify your power structure from the transformer/meter to the rest of your home. It took 2 person days to install my generator, rewire my main meter panel, install the transfer switch and extend my NG line. Figuring out how to modify your particular home is like a puzzle.

I also have an inverter drive AC system which takes way less power than normal HVAC to start up.

Finally, whole house generators are very much in demand. I had to wait almost a year for delivery after signing a contract.

The Powerwall may seem like a cheaper way to go but IMO that battery will not provide you the power you need for as long as a generator will. You need to do the math by seeing how many batteries will give you what a generator will and then compare the price. What you are doing now is comparing a teacup to a 55 gallon drum. There is no similarity to the two items so you really can't perform a great cost comparison.

The Tesla Powerwall can charge from the grid but is restricted by Tesla so that it qualifies for the Investment tax Credit. During certain storm events Tesla will allow to Powerwall to charge from the grid so you can enter an outage with the most backup capacity. As I mentioned on the other thread it can save you money and has no operating costs compared to a generator.
You are not likely to get much positive feedback about a battery installation on this forum. The best advice is to go to some other forums and get several viewpoints. it all depends on where you are standing.

The cost of providing any energy backup is more than future operating costs.

There are many things to consider in a backup source of power.
Among those considerations is cost.
In comparing costs of alternate methods of meeting an energy demand - particularly an emergency demand that will (hopefully) see little use, the idea is to discount all costs of having any energy source including all acquisition and future operating, fuel, maintenance and other costs to their current value and then compare alternatives and see which one requires the least amount of assets to meet the required duty.

At this time and for the foreseeable future it seems like a no brainer, to me at least, that the present value of acquisition and the future operating and maintenance costs of operating a fossil fuel fired generator on an emergency basis are far less than the acquisition cost and future operating costs of a battery system.

The generator may have somewhat higher operating maint. costs (but hopefully low fuel costs if sized right and not needed too much) but it kills a battery system in low acquisition costs.

Granted, the battey system may be of more everyday use, but the acquisition costs per installed kWh of capacity still mean that on a LCOE basis it's usually still cheaper to pay a high TOU rate from the POCO than for a kWh of energy from most storage devices that are available on a residential level.

Besides, to most folks who could afford a 10 kWh battery, that amount of energy would last them less than an hr. or so once the A/C is fired up.

Too bad most such folks are clueless about the scope of their energy use. If they more informed, they might also wonder why keeping the lights on for an hour can cost thousands of dollars if done with a battery.

I was curious about this so did some googling and found this page: https://suncommon.com/how-does-tesla...-power-outage/

It claims:

So maybe they changed how it works now so it won't hit the condition you are talking about.

I recall reading on another forum that a over the air software upgrade fixed the issue of the Powerwalls no being able to reboot without the grid coming back.

There are some firmware improvements but if a low sunlight outage is long enough any battery system that is turned on even periodically (e.g. 6 minutes every hour during the day) will eventually become drained. That's why people have generators but the Powerwall won't support it unlike other home battery systems.

My point was the firmware upgrade put the Powerwalls in standby to prevent them from being fully drained. Yes the lights might go off earlier but there might be enough reserve so they can boot if and when the sun comes out. Even my Outback has the ability to increase the LVD. There is a simple solution to solve the problem of totally draining a battery. I agree an extended outage with no sun even then could deplete any system because of overhead. Life is not without risks.

Hello!

I live on the East Bay in Rhode Island, and we went through the same decision gates you did. Our community is not plagued with many outages, and when they hit, rarely last more than a few hours. Though many of my neighbors opted for propane generator backups, we decided that was over kill for our home, and just went with a full battery back-up connected to our inverter.

One benefit we are reaping at the moment is that we are able to use the batteries to help offset the nightly grid tie. We keep our inverter set to "Self Supply" and they generally support the house while it's catching up after we turn in for the night (replenishing the HW, cooling down the interior, etc.). Generac offers "Outage Guard" that we have turned on - if a severe weather event is slated to roll over the region, it will alter the configuration of the inverter to "Priority Backup" and recharge the batteries to full well prior to the storm.

Is it safe to guess that if you sell your excess production back to the utility you do not get favorable rates?

Hard to say. We're only 3 months in, and we banked some decent coin with RI Energy in May; June and July we had a lot of storms, but I don't quite know how this works - if we just get a dollar value banked taken off the balance come depths of winter or actual kW. Ask me again next May.

2 Powerwall offer 24kWh of usable energy storage and 10kW of power output for $22k
1 generator for unlimited energy and 18kW of power output for $25k.

The key differences here are:

1. Max power output. Do you need 18kW of power during an outage, or would you be happy with 10kW?
   the answer lies in doing a list of all loads and a sub list of the loads you would consider critical during an outage.
2. Duration of power delivery. Based on a detail load calculation for the loads considered critical during an outage, you can calculate how long the 26kWh would last you if there is no sun during that period. That would be your worst case scenario, and you need to be comfortable with that.
   Then assuming there is sun available to recharge the battery during the day, and based on how many kWh per day you need to run the house with just the critical loads, you can see if this can sustain the house indefinitely in critical consumption mode or only a limited time.
   
   In my case for example, If I have sun, my battery takes me through the evening and night consumption, and the next day, I can both recharge the battery capacity that was used at night, and cover my daily Critical consumption with the day sun production. So I can last forever in that mode.

If the battery offers an acceptable solution to the two points above, for me its benefit in terms of ease of use and maintenance as well as benefits for optimizing Solar production makes it a better choice.
But if any of the two points above is a non starter with a battery, then a traditional generator is what you are after....

How would you not know what the POCO pays for excess production (or if they do at all)? That's usually a big part of the decision to go solar. Is it 1:1 cash/credit, wholesale cash/credit?