Utility+Solar+Battery Backup+Generator

[Seven-Delta-FortyOne]

Forgive me I know this has been discussed before. But I’m getting requests about this more and more.

I don’t work with solar much, so my understanding is that with battery backup, either the entire house is run through the batteries (small system), or the system transfers over to battery through an ATS on utility failure.

My thought on adding a generator would be either coordinated transfer, where batteries would kick on first, then gen power would come on when batteries are depleted. That one seems more complicated.

Second idea is to have the generator come on when battery voltage drops to a predetermined level, and have a smaller generator that just charges the batteries.

Obviously, this depends a lot on the system already in place, like how much battery storage, whether the batteries run the entire unit or just critical loads, etc.

I know on the Generac controller, you can adjust the utility drop out and cut in voltages. I wonder if it would work to adjust those voltage level to correspond to a level of battery depletion, using line voltage through an inverter of course, to make the generator kick on to charge the batteries.

If anyone here has built out a system like this, I’d love to pick y’all’s brain about it.

 

[tortuga]

Are you saying a customer that already has PV calls you for a generator? If so it will totally depend on the PV system already installed.

 

[Seven-Delta-FortyOne]

Yes.

One I just got an email about evidently there is PV and battery backup.

Depending on how much storage and how the system is setup, my thought is either have the gen charge the batteries, or have synchronized transfer equipment

Just kind of hoping I’m on the right track here, and there isn’t a simpler system already designed for this that I don’t know about.

I know Generac was planning to come out with a DC generator that integrated with PwrCell, but my understanding is that hasn’t hit the market.

And of course you’d have to have PwrCell

 

[Birken Vogt]

You are trying to reinvent the wheel.

When you have a system you described, you basically have an off grid system. Given your location you must know a number of people who live totally off grid.

In order to have this kind of system work, the solar DC must feed into the equipment room (or building). And you have to have the right battery inverters to support it.

As soon as the grid drops out, you have an off grid system that operates just like Maw and Paw up on Hornswoggle Creek.

Systems that are worth a hoot:
Outback FX(R)
Outback Radian
Sol-Ark
SMA Sunny Island
Schneider XW
Trace (old)
Magnum
Franklin
Fortress
EG4

All of these, the battery inverter will call for the generator to start when it needs it. The generator just does what it is told. On Generac you would convert it to 2 wire start mode. Kohler comes already ready for this.

Don't bother with other brands I did not list here. Not worth the pain.

 

[Seven-Delta-FortyOne]

You are trying to reinvent the wheel

Well, not really. I’m trying to learn about the systems.

Yes, lots of off grid homes up here. I don’t really work with solar, so I’m ignorant of some of the details.

So on a system that has battery backup, I assume transfer could take place nearly immediately, so if you set the generator for say a 10 second delay, you won’t have to worry about it starting before the battery kicks in, correct?

I assume that battery backup with utility uses a transfer switch, or is it more like a UPS, where all power goes through the battery bank, and utility essentially just charges the batteries?

Could the home power be used to send the start signal to the generator? I know Generac factory setting is 196 volts on utility sense, to start the generator. I don’t know if this is too low when on a battery. Suppose you have a 24 volt system, where 25.77 volts is “fully charged”, and 23 is where you would want the gen to kick on and start charging. What would that voltage be on the A/C side? 230 volts? Would you run into problems with the gen starting based on a temporary voltage drop because of a large load starting up?

 

[Birken Vogt]

The battery inverter operates just like a UPS on a computer. I assume you are familiar with those. All the switching is built in. Utility drops, inverter takes over, no interruption in power.

The battery inverter has all the brains. When it decides the battery is low, it calls for the generator to start. Generator is just another set of input lugs on the battery inverter. It takes generator power and uses it to charge the battery until the battery is full. Then it calls for the generator to stop.

It really is a great way to operate, but it is full of nuance and art about learning which brands and combinations work together and what is garbage. And there is a lot of garbage out there.

There are a number of companies, the big name ones that were not on my list, that will tell you they can do it too, but they cannot. They jerk people around on tech support and finally ghost them when it never works right. It is hard enough to get the ones I mentioned to work right.

The home power never wavers (much) with one of these systems.

 

[Seven-Delta-FortyOne]

Appreciate that. I had no idea the inverters were controlling all that.

Sounds a lot simpler than I was imagining it to be.

I see Xantrax didn’t make your list. Not that good?

 

[Birken Vogt]

Schneider XW is Xantrex. And not all the ones on my list do I consider to be "good" either.

 

[Birken Vogt]

Sounds a lot simpler than I was imagining it to be.

The concept is simple. The execution (choice of brand, tech support, code compliance, solar arrangement, battery selection, generator parameters, generator selection, scale of system to stay within customer budget) is not simple.

Fuel burning generators are far more economical for backup purposes.

But PG&E high rates pretty much make these systems economical now.

 

[jaggedben]

Forgive me I know this has been discussed before. But I’m getting requests about this more and more.

I don’t work with solar much, so my understanding is that with battery backup, either the entire house is run through the batteries (small system), or the system transfers over to battery through an ATS on utility failure.
...

It is not really either/or between those options.

First, try to understand the difference between an Microgrid Interconnect Device (MID) and an ATS. Many solar/battery backup inverters don't need an ATS to *transfer* the load to them because they have a grid-tied mode and are therefore already normally connected to the load. What they need is a device to disconnect the grid, so that they can operate in a microgrid island without trying to power the whole state. The only difference between whole home and partial home backup in these systems is whether all or just some of the house loads are connected on the microgrid side of the MID.

The MID can be separate from the inverter (e.g. Enphase System Controller) or built into the inverter (e.g. Sol-Ark, Outback, many others.

Not all solar and battery systems are compatible with running a generator in the microgrid. When they aren't, one option is an ATS downstream of the battery backup, so that you have cascading backup systems. Grid fails, battery+solar takes over; battery runs out, ATS flips to generator. For these systems the ATS must be between the loads and the solar/battery sources.

I recommend Enphase. They are the only company I know of that offers a separate 200A MID as well as generator support with their battery system. The only downside is they don't support compatibility with other brands of solar. For people with existing solar I'd probably look at Sol-Ark and/or Fortress for AC-coupling.

 

[Birken Vogt]

Enphase is the one that has a ridiculous rigid list of "approved generators", 3/4 of which are no longer even in production, and makes you enter it on system commissioning.

There is a reason they were not on my list.

edit: Reading it more carefully, it appears they have updated to most of the ones I would use now, which is good news. But it is still silly that you can't just use a generator that meets specs.

 

[jaggedben]

On the flip side of that argument, show me another manufacturer who has a 5 page list of generators that they have declared tested and supported.

 

[Birken Vogt]

That list is so long, I highly doubt they put very much time and effort into testing each one.

If their product is so sensitive to generator power, then it is not a very good product. We've been doing this for over 30 years with the pioneering brands which would accept almost any garbage power you fed them.

 

[Seven-Delta-FortyOne]

Thank you very much @jaggedben and @Birken Vogt

I have not kept up with the solar end of things, and my thinking is still the old school stand alone components of 30 years ago.

I should probably get some education on the solar end of it, as more and more opportunities are coming my way.

 

[jaggedben]

That list is so long, I highly doubt they put very much time and effort into testing each one.

If their product is so sensitive to generator power, then it is not a very good product. We've been doing this for over 30 years with the pioneering brands which would accept almost any garbage power you fed them.

I don't think their product is sensitive. I think they want to offer good support when some newbie like our OP calls up. And they do answer the phone in 5 minutes.

 

[Birken Vogt]

Everything is in upheaval right now. Schneider/Xantrex, Outback, etal used to be the big players but they got sluggish.

Then Tesla, Solaredge, etal came along with their big business practices and said, you will do it our way, seemed they had nobody who had ever seen the way the legacy systems work.

Now we have Sol-Ark, EG4, and a few others who are assembling all-in-one solutions straight from China but have cut way down on the massive wall of components. They also seem to have limited understanding of legacy systems.

I thought by now the number of players would have consolidated but instead they are growing like mad. Not to mention the number of battery mfrs.

But with power prices in California, there is more to come.

 

[Seven-Delta-FortyOne]

So I would guess that generator sizing on these systems is based on battery capacity and recharge rate, not necessarily on residential load, like is usually done, correct?

 

[GoldDigger]

So I would guess that generator sizing on these systems is based on battery capacity and recharge rate, not necessarily on residential load, like is usually done, correct?

Battery powered inverters may or may not have the necessary short term overload capacity to start a large motor (or even a refrigerator when other loads are near maximum.)
If they do, then the generator does not need to be sized to peak/motor starting, or even short term (non-continuous) steady load.
But it would still be a good idea to have the generator at least close to handling full load in case there are problems with the battery-based system.
As you imply, yes, a battery based system could let you size a generator for average load rather than peak load.

 

[jaggedben]

So I would guess that generator sizing on these systems is based on battery capacity and recharge rate, not necessarily on residential load, like is usually done, correct?

I think you really need to read the manuals on the system you're interfacing with.

 

[Seven-Delta-FortyOne]

I think you really need to read the manuals on the system you're interfacing with.

Thats always what happens.

I was looking more for some basic info on these systems, as it wasn’t something that was even around in my apprenticeship days, and hasn’t been something I’ve pursued until recently.

I’ve picked up some professional training materials and textbooks, and I will look into manufacturer training and/or solar specific training if I decide to chase this particular niche.

Appreciate everyone’s help.