Backup to a generator for prolonged grid down scenario

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I've been researching and reading about solar/battery solutions for a few months and haven't quite figured out the best approach to meeting my requirements. I'm hoping someone here has gone through the same process and can offer some advice for my current situation.

I'm trying to prepare for a prolonged grid down scenario, but I want to keep costs to a reasonable level since I'm not planning on a full solar install to be used daily. Whatever system I come up with won't be paying for itself by replacing grid costs with solar on a regular basis. The reason for this is I may be moving in the next couple of years and don't want to invest in a whole house system install. I live in a heavily treed area and my roof orientation isn't ideal, not to mention any installer would recommend a new roof prior to any rooftop panel installation. I have a spot in the backyard near a small garden that I can use to setup a few panels if needed...figure a 1.2-1.5kW array.

If we lose power, I have a Honda EU7000is generator that has been converted to tri-fuel. I have a natural gas hookup that originally used to feed a gas fireplace insert (since removed) and the line now serves as the generator fuel supply. Whenever we lose power, I take the generator out of the garage, roll it to the backyard, hook up the gas line, hook up the 30A 240V cord to an inlet box which feeds a 30A breaker via an interlock kit installed in the main load center. I built a dual panel meter box so I can monitor each leg of the 240V generator output as I switch on the circuits I need and it's located near the load center. It also has an L14-30R receptacle connecting to the same breaker. This system works great, but if something happens to the fuel supply (gasoline or natural gas), then I have no other way to provide power to the house. I realize that losing both the ability to get gasoline and natural gas would be an extremely rare event, but it doesn't hurt to be too prepared. The Honda is the only generator I have, and while they are super high quality machines...they can fail.

I've been looking at a secondary way to provide power and have been focusing on the Ecoflow Delta Pro units connected via their double voltage hub, which would provide up to 7200W continuous output power. While these units are expensive, they seem to fit the bill for an easy and portable way to provide secondary backup power in the event my Honda generator isn't running (either due to lack of fuel or requires repairs or maintenance). What I like about the Delta Pro units is that when the generator isn't being used, I could simply make a suicide cord and plug it into the extra power meter receptacle, replacing the generator output directly via the existing breaker and interlock setup. No need to run a cable outside to the input box. The downside to the Ecoflow units is cost and battery storage capacity. Yes, I could spend $18k to get the full system with 4 extra batteries, but there is no way I could justify the cost since I wouldn't be using them on a daily basis. I also don't have any solar panels yet. I was thinking I could get a few panels and run some wires to the backyard to setup a temporary ground system if the grid was down for a few weeks. I could either recharge with solar and/or use the Honda for recharging, running the Delta Pros at night. The Honda is very quiet, but the Ecoflows would be practically silent since they'd be in the basement.

My question for you all....if you were me and didn't want to go with the Ecoflow setup, which cost effective 240V inverter and battery solution would you want to install, assuming that it would only be used for backup power? Is there a specific 240V hybrid inverter that is more cost effective for this kind of use? I'm thinking a pure sine wave low frequency inverter would be best. It would be great to have an inverter that can provide twice its rated continuous power for peak surges of a second or two. The Sol-Ark 12k seems like a nice unit, but way over budget. Which batteries would you recommend? I like the idea of the rack mount 48V units. I'd need enough batteries to meet a peak DC current demand of about 300A for a second or two with a storage capacity of about 20kwh. If I'm not running large appliances, my house power draw is about 1-2 kw per hour.

I don't want to spend more than $10k for the whole setup, including a few panels. Is this even possible? Thoughts?
 
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Hedges

I See Electromagnetic Fields!
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I use Sunny Island and SunXtender AGM for backup.
You can find new in the box Sunny Island on eBay for $3000 (about 60% of MSRP).
They are 120V; for 120/240V split-phase either two or a transformer.
6000W continuous at nominal temperature, 11,000W surge for 3 seconds.

You would need a battery charging solution. Either DC coupled charge controller or AC coupled e.g. Sunny Island or any inverter with frequency-watts function.

Batteries are the most expensive part. I paid $5000 for 20 kWh gross, 14 kWh usable, 405 Ah 48V. I think they're about $6000 today.
Depending on your needs you might get by with 100 Ah.
 

timselectric

If I can do it, you can do it.
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Growatt SPF-5000-ES
240v 5k output
Can connect up to 6k solar
Can be paralleled up to 6 units
For under a thousand dollars
Just add solar panels and batteries
 

Ampster

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Kenwood, California
question for you all....if you were me and didn't want to go with the Ecoflow setup, which cost effective 240V inverter and battery solution would you want to install, assuming that it would only be used for backup power?
I do not have any idea what the kWh capacity of the Ecoflow setup. My metric for batteries is cost per kWh. I was fortunate to purchase 42 kWh of LFP batteries at a cost of about $125 per kWh. I did install them with an Outback Skybox in a house that I subsequently sold. I moved the batteries and inverter to my new home. If I were to do it over I would have installed a generator port with a transfer switch and made the system more portable. The generator port might have been attractive to a future purchaser because our area of Northern California is subject to frequent outages. Long term, a hybrid inverter with batteries can provide a decent return as well as offering resilience. Clearly in the short term a generator offers the least initial investment but does have operating and maintenance costs.
There are also similar threads discussing this issue listed at the bottom of this thread.
 

wattmatters

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I'd need enough batteries to meet a peak DC current demand of about 300A for a second or two with a storage capacity of about 20kwh. If I'm not running large appliances, my house power draw is about 1-2 kw per hour.
If extended grid outage supply is the aim, then the first thing I'd be doing is working on the demand side, not the supply side.

Why so much power draw when the home is "idling"?
Is all of that really needed during outages?
What energy efficiencies can you make to your home to reduce energy demand in the first place?
Which components of your energy consumption can be backed up in other ways?

Once you know what you actually need to power during outages, then the solutions might become more apparent.

I have a spot in the backyard near a small garden that I can use to setup a few panels if needed...figure a 1.2-1.5kW array.
That's not a lot, and will not come close to covering the sort of energy demand you are quoting. It's an order of magnitude too small.

BUT - if you can reduce your energy demand to essentials/basics and use alternative energy sources for parts of your energy supply, then a small PV system with a portable power station can be part of the solution. But I think at times (probably often) you'll need to recharge the power station(s) with a generator as the small PV array won't be able to manage all of it.

I don't know what sort of gas your generator runs on but you can store bottled propane it will happily sit there for years without spoiling. And perhaps a second generator for redundancy.

As a rough guide, you'll get something like 2.2 kWh of electrical energy out of a generator per kg of propane (check these figures though as I have not done strong due diligence on this).

So a 90 kg tank can provide perhaps ~200 kWh of electrical supply. Used with appropriate frugality that might represent 2-4 weeks of electrical supply / battery recharge capacity.
 

Browse

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If extended grid outage supply is the aim, then the first thing I'd be doing is working on the demand side, not the supply side.

Why so much power draw when the home is "idling"?
Is all of that really needed during outages?
What energy efficiencies can you make to your home to reduce energy demand in the first place?
Which components of your energy consumption can be backed up in other ways?

Once you know what you actually need to power during outages, then the solutions might become more apparent.


That's not a lot, and will not come close to covering the sort of energy demand you are quoting. It's an order of magnitude too small.

BUT - if you can reduce your energy demand to essentials/basics and use alternative energy sources for parts of your energy supply, then a small PV system with a portable power station can be part of the solution. But I think at times (probably often) you'll need to recharge the power station(s) with a generator as the small PV array won't be able to manage all of it.

I don't know what sort of gas your generator runs on but you can store bottled propane it will happily sit there for years without spoiling. And perhaps a second generator for redundancy.

As a rough guide, you'll get something like 2.2 kWh of electrical energy out of a generator per kg of propane (check these figures though as I have not done strong due diligence on this).

So a 90 kg tank can provide perhaps ~200 kWh of electrical supply. Used with appropriate frugality that might represent 2-4 weeks of electrical supply / battery recharge capacity.
These are all good points. As I mentioned, the solar/battery solution will basically be a secondary backup for the generator. We lost power about a year ago in the summer for 3 days and I monitored the generator pretty closely. We couldn't run our main 4-ton HVAC unit, but were able to use a mini-split in the basement which drew less than a thousand watts. I have a variable speed pool pump that can be throttled down to a few hundred watts. We have 2 full size refrigerators, a full sized freezer and a mini freezer that all need to be on. Add a few TVs and computers and we're in the 1-2kw range. Most of the major appliances run on natural gas, and the generator also runs on natural gas...so as long as we have a natural gas supply, we should have generator power and power for cooking, laundry, heat and hot water. Only the oven is electric with a large power draw and during an outage we would either use the toaster oven or the gas grill if needed.

If we decide on an inverter with batteries and a few solar panels, it would basically be some extra redundancy to the generator. If I can find a decent lower cost 8-12kw split phase inverter and 3 or 4 rack mount 48V 100Ah batteries for an easy setup using my existing interlock, that would be ideal. The Ecoflow units are the easiest solution but costly per kwh.

Thanks for all the great replies!
 

timselectric

If I can do it, you can do it.
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I've never heard of using solar for a backup plan.
Solar usually becomes the main plan. And the grid becomes the backup plan. With the generator as plan C.
 

Browse

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I've never heard of using solar for a backup plan.
Solar usually becomes the main plan. And the grid becomes the backup plan. With the generator as plan C.
Yep...this will be our plan once we sell the house and move to our retirement location. We'll be looking at a whole house system at that point, which will likely be over $50k in equipment.
 

justgary

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Stay out of the freezers and extra refrigerators and run them two or three hours a day. Turn the pool pump off. If you must watch a TV, use only the smallest one. When our power is off (which thankfully is incredibly infrequent), we go into deep conservation mode.

Your solar plan is not a backup to the generator because it doesn't have anywhere enough battery storage. If you are going to spend the money, plan to make it a working part of your power plan. In other words, make it pay itself back by actually using it.

The number one thing I would love to get on solar at my house is the three ton air conditioner.
 

timselectric

If I can do it, you can do it.
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Yep...this will be our plan once we sell the house and move to our retirement location. We'll be looking at a whole house system at that point, which will likely be over $50k in equipment.
$50k ?
You could build it yourself for less than half that.
 

740GLE

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Oh man when the pool pump is considered critical load I remind myself why Cali is like Cali!
 

Hedges

I See Electromagnetic Fields!
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Perhaps inverter and battery can serve to shorten generator run-time.
Batteries cost more than grid, but less than generator + fuel + oil.
The thing to do would be run generator a short time for large loads (e.g. well pump, maybe laundry) while recharging battery, then shut off generator and let inverter power everything small until the next day.
PV of course helps further, so battery should only have to be sized for minimal night time loads.
 

wattmatters

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We couldn't run our main 4-ton HVAC unit, but were able to use a mini-split in the basement which drew less than a thousand watts. I have a variable speed pool pump that can be throttled down to a few hundred watts. We have 2 full size refrigerators, a full sized freezer and a mini freezer that all need to be on. Add a few TVs and computers and we're in the 1-2kw range.
A pool is not essential. Like the main HVAC it can stay off.

Sounds like you need more efficient appliances. Modern fridges, TVs, computers use a fraction of the energy of older appliances. Like 1/2 to 1/4 of the power. I'm not saying to ditch functioning equipment but stuff can be sold on and replaced. I replaced a TV not so long ago, new one uses ~25W, old one same size used ~145W. It's chalk and cheese.

And there is no need to use them all when operating on backup. Be clear about what is and is not essential.

The contents of the mini freezer can go into the large freezer for the duration. Consider using a chest freezer if you don't already have that, and make sure it's an energy efficient model. Same with fridges, older units are terribly inefficient.

We have 2 homes and 3 buildings in total, 3 fridges, TVs, computers, routers, lights etc. When operating on backup overnight we draw ~450 W. Daytime ~600 W. Even that's pretty bad but we are gradually working on efficiency improvements and I have scaled our backup system accordingly.

Small split aircons can be pretty good, the one in our second dwelling will operate on ~500 W. But when operating on backup an aircon would only be used if absolutely necessary. It would have to be a filthy hot day to use it. Otherwise a few fans does a good job. It's not a permanent state of affairs.

I'm getting a good test of our system tomorrow - there will be a scheduled maintenance grid outage from 9am to 4pm.
 

walkingonsunshine

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If extended grid outage supply is the aim, then the first thing I'd be doing is working on the demand side, not the supply side.

Why so much power draw when the home is "idling"?
Is all of that really needed during outages?
What energy efficiencies can you make to your home to reduce energy demand in the first place?
Which components of your energy consumption can be backed up in other ways?

Once you know what you actually need to power during outages, then the solutions might become more apparent.


That's not a lot, and will not come close to covering the sort of energy demand you are quoting. It's an order of magnitude too small.

BUT - if you can reduce your energy demand to essentials/basics and use alternative energy sources for parts of your energy supply, then a small PV system with a portable power station can be part of the solution. But I think at times (probably often) you'll need to recharge the power station(s) with a generator as the small PV array won't be able to manage all of it.

I don't know what sort of gas your generator runs on but you can store bottled propane it will happily sit there for years without spoiling. And perhaps a second generator for redundancy.

As a rough guide, you'll get something like 2.2 kWh of electrical energy out of a generator per kg of propane (check these figures though as I have not done strong due diligence on this).

So a 90 kg tank can provide perhaps ~200 kWh of electrical supply. Used with appropriate frugality that might represent 2-4 weeks of electrical supply / battery recharge capacity.

Redundancy is one of my best friends. Two is one and one is none. I share that with my friends using a camping analogy of having more than one way to start a fire and make water safe to drink. That they can easily understand and hopefully connect it to other parts of their life.
 

walkingonsunshine

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79
Stay out of the freezers and extra refrigerators and run them two or three hours a day. Turn the pool pump off. If you must watch a TV, use only the smallest one. When our power is off (which thankfully is incredibly infrequent), we go into deep conservation mode.

Your solar plan is not a backup to the generator because it doesn't have anywhere enough battery storage. If you are going to spend the money, plan to make it a working part of your power plan. In other words, make it pay itself back by actually using it.

The number one thing I would love to get on solar at my house is the three ton air conditioner.

Deep conservation mode... A+ We try to do the same, but I have to try to see what the new Bluetti will do with a small mini split HVAC as it gets way hot and humid here in Florida. I currently do without AC now when power is out. Fans become my friend.
 
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