diy solar

diy solar

Another new guy, building a home battery backup system.

Q-Dog

¯\_(ツ)_/¯
Joined
Dec 22, 2020
Messages
2,071
Location
South Louisiana
Hello.

Last year we had about 3 weeks worth of power outages due to hurricanes, the longest being 6 days, so I decided to make some changes to how we do backup power. We have a small inverter generator that can handle our basic needs, but we need to move it around and run extension cords through the house to get power where we want it. So, first I decided to run a couple of dedicated circuits for critical loads. While researching how to do that I came across various portable battery "solar generators", which then gave me the idea to build my own battery backup system permanently mounted inside the house. I guess, a UPS for the fridge, computer and network gear, and a few lights. My thinking was something big enough to keep things going overnight until I decided to drag out the generator.

After lots of calculations and studying spec sheets for batteries and inverters I settled on a Victron Multiplus and 200AH of 24 volt LiFePo4 to get started. I chose the Victron for it's power boost function and ability to vary the input current draw which should work fine with my small generator. I now have batteries and the Victron mounted to the wall in our laundry room and did some tests to see if it would do what I hoped. I was able to run the main fridge and small dorm type fridge for 30 plus hours and still had some capacity left in the batteries, so, my calculations so far are about what I expected. We had a storm the other night and when the power flickered I plugged a couple of loads into the Victron and actually hoped for a power outage. The switchover from grid to battery was seamless and I have to say I am now ready to permanently wire this thing into the house.

My thinking is to run the system separate from the regular house circuits, and drop new outlets behind the refrigerator, TV and network stuff. This would give us the ability to choose battery backup or normal grid outlets.

I really don't know much about solar except that when I first looked into it 30 years ago it only made sense for people who didn't have access to grid power. That said, I realized with a few solar panels on the roof, the system could practically run our fridge forever. And that's how I ended up here, looking for DIY solar to add a little capacity to the battery backup system. I signed up just to be able to see the photos and diagrams people have posted on the site ... but now I am posting. I'll probably have a few questions later, but I am the kind of person that tends to look up things and try to find answers on my own before I ask for help.

We have cheap electric rates, so I am not doing this to save dollars. But, I do like the idea of being a little bit more self-sufficient. And driving 20 miles to find a gas station when your power has been out for 3+ days isn't that much fun, so solar charging the system makes more sense every time the power flickers.

I wish I had found this site before I bought my batteries. I am pleased with what I have, but I could have gone bigger for not a lot more dollars. Oh well. I have a feeling I'll be adding more battery capacity in the future.

Brian
 
We have a small inverter generator that can handle our basic needs, but we need to move it around and run extension cords through the house to get power where we want it. So, first I decided to run a couple of dedicated circuits for critical loads. While researching how to do that I came across various portable battery "solar generators", which then gave me the idea to build my own battery backup system permanently mounted inside the house. I guess, a UPS for the fridge, computer and network gear, and a few lights. My thinking was something big enough to keep things going overnight until I decided to drag out the generator.
:love:, this is so close to what I want to do!

I haven't started with anything "battery" yet, am still just using an inverter generator. After the mess of running extension cords everywhere once, I added a generator outlet on the side of the house that connects to a circuit breaker in the panel that can only be flipped on if the main breaker is flipped off. My inverter is only 120V, but with a modified cable this allows me to get power to all of the 120V breakers in the panel without worrying about accidentally back feeding to the grid during an outage.

We don't get a lot of outages. Usually just one or two a year due to car crashes and usually power is back within an hour or two. After a hurricane we may lose it for 5-6 hours while they repair lines outside of our neighborhood. The inverter generator has been working great, but pulling it out, setting it up, making sure there's "safe" gas to use is kind of a pain.

I love your setup. I'm super new, but from the month of researching I've done so far, this is very much like what I was thinking. I want UPS-like automatic failover to battery when the grid goes down, so I'm thinking I need to figure out the critical circuits (fridge, electronics, TV/TiVo, etc) and move them from the main breaker panel over to a smaller panel like you have here.

We have cheap electricity here too, but I have some interest in maybe adding some solar to a system like this. After hurricanes when we have our 5-6 hour outage, it's almost always sunny as heck. I think it'd be great to run things off of solar vs. draining the battery during the day at that point. But that's more of a "sounds like fun, why not" kind of thing vs. a "must have".

Thanks again for sharing your build!
 
Last edited:
PV is cheap now, so you can over-panel, let production be curtailed when not needed.
Fridge/freezer and some other loads could be run just when the sun shines (or grid power is present), reducing nighttime drain on battery.
Load-shed of less important loads saves charge for more important ones. Difficult to sense by voltage of LiFePO4 but Victron may count coloumbs for you.
 
My thinking is to run the system separate from the regular house circuits, and drop new outlets behind the refrigerator, TV and network stuff. This would give us the ability to choose battery backup or normal grid outlets.

Swapping power cords between "grid" sockets and "UPS" sockets. As an alternative ...

There are some transfer switch panels with SPDT and DPDT switches, let each load circuit connect to either breaker from main panel or breaker from UPS panel.

Others have a single transfer (two interlocked breakers) so the entire sub panel is fed by either grid or UPS. That's what I've put in. It would let me bypass the UPS in case of failure, go back to straight grid power.

I also have an interlocked breaker in my main panel so I can disconnect from grid and feed any circuit from the UPS. (manually turning off the breaker that supplies grid to input of UPS, and avoiding any excessive loads.) Biggest difficulty with that is no easy way to tell when power has returned.

If you do start feeding the inverter into any existing house wiring, watch out for circuits that have Romex 3 + ground, two hot wires red & black sharing one neutral white. The two hots always have to be 180 degrees out of phase with each other, so neutral wire only carries the difference between them. If red went to inverter and black went to grid (or both when to same phase), neutral could carry sum of currents, which would be excessive.
 
I am hoping the empty space between the inverter and breaker panel will fit a solar charge controller. My wife is really interested in having solar panels here. :cool:

Does the Victron inverter support AC coupling of grid-tie inverters, and do frequency shift to control them?
SMA, Outback, Schneider have models that do.

If you do go with DC charge controller, look into Victron's and their monitors, which can regulate battery charge current (measured by shunt) while allowing extra current to feed inverter. (More important for a battery like my AGM which accepts limited charge rates.)
 
I originally intended to install this next to our main panel, but, the main panel is in a small closet and we can't afford to lose the storage space. This location has plenty of room, but it is about 40 feet from the main panel. It is much easier to drop new circuits than to try and tie them all together with a transfer switch. Also, we are doing some renovations and some of the existing circuits will likely have to move anyway.

I'm still learning about the capabilities of the Victron. It has a lot more features than I intended to use.
 
Does the Victron inverter support AC coupling of grid-tie inverters, and do frequency shift to control them?
SMA, Outback, Schneider have models that do.

If you do go with DC charge controller, look into Victron's and their monitors, which can regulate battery charge current (measured by shunt) while allowing extra current to feed inverter. (More important for a battery like my AGM which accepts limited charge rates.)
Well, I found this in the Victron documentation, so, I guess the answer is yes.
"Frequency shift
When solar inverters are connected to the output of a Multi or Quattro, the excess solar energy is used to recharge the batteries. Once the absorption voltage is reached, the Multi or Quattro will shut down the solar inverter by shifting the output frequency 1Hz (from 50Hz to 51Hz for example). Once battery voltage has dropped slightly, the frequency returns to normal and the solar inverters will restart."
 
Sounds good, that's how my Sunny Island work.
This should let you add AC couple grid-tie inverters, up to the current rating of the pass-through relay in the Victron.
Old SMA Sunny Boy respond to frequency shift when set to "Island"
Newer Sunny Boy and some other brands have "Rule 21" for grid support. There are a couple different possible implementations.
One is to just tolerate a couple Hz out of range for 299 seconds, the drop off. That doesn't help you.
Some have "Frequency-Watt", reduce power output as frequency rises. That is what you would want.

The default setting of "island" for Sunny Boy is 100% output up to 61 Hz, ramping down to 0% at 62 Hz. If using that mode, would have to change from default to fit Victron's frequency range (or vice versa).

The description I find for "Rule 21" shows up to 62 Hz, but I haven't found details of "Frequency-Watt" under Rule 21.

 
Following this, as I am now looking at doing this at my house.
After my off-grid cabin build, I'm getting comfortable enough to look at a limited system at my house for power outages.
I would just create a stand-alone system to run the essentials. I would actually use the system all the time to lower my electric bill, but it would also be huge during power outages.

Thinking fridge/chest freezer, essential lights, outlets for charging phones etc...
I would run my own romex and create new circuits to a separate panel that would be run solar only.

The 2 things I need to look at would be the electric needed to keep the gas furnace running.
I believe the fan and thermostat would be the only needs for electric.
Also would need to figure out the power needed for the well pump for keeping water going during an outage.

Like many others, I don't want to grid-tie it because I want self-reliance and security.
I also plan to purchase a generator to help with things in the case that the power outage also happens during a period of very little solar activity.

I'm sure I'll be posting soon when I start the implementation.
 
I've been messing around with settings on the Victron, and now have it set up so it is disconnected from grid power until the battery gets down to about 40% capacity, then it connects and charges. I can set when it disconnects based on a few different criteria. Right now I have it disconnect at the end of bulk charging, which leaves me at about 94% state of charge. And with just the refrigerator running, I get about 30 hours before it charges again.

Adding solar means the Victron would only connect to grid when solar can't keep up. I might be getting close to adding a few panels!
 
The system had been working without any issues for about 3 months, so time to make some changes.

I pickup up a few watts of solar panels and a small charge controller to eventually install on my RV. But, until then I put together a small temporary ground mount and started experimenting. I have been charging the battery backup from solar for about a month now.

I started with 400 watts and that was almost enough to keep the system topped up on sunny days running the refrigerator and some internet stuff. But with 3 or 4 cloudy days the system needed a little charge from the grid to keep going. I added another 200 watts, so 600 total, and the solar charger will now finish absorption and hit float before the end of the day on a decent sunny day. The ground mount is light enough that I can move it around to track the sun ... good for trying to figure out best angle for a future permanent solar installation.

Today is my first cloudy day since adding more solar, so I don't yet know how that will affect things. By then end of a sunny day I have 99% of battery capacity and when the sun comes up I am sitting at 70 or 75% of capacity, and that is running the refrigerator, phone base/charger and a lamp on the system full time. I plug in the computer and network stuff when the weather gets bad.

We are doing some work on our house and I have some reflective insulation board, so tried to do a little experiment. As you can see, cats don't care about your little solar experiments. This photo also likely explains why the panel output would sometimes drop out for no apparent reason. I have no idea why they sit down in front of the panels.

IMG_2945.jpg
 
As mentioned in post #8, I don't have the room next to the main panel to install all of this. I would have to run cable from the backup to the main panel anyway to be able to install a transfer panel next to the main panel. It was easier to install everything in one place.

Plus, this way I can plug everything back into their original outlets and shut the system down if I have to leave for a few weeks, and not have to teach house-sitters how to operate the system.
 
Today was a very dark, overcast and slightly drizzly day and the solar panels aren't making any power, so I did a stress test. Plugged a 12,000 btu window air conditioner into the system and set it to High. Also, refrigerator and phone stuff are always running off of the system. Then I plugged the little 2200 watt inverter generator into the Multi and started it up.

The system ran for 2 hours and even managed to put some charge into the batteries. I shut down the generator to top off the gas tank, then restarted and the air conditioner and refrigerator didn't even hiccup. Fantastic! I did a few things like open the fridge doors and turn on an electric kettle. Switching from grid to inverter to assist was seamless.

The only issue I could find today was one plug on the extension cord I used for the generator got a little warm so I limited 120 AC input into the Multiplus at 10 amps. I already have some 10 AWG cable to build a bigger generator cord and my next project is to build a permanent generator input into the house. Then I should be able to run the 120 AC input at 15 amps to charge the battery faster.

Future project: My wife has figured out how to configure a Raspberry Pi to run the Victron Venus monitoring software, now I need to order a few things to make that happen.
 
I decided to make some changes to how we do backup power

Nice work.

I have been building my own power backup system as well. Where I am (northern regional NSW, Australia) we get an average of a dozen longer outages a year, typically 2-3 hours (I maintain full stats on our outages), plus a whole lot of short duration brownouts. Occasionally outage are much longer if the storm was bad and did widespread power line damage. Weather is mild to hot. A cold Winter night here gets down to 6°C (43°F).

I commissioned my system a couple of weeks ago and it's all working well, except for the solar array which is a month or two away from being added (I'll have a 2.5kW array). I'm using one of those generic all in one hybrid inverters (48V, 4kW) to make the job easier with a bank of 190Ah SLA batteries (used from data centre backup duties). I've load tested the batteries and they'll easily provide us with 6-7 hours of backup to about 50% discharge.

Supply to the home is via a power inlet wired via a manual cutover switch in the main circuit board. I like this as it means all our existing circuits are supplied with power during an outage if we want and everything can just stay plugged in where it is. High power draw items are excluded (e.g. oven) from the backup side though. The oven is our indicator of when grid power has returned - it bleeps when power returns and the clock comes back on so I know I can return to grid supply.

I had the power inlet and cutover switch already as that's what I used to enable the inverter generator to supply the home's circuits, so the inverter/battery system is just an alternative supply to the generator. Generator is now a backup to the backup.

I'll also do a write up at some stage.

Would it make sense to add to this thread, or should I create a new one? Like you, I'm just another new guy building a home battery backup system!
 
Nice work.

I have been building my own power backup system as well. Where I am (northern regional NSW, Australia) we get an average of a dozen longer outages a year, typically 2-3 hours (I maintain full stats on our outages), plus a whole lot of short duration brownouts. Occasionally outage are much longer if the storm was bad and did widespread power line damage. Weather is mild to hot. A cold Winter night here gets down to 6°C (43°F).

I commissioned my system a couple of weeks ago and it's all working well, except for the solar array which is a month or two away from being added (I'll have a 2.5kW array). I'm using one of those generic all in one hybrid inverters (48V, 4kW) to make the job easier with a bank of 190Ah SLA batteries (used from data centre backup duties). I've load tested the batteries and they'll easily provide us with 6-7 hours of backup to about 50% discharge.

Supply to the home is via a power inlet wired via a manual cutover switch in the main circuit board. I like this as it means all our existing circuits are supplied with power during an outage if we want and everything can just stay plugged in where it is. High power draw items are excluded (e.g. oven) from the backup side though. The oven is our indicator of when grid power has returned - it bleeps when power returns and the clock comes back on so I know I can return to grid supply.

I had the power inlet and cutover switch already as that's what I used to enable the inverter generator to supply the home's circuits, so the inverter/battery system is just an alternative supply to the generator. Generator is now a backup to the backup.

I'll also do a write up at some stage.

Would it make sense to add to this thread, or should I create a new one? Like you, I'm just another new guy building a home battery backup system!
Start a new thread and let's see what you have!
 
Start a new thread and let's see what you have!

OK!

I have:
 
Raspberry Pi and cable parts came in.
IMG_3018.jpg
I burned the disc image to a micro SD card a few days ago. It took a couple of minutes to put the cables together, so about 10 minutes after opening the box the Pi was powered up.
IMG_3021.jpg
 
The Raspberry Pi now resides mostly hidden on top of the breaker panel. This morning I had data on the VRM portal, accessible from anywhere in the world!
screen-shot-2021-05-13-at-9-51-17-am-png.48846
 
The system had been working without any issues for about 3 months, so time to make some changes.

I pickup up a few watts of solar panels and a small charge controller to eventually install on my RV. But, until then I put together a small temporary ground mount and started experimenting. I have been charging the battery backup from solar for about a month now.

I started with 400 watts and that was almost enough to keep the system topped up on sunny days running the refrigerator and some internet stuff. But with 3 or 4 cloudy days the system needed a little charge from the grid to keep going. I added another 200 watts, so 600 total, and the solar charger will now finish absorption and hit float before the end of the day on a decent sunny day. The ground mount is light enough that I can move it around to track the sun ... good for trying to figure out best angle for a future permanent solar installation.

Today is my first cloudy day since adding more solar, so I don't yet know how that will affect things. By then end of a sunny day I have 99% of battery capacity and when the sun comes up I am sitting at 70 or 75% of capacity, and that is running the refrigerator, phone base/charger and a lamp on the system full time. I plug in the computer and network stuff when the weather gets bad.

We are doing some work on our house and I have some reflective insulation board, so tried to do a little experiment. As you can see, cats don't care about your little solar experiments. This photo also likely explains why the panel output would sometimes drop out for no apparent reason. I have no idea why they sit down in front of the panels.

View attachment 44040
Cats love sitting on warm places, like reflective insulated boards, photocopy machines, polystyrene cases, telly decoders, etc. but tend to block the ventilation on electrical stuff. Also if you read books or newspapers your cat sits itself right in the middle. I don't know if they're big enough to effect the output from solar PV panels though. It could be the sun's angle.
I'd like it to stop raining long enough here, in the "sunny" S of France, to get on the roof and finish the installation of ours. It's been raining almost non-stop since last August. It's not normal here, and a real pain, but I guess for the weather changing, we can only blame ourselves!
 
Crawled under the house yesterday and ran some conduit for this handy dandy generator inlet installed on the back of the house. Conduit is big enough that I can pull in some heavier wire if I ever decide to get a bigger generator.
generator input.jpg
And on the other end is this ... grid on the left, generator input on the right. My generator has circuit breakers so I didn't install any on this circuit. This isn't much more than a built in extension cord. These are under the battery backup and next to the dryer in the laundry room. I use gray for all of the outlets associated with the battery backup system.
Generator outlet.jpg
I need to dig out the label maker.
 

diy solar

diy solar
Back
Top