Have Standby Generator + Solar, Want Batteries. Please help!

[riles246]

Hi all,

I have a house with a setup that seems pretty good for an AC coupled battery setup, but wanted to solicit advice as I haven't found any local contractors who are knowledgeable and it looks like I might end up DIYing.

I currently have 17kw of solar, across two systems. One is a 12kw solaredge system and the other is a 5kw SMA system. I also have a Generac standby generator; it's a little one- 7kw, but powers all of my important systems (well, septic, sump pump, hot water, some heating, lighting, telecom equipment, etc). We don't have outages terribly often, but when we get them, they can run for up to one week. Call it once or twice a year.

My generator is about 15 years old and is getting to the point where I'm considering replacing it. I can replace it for $2k, so of course this is probably the cheapest/easiest path. However, since I already have my important loads on their own subpanel (the Generac transfer panel), I figured maybe I could patch together a battery system that would allow me to access my grid-tie solar system during outages and get rid of the noisy generator. I don't mind dragging over a small 2kw inverter generator during an extended outage to top off batteries, so I'm less concerned about the number of batteries- I'm more concerned about enabling my solar during the day during outages and getting rid of the routine maintenance and that god awful weekly exercise noise on the standby generator.

I would definitely need at least 8kw of output from the inverter. I don't have high usage needs, but I have a couple loads that are very short but very powerful- the pumps, for example, run for maybe a minute or two every hour, but if they were all running at the same time they could draw up to about 6kw (one is on 240v).

Thinking out loud here, but would it be as simple as 1. dismantling/removing the old generator, 2. getting an Outback Radian 8kw inverter/charger and effectively connecting the output to my existing generator output (so the transfer switch would see the inverter as the backup power source), and 3. moving the output from my 12kw solar system onto the transfer switch panel? I'm trying to be lazy here by reusing the existing transfer panel but I accept that I might need a new panel for the backed up loads. After that, I would just add the minimum number of batteries necessary to support an 8kw draw for a short period of time- again, not focused on kwh, but just kw, since the solar would support the overall usage. My usage at night is very low too. I'm thinking maybe ~5-8kwh of batteries.

I'd also add an input receptacle for the generator input on the Outback system so that I could run a 2kw inverter generator to charge batteries on cloudy days or at night if needed (i.e. if it were a rainy day and I knew I'd be running pumps all night).

All in, I'm thinking I could get it done in the $5k-$8k territory before credits. Anyway, please- correct me where I'm wrong because I'm still in the investigation stage! Thanks!

[Mike90250]

First, when you have batteries, you have to have a generator to keep them charged and healthy. (like if a storm takes out the grid)

Then you will need a 600V MPPT charge controller to recharge the batteries
Then you need an inverter that can run off the batteries, and supply your loads

You basically keep the solar PV panels, and replace the rest of the gear. Or get a new, quieter generator and stay with what you have.

What you are asking about, is not going to be inexpensive.

[riles246]

First, when you have batteries, you have to have a generator to keep them charged and healthy. (like if a storm takes out the grid)

Then you will need a 600V MPPT charge controller to recharge the batteries
Then you need an inverter that can run off the batteries, and supply your loads

You basically keep the solar PV panels, and replace the rest of the gear. Or get a new, quieter generator and stay with what you have.

What you are asking about, is not going to be inexpensive.

Aren't the Outback Radian products both inverters and chargers? I figured the grid would keep the batteries topped off (through the Radian's internal charger) and the generator would only be needed on cloudy days. The magic of the Radian seems is that it has frequency shifting AC coupling so it can "wake up" the grid tie solar during an outage so that the grid-tie solar can keep the house fed and batteries topped off during outages as long as the sun is shining, and then a smaller generator can connect to the Radian's generator input to keep the batteries topped off during the night/cloudy days.

The one I'm looking at is an 8kw inverter, has a charging circuit for 48v batteries, and has a grid input and a generator output. The beauty is that it seems that I can reuse my existing grid-tie solar inverter. It's the GS8048A.

If not the Radian, I'm just thinking as to whether a one-stop-shop product exists for this. Seems like something at Outback or perhaps a competitor's product might do?

[Murby]

Get on Ebay, they have SMA Sunny Island's for sale with 10 year warranties for about $3000 each. (Get 2 of them)

Then just buy some batteries and you're done.

You don't have to modify your existing solar, but you will probably want to reroute your backup generator into the Sunny Islands.

Sunny Islands are capable of AC Coupling a grid tied array so no DC Charge controllers required. This is how my system is set up and it works very well.

Your biggest expense is going to be the batteries. You could go with lead acid but lithium is far better, but also a lot more expensive if you're not capable of building your own battery bank.

Some good SIND Trojans will probably set you back $4k to $5k.

[riles246]

Get on Ebay, they have SMA Sunny Island's for sale with 10 year warranties for about $3000 each. (Get 2 of them)

Then just buy some batteries and you're done.

You don't have to modify your existing solar, but you will probably want to reroute your backup generator into the Sunny Islands.

Sunny Islands are capable of AC Coupling a grid tied array so no DC Charge controllers required. This is how my system is set up and it works very well.

Your biggest expense is going to be the batteries. You could go with lead acid but lithium is far better, but also a lot more expensive if you're not capable of building your own battery bank.

Some good SIND Trojans will probably set you back $4k to $5k.

That's great, thank you! I just checked the SMA site, I might even be able to eek by with their new 6kw inverter as it can do 8kw for 1 minute, and I don't think I'll even be above 6kw for one minute. I'd prefer to have a single unit if possible- the 8kw Outback is under $4k new, so $6k for two SMAs seems slightly less efficient from a cost perspective. I see the 6kw version is around the same price as the 8kw Outback product.

As far as batteries, I might try and cobble something together from a used EV battery- I'm thinking maybe old Leaf or Volt batteries. I think I've seen them as low as around $200/kw. Although it sure would be simple to just buy 8 Trojans and be done with it. 10kwh would be plenty for my purpose, and I see that would run around $1600 or so.

Question for you- do you have your backed up loads on a separate panel? And if so, is your grid-tied solar feeding into that same panel or the main panel? Right now my grid-tied solar is on my main panel, so I'm trying to visualize how the inverter will draw from the panels when the grid is down, without backfeeding into the grid.

[Murby]

That's great, thank you! I just checked the SMA site, I might even be able to eek by with their new 6kw inverter as it can do 8kw for 1 minute, and I don't think I'll even be above 6kw for one minute. I'd prefer to have a single unit if possible- the 8kw Outback is under $4k new, so $6k for two SMAs seems slightly less efficient from a cost perspective. I see the 6kw version is around the same price as the 8kw Outback product.

As far as batteries, I might try and cobble something together from a used EV battery- I'm thinking maybe old Leaf or Volt batteries. I think I've seen them as low as around $200/kw. Although it sure would be simple to just buy 8 Trojans and be done with it. 10kwh would be plenty for my purpose, and I see that would run around $1600 or so.

Question for you- do you have your backed up loads on a separate panel? And if so, is your grid-tied solar feeding into that same panel or the main panel? Right now my grid-tied solar is on my main panel, so I'm trying to visualize how the inverter will draw from the panels when the grid is down, without backfeeding into the grid.

My normal grid tied system consists of 2 SMA Sunny Boy 6kW grid tied inverters on our array. We also have 2 SMA Sunny Island battery inverters to go off grid. Our backup inverter, kept protected, is an Outback Radian 8048a.

I can tell you that the Sunny Island inverters are better than the Radian in almost all aspects. Don't get me wrong, the Outback Radian is a very good system as its probably 2nd best, but the SMA's are better.

We do not have a critical loads panel, when the grid goes down, my entire home is powered as if nothing was wrong. Our off-grid backup system is not automatic as it is totally isolated when not in use.
When the power goes out, I flip two interlocked breakers in my circuit box. One breaker isolates the house from the grid, the other breaker closes the connection to allow our off-grid system to send power to the breaker panel. Typically, this is known as an "interlocked generator breaker", which is code legal to have.

I then plug a 4 gauge patch cord from the off grid system to the house and push the "GO" button and we're up and running. The entire process takes about 3 minutes to activate and less than 10 seconds to deactivate.

We also use Lithium EV batteries. Mine come from a Chevy BOLT and provide 25kWh of energy storage. If you go with a DIY lithium solution, don't mess around with cheap chinese BMS's. Go get yourself a REC, Batrium, Orion, or some other "vehicle quality" system.

Here's a picture of mine.
Post3.jpgDSC02598.jpg

[riles246]

Thanks so much for the great response! I get it now- so effectively your Sunny Island acts like a standalone generator- you flip the transfer switch then turn the battery system on. It's perfect in its simplicity!

For my purpose this might be perfect. I could literally just cut the old standby generator input wire and hook this into where my old gennie used to feed into my (already installed) automatic transfer switch. The only problem for me is that my grid-tie inverters don't currently feed into my backed up load box, but that's a simple enough fix by moving at least one into the backed up loads box.

[Murby]

Thanks so much for the great response! I get it now- so effectively your Sunny Island acts like a standalone generator- you flip the transfer switch then turn the battery system on. It's perfect in its simplicity!

For my purpose this might be perfect. I could literally just cut the old standby generator input wire and hook this into where my old gennie used to feed into my (already installed) automatic transfer switch. The only problem for me is that my grid-tie inverters don't currently feed into my backed up load box, but that's a simple enough fix by moving at least one into the backed up loads box.

Yup.. and then the generator gets hooked up directly to the Sunny Islands.. If you run into a string of dark cloudy days where solar just isn't cutting it, you can turn on the generator to charge the batteries. This is another huge benefit.. You can set the Sunny Islands to draw a specific number of amps from your generator, and regardless of what's going on in the house, the SI's will continue loading down the generator at a constant rate until the batteries are fully charged. This allows you to use the generator without having to run the darn thing all day long and only run it when solar isn't providing enough juice.
It cuts down on generator wear and tear as well as how long you have to listen to it, change the oil, fuel consumption, etc.

The SI's can automatically start the generator as well.. although if memory serves, I think the Radian can do the same but would have to double check the specs on that. I just use a portable generator and pull-start myself. I've only had one instance where the solar wasn't cutting it so had to add some charge to the batteries for a few hours if we wanted to continue living normally. The alternative was to back down our loads, shut some lights off, and conserve energy... like living on a critical loads panel.. yuk..

[riles246]

Yup.. and then the generator gets hooked up directly to the Sunny Islands.. If you run into a string of dark cloudy days where solar just isn't cutting it, you can turn on the generator to charge the batteries. This is another huge benefit.. You can set the Sunny Islands to draw a specific number of amps from your generator, and regardless of what's going on in the house, the SI's will continue loading down the generator at a constant rate until the batteries are fully charged. This allows you to use the generator without having to run the darn thing all day long and only run it when solar isn't providing enough juice.
It cuts down on generator wear and tear as well as how long you have to listen to it, change the oil, fuel consumption, etc.

The SI's can automatically start the generator as well.. although if memory serves, I think the Radian can do the same but would have to double check the specs on that. I just use a portable generator and pull-start myself. I've only had one instance where the solar wasn't cutting it so had to add some charge to the batteries for a few hours if we wanted to continue living normally. The alternative was to back down our loads, shut some lights off, and conserve energy... like living on a critical loads panel.. yuk..

Awesome, this is so helpful thanks. My 7kw standby generator is the loudest thing on earth, whereas I also have a little 2kw inverter generator that is effectively silent. I'd like to sell/scrap the 7kw + its enormous propane tank and just live with the little inverter generator; 2kw should be plenty for keeping the batteries charged on cloudy days given my backed up loads are nearly all just intermittent. I'd prefer not to run the main panel on the batteries because I have things like a hot tub, a mudroom heater, and some other large-draw but non-essential things.

You've really helped- this project is more on track than I thought. I think one 6kw Sunny Island plus a couple $k worth of batteries may be all I need to finally never hear that annoying Generac again.

[PVAndy]

Awesome, this is so helpful thanks. My 7kw standby generator is the loudest thing on earth, whereas I also have a little 2kw inverter generator that is effectively silent. I'd like to sell/scrap the 7kw + its enormous propane tank and just live with the little inverter generator; 2kw should be plenty for keeping the batteries charged on cloudy days given my backed up loads are nearly all just intermittent. I'd prefer not to run the main panel on the batteries because I have things like a hot tub, a mudroom heater, and some other large-draw but non-essential things.

You've really helped- this project is more on track than I thought. I think one 6kw Sunny Island plus a couple $k worth of batteries may be all I need to finally never hear that annoying Generac again.

Keep in mind that one Sunny Island put out 120V AC. You need either 2 or an autotransformer to get 120/240V

Andy

[riles246]

Keep in mind that one Sunny Island put out 120V AC. You need either 2 or an autotransformer to get 120/240V

Andy

Another helpful reply, thank you! Unfortunately I have two circuits that need 240v- the well pump and the heat pump water heater. The water heater is annoying- it uses so little power in "heat pump only" mode, but has this awful requirement upon power loss where it runs the full resistance circuit for ~15 seconds to make sure the water tank isn't empty. So it draws nearly 7kw for a few seconds, then goes back to drawing sub-1kw. On my existing generator setup I actually have to flip every other breaker off to turn on the water heater or else the water heater will go into fault mode and wait until you power cycle it. So this is really the only load that causes trouble for the whole setup. Even the well pump is only 3kw at full draw.

I'm really trying to make this work but given that the wiring is already in place, the absolute cheapest option is just to repair/replace the little Generac (they are under $2k shipped, brand new). I'm going to keep picking at it.

Thanks again.