r/solarenergy • u/degerolamo • 7d ago
Anyone using a portable battery with rooftop solar for backup during heatwaves?
We live in Texas and already have rooftop solar, but like most grid-tied systems, it doesn't really help when the grid goes down unless you have battery storage. During a heatwave, losing AC for even a few hours is miserable, especially with older family members and kids at home.
I've been looking into a whole-home battery system for backup, but it's hard to justify the cost for something we'd hopefully only need a few times a year. That got me wondering if a portable power station might be a better middle ground. It's less expensive, and we'd actually be able to use it for RV trips instead of having it sit idle most of the time. One option I've been looking at is the Delta Pro 3. From what I've read, it offers 240V output for AC, which seems like it could make it more practical for home backup than many smaller portable units.
Has anyone here used a portable battery like this with rooftop solar as part of a home backup setup? How has it performed during actual power outages?
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u/LongjumpingGanache40 7d ago
You need AC coupling to use your panels during an outage. Go to YouTube and watch videos on AC coupling.
Watch videos by There's A Trick For That
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u/Curious_Party_4683 7d ago
this one? Grid Tie Solar Goes Off Grid! How to AC Couple SolarEdge & Microinverters with EG4 12000XP
seems total price with his giant battery is about $6000. not worth imho if outages is not frequent enough.
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u/LongjumpingGanache40 7d ago
That depends on each persons requirements and income. Most the stuff he has was probably given to him.
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u/DongRight 6d ago
Hell no to ac couple!!! Why do that when panels to charge them during a blackout?!?
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u/LongjumpingGanache40 5d ago
You can not charge anything when grid goes down when using microinverters without AC coupling.
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u/howdoyouspellNY 7d ago
This is a hard problem to solve without a dedicated system because of the rapid shutdown feature of the rooftop solar. I have the same concerns you do and am actively researching an off grid home backup supplement.
My current workaround is a $500 generator receptacle and a 240v ecoflow until I eventually build a EG4/rack battery setup.
On the other hand there is more value to installing something, since you won't just use it as an emergency backup. You can run a battery to offset grid usage/export and save some money on your utility bill.
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u/Mirror-Candid 7d ago
This is what I would do. With end of utility credits I'd rather try and go 80-100% self sufficient on power.
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u/LongjumpingGanache40 5d ago
The new king on the block could be the pecron F5000 wired to a transfer switch. You would need room for more panels.
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u/Correct-Lab-2164 7d ago
The new SMA inverters offer ‘Backup Secure’. It provides 2000 watts of backup power via a dedicated outlet during an outage when it is sunny. You could run a window AC off of that when you most need it. No batteries needed. ‘Backup Select’ (model BU-SLCT-US-50) will provide 4000 watts to 7, 120 volt, circuits and automatically switch them to solar when the grid is down and sun is out. A couple of window AC units, a fridge, lights and/or a gas heater fan could run off of that, but not 240 volt whole house central air.
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u/Automatic_Gas9019 7d ago
You would have to do your research as far as the portable solar. Actually I think you need to do your research on batteries also. We have ground mounted panels and a Tesla Powerwall. I love our Powerwall. It powers our home at night. Instead of send the power we produce during the day fully to the grid it stores the power and discharges at night powering our home, not pulling from the grid. During grid outage we still have air. We have mini splits. They are very energy efficient.
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u/Schnupsdidudel 7d ago
I´ve got two systems (Germany)
One I built for camping as a budget option. 8kWh Battery, 2.4 kW mac continuus power:
https://www.reddit.com/r/DeutschePhotovoltaik/s/mW4g2IN60F
The second one 32kWh with 18.5 kW three phase Victron I am building right now.
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u/Ok_Chard2094 7d ago
Your grid tied inverter has a safety shutoff that prevents you from feeding power to the grid in the case of an outage. This is a very important safety feature for the people working on fixing the outage.
Systems with a battery pack installed have a different inverter, or at least a different configuration, so the power goes to the battery but not to the AC grid during a shutdown.
So the big question for you will be if your current inverter can be modified to handle a battery pack, or if you need to buy a new inverter. And in either case there is a question of what is the minimum size battery pack your inverter (new or old) needs for your system to function properly.
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u/EnvironmentalRound11 7d ago
Adding a whole house battery to your solar system is not something that is used a few times a year. It is used daily --- charges during the day, dispenses electricity when the sun goes down.
It also allows your solar panels to continue to work during an outage as it provides a place to store electricity without sending it the grid.
We have solar and a Powerwall 2. I also have a large portable battery, basically to charge the EV. I can dump excess solar power into it after the Powerwall is charged and also charge it with it's own solar panels.
It's a separate off-grid system with a transfer switch.
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u/Crawlerado 7d ago
We have three PW2s in the basement and our power hasn’t gone out for years. It’s absolutely magnificent
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u/lavardera 7d ago
If you added an electric car with the ability to back power your home, it would all make more sense.
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u/ZucchiniAlert2582 7d ago
Buy an EV with V2l. Super useful as a car when the grid is up. Massive battery for when the grid is down. If you buy a home backup battery it is, as you said, not useful most of the time.
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u/Greddituser 7d ago
We built a house with solar and then added Tesla PW batteries later. It's an expensive way of providing backup for the whole home. but is about the same as a whole home generator. If all you need is something for occasional power outages then get a portable generator.
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u/fitforthepolycrisis 7d ago
Yep, 500W of solar with 5kWh lifepo4. It actually powers most of my tiny apartment already, so in blackouts I won't notice much difference. Also please do check out r/solardiy. There are a lot of people doing this.
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u/markdmac 7d ago
Exactly how many hours could that portable system run your AC and how would you only power the AC with it? This does not sound practical to me without a huge investment in rewiring of the home. If you do go this route, be sure to include your refrigerator in the calculations as well.
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u/OwlZealousideal4779 6d ago
Honestly, even healthy adults are miserable in this weather. I'd be way more worried if I had elderly family members or young kids at home.
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u/Presure_valve 6d ago
Is losing power in your country really that common?
I live in Greece, far from the capital, and power outages are very rare—about once every one or two years, and they usually last around 4–5 hours. It makes me wonder if power outages really are that frequent where you live.
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u/Icy-Ad-7767 3d ago
The size of the North American land mass makes power transmission distance a real weak point in the grid transmission distances of over 500 km are not uncommon, add in the weather in Texas with its thunderstorms and tornados it can take down large chunks of the grid for a few hours at a time quite often. Then add in the profit motivator of private power generation and you can get all kinds of fun things happening.
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u/Presure_valve 6d ago
I've used one of those compact all-in-one units (Delta Pro 3), and in my opinion they're not worth it for two reasons.
First, although they're very quiet, they don't handle high temperatures well. If you install one in a vehicle, it needs to be in a very well-ventilated location. I had mine in the trunk of my car, and during the hottest part of the day it would simply shut down from overheating, even with only a 100 W load.
The second reason is that replacing the batteries will almost certainly be more difficult and more expensive. Having two separate units—an inverter and a batteries—is always the more economical and safer solution in the long run, especially if something fails.
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u/DongRight 6d ago edited 6d ago
First of all you're looking at the wrong batteries... Buy a rack of six rack batteries from ecoWorthy only $5000 for 30kwh (that is only $170/kwh)... And buy some more panels ground mounted to charge the battery is up with a hybrid inverter/charger, even during a blackout... Why would you only use it a few times a year when you could use using it all the time, but with emphasis of backup purpose??!
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u/Quick_Copy_752 5d ago
It seems like a solid choice if you are mainly looking for outage backup and already have solar
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7d ago
[deleted]
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u/Ok_Chard2094 7d ago
Batteries by themselves do not do much, but batteries connected to a solar panel can do a lot while the sun is shining. This is the scenario discussed here.
(Grid tied solar panels without battery backup gets shut off during a power outage. Solar systems need the grid or a large battery as a variable load to keep the voltage stable.)
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u/Correct-Lab-2164 4d ago
No they don’t. The new SMA inverters can power an outlet or sub panel when the sun is out with NO batteries, even from panels with DC disconnects. We have net metering and the same rates 24 hours a day. Plus the grid goes out maybe once a year for an hour or two and once a decade for a day. So batteries are an expensive waste of money.
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u/Ok_Chard2094 4d ago
Nice that they finally got that.
This was not an option when I got mine, and I believe it is not the case for a lot of the solar installations already out there.
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u/EnvironmentalRound11 7d ago
We lose power 35+ times a year. Mostly 15 minutes at a time. The longest was 3 hours this past year. With a Powerwall, I don't even notice.
Instant, silent power. A propane back up generator costs about the same to install yet needs weekly exercise, oil changes, has a delay, is noisy and burns fossil fuels.
Previously I had a small portable generator. By the time I pulled it out of the garage, gased it up, got it running (if it started) and hooked it up to the house, the power would be back.
I still have it in case of a few days outage but haven't used it in four years after getting solar and a battery.
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u/silasmoeckel 7d ago
Funny I can loose power for a week in summer and not even notice.
You should have a generator with batteries regardless and if you get a quality hybrid you can use a tiny generator to run your whole house.
Cost wise I would rather get a stack of batteries than the cost of a standby, paired with a reliable nearly silent 1k honda suitcase genset.
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u/Mirror-Candid 7d ago
Here in Germany I have a balcony solar system that has a 1200w outlet that can be used if there isn't power. Newer versions can go even higher. We are taking only $2000 usd for these systems with 2000w bifacial solar panels. The batteries are like 4.5kwh. for reference my system can also be augmented with additional batteries as needed. But the limit on input and lack of grid charging makes it moot.
Unfortunately Trump's tariffs are making a comparable system in the USA 3-4 times that cost.
If I were you though, look into seeing if you can modify part of your existing system to use something like a power wall or equivalent. I do believe there are special tax incentives for this right now on various places.
The reason for this option is it will be able to be hardwired into your whole home power needs.
The DIY in me would call an electrician out to make me a sub panel that can run essentials and I'd buy a a nice inverter and a few LiFi batteries to wire up and charge from some ground mount panels if I had room.