Blending solar and grid - which inverter can do it ?

[Mike Jung]

Hi guys !


I am curious which inverter ( all maybe ? ) can do this :

Power a load, say 1Kw or even less, using solar as much as possible ( available ) while supplementing simultaneously from grid if needed and without "looking" into the batteries. I think this is called "blending". I need a smallish inverter ( 5Kw or less ) which I will connect to four solar panels around 300W each. I need the battery to stay charged and unused unless grid power is down. Lots of thanks in advance ! Sorry for the stupid question but I scoured the Web for days and could not find anything relevant.

[Stray Electron]

   I'm not sure that I understand.  You want a grid tie inverter and you want to hang batteries on it but you don't want it "looking" (connecting to?) the batteries.  Exactly how do you want to connect the batteries?  Are they part of the solar system or do you just want to charge them via the AC power that is produced?  Or are you wanting a solar system that charges batteries but also ties to the grid and that can provide AC power (with or without the grid) when there is no sun? 

  I've been looking into a solar system too and I'm finding that MOST of the inverters used for grid tie systems also require an internet connection and have to be enabled by the manufacturer's website (and it appears that they require a constant connection to the manufacturer) and that the manufacturer, installer, the finance company and GOD only knows who else, can turn them off at will!  I was originally looking at APsystems DS-3 invertors.  You can learn a lot by reading their specs and their installation manuals on their website https://usa.apsystems.com/ds3/

   You might want to take a look at this forum too. https://diysolarforum.com/

[Faringdon]

myenergi may offer you all that solution with their system.
Your use of the battery is different than most, because most people whi have a storage battery want to use it to  take in solar in the day, then use it at night, so as to save money.
But i think you can program any of the solar/batt/inverter systems to do what you say.

I think powervault system may be able to do it?

..but hang on, you want to "island" your house when power goes down......due to regulations, thats not as straightforward as you may think.

[Mike Jung]

The idea ( for me ) is to keep the batteries charged for bad weather/night/load shedding and not to hammer them endlessly while in the same time using as much solar as available. Interestingly, I found a number of discussions about this "blending/mixing" capability and no clear conclusion.

[EEEnthusiast]

The Deye hybrid inverter can do all that.
https://deye.com/product/sun-3-6-5-6-7-6-8k-sg05lp1-eu-3-6-8kw-single-phase-2-mppt-hybrid-inverter-low-voltage-battery/

My friend has installed this for over a year now. He seems very happy about its performance and features/

[NiHaoMike]

Look for "zero export" inverters. Some of them also support backup but beware that many such inverters cannot zero export to loads on the "input" side, which would require external sensors. I'm aware of Sol-Ark supporting backup and zero export to the input side using external sensors, but it's one of the more expensive options.

It could be that the most economical option is an inverter that's just zero export and have a separate small inverter and charge controller for backup.

[Mike Jung]

It seems it can. But there is another problem : The Price !  

[gf]

What is your budget?
Do you care whether the inverter is certified for your country's grid code regulations? (if yes, this rules out many models)
Could you alternatively live with switch-over between solar/battery power and grid power? Pure off-grid inverters are less expensive.

[Mike Jung]

In short, no and no.

[gf]

Less functionaly, but seems to fulfil the requirements, too. Still too expensive?
https://www.powland.net/products/easun-5.6kw-hybrid-inverter-with-wifi
Of course you get what you pay for. And don't expect much support from this Chinese company.
And btw, be prepared that such an inverter can well have 50W (or more) self-consumption, even if the load is low. Maximum efficiency is only reached with high load.

[Mike Jung]

No, price is about right. But I could not determine from the manual if it can SIMULTANEOUSLY blend/mix solar and grid power if solar is insufficient. It might just switch between the two ?

[gf]

It certainly is one of the all-in-one models from EASunPower/Powland, which can also operate grid-tied.
I assume the "hybrid output function" (if enabled) is supposed to do what you want.

[kripton2035]

all these hybrid inverter from easun, powland, wks, are almost the same, and you can set priorities for solar, batteries or grid.
they are all around the same price, but you need to use them around 4kW, and not at the top 5.6kW if you want to not destroy them.
also keep in mind these inverters consume quite a lot of power (around 50-100W) with no load, and this can be not optimal for your usage
some more expensive brands like victron or studer have a lower standby current (20 to 40W).

[Mike Jung]

The power word here is SIMULTANEOUSLY . Many inverters can have "priorities" set but what they do is SWITCH between solar and grid. One or the other, NOT both in the same time.

It is baffling to me that such simple in issue has so little coverage on the Web. I scoured the internet for quite a few days and found almost nothing besides one or two reports that some inverters which apparently claim to do that, actually DO NOT.

The feature I am looking for is extremely important for prolonging the life of batteries, if installed. Thank you for mentioning the power wastage under load. I was aware it is not negligible - I could find a figure for only a couple of inverters and it was around 45W.

[gf]

The power word here is SIMULTANEOUSLY . Many inverters can have "priorities" set but what they do is SWITCH between solar and grid. One or the other, NOT both in the same time.

Any grid-tied inverter "mixes" grid power and inverter power. Since grid, inverter and load are connected to each other (as long as grid power is available), the mixing happens by itself due to Kirchhoff's current law. Consequently the following relation holds:

    Consumed utility power + generated inverter power - load power = 0

or

    Consumed utility power = load power - generated inverter power

A grid-tied inverter can decide (based on other criteria) how much power it generates. If it generates less power than required by the load, then the missing power is drawn from the grid. And if it generates more power than required by the load, then the surplus is exported to the grid (because the current pushed out by the inverter has to go somewhere if it is not consumed by the load).

To better understand the cross-relationships, it helps to understand that a grid-tied inverter rather act as AC current source, while the grid acts as voltage source, and an off-grid inverter acts as voltage source, too. I.e. a grid-tied inverter is regulated to push out a particular amount of AC current, while an off-grid inverter is regulated to provide a stable 230V AC voltage (and the current is then determined by the load).

Easun's all-in-one inverters have either "ISolar..." or "IGrid..." model names. The "ISolar" models are off-grid inveters and can only switch the load between utility and inverter. The "IGrid" models, OTOH, can also be configured to run the inverter in grid-tied mode. I pointed you to an "IGrid" model. The manual is unclear how load powering priorities and "hybrid output function" (grid-tie mode) interact, but I guess that the priorities are still honored in hybrid mode. It would not make sense not to honor them.

[nctnico]

Look for "zero export" inverters. Some of them also support backup but beware that many such inverters cannot zero export to loads on the "input" side, which would require external sensors. I'm aware of Sol-Ark supporting backup and zero export to the input side using external sensors, but it's one of the more expensive options.

AFAIK Growatt inverters should be able to do this as well (and these are amongst the most reasonably priced inverters over here). At least this is what I have gathered from the manual from the one I have.

[gf]

The SPH models from Growatt can (and possibly some others, too). But the (less expensive) SPF models are purely off-grid.

[Mike Jung]

I gathered from some forum that the Axpert King inverters can do it. Or at least that was the opinion ventured there. What baffles me is how superficial the manuals for the inverters. I id'ed a couple of inverters claimed to use solar and grid "in the same time". What exactly that means, is another matter....

[gf]

IIRC, Voltronic's Axpert King models do "double conversion". Mixing happens at DC. Any supplemented grid power is first converted to DC, mixed with battery and solar power, and then fed through the inverter to power the load. Maybe ideal for zero transfer time UPS, but line mode efficiency is less than 100%, and the inverter must be capable to drive the full load. There seems to be also a bypass mode, but I doubt that it can mix and provide zero transfer time in this mode as well.

[NiHaoMike]

AFAIK Growatt inverters should be able to do this as well (and these are amongst the most reasonably priced inverters over here). At least this is what I have gathered from the manual from the one I have.

Does it have connections for external sensors? A lot of "zero export" inverters that also have backup are only able to zero export to loads on the backup side. Granted, the market for zero export inverters has increased substantially as net metering has become less available, so I would expect a lot more "proper" zero export inverters that also have backup.

[gf]

Does it have connections for external sensors?

According to the installation manual, the Growatt SPH seem to support either an external CT or an external meter.

[NiHaoMike]

I just remembered that the US has an oddball 120/240V split phase system for most houses while most other countries use single phase 240V. That's probably why there were few zero export inverters available for the US market (due to increased complexity to handle that arrangement), and lots more for the international 240V market.