AIO as a UPS

[chefcam]

Hi there. Fairly new to this. But I have been heating my garage in Canada this winter with gas and want to switch to electric. The prices here are outrageous. As the batteries to cover a 1500w heater overnight when there's no sun would be an outrageous expense, I was wondering if solar panels with an AIO inverter that has UPS capabilities would work. I want to use the solar during the day and when the sun goes down I want it to start pulling from the grid. I know this won't cover all my power but it will cover a lot. From what I know of AIO inverters they can pull what they can from the panels and the rest from the grid. I also need it to be uninterrupted so I don't forget to turn the heater on at night and have my pipes freeze. So panels on my shed, wire run to the AIO inverter, also connect the inverter to the mains and I'm pretty much good to go right? Am I missing something here?

 

[wsaharem]

You would be surprised. Battery prices have dropped significantly. Just saw a 15 kWh from AliExpress for $2600. To be fully covered, I think you need a battery. What if it’s night and the grid goes down?

 

[Rednecktek]

From what I know of AIO inverters they can pull what they can from the panels and the rest from the grid.

Only some models can do that, most of the affordable ones are an either/or thing. Either it's powering from the batteries OR it's powering the load from the utility, and if there's enough overhead left over, charges the batteries.

I want to use the solar during the day and when the sun goes down I want it to start pulling from the grid.

You'd need a LOT of panels AND really good weather to generate enough power to feed a heater (unless you use a really small heater) to maintain the 1500w of heater, 300w of ineficies and losses, and charging the batteries up after they drained last night. The EG4 3Kw is about the smallest unit you could do it with as you'd want to try to max out that array capacity.

So some rough napkin math numbers to play with:

48v 100ah battery = 5100wh of power.

5100wh ÷ 1500w of heater = 3.4 hours in a perfect world. Call it 3 hours for napkin math.

Since rule of thumb is 20% less performance than what your panels say on the back...

1600w of load × 120% = 1920w of panels in perfect sun to feed the heater alone. Rule of thumb is 4 hours of sun a day to recharge the battery from last night, so:

5kw of charging ÷ 4 hours of sun = 1200w × 120% = 1440w of panel to charge the battery each day.

So, 2000w of load plus 1400w of charging = 3400w worth of panel, assuming you get good sun every day. Add in another 1400w of panel if you want to double your battery.

Just to think about.

 

[CRenner]

"So, 2000w of load plus"

Was the 2000 for running the inverter?

 

[TomC4306]

"So, 2000w of load plus"

Was the 2000 for running the inverter?

And heater. (Load)

 

[Vigo]

Only some models can do that, most of the affordable ones are an either/or thing. Either it's powering from the batteries OR it's powering the load from the utility, and if there's enough overhead left over, charges the batteries.

Actually, they pretty much all CAN mix solar and grid (aka ac input). What most of them CANT do is mix three sources like grid + solar + battery. Some Victrons can and there are probably others. But they can all mix grid + solar as far as i know. I cant think of one that can't.

Since we're talking about heating a garage, i would ask you to consider that installing a $500 mini split on one of the exterior walls which can provide the same heat as a 1500w space heater while only consuming ~300-400w, is going to be cheaper in the long run than it would be to power the hungry space heater with additional solar panels. Since the price of a space heater is negligible you could still keep the space heater plugged in as a backup to the mini split, and simply set its temp thermostat so that it only comes on at something like 50f, which would mean the mini split had failed or become ineffective. The possible caveat is that if it is so cold where you're at that a mini split would struggle in those temps and be going through constant defrost cycles, it wouldn't be worth the cost over the simple space heater.

Is this a detached garage?

 

[chefcam]

Actually, they pretty much all CAN mix solar and grid (aka ac input). What most of them CANT do is mix three sources like grid + solar + battery. Some Victrons can and there are probably others. But they can all mix grid + solar as far as i know. I cant think of one that can't.

Since we're talking about heating a garage, i would ask you to consider that installing a $500 mini split on one of the exterior walls which can provide the same heat as a 1500w space heater while only consuming ~300-400w, is going to be cheaper in the long run than it would be to power the hungry space heater with additional solar panels. Since the price of a space heater is negligible you could still keep the space heater plugged in as a backup to the mini split, and simply set its temp thermostat so that it only comes on at something like 50f, which would mean the mini split had failed or become ineffective. The possible caveat is that if it is so cold where you're at that a mini split would struggle in those temps and be going through constant defrost cycles, it wouldn't be worth the cost over the simple space heater.

Is this a detached garage?

Thanks for the info buddy. Where I live we just got 2 weeks of -45 Celsius so a heat pump wouldn't work for that. But generally in winter it's only -5 to -10. So I could use the heat pump and have the resistance heater for backup. It is an attached garage. I could heat the garage up to like 30 Celsius when the sun is out with the heat pump and let it go to 10C at night so it's not drawing much from the grid as it will take a while to cool down from 30C. So with this setup could I put some solar on the garage, hook up an All in one inverter to the panels, the grid and the heat pump and I'm good to go for uninterrupted power? I just know that if there's not enough solar and it needs to switch over to the grid I can't have it lose power or I'll have to go manually restart it. Maybe they make heat pumps that can automatically turn back on after an outage but I don't know of any. Also where are you getting a 500$ mini split? Here in Canada a cold weather one is looking like 2500-3k. If you have a link to one or use one yourself that you could recommend that would be great. Thanks again

 

[Vigo]

$500 is bottom dollar on amazon for a 9k btu unit here in the USA. You can sometimes find them brand new on fb marketplace for $400. But it may very well be that cold weather specific versions are much higher. I live in South Texas where it rarely even freezes and basically never hits 0f so i have the luxury of not knowing much about cold weather versions!

 

[fatjay]

Both the Growatt and EG4 3k's can do what you want. It's called SUB mode.

From Growatt manual, page 17:

SUB priority Solar energy provides power to the loads as first priority. If solar energy is not sufficient to power all connected loads, solar and utility will power loads at the same time. Battery provides power to the loads only when solar energy is not sufficient and there is no utility

From EG4's manual, page 18:

SUB priority Solar energy provides power to the loads as first priority. If solar energy is not sufficient to power all connected loads, utility energy will supply power to the loads at the same time.

You can see all of the modes available with details of the various functions.

https://eg4electronics.com/backend/wp-content/uploads/2022/07/EG4-3000EHV-48-V2-Manual.pdf

https://signaturesolar.com/content/documents/GROWATT/1519009-manual.pdf

 

[wattmatters]

If you use a heat pump (which will be use far less electrical energy than resistive element for the same heat output), choose a model rated for use in very cold climates. They will use a refrigerant more suitable for operating in those temperatures and have auto defrost modes.

If grid outages are an issue, then you will need backup as there is only so much solar PV and battery can do in Winter. If you are keeping the gas supply, that will do nicely. But without it you'll need another option.

 

[jarred125]

If cost is just the concern and not really "get off the grid" or drastically reduce power from grid ... I would just snag a heat pump mini split and run with it. We replaced all of our HVAC this year with three units from Seville and the power draw is super low.

It might be more cost effective to do that?