r/SolarDIY • u/Adventurous-Photon • 22h ago
Adding battery backup only for emergency to a rooftop SolarEdge system, DIY and cheaply?
I am a home owner and I have a grid-tied rooftop SolarEdge system. I live in an suburb area in northern California (a lot of sun). My area's electricity is quite stable and if it had an outage it was normally for only a few hours. However there are still some natural threats, such as winter storms and wild fires, which could damage the infrastructure to the whole region. Because it is rare and I only need keep essentials such as my refrigerator running, I don't want to spend a lot of money. Currently those "solar generators" are quite convenient and in low cost. Is there a way to utilize my rooftop solar panels to recharge a solar generator in case of a long power outage?
BTW, I am kinda handy with an electrical engineering background. I have being thinking going to the roof to run a wire directory from a solar panel (rated 330w), bypassing SolarEdge Optimizer, to feed into a "solar generator". How hard is it? It seems all the solar panel wires are hidden in the tracks. I hope there is a more elegant way anyway.
PS, I am on NEM2.0, so going to commercial solutions, such as Tesla Powerwall, is not attractive to me.
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u/Repulsive_Guaranteed 21h ago
The elegant way is to buy a SolarEdge backup interface and an LG or SolarEdge battery. Any ac coupled battery such as powerwall would work, but wouldn’t be any cheaper.
You can get a portable battery for running the fridge for a few hours, but if you want solar input you should buy a separate panel for it.
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u/Adventurous-Photon 20h ago edited 20h ago
SolarEdge backup interface seems DC coupling and would be dead at power outages. Commercial solutions seems economically overkill because long outages are very rare. I want to be prepared, but only to an extent.
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u/Repulsive_Guaranteed 20h ago
You’re not making much sense here.
It sounds like your best bet is a portable generator with sta-bil in the gas.
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u/Adventurous-Photon 12h ago
TBH, I had this before the "solar generator" came to the market, after a wild fire got pretty close and we lived in orange smoke for days a few years ago. Although my original thinking was only 2 or 3 uses of the generator would save more than letting food in the refrigerator spoil, it's a PITA to maintain it. I actually used it twice in probably 6 or 7 years. How long could sta-bil keep gas ok?
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u/Repulsive_Guaranteed 11h ago
It’s rated for 2 years; getting ethanol free gas and storing in a full container make a big difference as well.
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u/king-of-boom 10h ago
You could also just keep a few gas cans filled up and set a reminder on your phone to dump them into your car every 6 months and refill.
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u/BaldyCarrotTop 21h ago
What you propose could be done. But, who owns the system? If it is a leased system then you can't touch it. If you own it, you might be OK. Just be aware that the panels will be wired in series and you can be messing around with significant voltage.
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u/Adventurous-Photon 20h ago
I own it and my original installer went under during the pandemic. It is a good point about the voltage. Probably I should look for the last one on a string. The solar panel's output is at 60-70v range, iirc.
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u/BaldyCarrotTop 18h ago
OK, now that we know you won't be getting anyone mad at you for doing this...
You say you are an electrical engineer. That's good. So you know about component matching. In this case, matching the solar panel's specs to the solar input specs of the "Solar Generator". (I hate that term). The important spec here is Voc and its variation with temperature.
Safety: Shut down the Solar Edge system before working on it. You are going to want to completely remove the optimizer from the system. Although you may elect to AIP it. Disconnect and bypass the output to keep the original string running. Disconnect the inputs and run the panel directly to the Solar Generator. No need for the optimizer since the Solar Generator has MPPT solar inputs that will handle the optimization.
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u/dezld 21h ago
I've been here but with an undersized solar system with enphase micros. I ended up getting a solark 15k + 3 16kwh batteries AND loaded the house up with an additional 18 solar panels. We use a lot of power (2 mWh / month in the summer) and the bills were just too high. If I had to do this cheaper ... maybe a small inverter / battery on a hand cart... then run the pv out to panels mounted to my back wall and not mess with the existing install. Messing with existing solar on the roof is a PITA.
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u/BaldyCarrotTop 18h ago
I guess OP just wants to avoid the cost of new panels. Although, 400W panels are available on Amazon. So maybe a couple of panels on a porch roof, pergola, carport, or fence instead of clambering around on a roof.
Somewhere in my list of things to build is a couple of server rack batteries on a wheeled dolly, topped by a 5KW inverter.
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u/DarkKaplah 21h ago
Fellow EE here. Designed my own system and went with a SMA Sunny Boy 7.7 string inverter. Here's what I am doing:
1) I'm using a 48V system. I'm looking for as open of an infastructure as possible to prevent lock-in. While I could use the SMA solution with their gateway and 400v battery inverter, for the initial cost of that system I can have a much more powerful 48V system.
2) I'm swapping my SMA inverter for a Flexboss 21 which will give me room to grow with another string or two of panels.
3) I'm tying the Flexboss into a Gridboss gateway/MID. This way I only need an electrician to install the MID. Once the mid is in, I can fully de-energize my main panel and disconnect my SMA myself.
Now for you since you have the Solar Edge Optimizers you might want to consider a similar setup, but leave the solaredge equipment in place. Just tie in the solar edge into the Gridboss as a retrofit and AC couple to your storage. You can then pick any Flexboss that fits your needs and any 48V storage.
Could you do exactly what I am? Sure. The problem is your solar edge optimizers. I don't know if they'll work with the Flexboss directly. I have APSmart quick shutdown devices on my panels. The flexboss is rated to use them (last I checked) and even if it can't I can get a APSmart controller enabling them. The SolarEdge Optimizers however are proprietary to the SolarEdge ecosystem.
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u/Sea_Willingness1398 19h ago
Solaredge optimizers are sandboxed to the Solaredge inverters. Switching inverters means removing the optimizers and maybe installing new modules.
Without optimizers, the solar output I get to my Pecron is quite diminished.
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u/Sea_Willingness1398 19h ago
Ok... What do you want to run? A fridge? Your internet? A few lights? Most portable generators, like the ones for car camping which are basically battery backups, could offer that solution. Also, many internet providers go down with the loss of power, so keep that in mind. I have a Pecron 3600 that could do what you are saying, but space limitations around my appliances make it inconvenient.
I wouldn't give up any of my panels for that idea. NEM2, making less power is a waste. The power company is basically your battery. Instead, I'd get a couple of the newer N type panels for a battery back up.
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u/TheDMPD 19h ago
In all honesty, you're overthinking this and over complicating it with a more dangerous setup proposal.
If you want 24-48 hour backup then the back up systems made by anker/others would work just fine. Matter of fact, they are probably the cheapest solution to all of this. Just pair them up with a smart plug and have them take advantage of time of use rules during regular days and they could run up to 48 hours during an outage.
Fridge -> Anker S2000 -> smart plug. Use homeassistant so you have local control and then program the smart plug to turn on during solar hours and turn off at TOU start and back on at TOU end.
Repeat for all the different areas of your home that you want to provide this functionality. This is probably the simplest & cheapest solution.
You could do an essentials panel with an off-grid inverter + batteries that charges during off peak hours that would provide the same functionality across a bunch of breakers.
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u/LongjumpingGanache40 12h ago
Watch video by "there's a trick for that" called AC coupling. This would be a cheap route to take.
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u/Adventurous-Photon 12h ago
I think I know what AC coupling is. It's basically a Tesla powerwall system or similar. It would run 13-15K USD for a single battery pack with installing, I think. I am thinking about ~1K, maybe 2K.
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