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Grid tie inverter with charge controller?

Ahhk

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Nov 21, 2021
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Howdy!

I apologize if this has been asked before, but does there exist a grid tie inverter combined with a charge controller?

When the battery is fully charged, I want the leftover solar power to tie in. In other words, keep the battery charged for power outage purposes and consume the excess.

Unless I'm missing something, it seems to be one or the other - w/o any automatic switchover.

Or am I crazy for wanting this? :0

Thanks!

FYI. I just have a small (6 x 100w, 60A controller, 200AH batt) system.
 
Last edited:
Hi,

SolArk would be one. It can have 12kW of PV input, charge battery with up to 9kW and output up to 9kW AC (but not over 12kW combined). It uses a 48V battery. It will also manage AC coupled GT PV inverters that respond to frequency shift.

I think MPP has smaller ones, but not sure if it is grid tie and backfeeds.
 
Hi,

SolArk would be one. It can have 12kW of PV input, charge battery with up to 9kW and output up to 9kW AC (but not over 12kW combined). It uses a 48V battery. It will also manage AC coupled GT PV inverters that respond to frequency shift.

I think MPP has smaller ones, but not sure if it is grid tie and backfeeds.
Thanks. I appreciate the response, but I was only looking for a cheeseburger (600w) and youre talking about purchasing a whole cattle (12kW) that I certainly cant afford.

Is this forum only for huge systems?

I'm looking for something that costs much less than a new car. Maybe in the couple hundred $ range. hehe
 
This forum started off with Will's van life projects, and has links for his small van up to large RV suggested systems. But probably not backfeed.
A number of us do have 10kW to 30kW systems.


MPP LV2424 might do what you want (2400W but maybe $675)


 
Thanks, Hedges!

That is really close to what I was looking for and I am now on the right path with the info you provided.

:D
 
Could it be a solution to use these cheap chinese PWM and a grid-tied inverter together? (Together around 90-100 euros)

Like you connect the panels, the battery with BMS and the inverter to the PWM controller and then you find a way for the battery to operate at a high overdischarge voltage where you know you still have 80-90% of the charge available. This limitation can come from the PWM or the BMS itself (ranges should be checked before purchase because overdischarge voltage is not meant for that purpose). With such setup the battery is charged and discharged over the day but it always remains at 80-90%.

The system you want to feed with the battery, you connect it to the BMS (If the PWM is the one cutting the current at overdischarge voltage) or to the battery directly If it is the BMS which applies the overdischarge cut-off. For safe operation you would required a second BMS for the battery loads; but If you just require small loads, perhaps it would be okeish to not use it. A second BMS would definitely question the financial advantages of such method.

Another possible issue I see is those cheap chinese grid-tied inverters come with MPPT function so If this is connected to the PWM, one of the 2 parties might not like it, and hopefully it has no negative impact to the battery, but that is unknown to me.

There are also chinese grid-tied inverters in the range of 110 euros that have a "battery mode", which basically sends to the grid a limited chosen amount of energy with the MPPT function off. Inconvenient is that their adjustable load has a max at 350W which somebody can easily surpass with more than one panel. But with this function you could keep your grid-tied inverter working at any produced load under 350W without the MPPT messing with the voltage of the PWM or battery.
 
Could it be a solution to use these cheap chinese PWM and a grid-tied inverter together? (Together around 90-100 euros)

Might work. I was thinking a microinverter (or two) could provide grid tie in the 600W range OP was looking for.
There is the issue of both interacting with PV panel IV curve at the same time. MPPT rather than PWM could be more graceful.
Feeding microinverter battery voltage rather than PV is another possibility, although it would draw max power rather than just PV production.

Biggest concern if PV (or other DC) connects to both simultaneously is that grid tie microinverter may be non-isolated, driving DC input to line voltage. An isolation transformer on its output should take are of that.

Doing this with manual switchover would be almost trivial. Open a (suitably rated) switch to interrupt PV current, could be PV side or battery & grid side, then swap MC cables.

Switching PV is also possible, but needs rated switches. Up to 125VDC, Square D QO 2-pole breakers could be used. Relays, need suitable ratings, and consider also the possibility PV has grid voltage superimposed by microinverter.

PV panels are cheap enough that separate systems are the most convenient way to do this on a small scale.
 
What confuses me is how it seems like I'm the only person that would want to do this. Which explains why there isnt a simple cheap $300 controller with a simple SOC/battery voltage-based switchover to (grid tie) inverter.

Heck, even a simple charge controller that switches over to the "load" outputs when the battery is fully charged - to which a grid tie inverter can be connected to.

I realize that I may be naive here, but the primary purpose of my setup is to keep the battery charged - so that I can run the fridges all day when the power is out. But, if the battery is fully charged 99% of the year, why "waste" 99% of the annual solar generated power instead of tie'n it in?

And, without requiring a 50 Gigawatt system...hehe

I apologize if I sound like a newb, but what am I missing here?
 
It is a toy sized system, not much market because just a novelty, not a large benefit.
There is a big market for small PV/battery/inverter systems. Also grid-tie, typically larger but some are small.

A number of people have thought of doing that.
Many also thought a grid-tie PV inverter ought to be able to power AC loads while the grid is down. (some recent models do, it's just firmware)

A 300W panel getting 5 equivalent full sun hours per day, 365 days per year, produces 548 kWh/year.
If your rates are $0.20/kWh, that's $110 per year worth of power.
If the whole thing could be done for $1000 you break even in a decade or so. $500 and it gets more attractive. Rates vary.

The value of a small system is power where or when you don't otherwise have it.
To save money, people put in bigger systems, like 3kW, sometimes 12kW, so 10x to 40x the benefit, and some economy of scale. Most are straight grid-tie, which can give 3 year payback for DIY, 6 to 10 year commercially installed.

Cheapest way you could do a small system is buy another 300W panel (they can be had for about $100), and connect it to the grid with an Enphase microinverter. I think those work with nothing else needed, although I could be wrong.

At the big system end, we might add a battery inverter like Skybox, Schneider, or SMA for $2500 to $10,000 and a battery for $2000 to $20,000.

Somewhere in between are hybrids that do the job for $800 to $8000.
 
Toy system? Ouch. Sometimes you only need a toy. 600W/200Ah is good enough for powering the refrigeration w/o the noise and fuel consumption of the generators.

Thanks for raining on my parade with your break even math ...haha

Dayum. Yeah. No need to pursue that at 600w.

On a side note, where the heck can ya get a 300W panel for $100? We do get lots of sun here in Texas.
 
$100 +/- for the panel, $200 for shipping. :)
That's why I bought a truckload (well, 4 pallets, took to trips with my pickup to get them at the freight terminal (saving last mile cost.)


Check Craigslist and Ebay for sellers near you.

Sometimes smaller, more expensive panels are cheaper due to common-carrier shipping.

As I said, separate grid-tie setup can be cheaper than doing everything with one.
There is a 1000W GT inverter for about $350, don't know how good.
I've bought old-stock SMA inverters, 5000W for around $500.
A bootleg grid-tie system that isn't detected because it doesn't exceed consumption is one way to go. Should be UL-1741 for lineman safety.
Zero-export is a way to ensure production is reduced if loads are smaller. Some models support that, with current transformers around utility feed wires.
 
What confuses me is how it seems like I'm the only person that would want to do this. Which explains why there isnt a simple cheap $300 controller with a simple SOC/battery voltage-based switchover to (grid tie) inverter.

Heck, even a simple charge controller that switches over to the "load" outputs when the battery is fully charged - to which a grid tie inverter can be connected to.

I realize that I may be naive here, but the primary purpose of my setup is to keep the battery charged - so that I can run the fridges all day when the power is out. But, if the battery is fully charged 99% of the year, why "waste" 99% of the annual solar generated power instead of tie'n it in?

And, without requiring a 50 Gigawatt system...hehe

I apologize if I sound like a newb, but what am I missing here?
Without reading all the later messages, I just want to say that there are quite a lot of devices that do what you ask. I though they call them hybrid inverters and since they are smart, they cost 300 dollars (rare) and easily much more.

In Aliexpress I have found inverters which to some extend for 240 dollars could fulfill your purpose, but not sure If exactly as you request. Also, they would cost a bit more than the cheapest alternatives.
https://www.aliexpress.com/item/1005002783481311.html?spm=a2g0o.cart.0.0.6c613c00yqCTGf&mp=1

In the meanwhile, and thanks to the reply of Hedges I though of a new idea.

You can buy a chinese MPPT grid-tied inverter (85 euros, 600W) which you can connect to a plug and a 14,6V battery charger (2 Amp. for instance) that will charge the battery from another plug (or same plug with AC adapter). All the solar output optimized with MPPT function is dumped to the net and only a fraction is taken by the charger (all excess goes to grid). When the battery is full, the charger reduces significantly the load. If you want to avoid nigh charging, then you can add a AC adapter with timer to avoid battery charging during the night and eliminate on-hold consumption.

Inconvenient of this alternative is that you transform the DC from the panels to AC, then back to DC, so the battery charging is somewhat less efficient.
 
Thanks. I appreciate the response, but I was only looking for a cheeseburger (600w) and youre talking about purchasing a whole cattle (12kW) that I certainly cant afford.

Is this forum only for huge systems?

I'm looking for something that costs much less than a new car. Maybe in the couple hundred $ range. hehe
Supply good info for people to consider, and you will get answers that are appropraite for those considerations.
 
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