Why do so many off grid inverters have an AC charger.

[MarkDS]

I'm interested in buying the Growatt TL LVM48 off-grid inverter for self consumption. This inverter has an AC input which would be handy for the utility to power the loads when I don't have enough solar or battery power; however, I would never want to charge the battery from the utility through an AC charger. (It just occurred to me that people might want to charge their battery from a generator using the built in AC charger. But really? This is so important that virtually all off-grid inverters have an AC Charger?)

Also can anyone tell me how the Growatt accomplishes the switch from solar/battery to utility? Does it have a transfer switch so that it's just a pass through to the loads?

 

[AntronX]

Offering AC > DC charging capability is almost free in terms of components used. It's basically running inverter in reverse. So it's an extra selling feature for cheap.

Also can anyone tell me how the Growatt accomplishes the switch from solar/battery to utility?

There is a transfer relay inside that switches between grid/gen input and inverter to load out.

 

[Ampster]

I would not characterize an inverter which has an AC input as an off grid inverter. I would call it a hybrid.. Off grid invetters typicall only have AC out. I do not have a Growatt but can tell you how my Outback Skybox hybrid works to charge the batteries. The grid connection is always connected, The transfer switch only opens the grid connection when the grid is down to protect the linemen. The movement of energy is accomplished by changing voltage levels. When I have energy to export the voltage is increased on the inverter. When I need the grid the load of the charger pulls energy from the grid. It can vary back and forth so no switching needs to happen. It is physics not a switch in my hybrid that controls the flow. I also have a setting where i can tell my hybrid to use the grid as little as possible. Your mileage may differ.

 

[MarkDS]

Thanks AntronX. Just the kind of helpful response I was hoping for.

 

[McRod]

.... (It just occurred to me that people might want to charge their battery from a generator using the built in AC charger. But really? This is so important that virtually all off-grid inverters have an AC Charger?)

Umm, yeah. Solar is not the "end all, be all".

I live in Arizona, the sunniest state in the nation and even I use a backup generator.

 

[dianea]

The AC charger is super cheap to add, it's basically a rectifier charging the high voltage DC bus.

 

[OffGridInTheCity]

Another reason for AC charging is to use a generator's AC output to charge an off-grid system's batteries (instead of powering circuits directly) as a backup for low PV.

 

[MarkDS]

Another reason for AC charging is to use a generator's AC output to charge an off-grid system's batteries (instead of powering circuits directly) as a backup for low PV.

I'm assuming that you're talking about a stationary system - not boat or RV. Why not just run your loads from the generator's AC directly and only charge the battery with PV when available?

 

[iamrich]

I'm assuming that you're talking about a stationary system - not boat or RV. Why not just run your loads from the generator's AC directly and only charge the battery with PV when available?

Time of use is a big one... Especially if you don't have the neighbor friendly generator edition (yeah, I am looking at you Harbor Freight). Nothing your camping buddies love more than hearing the Champion 100000w super generator competing with landing jumbo jets for who is noisier Plus you don't want to be up all night either. You charge during the day when the noise might be more acceptable and you will be awake to monitor the generator, and then use the batteries at night.

 

[OffGridInTheCity]

I'm assuming that you're talking about a stationary system - not boat or RV. Why not just run your loads from the generator's AC directly and only charge the battery with PV when available?

Agree with @iamrich and....

Home Solar and trailer Solar. In both cases, the inverters produce and we consume (in spikes) way more than the generators can provide directly - so the generators charge the batteries over several hours at a lower rate. For example, I only have a 3000w generator for home but the inverter is 12,000w and we hit 5-9,000w in peaks here and there thru the day. Same with the trailer, the inverter is 3000w and we peak as the hot water refreshes etc... but the generator can only do 1600w continuous.

 

[McRod]

I'm assuming that you're talking about a stationary system - not boat or RV. Why not just run your loads from the generator's AC directly and only charge the battery with PV when available?

Generator = Gas = $$$

$$$ = PV = Free (dom)

 

[schmism]

(It just occurred to me that people might want to charge their battery from a generator using the built in AC charger. But really? This is so important that virtually all off-grid inverters have an AC Charger?)

Yes, there is no such thing as an offgrid solar house that doesn't use some form of backup power to recharge batteries or keep critical systems online. There will be extended times of no sun.

could you design a system with a week or more of battery... sure anything can be done, but then your asking yourself why are you spending tens of thousands of dollars more to avoid spending a fraction of that having a fuel generator backup. (propane,gas,diesel etc)

 

[John Frum]

Most sailboats have a diesel engine.
Off-grid solar installations often have an ICE generator.
Generators are noisy, dirty and a pita to maintain... but it sure beats having no power.

 

[OffGridInTheCity]

Yes, there is no such thing as an offgrid solar house that doesn't use some form of backup power to recharge batteries or keep critical systems online. There will be extended times of no sun.

could you design a system with a week or more of battery... sure anything can be done, but then your asking yourself why are you spending tens of thousands of dollars more to avoid spending a fraction of that having a fuel generator backup. (propane,gas,diesel etc)

Exactly.

I've been operating for a few years now and thought I had it figured out. I have a 13kw PV array (45 panels) and in the winter 3 months (Nov, Dec, Jan) I go down to 500-600kwh/month which is about 25% of summer.

I determined that the house can function on 1000kwh/month so I bought 12kw of used panels, stored under the house for Puerto Rico type emergency (long outages) that I can put out in the back yard and double my 500kwh/month to 1000kwh/month in those winter months. All set, congratulating myself on 100% solar solution.

THEN, last December, I had a rude awakening... only got 318kwh for the whole month. YIKES. It was rain/clouds/rain/clouds - unexpected! This means that even with the emergency 12kw I would only get 600kwh for the month. That's 400kwh short for the minimum I need. It was soooo bad that 1 day I only got 0.3kwh on 12kw PV array - unbelievable. Had multiple 3, 4, and one 6 day stretch of only 5kwh/day. The whole month was bad and can't make a battery big enough - would have to be 400kwh? 600kwh? charged up at the beginning of the month.

Sigh... I've reluctantly started setting up storage + generator for 100lb propane bottles. At 22gal per bottle * 4-5kwh / gal, that's about 100kwh/bottle. 4-5 bottles would get me that extra 400kwh.

I'd just can't panel my way 100%! And I don't have wind or water.

 

[jeremyee]

I normally don't use the charger feature but it's nice if I know a storm is coming up or some other emergance I can quickly charge the battery bank. This way I can use the Grid as primary power and the battery's as UPS/Backup.